HIGH comp Big port carby build with MANY questions

[nyberrg]

Yo! So this is gonna be a pretty long explanation before getting to the point..

I've been building a big port for a couple of years, as fast as my wallet has let me. The parts are a mix of things I came upon and planned purchaces, I don't really know what I built Anyways, it's together now and idles fine, but I have some questions about what the next step could be to make sure it keeps running fine.

I will start by listing some specs:

• Bored Big port block and shaved head, it was a bit warped before.
• HKS 264/272° cams.
• HKS Valve springs
• Supertech valves/guides, stock size
• ZRP con rods
• Wiseco oversize, high comp pistons. I'm unsure about the exact specs on these. The crown was above the block at TDC, by a bit and then some!

The engine runs on mikuni bike carbs and nodiz pro2 ignition. It has got a big radiator that keeps it cool + an oil cooler.

I ran a compression test on the cylinders and they all read high, really high, like 15 bar high, except for the first cylinder which was "only" at like 13.5 bar or something like that. I'm not too worried about this yet, really. I only did one test.

So, on to the questions:

• Since the compression is so high, is it a good idea to run extra crank case ventilation? Is a catch can a good idea?

• Is the compression uncontrollably high to run at 98 octane fuel? I could order a thicker head gasket down the line.

• What is a good AFR reading on a carbed 4A-G? I've heard so many different numbers by now..

• What is the weak point of a 4A-GE, how do I counter it? What supporting mods are the most important?

Cheers!

[totta crolla]

I guess you built this engine to give more power than standard... otherwise why bother? At least two of your questions would be answered by taking the engined to a dyno / rolling road, 98 octane fuel and a good AFR. The weak point of the 4age? The person who tunes it.

[jondee86]

- Blowby is primarily driven by the combustion pressure which is many times higher than the
cranking pressures. So blowby is pretty much proportional to engine rpm. A new engine with
tight clearances and good ring sealing won't have a lot of blowby and the standard single cam
cover vent will be adequate. However, a catchcan is a good idea and probably easier to hook
up than trying to vent the fumes into your carb manifold.

- One rule of thumb says that cranking pressure above 200 psi (13.6 bar) is likely to result in
detonation under load at low rpm's. I'd suggest dropping the cranking pressure back to something
like 180 psi by adjusting the inlet cam timing if you want the engine to live long and prosper.
Closing the inlet valves a little later will drop the cranking pressure. Run 98 octane and use
conservative ignition timing until you can see if you have a detonation problem.

- Carbed engines should be able to run similar AFR's to injected engines. I'd shoot for slightly
rich at idle (say 14:3), a bit leaner for light throttle/cruise (say 14:5) and around 12:1 at WOT.
Basically you will have to tune on a dyno (quick but expensive) or on the road with a WBO2
gauge and a quiet exhaust so you can listen for any knocking. It will be important not to run
that engine lean under load so if you have to, err of the rich side when selecting jets.

- The 4AGE does not have any specific weaknesses when treated with a degree of mechanical
sympathy Change the oil and filter regularly, keep the revs under 8000 and use the gears
to avoid WOT at low rpm's. Resist the urge to do hektic skids/burnouts with the engine held at
extreme rpm's and little load. Apart from that just drive the crap out of it

Cheers... jondee86
-

[oldeskewltoy]

I hate those pistons.....



dome volume approaching 5cc... just too much.

Jondee's recommendation is good... that may help.

You wrote the cams as 264/272 - am I right that you have the 264 cam on the intake side? Any chance you can swap cams to the 272 in the intake side... that should help in lowering cranking compression.

If you are still too high, you might look at a 280, or 288 type cam

[nyberrg]

- Blowby is primarily driven by the combustion pressure which is many times higher than the
cranking pressures. So blowby is pretty much proportional to engine rpm. A new engine with
tight clearances and good ring sealing won't have a lot of blowby and the standard single cam
cover vent will be adequate. However, a catchcan is a good idea and probably easier to hook
up than trying to vent the fumes into your carb manifold.

- One rule of thumb says that cranking pressure above 200 psi (13.6 bar) is likely to result in
detonation under load at low rpm's. I'd suggest dropping the cranking pressure back to something
like 180 psi by adjusting the inlet cam timing if you want the engine to live long and prosper.
Closing the inlet valves a little later will drop the cranking pressure. Run 98 octane and use
conservative ignition timing until you can see if you have a detonation problem.

- Carbed engines should be able to run similar AFR's to injected engines. I'd shoot for slightly
rich at idle (say 14:3), a bit leaner for light throttle/cruise (say 14:5) and around 12:1 at WOT.
Basically you will have to tune on a dyno (quick but expensive) or on the road with a WBO2
gauge and a quiet exhaust so you can listen for any knocking. It will be important not to run
that engine lean under load so if you have to, err of the rich side when selecting jets.

- The 4AGE does not have any specific weaknesses when treated with a degree of mechanical
sympathy Change the oil and filter regularly, keep the revs under 8000 and use the gears
to avoid WOT at low rpm's. Resist the urge to do hektic skids/burnouts with the engine held at
extreme rpm's and little load. Apart from that just drive the crap out of it

Cheers... jondee86
-

This is what I was looking for pretty much.

I have 160 main jets in the carbs now, pretty much the biggest I could find so I'm hoping that isn't too lean. I have one set of 150 or 155 extra, i forget which.

I welded a nut to the block in the position where the smallport has the knock sensor way back so I might be able to get knock monitoring when I get to a dyno, which I will!

I don't have adjustable cam gears (yet) sadly so I cant adjust cam timing as of now...

[nyberrg]

I hate those pistons.....



dome volume approaching 5cc... just too much.

Jondee's recommendation is good... that may help.

You wrote the cams as 264/272 - am I right that you have the 264 cam on the intake side? Any chance you can swap cams to the 272 in the intake side... that should help in lowering cranking compression.

If you are still too high, you might look at a 280, or 288 type cam

The whole build is pretty much based around those pistons They were laying around from when my father owned an 86 so I decided to use them.

The 272° cam is on the intake side, don't know why I flipped the numbers

[Nick94tt]

I hate those pistons.....

The whole build is pretty much based around those pistons

Sorry, but random drama is helping me cope.
(even if I have to manufacture it in my head )

Admittedly those remind me of some old school big block high dome pistons I saw when I was younger.

Any chance of running E85? Assuming your fuel system is compatible it would give you some additional margins.

[totta crolla]

You asked this question: "What supporting mods are the most important?"
Throwing those camshafts in and having no facility to fine tune them is a complete waste of time. Here is the thing, to make the power that your build may be capable of you will need to set the carbs up properly but you will also need to time the cams in and each time you change the cam timing your fuelling requirements will also change. Arguably your most important "supporting mod" is the person that can tune the cams/carbs/ignition and operate the dyno.

[nyberrg]

You asked this question: "What supporting mods are the most important?"
Throwing those camshafts in and having no facility to fine tune them is a complete waste of time. Here is the thing, to make the power that your build may be capable of you will need to set the carbs up properly but you will also need to time the cams in and each time you change the cam timing your fuelling requirements will also change. Arguably your most important "supporting mod" is the person that can tune the cams/carbs/ignition and operate the dyno.

Your passive aggressive answers bring nothing to this discussion mate, just stop.

[totta crolla]

Sorry if the truth doesn't suit you.

[jinx]

i think totta was stressing the importance of getting the combination totally 'dialed in'.
Tuning can make or break any project. VERY ez to wind up with costly parts delivering shitty performance

[totta crolla]

That's it jinx, in a nutshell.

[nyberrg]

Sorry if the truth doesn't suit you.

The truth is it's a fucking work in progress. I could tell every detail of what I have done and so on so that you might understand where I'm coming from but I wont. Please just stop assuming im stupid instead.

[nyberrg]

i think totta was stressing the importance of getting the combination totally 'dialed in'.
Tuning can make or break any project. VERY ez to wind up with costly parts delivering shitty performance

I didn't ask "is it important to tune a car?" though. I know that already. I simply wanted some input from people who know a thing or two about high compression 4A-GE:s. The others, including you, managed to answer without coming off as assholes.

[totta crolla]

No assumption required, anyone who builds an engine and is then surprised by the compression ratio...

"I don't really know what I built"
"I ran a compression test on the cylinders and they all read high, really high, like 15 bar high"

[nyberrg]

No assumption required, anyone who builds an engine and is then surprised by the compression ratio...

"I don't really know what I built"
"I ran a compression test on the cylinders and they all read high, really high, like 15 bar high"

Refer to previous response ¯\_(ツ)_/¯

[Nick94tt]

I'm curious about the 22psi variance for one cylinder since it's a 10%+ gap from the other three cylinders on a fresh build. Hot or cold test? If cold, try one at temp.

Motor run in enough for the rings to be seated? Did the combustion chambers hold alcohol/water once the valves were lapped? Valve clearance correct?

Outlier cylinder rings may not have seated quite right, gaps too big, or the gaps are all in one line vs the usual offset (the angles vary per the motor and ring/piston manufacturer specs)

Bothers me more for a high compression performance build than say my 16v stocker.

Could try a leakdown test to see If you need to pull the head to touch something up. Quick way to figure out if the compression difference is valvetrain, bottom end, or head gasket. Air noises and bubbles make that fairly straightforward.

[nyberrg]

I'm curious about the 22psi variance for one cylinder since it's a 10%+ gap from the other three cylinders on a fresh build. Hot or cold test? If cold, try one at temp.

Motor run in enough for the rings to be seated? Did the combustion chambers hold alcohol/water once the valves were lapped? Valve clearance correct?

Outlier cylinder rings may not have seated quite right, gaps too big, or the gaps are all in one line vs the usual offset (the angles vary per the motor and ring/piston manufacturer specs)

Bothers me more for a high compression performance build than say my 16v stocker.

Could try a leakdown test to see If you need to pull the head to touch something up. Quick way to figure out if the compression difference is valvetrain, bottom end, or head gasket. Air noises and bubbles make that fairly straightforward.

At the time I do remember thinking that it could be due to the engine not being used enough before checking. I honestly don't remember if the engine was hot or cold, but as I said there is a big chance that the difference was just cause my test wasn't sufficient. I'm afraid I'm not sure what "lapped valves" and "valve clearance" means (english is not my native language, sorry).

I remember I made sure the piston ring gaps were not all in one line. I did not follow a certain degree spec though. IIRC I tried to put them about 90 degrees apart.

A concern of mine has been the headgasket, ever since I put the head on. It's just a stock headgasket cause I didn't want to run the TRD 0.8mm I had laying around, since that would bump the compression up even more. I'm pretty much counting on the headgasket to blow sooner rather than later, at that point I'll buy a thicker than standard aftermarket one in an effort to make everything a bit milder in the explosion department

[totta crolla]

Here is a video on valve clearance:
https://www.youtube.com/watch?v=nB8uVQxr3Pw
And one on valve lapping:
https://www.youtube.com/watch?v=YA-edFt6TuU
Some people say that valve lapping is not necessary these days, l'll not comment on that!

[Nick94tt]

Some people say that valve lapping is not necessary these days, l'll not comment on that!

In my case it was. It went from leaking to holding alcohol for an hour+ until it started raining.

Unless crossing your fingers that carbon buildup will seal it eventually is an actual plan. Sure it's less of an issue with all new parts. Mine were just 200k stockers buzzed clean with a scotch brite wheel.

I can understand some reluctance on a freshly machined tight tolerance setup though.

[nyberrg]

Here is a video on valve clearance:
https://www.youtube.com/watch?v=nB8uVQxr3Pw
And one on valve lapping:
https://www.youtube.com/watch?v=YA-edFt6TuU
Some people say that valve lapping is not necessary these days, l'll not comment on that!

Thanks! that's all within spec, lapping was done by pros and the clearance was adjusted by me.

[mr2mk1hero]

As someone who has gone through a carb build here's my advice. Get an AFR gauge if you haven't already. I think I remember your name actually, we messaged on Instagram once? And I mentioned an AFR gauge? Tuning carbs without one is just guesswork. Someone with A LOT of experience can tune carbs without one, but a novice with an AFR gauge will still likely do a better job than most experienced carb tuners without one. Jets make or brake carb performance. You can find 165, or even 170 or 180 main jets online easily? I bought 170s long ago.
When it comes to the actual AFR numbers, in my experience they really like to idle at around 13.8 - 14. But don't be obsessed with idle AFRs, they'll change often with temperature, humidity, etc, sometimes they'll go crazy for a second or two, especially with big cams. Half throttle works great on the leaner side for me and the engine pulls really well at half throttle around the 14.5 mark. If your AFR gauge responds fast enough, you'll see 15:0 every once in a while for a split second when you initially dip in the throttle suddenly. Wot works best around 11.8-12:2 as jondee said. But even a richer far at WOT worked great for me. i ran 11.5 for a long time and for some reason it worked really well for acceleration above 120-130 km/h at wot. Carbed afrs will always be a bit more unstable than EFI afrs, but that's ok, it's an archaic "imperfect" method of fuel delivery
Also, adjustable cam gears. Here's my experience on that one. I had adjustable cam gears from the start and I kept experimenting with different settings with the cams, without much luck. At the same time my AFRs were too rich at WOT (like 10.5). I was naive enough to think one had nothing to do with the other. So I visited a friend who''s an experienced tuner to get the cams dialed in and he set them using a dial indicator to the lift recommended by catcams at TDC, and all of a sudden, voila, WOT afrs were spot on.
I'm glad you're running nodiz because, other than an afr gauge, that was key for me for getting the kind of performance and responsiveness I wanted. Carbs really have more potential than people give them nowadays and if you do the supporting mods right and take a disciplined documented approach to tuning jets you'll be really happy with the end result.

[nyberrg]

As someone who has gone through a carb build here's my advice. Get an AFR gauge if you haven't already. I think I remember your name actually, we messaged on Instagram once? And I mentioned an AFR gauge? Tuning carbs without one is just guesswork. Someone with A LOT of experience can tune carbs without one, but a novice with an AFR gauge will still likely do a better job than most experienced carb tuners without one. Jets make or brake carb performance. You can find 165, or even 170 or 180 main jets online easily? I bought 170s long ago.
When it comes to the actual AFR numbers, in my experience they really like to idle at around 13.8 - 14. But don't be obsessed with idle AFRs, they'll change often with temperature, humidity, etc, sometimes they'll go crazy for a second or two, especially with big cams. Half throttle works great on the leaner side for me and the engine pulls really well at half throttle around the 14.5 mark. If your AFR gauge responds fast enough, you'll see 15:0 every once in a while for a split second when you initially dip in the throttle suddenly. Wot works best around 11.8-12:2 as jondee said. But even a richer far at WOT worked great for me. i ran 11.5 for a long time and for some reason it worked really well for acceleration above 120-130 km/h at wot. Carbed afrs will always be a bit more unstable than EFI afrs, but that's ok, it's an archaic "imperfect" method of fuel delivery
Also, adjustable cam gears. Here's my experience on that one. I had adjustable cam gears from the start and I kept experimenting with different settings with the cams, without much luck. At the same time my AFRs were too rich at WOT (like 10.5). I was naive enough to think one had nothing to do with the other. So I visited a friend who''s an experienced tuner to get the cams dialed in and he set them using a dial indicator to the lift recommended by catcams at TDC, and all of a sudden, voila, WOT afrs were spot on.
I'm glad you're running nodiz because, other than an afr gauge, that was key for me for getting the kind of performance and responsiveness I wanted. Carbs really have more potential than people give them nowadays and if you do the supporting mods right and take a disciplined documented approach to tuning jets you'll be really happy with the end result.

Yeah we did message on Instagram!

Can't get an AFR gauge now but I do have a spot for a sensor and I can borrow one for when tuning day comes so that's no issue. Where have you found the big jets? I bought 150's and 160's from DanST engineering but I think they only sold up to 165. Other than that I only found kits with a ton of stuff.

Did you swap out anything else in your carbs to get it to run right?

[mr2mk1hero]

https://www.jetsrus.com/
These guys have pretty much every jet in every size you can imagine.


Ok I had two pretty successful carb settings.

Carbs are 36.5mm Keihin from CBR600 F4.
First setting is on the rich side
3 turns out pilot screws
stock pilot jets (42)
jet needle on two factory washers (stock is 1 washer)
140 main jets (stock is 135/138)

The beauty of this setup is that it had an amazing responsiveness on low and half throttle. Nice fat torque too. The downside is that you didn't feel much additional drama on wot, so wot felt a bit underwhelming. The biggest advantage of this setup is fifth gear wot on highways. Acceleration was very impressive beyond 100km/h. Reaches 200 km/h with ease (for a bigport NA 4age It really felt like a larger engine than it is and it was really fun around town. Great for casual semi-aggressive driving through mountains, when you can have fun without going wot all the time. Wot afrs were 11.2-11.8 or so.


The second setting is a bit leaner
2.5 turns out pilot screws
stock pilot jets (42)
jet needle on one thick plastic washer (equivalent of 3 stock washers)
135 main jets (stock is 135 outer two carbs 138 inner two carbs)
This is the setting I have now, and I kept it because it feels more natural. There is a nice linear progression through throttle positions, wot feels like wot and light throttle like light throttle, and the upper rev range seems to be making more power. wot AFRs are 12.1-12.5. I haven't tested it on highways yet.

I think the last setting that I want to try is 140 main jets and just one stock needle washer. This might be ideal.
The 160 mains that everyone recommends including danst was absolute garbage for me. 9.5-10 wot afrs. No matter the cam settings, no matter what I tried, and I tried it all. 160 main jets, 150 too. Absolutely sucked. My compression is 160-165 psi across all cylinders, tested three times.

Also, what kind of air filter are you running?

[nyberrg]

First few dyno pulls are done. And it runs pretty good. My carb adjustments do not seem to be close to yours though, mr2mk1Hero..

It ran on 160 main jets, and it still needs more fuel. I haven't played with the needles at all though cause I can't figure out how to separate the needle from the diaphragm... Anyone know about that? Mikuni carbs from a ZX6R Ninja. The AFRs were pretty ok throughout the rev range but went a bit high (14.0-ish) at 6000-7000 rpm. If anyone could give me some input on what adjustment would be good to tinker with to fix that I'd appreciate it. My best guess is even bigger main jets..!

For a first try I'm very happy. Around 130 whp with only minor ignition tuning and a red line of 7300 rpm. Once I get more in to cams and fuel I hope that number can rise a bit more!

I don't know how to embed videos so here's a link!

https://youtu.be/ImPk-qpuJf0

[24milespergallon]

What distributor are you using?

[nyberrg]

What distributor are you using?

No distributor. Crank sensor and trigger wheel.

[oldeskewltoy]

Do you have a print out of the dyno??

[nyberrg]

Do you have a print out of the dyno??

Here's a photo of the computer screen from one run https://i.imgur.com/nHOhoFt.jpg
Apparently it's too large to embed

I didn't get to fiddle with cam timing as the dyno decided to break and read my RPMs somewhere around 170k. For now it runs with jets drilled to 180 (so probably 185-190). It's a bit rich but it'll do for now. Once I get a wideband for myself I will continue with the needles since I figured out how to adjust them now!

[nyberrg]

Might as well continue on this thread as it exists and it is about the same engine. Everything is chugging along nicely. I drive my car regularly and the engine is pretty much good, except for a few things...

The cooling system is very home made with FWD 4age parts. I use an NB Miata radiator with a 1.3 bar cap and a simple soda can as an overflow that has been empty at all times, hot or cold.

I have this issue where water dissapears from the radiator. I see no signs of a leak (as in no water on the floor of the garage), there is no white smoke, and there is no sign of water in the oil.

There is also no issue with the car getting hot as the radiator is massive. If it starts to creep above 90 I can rev it twice and the temp goes down instantly as the waterflow increases. I don't fill the radiator all the way up. I leave it somewhere between over the tubes and completely full.

I have tried my best to air the system, cycle the temp up and down until no more bubbles are coming out. Still didn't work. I thought it was a headgasket issue but it's been going on so long now that if it was the headgasket it should have showed more symptoms by now.

My catch can fills up pretty quickly, I use dual oil filler valve covers for more ventilation. It's pretty much only water in there though, and it smells a bit of oil. But if that water was coolant that was actually in the oil, shouldn't I be able to see a sign on the dipstick or in the oil, which I recently changed. There was no sludge really. I do however have a small amount of sludge in the filler caps. It is really not a lot though.

Is this just a product of me not using a proper overflow tank or what? I'm confused...