At some point I would like this to be a sticky for those interested in boosting their NA 4AGE or converting to turbo.
I think before that happens this thread should just be to get other peoples input and opinions and get the heated firefights and disagreements out of the way haha.

I will continue to edit it and also let my GF read it, edit it and make it look like I know how to use the English language.
Once all that is said and done I will add it to my website and maybe then it will be sticky worthy.




After answering many of the same questions many times over I decided to make a thread that lays out the basics. This will give people a good starting point to head out on their own and find more info and ask more educated questions.
As always the “use the search button” suggestion still rings true. There is a lot of good information out there and the more you find the more knowledgeable you will be. It helps a lot getting different peoples perspective and sometimes one persons explanation of something may help you understand better than anothers. There is also a lot of bad information out there as well as outdated information that was the best we had at the time but is no longer pertinent or perhaps even accurate. Use your best judgment out there to decide what is what. If you ever question any info or want to know more about it then ask.
It is also very beneficial to post up and lay out a game plan before you act. The research before hand feeds you a great amount of info and keeps cranky old farts (even if only metaphorically old) from needing to answer the same old questions over and over again. Laying out your game plan before acting can give us time to catch any bits of misinformation or outdated beliefs or concepts. This will help you get to your goal of most power, fun, happiness and success, with the least amount of money, frustration and failure.
The best places I know of for finding information on boosting the 4AGE are
mr2oc.com
club4ag.com
mr2.com
There are also some good books on general turbo theory and implementation.
The one I know of personally is Maximum Boost by Corky Bell. It was written a long time ago and has some outdated information in it as well but it's still a good primer on the subject. I know there are other very good ones out there as well but don't have personal experience with them. I will add more if other people recommend them.





One of the most common questions is how much boost can a stock 4AGE take or how much boost can this setup or that setup take.
This is an impossible question to answer and more importantly it is not the important question to be asking. Boost does not make HP, boost is the air that doesn't make it into the engine. Mass of air moving through the engine and the efficiency at which the engine moves that air through it along with basics like fuel and timing is ultimately what makes power. How much boost an engine can take is Dependant on so many variables that it can't even come close to being answered with out some of the variables filled in. A stock internals 4AGE might be able to run 30 PSI boost if it was running race gas with meth injection and a perfect tune. You could just as easily blow it up at 6 PSI if you did something wrong.

Gauges and sensors
Different gauges will have different levels of importance for different builds.

Wideband AFR gauge
In my opinion this is vital for any build beyond light mods. NA or turbo if you vastly effect the amount of air going through your motor you will want to be able to monitor the ratio of fuel going through the motor.

Knock monitor
This is the second most important gauge for tuning. If you are doing a low comp GZE longblock at 10 PSI with conservative timing this may not be a very vital gauge. If you are doing a turbo build on a LP NA 4A this is a pretty important gauge. For one the NA ECU doesn't have a knock sensor so if it does get detonation the ECU can't do anything about it. Second you are running boost on higher compression pistons that are relatively weak. Though the NA pistons have been known to take a bit of boost they are not forgiving at all when it comes to knock.
Running boost on an NA smallport, silvertop or blacktop with stock internals a knock sensor will be all the more vital due to the very high compression that they run. I would not consider those to be very good beginner builds due to the very narrow margin for error you will have before something pops.
I call it a gauge out of simplicity but there are a number of options from DIY detcans at the $20-$50 range, knock lights in the $150-$250 range all the way up to the J&S saeguard which is able to actually pull timing to save your motor but you do have to pay for it. Finding what is the right balance of cost to security will be a choice for you to make.

On a largeport NA turbo I would highly recommend this even for a 6-8 PSI build. I would say it's essential for anything over that.
For the SP or 20Vs I would say it's essential before you throw any positive air pressure at them.


Last is a pyrometer. Again if you are doing a GZE longblock with low boost and a Conservative tune this is not a very vital gauge. The more you plan to push your tune the more important it becomes.
A pyrometer is the most important with the high compression builds because retarding timing leads to higher EGTs. Higher EGTs lead to pistons and valves melting. In a high compression build you may have to retard the timing to keep the engine from knocking. As you do this you need to monitor your EGTs to make sure you don't start melting things.

On a NA largeport at 6 or so PSI I would say this isn't a terribly important gauge. If you can keep near stock timing and good AFRs your EGTs are likely fine. If you want to start pushing the NA pistons and or ECU further than that it will start becoming more important.
On a turbo SP or 20v build I would consider this vital for any level of boost.

Now these are just suggestions and many people have ran aggressive builds without them. Some successfully, some not so much. The question you want to ask yourself is if you would rather risk it and have much greater potential for serious and expensive engine damage or if you would rather play it safe and spend a few hundred dollars on monitoring equipment to greatly reduce your chances of doing big damage.

Next let's talk about internals.
People will often ask what do I need to make X power or run X boost.
The first answer and only one that's easy to answer is a good tune.
So I will start with one of my favorite quotes.

Squelch wrote:I ran a bone stock 3 rib block with about 60k miles on it (Bone stock, 9.8:1 compression, stock oil pump, stock, stock, stock !!! as removed from a 1986 MR-2 that was in a front end wreck, not opened, no seals replaced, no rings replaced, NOTHING REPLACED ! STOCK ! ) Engine ran great. Took 4th place in my race with about 30 cars in my class.


When I installed the engine (Late April 1994) I had been running a fully built 8.0:1 engine. I adjusted the timing a couple of degrees, and dropped the boost to 15 psi. I needed it to last for ONE race and that was all I expected to get out of it, it kept running, every race after that I expected to be it's last.. and it kept running. Please don't ask for a horsepower number, because that engine was never on a dyno.

After I pulled it out, I gave it to a friend that was doing local oval racing in a Corolla, running it N/A He ran it four seasons before an oil related failure.


So, the question was:

"How much boost and hp can a 3 rib block hold?"

Answer:

It all depends on your budget and tuning.

The three rib block is the weakest 4A block. It has the weakest crank, some of the smallest rods and weak pistons.
Now this isn't to say everyone should try to do this, it just stresses the importance of a good tune and shows what can be done with one. People have blown up much more robust builds with much less boost.

Since they are the biggest weakness in all NA 4AGEs we will start with pistons.
As seen above the NA pistons can take a decent amount of boost if tuned right.
If someone wants to get into boost on a budget and has a healthy motor I will often recommend starting on the NA pistons. I will also recommend planning on starting with low boost and building up as your knowledge and skills grow. You can decide to play it safe or you can decide to see what it will take before something lets go. With the right tuning and monitoring you would likely be quite surprised how much it will take.
If you are already going into the motor for a rebuild or building it from the ground up then you should just start with good pistons. The OEM 4AGZE pistons have proven so robust and so reliable it's a rare case you will see someone recommend or run anything else.
I am a fan of high compression. The more compression you run the more power per lb of boost you will make. It also improves off boost power, spool and gas mileage. For 200-250 WHP I would try to get back close to the compression of the NA motor or about 9.5:1. This can be done with the later 8.9:1 GZE pistons and a head shave.
For 250-300 HP the 8.9:1s should work nicely. If you are going for big numbers then the older 8.1:1 pistons may be the safest route. Of course you can try running a lot more compression if you want to be adventurous and you can also blow up a motor running a lot lower compression if you are reckless.


The rest of the 4AGE is notoriously robust. The original 3 rib is the lightest of the generations including a smaller lighter crank and smaller rods. This motor still rarely sees inexplicable failure even when pushed far beyond it's original design criteria. It should be noted though that the early crank and rods will not work with later pistons including GZE pistons. If you want to run GZE pistons you will need the later crank and rods and at that point you might as well get a 7 rib shortblock or longblock as the block is also stronger. If you can find a 4AGZE shortblock or longblock for a decent price then that can be a great route. If you can only find a 7 rib NA block remember the only difference between the 4AGE and the 4AGZE is the pistons. There are a couple ancillary differences. For example most NA blocks don't have the bung for the knock sensor drilled. They do all have the bung though so if you need a knock sensor you can drill and tap it yourself. Just be careful not to drill through the block.

The one other motor that has small rods is the 20v blacktop. Many people will tell you not to run those rods in a boosted motor. They will tell you this because the rods look small and people assume that boost is hard on rods.
I have put the challenge up on the boards to find people who have had BT rod failure only to find out that as with most other 4AGE components they seem to be very hard to kill. I have yet to find one person who could attribute rod failure to any reasonable amount of abuse.
More importantly as explained in Maximum Boost, the most stressful time in a rods life is under tension on the exhaust stroke as it is forced to a halt at the top of the cylinder and yanked back in the other direction. This force is so great that on the compression stroke the air and fuel in the cylinder actually acts as a cushion and reduces the tensile stress on the rod. The one time this may not apply is under detonation or preignition where cylinder pressure builds too early. So the strength requirements of the rod comes more importantly from how fast you want to spin the engine. Many people will tell you that if you want to spin the BT faster than stock you should also replace the rods but once again from the people who have actually done it I haven't heard of unreasonable failures.
I have also seen no proof that the BT rods are any weaker than any of the rest. I have seen no testing data, no alloy composition and they have proven themselves in real world testing so the only thing we have to say they are weaker is because they look weaker.

While on the subject of 20 valves the one issue with them is choosing a piston. The 20Vs did not come in boosted form from the factory so unfortunately we have no perfect OEM solution like the 16Vs. Many people run 16V GZE pistons. This has proven to work pretty well. If you add a small counterbore for the fifth valve you can maintain the non interference aspect of the 16Vs and the Silvertop.
If you don't notch it for the fifth valve it becomes an interference motor just like the Blacktop.
The one concern with this is piston topography. A piston is designed very specifically for the dome it will be used with. Squish area and the overall shape of the piston are very important and how they react with the head is very important. This is much more vital in very high compression motors where the piston is very close to the head. It may actually have no significant downside on a dished piston like the GZEs. It is however something important to think about.
Unfortunately the same concerns arise with aftermarket pistons. The original designers of the motor get to design everything as a unit optimized to it's self. It has been proven (at least with the 4AGE) that many piston manufacturers don't pay the same attention to the cylinder head they are designing around. You will see this often through misadvertised compression rating of their piston or misadvertized cylinder volume. If they don't actually know the volume of the dome they made a piston for how can you be confidant it has been modeled and optimized to that head?

I would like other peoples input on the best 20V boost piston options here.

Next we will talk about engine management. The path you choose will likely be influenced by what you are starting with and where you are going. I am not familiar with boosting on all NA ECUs so I will talk about what I know and go from there.

You can run a little boost on almost any ECU. How much depends on many things.
Before you even order turbo components you should have a wideband ready to install. It would be good to have it installed a while before boost so you can get familiar with how the car behaves in stock form.
Same if you are converting from GZE to GTE or even throwing on a bigger SC pulley.

NA 4AGE ECU
The NA 4AGE can run a few lbs of boost with minimal adjustments. The AFM and FPR will add fuel to compensate for the added air. Once you get over a few PSI these components alone don't have the ability to compensate enough. At this point you need to decide if you want to start throwing time and money at the ECU or if you should just step up to something better. Both have their advantages. Stepping up to something better means you don't waste time and money with something you are going to replace anyway. Tuning on that ECU gives you time to get familiar with AFRs and basic tuning principles before needing to learn to tune aftermarket engine management. If you are going to have someone else tune for you then this is all irrelevant.
The 16V NA ecu has been taken up to at least 8 PSI on numerous occasions. On top of your wideband you will need to either play with different sized injectors or an adjustable FPR (fuel pressure regulator). One of these in conjunction with AFM tweaks should get you in the range of 8 PSI pretty easily.
A knock monitor at this point is highly recommended, especially since the NA ECU has no knock monitoring.
I put 8 PSI as the practical limit for the 4AGE ECU. It has been done and documented by others and should be relatively cheap and easy. I am confidant that with a combination of injectors, FMU, AFPR and possibly some other things you could run a lot more boost on it but at that point you will have spent as much time and money as many engine management options that will give you much more control.


Largeport 4AGZE ECU.
Many people think this is a logical step in the progression. Why not just install a GZE ECU and sensors or why not just buy a GZE longblock with ECU and wiring.
The US GZE ECU has a huge handicap called low end leanout. Under 3500 RPM it caps the AFM signal. This means that if the motor sucks in more air than that under 3500 RPM the motor leans out because the ECU doesn't recognize the increase in airflow. You can add a gruntbox which uses the cold start injector to add more fuel and helps counter the low end leanout. For people who have the GZE ECU already in there car and are looking to run moderate boost this can be an acceptable solution but if you don't already have it in the car then the time and money to buy and install the ECU, sensors, and gruntbox will exceed the cost of some of the cheaper engine management solutions such as Megasquirt.

If you are starting with a 4AGZE and want to turbo it then up to stock GZE boost levels all you need to worry about is the turbo kit. If you want to run more than 8 PSI you need to decide if buying a gruntbox and working with what you have will be the best route or if you should upgrade to something with more control.

Smallport 4AGZE ECU
I don't have personal experience with this ECU.
I have heard it tends to have an issue with power falling off around 5500 RPM. One theory I have heard is it reacts to a false knock and pulls timing. You will also be limited on how much boost you can run before maxing out the MAP sensor. Like the LP ECU I wouldn't go very far out of my way to install this ECU. If you are swapping in a full SP GZE and are only hoping for near stock power levels then it may be the best choice. If you are looking for much over that then I would at least consider the other options before wiring it in.


Next are the Map based SP ECU, the Silvertop and the Blacktop ECU. I am unfamiliar with running boost on any of these. I am confidant any of them could run a little boost but combined with the high compression of the motors they come with and the aggressive timing maps to make them sporty I am confidant it would take a wary and patient person to see what could be done with these setups without hurting the motor. Unless you already have the ECU wired into the car it would probably be the better choice to just wire in aftermarket engine management from the get go.

If you have a GZE ECU and wiring in the car you can run a BT or ST on GZE ECU and electronics.
This is actually a pretty good combination because the GZE ECU can only take about 8-9 PSI before leaning out and that's pushing a stock 20V pretty hard. I have been running a stock internaled blacktop on a GZE ECU with 7 PSI boost for 10k to 15k miles now.. On this setup I would consider wideband, knock monitor and pyrometer all mandatory. Even with the GZE ECU in the car this may or may not be a great way to go. If you don't already have a GZE ECU then I would say no way it's worth the time or money to go this route.

We have a number of aftermarket engine managment options available ranging from a couple hundred dollars up to thousands of dollars. I am far from familiar with all of them and even if I was this would hardly be the place to get into the details.
As with most things I am more familiar with the cheaper options.
There is basic Megasquirt which can be had new for a couple hundred bucks and used even cheaper. This does require you building and tuning the whole thing.

DIYPNP
This makes it a little easier on you. There is still some electrical assembly required but once done it plugs right into your harness. It should also be relatively easy to find decent basemaps to start with.

MSPNP and a couple at a similar price point come pre assembled and should be pretty easy to plug and play at least on a base level. It will need tuning from there.

There are people running many of the available systems so if you have questions search around or start a thread.

Choosing the turbo and surrounding components
This decision will come down to a lot of personal factors. You have to balance price, availability, long term availability, compatible components and your goals.
You might be stoked you found a great deal on some oddball turbo locally but if you design your system around that will you be able to find a manifold and downpipe to go with it or a replacement if it fails? Will you be able to upgrade to a bigger turbo if that one no longer suits your goals or move down to a smaller turbo if you decide it's too big and laggy?

One concern is product compatibility.
It is wise to see what manifolds are available before looking at turbos too much as that will likely influence your options.
Before I made the made to order mani I am selling right now there were very few options especially for the transverse layout. Unless someone could do something custom themselves they would be limited to run a turbo that fit one of the very few manifolds available.
As of the writing of this I do make a manifold and will attach any flange for any turbo. I will also make a downpipe for any turbo. Some are still easier than others. If I can find a flange it's relatively cheap and easy. If I need to make a flange then it will take considerably more time and money. I do have a source for most big name flanges though.
This opens up options a lot and allows you to find the turbo that will work best for you.

The final question is how much money do you want to spend and how leading edge do you want to be?
Used turbos can save you a lot of money and for most of us will suit our goals just fine. From now on I will refer to these as JYD or junk yard dogs.
Buying a used turbo always has it's risks. You could put it in and get 100k miles out of it or you could blow the bearings out the first time you step on it. Careful buying and preferably careful first hand inspection can greatly increase your odds. There are many sites, pages and threads on inspecting a turbo so I won't get into that here. Another option is to rebuild the turbo or get it rebuilt.
The other option is to buy something nice and new off the shelf. This is very nice because the turbo is brand new and you can feel confidant it will last you a long time without trouble. Unfortunately many new turbos cost more than the cars we plan to stick them into. That can be a big pill to swallow.

There are also journal bearing turbos and ball bearing turbos. BB turbos are generally more expensive. They spin more freely and last a long time if treated right but if there is any issue you generally need to change out the whole bearing cartridge which is not cheap. For most of us these turbos don't benefit us enough to be worth the extra expense. This is especially true for people looking to run moderate levels of boost on a budget. The BB turbo can shave milliseconds off spool time and the bigger turbo and longer it takes to spool the more effect it will have. For anyone looking for less than 180 HP/liter and a turbo capable of producing that I don't feel that a BB turbo will be worth the extra cost unless you are seriously racing the car or in other situations where milliseconds do actually matter.

Picking a JYD
If you decide to go the route of a used turbo what one do you pick?
Of course you want one that will fit your current needs and goals. If you know exactly how you want your car to end up that may be enough. If you think you might want to grow at some point then you will want to find a line of turbos that use the same flanges so you don't have to change much if you get a bigger or smaller turbo. The most important part is the turbine side flanges for your manifold and downpipe. You spent good money for those parts and the last thing you want is to need to redesign your system and buy other parts or modify the ones you have.



Since the following talks a lot about MHI turbos I will go into brief detail on how they are sized and rated. There is a designation that starts with TD ie TD04, TD05, TD06. This tells you the size of the turbine wheel. Bigger number relates to a bigger wheel.
Next you will see something like 13T, 14B etc. This tells you the size of the compressor wheel.
The last thing you will hear people talking about is x cm turbine housing. This is the same thing as the A/R on other turbos. Instead of a ratio of the area to radius the mitsu turbos just refer to the area where the scroll begins. Bigger number means bigger surface area equaling a larger A/R.
There is much more info easily available on these turbos. One of the best places to start is here.
http://www.vfaq.com/index-main.html

Mitsubishi turbos have always been my go to. First off because I first got into boosted cars in the DSM scene and secondly because the turbos are very good units that fit the above requirements. There are quite a few turbos that all share the same flanges.
These range from some smaller TD04s like found on the 3000GT up through some TD06s capable of rather large numbers. There are also quite a lot of mix and match options easily available meaning you could play with your own combinations relatively easily. One downside of the DSMMHI flanged turbos is that most or the smaller options are getting older and harder to find. Turbos from the first and second gen eclipse, 3000GT and early Evos are all great turbos but also come off cars 18+ years old. This means they are going to get harder to find and generally with more time comes more wear. They are definitely not as plentiful as they were 10 years ago.
Unfortunately the Evo 4 reversed the direction of the turbo and went twin scroll. This means they are not compatible with any of the older turbos. They are also not compatible with much else smaller or bigger. The Evo 10 went back to the standard direction of rotation but still has the EVO twin scroll flange.
The DSM T25 is actually a Garrett turbo but has a DSM/MHI exhaust housing so it bolts up to the same mani and downpipe. It is a great turbo for those looking for quick spool and less than 250 hp. You do sacrifice a good bit of top end restricion for the quick spool but it Is often worth the trade. It is also the most common turbo I have seen run on 4As.

Subaru turbos have caught my eye recently because subies are so plentiful and I expect the turbos to be for some time. Many of them are also MHI turbos which I am fond of. Unfortunately they use a different turbine side. I am much less fond of the flange design on the subie turbos, especially the fact that they are only a three bolt flange to the mani. That said the subie TD04s are pretty common, pretty cheap and a pretty decent option for anyone looking for less than 250 HP. They are still a TD04 meaning if you found a healthy TD04 DSM turbine housing you could put it on a subie TD04 and run it on a DSM flanged mani. There are nowhere near the OEM variations that the MHI flanged turbos have but there should be a decent flow of used after market turbos coming out of the Subaru community meaning you could probably find some interesting options available. If you can find a Subie flanged TD05 or TD06 housing it also means you could run many of the other MHI turbos.

Another nice option is the Garrett T25/T28 flanged turbos. These turbos are found on a number of cars and are still pretty plentiful and cheap. They are found on a number of nissans such as the 300 ZX and SR20s. Some are smaller and good for maybe 250 hp. Some may get you into the 300s.


Another very common flange style is the T3/T4.
I am completely unfamiliar with these turbos, their options, performance or OEM applications.
There is plenty of information on these turbos online.
I will also add any info anyone else has on these turbos or any other good options I have overlooked.

Aside from the manifold and the downpipe one of the bigger hurdles the average DIYer will face is the oil drain into the pan. If you are asking yourself if you can just use the oil cooler drain already in the pan trust me that you cannot. The diameter is too small and it will cause the oil to back up in the drain and flood the turbo. It is also on the low side. You want the drain as high as possible and definitely above the standing oil level. ½” is the absolute smallest line you will want to use. I highly recommend ¾” or 12 AN. This gives the oil a large passage and more area to flow through.
Most lines you find online are 1/2”. They will also require you to fabricate the bung in the pan.
I offer the service of modifying your pan with a 12 AN bung and building a steel braided 12 AN line to perfectly fit your turbo.

A couple other notes.
There needs to be a substantial drop on the oil drain line. The drain side is not pressurized and needs to flow freely into the pan. Oil that has passed through the turbo also becomes very frothy and won't drain as easily. Any transverse manifold for the 4A puts the turbo very low. You have to make sure there is enough angle on the drain line. This also means there isn't enough room for an adapter plate to run a different turbo on a different flange.
The reason you need such a big line and steep angle from the turbo is because turbos are designed to have oil lightly splash over the bearings and quickly drain. If any oil starts to build up in the CHRA it will start to leak past the seals and into the intake or exhaust. This will cause the car to smoke and won't take long to damage the seals.

Oil feed line. I can make an oil feed line for just about any application. I haven't found it to be worth advertising it much since there are so many large scale production feed lines out there much cheaper than I could offer them. Be wary though. Remember that this is one place where you don't want to cheap out or half ass things. Almost all AW11 turbo fires are related to oil dripping on the exhaust manifold. This is something you do not want to happen to you. The oil going into the turbo is under high pressure and sits right next to the header which can get extremely hot. On that note route the oil line as far away from the header as possible and don't be afraid to use some heat shielding if you are at all concerned.

Piping turbo to intake.
You want to use metal for your piping. I highly suggest something that cannot oxidize and flake material into the intake. For this reason I never use mild steel intake side. Stainless steel and aluminum works great and aluminum will generally be the cheaper of the two.
I prefer not to cheap out on parts or materials but there are times I just can't justify the added expense. I have fabricated with, welded and run piping from Burns stainless as well as CX racing and no name ebay brands. The cheaper CX racing and no name piping welds just as well works just as well and usually comes with a nicer finish. I love to shop local, buy USA etc but this is one place where I buy the cheaper stuff. Since the no names are no names I can't speak for them in general but I have been happy with all piping I have gotten from Cxracing and ebay.
One thing to remember is pre compressor the air is moving faster but after the compressor it is moving at about the same speed as when the motor was NA it's just much more dense. For that reason post compressor you don't need bigger piping when you run more boost.
One of the most important things though is having as few diameter changes as possible. For this reason 2.5” works pretty well for most 4A builds. There are a lot of piping kits available in that size, it's pretty close to but slightly larger than the diameter of the AFM and there are many intercooler options in 2.5” inlet and outlet.
If you use a JYD intercooler with smaller then you may be better off trying to match piping closer to that. I would never recommend going smaller than your AFM or throttlebody diameter.

Water lines
Not all turbos are water cooled but these days most are.
For the 16 valves it's easy to route the coolant line running to the throttlebody to the turbo. Make sure the water flows to the TB first and then to the turbo. The TB uses the coolant temp to control the idle speed. If you route the coolant from the turbo to the TB it will mess with your idle due to it changing the temp of the coolant.
20 valves don't have coolant running to the TB. On mine I teed into the heater line inlet and outlet. I don't have any proof on how well this flows but I do have about 15k miles on the used T25 I thew on this setup and it's still doing great.

Intercooler selection
This is another huge variable in the build. You can spend anywhere from nothing to thousands of dollars on your intercooling.
I would recommend running IC on any turbo build. If you want to run low boost this could be a cheap used OEM intercooler found at the junk yard or on ebay. If you want to run moderate to high boost I would put a little more thought into your system. Hot air is one of the greatest enemies of a boosted system. One of the hardest parts on MR cars is getting airflow. Front engine cars can do great by just sticking a big A2A IC in front of their radiator. To do that on a MR car would require 30 feet of piping.
There are some other options. Some have done roof mount ICs and or roof scoops to route the air into the IC. This does however increase the frontal area of the car and add drag. It also makes it pretty apparent that your car has been modified. This may be very undesirable in some areas or for some people. Others have moved their exhaust and put the IC under the trunk. This has it's own pros and cons. To actually get good flow you have to cut up your trunk and somewhere for the air to flow out of the trunk, it's still likely to see some heat from the exhaust. It's also very susceptible road debris and other things that could damage it. Many have gone water to air and then run the heat exchanger to the front of the car or in my case to each side of the car. This adds cost and complexity but is a very good way to get the efficiency of your IC as close as possible to that of front engine cars.
What intercooler you choose will have to be a balance of cost, effectiveness, space requirments and simplicity. If you are looking for a decent amount of power this isn't somewhere you want to cheap out.

I've done several turbo setups in my time messing with these engines and by far the easiest swap was using all oem parts..the simplest was ae101 engine minus all the S/C specific parts with a redtop RWD converted intake manifold. ecu, map sensor, harness and injectors all remained the same, HKS manifold with a t25 from a silvia or similar engine...custom intercooler piping with a evo or galant vr4 intercooler and that was it.....I also use a SAFC to tune the fuel a little and easy 250-270 with 10-13psi....very reliable as well until you decide you want more boost...every time i turned boost up i burnt a piston....but those days i was in japan so engines were a dime a dozen...just my .2 cents

subscribed! good info!!!

A post on the MR2OC got me thinking a little about fasteners and I wanted to get peoples opinions on the subject. At what point does it become important to upgrade to ARP over OEM?


I don't feel like head bolts or main studs should really be needed unless you will be chasing higher levels of power.
I also don't feel like bottom end fasteners will be significantly effected by moderate levels of boost. It seems to me they would be much more stressed by RPMs.
After my recent bad experience pulling my old motor I would be very tempted to go ARP on the rod bolts for just about any build. That is because not only was one rod bearing toast and the bolts horribly stretched but the bolts on every other rod were terribly stretched as well. I didn't put the motor together last time though and I also know that the people who worked on the car before me had no business doing the work they were doing so it may just be that they overtorqued the bolts or used already stretched bolts or who knows what.

I don't think I have ever heard of stock main bolts failing in normal operation.
The head bolts are one thing that are most definitely effected by boost but I think they are pretty safe up to pretty high levels.
What are other peoples experiences? How hard have you pushed stock hardware? What has survived and what has failed? At what point do you think you should upgrade what parts?

Choosing a turbo that's right for you.
I'm not going to get into the details of all the variables that effect the performance of a turbo. There are entire websites, books, and forums devoted to that. I also respect that it can all be pretty overwhelming at first. Doing the research and finding those websites, books, threads and forums will help you out greatly. I also understand how it can be overwhelming trying to learn everything like compressor and turbine maps and what everything means.
I will recommend a couple websites that will help you fake it till you make it.
This will plot out your inputs on various turbo maps. One thing to beware of is that all those inputs have a huge effect on the result so the more you learn and understand the more accurate the calculator will become. It is still just a reference. It also only has compressor maps. It does not address the turbine map but few things do. It's rarely even possible to get a true turbine map.One of the best things you can do at that point is research the turbo on educated sites and find out what it has been proven capable of.
At that point start asking questions of your own.
http://www.squirrelpf.com/turbocalc/

This page will help you calculate intake temps.
http://www.stealth316.com/2-turbotemp.htm
And this page helps understand why and also how it pertains to the compressor map.
http://www.stealth316.com/2-adiabat1.htm
There is also a ton of other good information on that forum.

good info!!

Very informative and good guide too.

Hats OFF...

Thanks for this topic. I'm still learning about turbos and building a 4A-GTE. I have most of my parts rounded up, but decided in the meantime to wait on the head & block rebuild and get my AE95 ready in other areas before dropping a built motor into it. Can't go tearing around corners with jelly suspension and a clunking rear diff / driveshaft...

Anyways I'm curious if using a lightweight flywheel (like Fidanza) makes any difference, positive or negative, for a built up 4A-GTE (running on an aftermarket ECU).

There are different schools of thought on the flywheel. Some people prefer a light flywheel for the reduction of parasitic loss. Others prefer the heavier FW to keep revs up between shifts. A light FW will drop revs farther faster so a bigger FW could actually help maintain RPM and therefore reduce spool time.

Interesting... thanks for the reply. I'll have to give more thought to selling off the Fidanza 4A-GZE flywheel that I bought...

gaijin_rokurunner wrote:I've done several turbo setups in my time messing with these engines and by far the easiest swap was using all oem parts..the simplest was ae101 engine minus all the S/C specific parts with a redtop RWD converted intake manifold. ecu, map sensor, harness and injectors all remained the same, HKS manifold with a t25 from a silvia or similar engine...custom intercooler piping with a evo or galant vr4 intercooler and that was it.....I also use a SAFC to tune the fuel a little and easy 250-270 with 10-13psi....very reliable as well until you decide you want more boost...every time i turned boost up i burnt a piston....but those days i was in japan so engines were a dime a dozen...just my .2 cents

Sounds like an awesome little engine though for not a lot of money!
Would that apply to a USDM MR2 engine too?

I have updated and made some modifications to the version on my website. I also have made links to many of the products I suggest in the article.
http://matrixgarage.com/content/yoshimi ... oing-4a-ge

Question about intercoolers... is it possible to get a top mount intercooler (TMIC) fitted to the NA bigport or smallport valve covers? I know the GZE vc's have bolt holes on top, ot at least they seem to. Are there any aftermarket options for a TMIC? I'm asking because of having an AE92 engine bay, with limited space, I'm thinking about an intercooler sitting on top on the engine rather than shuffling around the battery, radiator fan, etc. I have and will be keeping AC. It's too hot where I live to be without it, so a FMIC is out of the question. I also sometimes go off-road, not real crazy, but I would hate to damage an IC that was mounted low.

I've also considered a water to air intercooler, but I'm not so sure there's enough room for one where the OEM airbox is located.

Does HP play a part in the size of the IC used?

Turbo efficiency and boost both play a big role in how much intercooling you will need.
Putting an IC over the engine is about the worst place you could possibly put it aside from maybe right over the header. Some people call the IC on the engine the interwarmer which is probably more accurate. You need cool air flowing over it to get effective cooling.
With some work you should be able to put a FMIC in front of your condenser. If that's not an option then I would try to put an IC over the trans. This may require relocating some things but I have seen some pics of similar setups. Water to air might also be a good option. Looking on google there are a couple decent looking setups.

This setup looks pretty good. It may require moving the AFM. It might be possible to move the washer bottle, put the AFM there and put your intercooler over the trans.

Thanks... I had a look at a site a friend told me about called Frozen Boost. I found that same (or similar) IC pictured above in their store. I like that idea for its placement. Looks like the stock location for the battery is retained. I was fearing I'd need a larger IC even for water to air. However I do need to figure out where to place the heat exchanger and water pump for such an IC. Last time I was under the car (though not taking measurements), I saw an empty area right in front of the left-front wheel that could work. The heat exchanger could sort of hang from the frame there. Only thing is an air scoop for the gearbox is in part of that area.

Poor crowded AE95 engine bay...

I can get stuff through frozenboost. If you decide to get anything let me know. I might be able to save you a couple bucks and I get to make a couple bucks on the deal which always helps me out.
I can also get stuff through CXracing as well as a bunch of the big name guys like Greddy, Mishimoto, HKS, Vibrant and others.

If you aren't making a ton of power you could probably get away with a small air to air in the same location as the A2W in the pic above. Or you could even do a side mount like DSMs http://www.3si.org/forum/attachments/f3 ... all_02.jpg.
It's also likely you do have room for a heat exchanger or intercooler in front of your condenser and still high enough to be safe.

Cool, thanks. You're definitely in my consideration for a turbo manifold as it is. But it will be a while before I'm ready. I need to save up for headwork and an engine rebuild, and apparently a different set of crank & rods

So if I have a 16v red top , should I keep the original pistons or should i install the 4agze pistons ?incase I want to open some boost is it safe ?

saifmansour wrote:So if I have a 16v red top , should I keep the original pistons or should i install the 4agze pistons ?incase I want to open some boost is it safe ?

I choose to ignore top color since it's misused more often than not.

What's important here is whether you have 9.4:1 or 10.3:1 pistons.
In either case you could boost them but the 9.4:1 pistons will take a little more boost.
The biggest thing here is tuning. The pistons aren't particularly strong so even a little detonation could take them out when a stronger piston might handle it better. Either way you don't want detonation and as long as you can stay out if it then you should have no problem running 5-10 PSI on the stock pistons.

will installing a 4agze pistons give me more boost ? and more safety ? p.s its a daily driven car . thanks a lot for your help

saifmansour wrote:will installing a 4agze pistons give me more boost ? and more safety ? p.s its a daily driven car . thanks a lot for your help

IMO the GZE pistons are too low of compression unless you are chasing very big numbers. The SP 8.9:1 pistons should be good for well over 300 WHP. More with a high VE build. Unfortunately they are pretty scarce in the US.
The 8.1:1 pistons are just tool low for my taste unless you are going for crazy power.
Budget is always an issue but I much prefer choosing or designing pistons around someones particular build and goals. It's not as hard or expensive as many think.
Let me know your power goals and I can help more as far as suggestions for compression and turbo size.

I have the 10.3:1 pistons , my power goal is not more than 300 hp . What's wrong with gze pistons ? I will be able to have some boost right ?

saifmansour wrote:I have the 10.3:1 pistons , my power goal is not more than 300 hp . What's wrong with gze pistons ? I will be able to have some boost right ?

Compression ratio has a lot to do with BSFC which breaks down to how much HP you get out of a unit of fuel. It also effects a whole range of other efficiencies.

Higher compression means you make more HP per lb of boost. This means the turbo doesn't need to work as hard, it doesn't need to spool as high to hit full boost, your intake temps will be cooler and the whole system will work more efficiently. You will make more power off boost, you will get better gas mileage and you will have quicker smoother transitions from off boost to on boost.
Too much compression, timing and or boost can cause the motor to knock and damage internals. The higher you go the narrower your margin for error and the more aggressive you have to be on your tuning and monitoring. It will be up to you to choose how much margin for error you want, and how far you want to push things but I still consider the 8.1:1 GZE pistons to be outdated and too low for most builds. Gas has gotten better, technology has gotten better and science of the internal combustion engine has progressed further. This is why my 55 Studebaker runs NA about 7:1 compression and out of about 4.2 liters only makes about as much power as a stock Blacktop.

As far as your power goals, you are right on the cusp of a number of my favorite turbos.
In the smaller category we have the T25s including DSM, Nissan and other OEMs and the Garrett aftermarket turbos, and the 13b and 13t. These are all turbos that can make 220-250 WHP. The great thing about them though is they spool insanely fast. For most applications I would rather have an AW11 or AE86 with one of these turbos spooling lighting fast and putting down 225 HP than have a bigger turbo making a lot more power spooling a lot slower.

Next step up would be the OEM T28s, Garrett aftermarket T28s and the DSM/MHI 14b. These turbos can all get you into 300 hp territory. They spool a bit slower but still give you relatively quick spool and a broad powerband.

Next step up would be turbos around the 16G and 2860. These turbos should be able to get you into 350 HP territory but will be a good bit slower to spool.

That was really helpful ! Ok now the picture is clear I would like to ask you some other questions :
1- can I take the turbo oil line from the oil filter adapter ? And the the other line should go to the oil pan ? Will this effect the oil pump pressure ?
2- can I keep the original intake manifold ? And can I do any cheap modifications to it ?
3- do I need to change the ecu ?
4- is there any parts I need to change ex: injectors, pumps, ...

saifmansour wrote:That was really helpful ! Ok now the picture is clear I would like to ask you some other questions :
1- can I take the turbo oil line from the oil filter adapter ? And the the other line should go to the oil pan ? Will this effect the oil pump pressure ?

That's exactly what I did. I tapped a 1/8" hole into my oil filter adapter in a good meaty section and threaded in an NPT to -4AN adapter and ran a steel braided AN line to the turbo.
You will also want to add a restricter in the feed line. The size will depend on whether you run a BB or journal bearing turbo.
The restrictor is so small it will have no significant effect on oil pressure.
Yes you want to run the oil drain to the pan. The drain side needs to be as steep as possible and enter the oil pan as high as possible. Many drain kits use 1/2" or -8AN I highly reccomend at least 5/8" or -10AN.
If I make you a turbo mani or if I have your mani, turbo and oil pan I can make you a drain line. If you want to make it yourself I can help you find the parts you will need.

saifmansour wrote:2- can I keep the original intake manifold ? And can I do any cheap modifications to it ?

One of the biggest misconceptions with boost is that since you are moving more air you need to run bigger piping, runners etc. This is not specifically true.
Boost increases density, not volumetric flow. Air passing through the TB and mani under boost will be traveling roughly the same speed as NA. So you don't need to change your intake setup to run boost. If however you make a lot of VE mods like big cams or increase the redline then just like in an NA motor a boosted motor could benefit from improvements like intake manifold and port and polish.

250 hp I wouldn't worry about intake mani or head work. Between 250 and 300 is around where you will start benefiting more from cams, intake, exhaust improvement and PNP work.

saifmansour wrote:3- do I need to change the ecu ?
4- is there any parts I need to change ex: injectors, pumps, ...

You can start out on the stock ECU and electronics. This gives you a chance to get familiar with boosting and basic tuning without the somewhat overwhelming prospect of aftermarket engine management and heavy wiring. This will only get you to about 160 WHP with some moderate tuning. That's a very vague estimate. Much more could be possible on the NA ECU but around that point it's going to start taking more time and money than is practical and at that point you are better off going aftermarket.