7A-FE 4A-GE hybrid

[AE86represent]

Hey Dudes,

I have just aquired a 7A-FE engine for a pineapple ($50) and I am consideing building an 7A-GTE (7A short block, big port 4A-GE head, stock S15 turbo).

The only issue I can see is the strength of the 7A crank. I have heard they are quite weak, does anyone know what sort of stress they can take??

[slydar]

crank is fine. only it is 6 bolt. use 4ac flywheel.

rods are weak. seem to hold up ok in na applications, turbo might be pushing it.

without changing the pistons, using the 4ag head, you will end up with a higher CR i am pretty certain.

so to do one turbo.. its a fair bit of work.

now this is going to sound like im discouraging you for my own gain.. but ill buy it if its too much work

[driftism]

can you use any other standard rods instead? is there any websites on this conversion that are good...

[rthy]

as far as I know the forced induction has little effect on the crank, its stress from reving the thing that causes it to break. However if you add 4agze pistons in there then your adding to the recipricating weight and hence the force on the crank. If you keep the crank stock then you be very limited in how hard you rev it.

[Hen is a total nutcase]

There is a on toymods at the moment. Johnny knows what he is talking about.

For the lazy:
- FE pistons + GE head = 7.5:1 ish compression
- Rods are a weak point. Good to 7500ish
- Rod bolts are a bad design and are liable to let go. Again contributing to the lower safe rev limit

Hen

EDIT - Sammy boy McQ makes some very valid points too.

[rileymoore05]

i have a similar engine in my car, (7afe block, crank, rods and pistons) running a t25 turbo (for now).
havent started it as yet, but im already considering rebuilding it.
it is true, the rods are definelty not up to the job of a turbo motor. while the crank is a pretty good thing i wouldnt trust it over 7500 rpm for a few resons.
first is as previously mentioned, only 6 bolts on the flywheel, this can be overcome somewhat by doweling the flywheel to the crank, and secondly the crankshft drillings are not as effective at oil distrubution under high revs causing premature bearing failure (apparently). this is from information i have gathered from various sites and from my own analyisis of these engines.
im considereing machining the big end journals down on the 7a crank and fitting 4agze rods and pistons in a 7a block, then machining the deck back to spec. i think this will produce a very strong and torqey engine.

[slydar]

I am Dimitri, thats my thread

doubt youll be able to machine the deck back that far.

there are oe rods that can be used but not without machine work. there are apprently mitsubishi rods that will work, and bmw. people who know the specific rod to use arent very forthcoming though with the info, trade secrets.. gay.

remember it is not only the big end a little end diametre, but also the width and the journal that need to be right.

if you cross referance on say a crower (aftermarket rod builders) site youll soon work out there is nothing that will directly fit without machining.

6 bolts is fine for a crank. rb26s are 6 bolt. as are 18r's and 3tgs. there are heaps of really hardcore engines built around 6 bolt cranks. not really a big deal.

[rileymoore05]

yeah, the dowleing was just a precation really. dont like the idea of having my feet removed!
i havent worked it out yet but i think you are right in saying i wont need to remove much from the deck of the block.
i noticed in some jap imports mag (dont rember which one) there was a guy with a turbo 7afe in a rolla and he was using some type of aftermarket rod in that. I cant seem to find any aftermarket upgrade 7AFE rods so it looks like i might be maching the crank to fit the 4agze rods. i might try running the motor with the stock rods for a bit, im only running 10psi max. if it breaks im not too concerned as the bottom end owes me nothing anyway, got it from work for a case of beer..

[AE86represent]

Thanks for the input guys,

Now that I have the engine stripped and have examined the rotating assembly it is obvious that it will require a significant amount of work to build it into a reliable turbo engine.

I think that a simple nitrideing and balancing of the crank should be fine. The real issue is the rods (they look full sus spec , and obviously never designed with performance in mind)

I know Crower do custom billet light weight I beams for about $200-250 per rod, which is quite reasionable. And it shouldn't be too hard to find a forged piston that will both fit in the bore and work with the 4A-GE combustion chamber out of a Maile or CP cataloge (fingers crossed), all that is required is to get the rod designed to suit the piston.

My next question is big port 16V or 20V head?? I have read that the 20V head is much better for forced induction. But the 16V big ports are dime a dozen and much easer to setup in a AE86.

As for dowling the flywheel, Phaa, I would just run a blast blanket on the bell housing just in case.

[slydar]

big ports are good for nothing. haha no but if youre doing a build, youd never use big port. there has been enough discussion on the topic already.