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4AGE RWD Conversion: Modifications 

This section is relatively brief as I have no real first hand experience at modifying 4AGEs for increased performance. As I have said all along, my firm belief is that the most cost effective way of obtaining more performance is fitting a more powerful engine.

Having said that, I have learned a few things over the years, which are included within this page. As far as I know the information is accurate, but as I have not actually undertaken these modifications myself I am unable to confirm their validity 100%.

Page Contents 

Carburettors Ignition Systems Turbo Charging Blow Off Valves
Twin Charging Intercoolers 4AGZE Mods 7AGE

Conversion to Carburettors 

Many people (poor, misguided souls!) convert 16 Valve engines to carburettors. 40 or 45 mm Weber or Dellorto side draught carburettors tend to be used. 40 mm tend to be a little smoother, however, 45 mm give more power but are a little less tractable - although by no means difficult to live with. Be aware that the correct intake manifold must be used for the engine: TVIS engines require a different manifold to later models. I do not have the owner’s details for what follows - if this is your car please tell me and I will give you the credit:

"With TRD 268 duration L10 Cams on a head with 10.1 compression (via skimming), tuned headers and 45 mm Webers I use 145 mains, F15s and 190 correctors. It's pretty much set up for high end power and is a bit fluffy down low. It gets driven relatively hard (at least in low gears) most of the time, and I seldom get into 5th gear".

The 20 Valve engine could also be run on carburettors, however, a RPM trigger would be required to activate the cam timing solenoid valve at around 4500 rpm and an inlet manifold would have to be custom built.

Carburettor Ignition Systems 

There are a few different options to get the ignition system to run with the engine converted to carburettors. One way is to use a stock distributor but operate it via an aftermarket ignition module. These can work well, but cost the equivalent of about $250 US in New Zealand.

Bill Sherwood (crazy damn Australian) has his AE 86 Sprinter running a fuel only aftermarket ECU EFI system. His stock distributor is controlled by Bosch ignition module part no 249-9-222-067-016. It does not allow advance, but this may not be a real issue for you if you are track racing etc. Bill’s car is street driven and works OK.

The module has 4 terminals. On Bill’s car (first generation 4AGE) Terminal '15' is fed with 12 volts when the ignition is turned on. Terminal '16' is wired to the negative post on the coil (any old coil will do). Terminal '7' goes to the black wire coming from the distributor. Terminal '3' is connected to the red wire. The white wire is cut and not used. The modules cost about $30 US from a Bosch Dealer. Bill has a huge page on all things automotive, including modifying the 4AGE up to about 240hp - check it out here

Another option is to replace the 4AGE distributor with a more conventional one. 2T or 2K electronic ignition type distributors are a popular option, but require a bit of modifying to fit, including fitment of the 4AGE distributor drive gear. You can then run vacuum and mechanical advance and use the standard coil/igniter pack.

Ross Mackenzie runs a 'Fraser' Lotus 7 replica powered by a 3SGE on carbs. He uses a Nissan distributor to run his engine, as follows:

"The dizzy in my car is from a Nissan E15 non turbo engine. These were fitted to mid 80's Pulsars and Sentras (probably others as well). The end of the dizzy body needs to be machined down to match the std 3SGE dizzy dimensions as does the end of the shaft, which is then fitted with the Toyota drive gear. A clamping block needs to be machined (or filed). This block is bolted to one of the original clamping holes on the head. I have utilised the Nissan adjustment slot which bolts to the clamping block, giving a good range of rotation. Once the dizzy is positioned on the engine the basic geometry of the block and dizzy adjustment will become self evident.

The vacuum advance is removed and the base plate is locked down. I have sealed the hole with a piece of aluminum glued in place with Devcon. Use the standard Nissan dizzy cap and aftermarket 8mm leads. If you wish to retain the Toyota plug end they will have to be drilled out to accept the 8mm leads. I guess you could use aftermarket ones. All the electrics are contained in the dizzy (no separate igniter) with only 2 wires. On mine they are blue (-ve) and black and white (+ve). Just hook them up to the coil.

The advance is 15-17 degrees at idle and 32-34 degrees at around 3000 rpm. According to Lynn Rogers and Neil Fraser, this is perfect for the 3SGE. Total cost.... around $US 75.00 including Dizzy, new rotor, cap and leads. I got the machining for free.

To answer your question about why I removed the mechanical advance - well, because I was told to. I'm not sure of the reason for only using mechanical advance, but it is an old method. I think that it is because we are already running so much advance at idle (16 degrees-ish on mine) that it just isn't required. Regardless of theories it works well. It is pretty much the same as far as the advance curve goes - I don't have a good understanding of the intricacies of this subject, but at the end of the day this particular dizzy has the required range and rate of advance. I believe that the advance curve is similar to that in the custom computers - remember that this mod has only been used on carbed engines. Most of us are running 45mm DHLA or DCOEs with 40mm chokes and jetted to suit the intended use (road or track)."

I would be curious to know if it goes any different with the vacuum advance connected. Also the distributor off the 3A engine looks like it may have some promise - it is all self contained also. If anyone has managed to modify one to run a 4AGE please let me know.

Turbo Charging 

The Supercharged 4AGZE has a steel crank, stronger block than the earlier models and forged pistons (which is why they rattle a little until they warm up), so if you want to build a turbo engine then this is an excellent starting point. People have also used this engine’s crank and block as the basis for naturally aspirated race engines. In many ways the earlier 4AGZE engine is better for high horsepower as it has bigger head ports and slightly lower compression.

Frankly I think that turbo charging a 4AGZE is more effort than it is worth. While I believe a 4AGZE is an excellent basis to add a turbo to - face it, other than fabricating an exhaust manifold there is very little else the engine requires in way of modifications - the concern I have is the cost then incurred with an aftermarket EFI system, and even more importantly is the inability to find an adequate gearbox to channel the power through. 

I suspect that in excess of 200 horsepower is very easily achievable from a turbo'ed 4AGZE, however, I also believe you will be changing gearboxes on a regular basis. I will say it again - if you want 200-250 horse fit a 3SGE. If you want 250-350 fit a 3SGTE. At least you can get gearboxes etc that will handle the power easily, and also you can still run a standard ECU. Comes down to how much you want to spend I guess.

If the following info is yours, please let me know.

"Turbo: T-25, or T-3 $400-$500 new, you might get a rebuilt, or used one cheaper.. Why anyone would undertake a project like this with a used unit is beyond me.... 

Turbo: CT-26 or even any Garret T-25.. which might even be cheaper and smaller. The T-25 should be able to handle 250hp, and are very plentiful... I would suggest getting a oil & water cooled one, just for reliability sake, but an oil only would be fine. Get two small "T" fittings, and splice into the heater lines, run the open ends to both connections on the Turbo...

Fueling: Here’s the tricky part. I would not use an AIC (additional injector controller) on most motors, especially if the distribution to the cylinders is uneven. The best, simplest bet would a rising rate fuel pressure regulator. Harder to get tuned just right, but easier and cheaper to install... If you really get serious, skip the AIC step and just get bigger injectors and a reprogrammed ECU/ aftermarket digital fuel injection setup....

Ignition - Stock ignition should be fine to 10psi, but you may want to run some kind of boost-dependant ignition retard..."

Blow Off Valves 

If you want a good cheap blow off valve then an excellent option is a plastic Bosch unit, part no 0-280-142-103 or W-040-440 (Both numbers are on the box, I am not sure which is the part no!). They are just as big as the high dollar big name anodised aluminium ones but cost about ¼ of the price. If you want a bigger airflow, buy two. These are standard fitment on SAAB turbos etc, so they aren't too bad.

As for plumbing the blow off valve in, if the car is MAP sensored you can dump the air to atmosphere. If it is AFM then you need to vent the air back to the inlet side of the turbo, otherwise you will confuse the EFI system, as it has already measured the air you are now dumping to atmosphere, hence the injectors will be over-fuelling for the air the cylinders receive.

A question though. Say you fit your blow off valve, and so the turbo no longer spools down between gear changes. That is all well and good, but surely if you didn't have a blow off valve then although the turbo spools down a little between changes, it also pressurises the inlet tract between the shut throttle butterfly and the turbo - effectively building up a reservoir of air to fill the vacuum when the throttle snaps open again? This is the exact air that the blow off valve dumps, so when you open the throttle again the turbo has to pressurise a larger volume...?

Is anyone able to provide figures on performance with and without blow off valve connected?

Twin Charging 

Twin charging is when you run both a supercharger and a turbo together. The idea is that the supercharger reduces lag by providing boost at low RPM while the monster turbo spools up. If this is you please let me know:

"I currently running the turbo and SC in series together. I run about 21psi of boost. The original HKS kit had a bypass valve installed to divert air around the SC and then it would shut off the SC. I have the same thing on mine. I have the bypass valve open at about 14 PSI, and the SC disengages shortly after that. 

Now, since the bypass valve bypasses the throttle, I have wide-open throttle. Not a problem when I’m accelerating.... but, when I let off the gas, the valve stays open for a second and the car is still accelerating. Now, this is the same way the HKS setup did it, so I know there must be a way to do it properly. Gerald San Agustin (‘88 MR2 Twin charged) told me he is using some type of a VSV to cure the problem.... Any ideas? Basically, I need the valve to open at 14 PSI, but I need it to instantly close as I let off the gas...

For fuel I’m using 550 injectors from RC Engineering and an SDS engine management system.

Matt '88 Twin charged"

My above comments about ECUs and gearboxes remain! It is easier with a transverse transaxle arrangement  as the 4AGZEs already come with the super heavy duty unit the 3SGTEs use.

Of course, maybe I should go into business making bell housings to bolt Supra gearboxes to 4AGES...


The supercharged engines come with a factory intercooler. On FWD cars it has 12 rows and sits on top of the head. Cooling air is delivered by means of a bonnet scoop. MR2s have an 18 row intercooler located on the side of the engine compartment and a fan is used to help draw air though it. In both cases the plumbing from the supercharger to the inlet valves is biased towards the rear of the engine hence a fair degree of modification or fabrication will be required if you turn it around for RWD.

The intercoolers themselves have both the inlet and the outlet on the same side. Obviously if you can fit an intercooler behind your grille then you will gain better cooling effect. And by the way, water/air intercoolers should only ever be used if your space restrictions prevent you running an air to air intercooler - they will NEVER perform as well as a straight air to air unit. It is all to do with thermodynamics and heat transfer losses. The more heat transfers you have, the less efficient the cooling process is.

The catch 22 is that an air to air intercooler will require longer air system plumbing, hence adding to lag.

4AGZE Modifications 

It is possible to put a larger crank pulley on the 4AGZE to drive the supercharger faster and so make more boost. 165 mm is the largest pulley that will fit, and one will make about 10 PSI boost. Boost over this can be achieved by fitting a smaller diameter SC pulley, however the SC rotors are Teflon coated and this can apparently melt above 10 PSI (although some say 12). Apparently up to 16 PSI is possible, however, this may only be wise for short duration use - such as drag racing etc - I would not recommend it for road use. Mo had this to say:

" I feel pretty good about my ability to get 200 streetable hp out of this engine, based on HKS's "stage 4" configuration for a US Supercharged car, which simply includes an exhaust, intake, ignition, pulley, cams and cam gears. They claim 188hp for that set up."

And on the subject of modifying the 4AGZE Ron Scanlan says:

"Why change the pistons? They are already ceramic topped and forged. The bottom end of this engine is bullet-proof, so why waste your money? Run it and stay out of detonation and you'll have no problems. If one day it gets tired, throw another good block at it.

My old 4AGZE has had the life thrashed out of it for 18 months now and its running just fine. :-) It has 156HP at the wheels, and when I chucked in a couple of 288 deg cams for a laugh it shot up to over 188hp @7000+ The idle sucked unfortunately, and the HP was not in a sensible place, so I took them out.

Mind you, it was fun to floor it off the line and get traction, only to have it break away as you got to 7000rpm !!! ;-> The pulley's that I do, exchange, are the same diameter as the HKS unit, which is 165mm o/d . This gives 0.7 bar (10 lbs) of boost."

The supercharger runs a very thin oil, which is critical. Ron again in reply to a question: "What oil did you run in the supercharger? I'm unsure on the availability of the Toyota oil. I've various comments about using 90 weight gear oil and the like but what did you use?".

"I ran Castrol VMX, and it has never given a bit of trouble. Even the local Toyota dealer asked me about this one. It sure is cheaper !!! I looked at the oil that came out and it was pretty thin, it also needed to be a gear oil. So it occurred to me that VMX should work just fine."

The 4AGZE has a ‘SC 12’ supercharger, whilst the 6 cylinder 1G-GZE (which looks like a 6 cylinder 4AGE) has a ‘SC 14’, which is bigger. This supercharger will NOT fit on a 4AGZE as it is longer than the SC 12, and therefore interferes with the intake plumbing. If you are fabricating your own intake system this will not be a problem.

HKS produced a kit that added a turbocharger to the 4AGZE, which is known as ‘Twin Charging’. This is very expensive to do (US $6000 at last listed pricing), but can reliably deliver over 300 horsepower. These kits are extremely rare.


The 4AGE is part of a family of engines - there are also 2A, 3A and 7A engines which correspond to 1300, 1500 and 1800 cc capacities respectively. It is possible to mix and match parts within the A-series engines, hence producing a 1300 cc 16 Valve motor, which some people are doing for 1300 cc competition classes, or an 1800 cc supercharged engine…..

This is an area of fairly recent interest and information is scarce, however, the 4AGE is the only real performance version and so has stronger cranks, con rods, pistons etc, so although you may be able to bolt the head etc on the bottom end may become a weak link. Grant J Mikosz has this to say on modifying 7AFEs and making 7AGEs:

"Actually there are 'serious parts' out there for the 7A-FE...people have already "been there, done that"...know what I mean? For example...
Pistons: 4A-GE pistons fit perfectly, just pick the C/R you want and go for it. 
Rods: I know of at least one individual that has steel rods for the 7A engine, so they do exist. 
If you plan to use the 'G' head, the timing belt from a Porsche 924 will work just fine. 
I'd say that 250hp at the wheel of a 7A-FTE is certainly achievable, but be aware that he crank is supposedly not as strong as the 4A-G....that said I know a car here that is turning 8,000+ rpm on a stock bottom end, with a ported 'G' head and 304º/288º cams and carbs etc.. 
The difference in displacement comes from the longer stroke in the 7A, but aftermarket rods exist, however, an aftermarket crank does not. Even so, the stock bottom end should deliver 200hp without serious trouble." 

Toyota is reputed to have built an 1800 cc 20 Valve for the 1995 Tokyo motor show… Having said all that - repeat after me: if you want 250+ horse put a 3SGTE in... 

Next: EFI System Operation in Detail 


Copyright © 2000 SpeedTECH Last modified: January 23, 2000