3400 Bottom end in a Fiero

[atomicpunk]

Hey guys. I'm looking to do something a little strange. I have a 88 Fiero GT 2.8 5 speed. It had a blown head gasket when i bought it, so i decided build the engine up right while i have it apart. I have a 3400 block at my house from a 99 Grand Am. I've been doing some port and polish work on the 2.8 Iron heads. I've also been porting the intake manifolds and exhaust manifolds. I'm trying to keep the engine bay looking as stock as possible. Will the 2.8 top end fit on the 3400 bottom end? i've heard that i'll need higher compression pistons from the 3.4 dohc. i know that the 3400 will bolt to the getrag 282 thats already in it, but are the engine mounts the same or similar? also, would a stock 3400 be ok? or would i have to use a different cam? also, what head gaskets would be necessary. what about lower intake gaskets? thanks for any help

[mickaz]

No the bore is too small ANYWAYS, 3400 aluminum heads will OUTFLOW ported 2.8 iron heads.

[atomicpunk]

i know the aluminum head will flow better. in fact i have a set of 3500 heads in my garage as well. but i'm trying to keep it looking as stock as possible. i dont want to have to run a new wiring harness or anything crazy. also, i'm not looking to make gobs of power or anything. i was originaly just gonna use the 2.8 block, but figured since i have a 3400 block laying around, i'd give it a shot.

so the bore of the 3400 block is too small to fit a 3.4 dohc piston in it? if so, is a higher compression forged piston my only option? or does the iron head 3.4 have a higher compression piston?

[Joseph Upson]

i know the aluminum head will flow better. in fact i have a set of 3500 heads in my garage as well. but i'm trying to keep it looking as stock as possible. i dont want to have to run a new wiring harness or anything crazy. also, i'm not looking to make gobs of power or anything. i was originaly just gonna use the 2.8 block, but figured since i have a 3400 block laying around, i'd give it a shot.

so the bore of the 3400 block is too small to fit a 3.4 dohc piston in it? if so, is a higher compression forged piston my only option? or does the iron head 3.4 have a higher compression piston?

The 2.8L heads and intake will bolt directly to the 3400. You have a further advantage of having the second design timing cover which is the only one that will accomodate the aluminum oil pan. Be aware that you must plug the hole in the timing cover beneath the water pump at the water inlet. You will also need to widen the diameter of about 3 of the bolt holes in the timing cover and water pump, or helicoil the holes in the 3400 block to accept the bolts from the 2.8L

The 88 has a different style front engine mount barcket and cradle mount pad. The mount pad will need to be clearanced for the aluminum pan and you may have to switch to the 87 and below "L" shaped engine mount bracket.

Contrary to popular belief, you can put the iron heads directly over the stock 3400 pistons and run the engine as is. I've done it on both the 3100 and 3400. Both were turbocharged however. The 3100 with iron heads on the stock pistons managed a high of 27 mpg with the performance (4.10 FDR) 4 speed Muncie in place. So although the compression was down, the driveability and economy was fine even with a turbo blocking the exhaust.

My advice to you is swap the complete engine (Fiero forum can help you here) which you've already decided against. You should be able to use pistons from the 94-95 camaro/firebird 3.4L also. I felt about the same as you regarding the wiring issue when I acquired my first 3100 and 3400 engine. The process is really not that bad using the Fiero harness as a start platform and a swap to the 730 ecm (covered on the Fiero forum) and starting with the Beretta code mask and an injector change would get you close.
Regardless of which route you take you're going to need some tuning.

[atomicpunk]

I understand what you're saying, but I'm not looking to boost this engine or anything crazy. I'm not looking to make 300 at the wheels or anything like that. Maybe one day, I'll do the whole 3400/3500 engine, but I'm just looking for a quick and easy bottom end swap. I really want to keep the car as stock/sleeper looking as possible. But if I was to swap in the 3400 bottom end with a 3500 top end, would i have to have a completely new wiring harness made?

[Pretty Boy]

The answer to this is yes i'm in the process of putting a hybrid 34/3500 into my 87 gt right now

[geoffinbc]

It is very doable. You will want to swap pistons to get compression back in the 9's. Use a 3.4L Iron head gasket. The ECM and top end will run the engine but you may need to fiddle with injectors and fuel pressure to get it to run nice. It is a similar swap to what us truck guys do when we swap out our 2.8L's for 3.4L's. The power gains are worth the effort despite what anyone else says. Although 3400 or 3500 top end parts make more power they are simply not as budget or time friendly.

[Fierobuffoon]

i agree with better, you can use Dohc pistons and rods int he 3400 OHV block, check your clearances, use the second design head gaskets from the 94-95 3.4 Cam/birds, install crane roller rockers or the 3.4 ones check to se eif they fit I use cranes.. use the 87 front mount with your oilpan and timing cover, id use the entire serpentine setup for simplicity, get an TPI adjustable fuelpressure regulator, and soem Mustang 34# an hour flow rate injectors then trim your Fuel pressure curve accordingly, the stock 88 Ecm is a batch fire as you know, the timing will be a little more advanced.. I would coat the Upper plenum gaskets in synthetic grease so you can pull and check the Fp for leaks etc.. Port and match up the Mid and lower intakes as best as possible, remove the Hump under the Injector nozzles on the lower manifold, as you knwo the stock plenum is restrictive past 5200 rpms anyways*4500 eng* but shoudl make very good torque

[IsaacHayes]

If you want the ironhead top end for looks, then why not use the 3400 block, 2.8 top end, and camar 3.4 RWD pistons and head gasket? That would get you to the same compression I would think since the camaro 3.4 is still gen1 iron head....

If you use DOCH 3.4 pistons you are going to have even higher compression than the iron head pistons would get you.

Camaro/Firebird 3.4 pistons will work in a 3400 block... That's whats in my 11.5:1 compression 3400/3500 hybrid.

[Velox65]

I'm doing the same thing with my 85, I'm using dohc rods and pistons and 3.4 fbod head gasket. The only thing I didn't see you mention is pushrods, with the roller am and iron heads I've read that you need shorter pushrods, however I'm not positive on that as i haven't gotten that far yet.

[Superdave]

If you want to keep it looking as stock as possible just finish rebuilding your old 2.8 and throw it back in. At the very least throw in a 3.1 crank and some 3.1 pistons, that's worth about 10 HP and 20 ft-lbs.

IMO bolting the iron stuff onto a stock 3400 short block is a complete waste of time and effort. Save the 3400 for when you want to go faster.

[2.8-350TBI]

I would take superdave's advice and listen very carefully. Thats a realm you almost want to avoid, especially using iron heads on bigger displacement engines.
Just take for example, iron head 2.8's feel like they lose steam somewhere around 5000-5200 (at least mine) and on a RWD 3.4 it feels like it loses steam right at 4500, thats when it becomes asthmatic.

But hey, its your motor and your car and it is very doable. You wouldnt need the crank or cam sensors, and you will also have to add a dizzy, and probably custom length pushrods. Oh yeah, pistons out of a TDC or RWD 3.4