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For a little touch of torque...
Introduction The concept of increasing the stroke to gain displacement in a gasoline engine is an old trick. Nevertheless, it is still a very effective form of tuning today and the 4A-GE is no exception. In the late 80’s, HKS developed a conversion kit consisting of longer stroke crank and pistons for the 4A-GE. The line has been expanded to array of configurations, which range from 8.0-11.6 in compression rates. This kit was called appropriately, the 5A-GE kit. Also in the early 90’s, Toyota revised the Corolla engine and 7A-FE was introduced. This larger stroke cousin of the 4A-GE produced as much power as the 4A-GE, but was designed for a more mundane driving use. It wasn’t long before tuners discovered that the 4A-GE head could be adapted to the 7A-FE block to make a hybrid engine commonly nicknamed the 7A-GE. Both the 5A-GE and the 7A-GE is still a viable option today for those looking into the performance characteristics offered by such conversion, so we’ll take a quick look at these “stroker” modifications. Keep in mind though, that displacement isn't the only way to make power and a 4A-GE does have many other options.
Once a very popular mechanical tuning approach to the 4A-GE engine, the 5A-GE engines proved that more torque could be had in the otherwise peaky nature of the 4A-GE. It wasn’t without demerits but the 5A-GE did fare reasonably well in the enthusiast market. HKS makes a range of internal components to suit your needs and 5A-GE was one of them. The 11.6 compression kit comprised of longer stroke crank, 81.5mm pistons and various bearings, rings and fastener sets is the most aggressive. They are designed to be built using the 4A-GE and proved to be very high quality in design and materials. However, the 5A-GE isn’t without pitfalls so we’ll discuss a few here in detail. The first thing we must note in the 5A conversions is the fact that the block needs to be modified somewhat to make room for the longer stroke crankshaft. The 5A-GE kit uses this long crank stroke to make approximately 1700cc displacement but slapping this crankshaft into the 4A block; one will immediately discover that it won’t spin without hitting something. No, it’s not a defective unit… So we modify the block by grinding away the inside of the crank case…. by placing the crank and working away where it hits. The clearance here should be no less then 1mm so you can avoid damage when there’s engine failure elsewhere. Next, attach connecting rods and repeat procedure. One note here…never grind the rod or crank as this will upset the balance and strength of the moving pieces…unless you are doing it for the purpose of getting better balance.
1. grinding away after careful inspection 2. Places to hit outside the cylinder walls too...
Second step, and the one most people forget, is the dynamic balancing of the crankshaft. Although the finish and materials is top notch when using HKS, the problem still lies in that the crank is longer in stroke. Often, the crank has worse balance than the 4A-GE unit that you took out, which is a real problem on an engine you plan to take to 7200rpm and beyond. An incorrectly balanced shaft can rob you of power beyond 7000rpm and more at higher rpm due to the inconsistent cylinder pressure and piston timing. Not to mention a myriad of failures it may induce in all sorts of places. The crank takes about 4 tons of force every stroke so think of it as being very flexible, contrary to how it may look when stationary. Balance, balance, balance…
3)Sanding the surface 4)install connecting rods 5)done! 6)the use of late model 4A-GE Block is highly recommended
Areas for grinding on the block for clearance of a stroker crank and connecting rod bolts. Crank and connecting rods should be hand assembled and checked for adequate 0.050 inch. clearance between block and connecting rod bolts.
Use 8mm Allen head to remove the front and back oil galley plugs for inspection and cleaning.
Next, always use pistons designed for the 5A-GE or similar stroked crank. The 5A-GE pistons have a different piston-pin height, therefore cannot be crossed over. Furthermore, the block to be used should be as late model as possible. The 4A-GE, as we all know bay now, went through many production design phases and with each iteration the performance potential increased in terms of strength and heat resistance and dissipation. Not all 4A blocks are equal! Lastly, most important perhaps, the 5A-GE is an expensive and labor-intensive modification. So, its final outcome is whatever you put into it. Taking time and some careful planning of funds and components will give you a strong, high torque rating engine that’s as free revving as your 4A-GE. But shortcuts will cost heavily and the final product will just as easily be rough and unwilling to perform.
With the introduction of the 7A-FE, the 4A-GE tuners gained an easy option to use the longer stroke 7A-FE block to gain higher stroke figures previously reserved for the daring and the well financed. The 7A-FE made its debut on the more mundane Corolla sedans in 1992. The block design of the 4A was kept thus came the possibility to use the 4A-GE head. The birth of the 7A-GE hybrid… The characteristic of the 7A-GE is generally more subdued than in the peaky tuned 4A-GE, but for all of the maximum revs lost to the 4A, the 7A makes up in torque. With longer crank stroke, the 7A-GE’s cannot be revved as far due to known failures of connecting rods and bearings. The maximum power band usually falls at as little as 6800rpm, a sign of internal stress, meaning it’s way-past the physical redline… Most tuners recommend its use below 7500rpm. Despite its conversion to the true-twin cam design and free-flow head, the modification still produces all of the 117ft/lbs of torque of the original 7A-FE configuration, and the power gains from the 7A-GE varies but is in the general area of 10% over a similarly equipped 4A-GE. Note however, that in the 7A-FE, the peak power comes in earlier at around 5700rpm compared to the 6600rpm of the 4A-GE. Because this is a custom application, the figures may vary by individual project. Like the 5A-GE and more so, the 7A-GE is a very universal in drivability and is highly recommended for street machines looking for that little extra push, who see occasional autocross or ET traps. Those looking into more elaborate systems like turbo or high-rpm usage should, however stay with the 4A-GE design for it’s intended sporting nature and previous data and upgrade parts availability. Also, the flywheel attachment of the crankshaft is inherently weak on a 7A-FE so making it rev high or boosting too much power on it is a little bit risky. Having said these, let’s dive into the world of 7A-GE.
Conversion to the 7A-GE hybrid need not be as complicated as the 5A-GE. This is because the block internals need not be torn apart and modified. Starting with a cleaned, adjusted and polished 4A-GE head, it can bolt right onto the 7A-FE block. This process is fairly elementary in nature… There are few differences in peripheral components depending on the engine orientation and the chassis it’s installed in, but all of the components should be readily available from one of the 2 engines you should have on hand the 7A-FE and the 4A-GE. The problem most people run into in this configuration is the timing belt. Because of the taller block of the 7A, the 4A-GE timing belt proved to be too short for the increased deck height. Why not use a 7A-FE belt? Well, the “FE” design head is a twin cam but is driven by the crank only on one cam. The other cam is driven off the powered cam by gears. A “slave-cam” twin. So what do we do? Traditionally, we had to go hunting in the bin at a parts store or junkyards. But, thanks to the few who visit Club4AG, a Porsche 924/944 has been rumored to fit. For this application, the crank cam-pulley from a 4A-GE has to be used… Obviously, the 7A-FE pulley will not drive the GE cams at the correct speed anyway… All else being done, the engine should have 1800cc and compression ratio of between 9.8 and 11 depending on which piston and 4A-GE head you used. Most applications use similar ECU and peripherals from the 4A-GE and seem to work quite well despite it’s increase in displacement. 7A-FE ECU is avoided because of it’s low rev-limiter and complexities in placing it in a car originally equipped with a 4A-GE. Perhaps an aftermarket ECU like the “Freedom” is potentially helpful in making it perform at it’s peak output with a particular grade of gasoline.
Here are some postings you might find helpful: (from Tech Talk BBS in the past) “…7AG does not feel or sound like the way the 4AG would rev. But it does like to rev and have no problems at this point in reaching 7500 rpms...I'm still babying the motor and just barely hit the 500 miles marker as of today...The deck does not need to be milled for the 924 belt! I have the 924 belt fitted tightly on the 7AG, provided that you use the 4AG Crank sprocket. The power band is quite impressive. As TruenoGTS and I completed the motor swap, he pressed that we have a drag run to see the difference of his stock AE86 and the 4AG. Promising to keep it under 4000 rpms on shifts, I agreed to the run (dang we just finished the motor...I don't want to blow it up!). So we're in the streets, and on first gear, I had about bumper and a half ahead of him. On 2nd gear, he was at my rear quarter panel. On 3rd, I had a car and a half on him. Finally on 4th @ 1500rpms, I was reaching 2-3 car away from him. We did a few more runs, and it averaged out the same. But the funny thing was when we got back to his garage, he told me he cheated and shifted approximately 5000 rpm! I said to myself," Not bad, not bad at all." :)…” –AE86GUY
“…We used the 4AG stock head gasket and did not see any need to modify the holes. So far the car is running within the normal operating temp. We didn't have to shave the head at all to fit the 924 timing belt. Although it might have been a good idea to get even more compression!! Hehehe…” --TRUENOGTS
“…if were going to do all this work anyway why not start with a motor with new pistons, rings etc. Plus this gave us peace of mind that the motor will last (provided that we don't dog the motor too much!!!! hehehe). If you can go without the car for about two weeks then I would go for the oversize pistons (from AE92).” “…There are a couple of pages to check out that could help: http://www.corollaperformance.com ” --ROSS
“…if you don't want to do the HKS stroker kit (Which cost hella bucks!) then this is the bang for your buck. Though it can still cost ya anywhere from $750 to $1000 (main -&- head bolts, gaskets, new timing belt, 7a bottom, flywheel, and machining if you decide to go with O.S. pistons). You can use your original pistons on this conversion to keep the same compression, provided that your pistons in good condition of course. The swap is pretty straight forward…” --AE86GUY
“…Hi guys, I and a friend did the conversion on his ae92 and I don't agree on the fact that it doesn't feel or sound the same as a 4ag. It's as rev happy as ever…. I'm sure there would be more power past that but the rev. limiter is in the way and who knows maybe we would be pushing our luck? And the other thing I don't get is the t-belt... We tried a 924 belt and there is no way in the world that would fit, might as well try to fit a timing chain from a 350 GM!!! The 944 belt fits right on like it was designed to go there. I found this out after comparing the specs from a 4ag belt and a 944 belt. Anyways, hope you have fun as much as we do with the 7a conversion…” –Pranchon
“When I ask for the 924 timing belt, Jason at McKenzizes brought 2 timing belt for the 924. He told me that I will need both of these belt to do the timing belt job. One timing belt was for $17.19 and the other was $39.00! I opened cheaper one and compared it to the 4AG belt. It was approx 2-3 inches larger than larger than the 4AG and it fit the 4AG crank sprocket teeth. So I decided to buy cheaper of the two and didn't bother to look at the other belt. Also, Jason showed me that those two belt are called timing belt on his computer. So when you buy the timing belt, ask for the belt that goes direct from the cam to the crank.” –AE86GUY “There are a few people there who have done this conversion and has not yet have any problems with their motor. ” –AE86GUY “…On the pistons I meant does the compression change very much in the 7AG i.e. 10.3:1 4AG pistons yield approximately 10.3:1 when used in a 7AF block with 4AG head. It depends what the cylinder (not head) volume is in the 7AF. Even if these are the same the compression would go up slightly because of the increased displacement...” –Patrick Ray
I'll try to answer them the best I can: 1 - I'm using the 7A oil pan, the front of the 4A oil pan doesn't match perfectly. 2 - 4AG NEW head bolts are fine, ARP would be even better. 3 - 7A flywheel again would be a better route, but you can confirm 4A flywheel by checking the specs against the Centerforce clutch specs and the Toyota Dealerships(They ahould know). 4 - Yes you can use the AE92 pistons...I'm using the 81.5 mm OS pistons from Toyota. 5 - Minor, you won't be able to use the left -&- right lower engine to transmission mounts (unless you do some major cutting of the back of the oil pan.) You need to fabricate a longer pipe from the head to the water pump. (I cut the original pipe in half and extended it with a hose and 2 screw clamps...) You will have to remove the heat shield from the downpipe, because the downpipe mount to the transmission will get in the way...(If you have a aftermarket headers, this will not be a problem for you or if you cut the back of the oil pan that will work too. Everything else is straight forward. 6 - Don't know that one...gots to dyno it... Hint: Best you get adjustable cam sprockets...you will know what I'm getting at will you slap on the timing belt and align the marks. Good luck to you...Race on! ~AE86GUY~ to Juan...
Special Tanks to all those who participated in posting and questioning on "Club 4AG Tech Talk" on the topic of 7A-GE and the help of all those who read and responded... This page is dedicated for you and by all means, e-mail any additional inforamtion you may have on this. I will gladly update and add as more information is gathered...