4A-GE pistons in a 7A-FE engine

[Donald]

I have installed the pistons from my "broken crankshaft" 4A-GE into a 7A-FE that I am reconditioning. The intent of this mod was to increase the compression, to see if this might be an easy way to increase the power output of the 7A-FE.

The result is an inteference engine.

The 4A-GE pistons and pins fit quite nicely on the 7A-FE rods.
With the timing belt installed (and timed) everything clears. I did not have putty to measure how close the pistons and valves come to each other, but with the timing belt off, there is contact.

Both piston crowns come up to about the same level in the cylinder. The 7A piston has a recess in the top, whereas the 4A-GE piston has a slight dome with valve reliefs cut in it.

The difference in the angle at which the valves are set in the heads means that the narrower included angle of the 7A valves cause them to contact a part of the 4A-GE piston dome where there is no relief cut into it.

This installation was with the 7A head gasket. Maybe with the 4A head gasket it might clear, since that is a thicker gasket.
Unfortunately, that will bring the compression back down a bit, making this a questionable exercise, since I have no idea how much the increase might be to begin with.

[toyotaspeed90]

I was going to say that it will work, you will have high CR, but it will be an interference motor... the cutouts for the valves are at the wrong angle

[Donald]

A 4A-FE head gasket did the trick, my 7A-FE with 4A-GE pistons is no longer an interference motor.
The 7A-FE gasket is 0.7mm thick, and the 4A-FE head gasket is 1.4mm thick. That extra 0.7mm was enough to get clearance.

The engine is now almost completely built up. The crank, pistons, head, oil pump, oil pan and water pump are installed.
I think I will need to get a SR-5 radiator as the water hoses are run differently between the 4A-GE and the 7A-FE. I had bought a Civic aluminum radiator for that reason, but I now think it is too tall for the coupe body.

Tomorrow I hope to be able to install the light weight flywheel and clutch, and maybe even attach the gearbox.

The 4A engine and gearbox are still in the car, and I haven't done the wire harness swap yet, so I will probably be very busy this week.

Oh! for those of you who don't already know, the original plan was to swap the 7A-FE into my 1989 GT-S temporarily, while I try to find a 4A-GE smll port cylinder head and pistons, to make a 7A-GE.
If the compression increase I am trying to achieve yields reasonable performance, I might just keep the
hi-compression 7A-FE and not bother with the 7A-GE.

[4doorGTS]

Why bother with all the work to get the 7afe running in your gts just to redo it all anyways? just slap your head on it and be done no need to mess with the wiring.

[Donald]

Originally Posted by 4doorGTS

Why bother with all the work to get the 7afe running in your gts just to redo it all anyways? just slap your head on it and be done no need to mess with the wiring.

Well, (1) my GE head got screwed. When the crank broke, metal shards got up into the cam journals and chewed up the head and the cams. If it was good, I'd put it on and be done with it.

(2) Many people decry the 7A-FE as a piece of crap, although for stock Corollas the 7A-FE powered DX, posted one of the quickest 0-60 mph times, I think beat only by the FX16 GT-S (a lighter car). That doesn't take into account the models after the AE101, I haven't seen figures for those.
If this engine performs satisfactorily, I might just keep it the way it is.


Modification: When you change something to what you think it should have been from the begining

[4doorGTS]

I missed the part about your head being toast, I have a small port head with no cams but complete otherwise, I also have two bigport heads, I just don't know how bad shipping is going to be for ya crossing the boarder.

[Donald]

4doorGTS, you got PM.

Also, If I go to a small port head later on, I can run it with the 7A ECU and wiring. Won't need to use the AFM, no TVIS.

[Donald]

The 7A engine and gearbox are now installed.

I also put on an OBX 4-2-1 header. It almost fit perfectly in my GTS, but it comes up about 2" short of the catalatic converter. I'll have to have the muffler shop strech it a bit.
I also had a fitment problem at the head, where the alternator mount bracket and the header needed to occupy the same space. I had to do some grinding on both of ftem to make it fit. I have installed OBX headers twice before, and they fit perfectly. This one surprised me.

My '95 Corolla wiring manual just arrived, so I am starting the wiring process. As mooreofit said in another thread (7A-FE engine for AE92 sedan), it is not a job for the faint hearted. You definately need to be able to read a wiring schematic, and have a lot of patience.

[toyotaspeed90]

Originally Posted by Donald

4doorGTS, you got PM.

Also, If I go to a small port head later on, I can run it with the 7A ECU and wiring. Won't need to use the AFM, no TVIS.

you can, but then you need to find a very difficult to find distributor.

[REN69]

Originally Posted by 4doorGTS

I missed the part about your head being toast, I have a small port head with no cams but complete otherwise, I also have two bigport heads, I just don't know how bad shipping is going to be for ya crossing the boarder.

Too bad it's not a complete smallport... otherwise I'd be interested.

[toyotaspeed90]

I almost feel bad having as much stuff as I do here...... nah.

7afe vs 4age smallport piston (both on a 7a rod);

[jmaz87]

so were you just lucky that the wrist pin diameter was the same??? so smallports and 7afe's are the same but 4age is fully floating?

i am starting to piece my large-port 7ag together and i don't want the wrong pistons...

[toyotaspeed90]

Originally Posted by jmaz87

so were you just lucky that the wrist pin diameter was the same??? so smallports and 7afe's are the same but 4age is fully floating?

i am starting to piece my large-port 7ag together and i don't want the wrong pistons...

not lucky.....

early 4age's have 18mm full floating wrist pins
later 4age's, smallports, ST 20V's, and 4agze's all use a 20mm full floating wrist pin

7afe uses a pressed 20mm wrist pin

[jmaz87]

what about 1st and 2nd gen 4afe? the reason i ask is that i have a 7-rib 4af short-block and if i can just buy a gze crank, rod, and pistons and be done!!!

since i'm still using the 4afe head which isn't good for high-rev, would forged rods be a giant waste of money???
the reason i ask s because i always think of rods for high revs and pistons for taking boost/compression so i should only need the crank, oem rods and forged pistons right??? (staying under 18psi with MS)

[jmaz87]

OH and i Dyno'ed again yesterday i will scan the updates and post today