Setup 7ag/5ag

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Information tirer de: club4ag.com
Liens: http://club4ag.com/faq%20and%20tech_pages/5A%20and%207A.htm

5age/7age


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.

The 5A-GE
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.



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…





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.




The 7A-GE
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.