Different 3.4l piston/head compatibility (Page 6/7)
lou_dias AUG 14, 06:20 PM
I built a 3100 block in 2015 that I over-bored to 3.4L and used stock F-body 3.4 pistons (no over-bore) for my daily driver Formula. I sold it after putting 30k miles on it. Still ran great until the next owner trashed the car. It made about 170rwhp at the wheels once tuned.
I kept the stock 3100 roller cam and used a ported throttle body, ported Fiero heads and a ported intake including the DAWG-mod and used 1.6 roller rockers as those engines come with but upgraded them to narrow-body full-roller rockers from Summit Racing.
I also used Fiero Store SSI valves for a little extra flow. I used Fiero Store short-headers and their cross-over pipe for better exhaust flow. Ocelot exhaust.
Edit: I used stock Fbody 3.4 injectors which worked well with my 88 ECM. Others with pre-88 ecms have problems with them and need to order pintle-style injectors.

You can follow directions here like I did. Compression was 9:0:1 ... though the Fiero Store valves raise it slightly.
http://www.fierosound.com/34engine/3400details.htm
Please read every detail. Admittedly I went the extra mile with some basic porting and valves, etc...but it was worth it.

For reference, a stock 3.4 will make about 135rwhp in a Fiero with no porting or exhaust work done. A 3400 swap will generally net you 155rwhp again with no extra work done.

Before that build I had a 3100 swap that blew a head gasket. That motor became the donor for my rebuild. I then installed a 3400 in place of the 3100. That one blew an intake gasket. I sold the car. They don't seem to like the Fiero's cooling system. For the amount of effort, it's cheaper and more reliable and more rewarding to do a 3800 swap thanks to many people offering parts for the swap.

I also built a version of that motor with the DOHC pistons with a bigger port job on the heads and Trueleo headers...and made 187rwhp on the stock 3400 cam. I've since built another one over-bored to 3.5L with custom pistons, cam and rods and bigger valves making on my last dyno did 216rwhp (but I'm not done tuning yet, still working on issues). So it it's really about how much you want to invest and what your goals are.

While I've snapped my share of axles, I've never blown a gasket.

[This message has been edited by lou_dias (edited 08-14-2024).]

1985 Fiero GT AUG 15, 09:42 PM
Well, I picked up the engine today, it appears in pretty good shape, rotates just with my hands on the crank pulley, but has the compression bumps (seems harder to turn over with a ratchet through the compression than my Fiero currently). It was loaded in my trunk with a backhoe, I drove with it in my trunk for 250kms, and unloaded with a lawn tractor with the arms on the front, worked surprisingly well, my Sebring is a beast haha.
82-T/A [At Work] AUG 16, 08:27 AM

quote
Originally posted by 1985 Fiero GT:

Well, I picked up the engine today, it appears in pretty good shape, rotates just with my hands on the crank pulley, but has the compression bumps (seems harder to turn over with a ratchet through the compression than my Fiero currently). It was loaded in my trunk with a backhoe, I drove with it in my trunk for 250kms, and unloaded with a lawn tractor with the arms on the front, worked surprisingly well, my Sebring is a beast haha.



With a low mileage motor, you should not be able to turn the crank with your bare hands... the compression would be too great. I'm 6'3" 225 pounds... a fairly big guy, and I cannot turn the crank on my daughter's rebuilt Iron Duke without using a socket wrench. But by comparison, when we took the motor out, it turned easy. A lot of that has to do with clearance and bearings of course... but mostly it's the compression.

I'd definitely recommend you replace the bearings and rings. You should be able to get all of that (a complete set) for $200 bucks. You just need to match the rings up to the pistons. I mean, you can do a lot of the stuff yourself of course (like honing the block). But at a minimum, I'd change the bearings and rings. You should STILL consider taking it to the machine shop and having the cyl walls honed if it's out of round or too worn. It's a lot of work to get that motor in there, haha... so do it right the first time.
1985 Fiero GT AUG 16, 08:36 AM

quote
Originally posted by 82-T/A [At Work]:


With a low mileage motor, you should not be able to turn the crank with your bare hands... the compression would be too great. I'm 6'3" 225 pounds... a fairly big guy, and I cannot turn the crank on my daughter's rebuilt Iron Duke without using a socket wrench. But by comparison, when we took the motor out, it turned easy. A lot of that has to do with clearance and bearings of course... but mostly it's the compression.

I'd definitely recommend you replace the bearings and rings. You should be able to get all of that (a complete set) for $200 bucks. You just need to match the rings up to the pistons. I mean, you can do a lot of the stuff yourself of course (like honing the block). But at a minimum, I'd change the bearings and rings. You should STILL consider taking it to the machine shop and having the cyl walls honed if it's out of round or too worn. It's a lot of work to get that motor in there, haha... so do it right the first time.



I obviously can't fully turn it over by hand, it rotates a few degrees until there's compression then only a wrench will rotate through that, and it is harder to turn with a wrench through the compression than my Fiero's current engine, aka, seems to have higher compression in this very very inaccurate test.
82-T/A [At Work] AUG 16, 08:43 AM

quote
Originally posted by 1985 Fiero GT:

I obviously can't fully turn it over by hand, it rotates a few degrees until there's compression then only a wrench will rotate through that, and it is harder to turn with a wrench through the compression than my Fiero's current engine, aka, seems to have higher compression in this very very inaccurate test.



Still man... don't go through all this trouble and do something half-assed. At 170k miles, that motor is shot. I'd at a minimum replace the bearings and the rings. You got this...
1985 Fiero GT AUG 16, 08:49 AM

quote
Originally posted by 82-T/A [At Work]:


Still man... don't go through all this trouble and do something half-assed. At 170k miles, that motor is shot. I'd at a minimum replace the bearings and the rings. You got this...



Kms not miles, it's about 105,000 miles, I will replace the bearings, maybe not the rings, pmbrunelle overbored the cylinders and installed slightly undersized pistons and rings to deal with heat from the turbo, I figure any wear on the rings/block now should be equivalent to that, but I'll keep it in mind, as I open up the engine, I'll obviously replace anything that is obviously worn/broken.
1985 Fiero GT AUG 16, 02:53 PM
For pushrods, I read I'll need 5.85" long pushrods for the roller lifters to the Fiero heads. Does it have to be exactly that, as I can't find any right now, how much of a variance can there be, as I can get 5.75" long ones easily.
82-T/A [At Work] AUG 16, 03:04 PM

quote
Originally posted by 1985 Fiero GT:

For pushrods, I read I'll need 5.85" long pushrods for the roller lifters to the Fiero heads. Does it have to be exactly that, as I can't find any right now, how much of a variance can there be, as I can get 5.75" long ones easily.




I know the heads are "new"... but you may want to consider taking the opportunity to port the heads a little bit. Or even better... you leave the heads on the 2.8 block (since it runs and can be a backup) and then go to town on the heads you took off... and just get new valves for them. Just a thought... you have the spares... might as well start building it up so your car doesn't have to be out of commission for too long.
1985 Fiero GT AUG 16, 03:06 PM

quote
Originally posted by 82-T/A [At Work]:
I know the heads are "new"... but you may want to consider taking the opportunity to port the heads a little bit. Or even better... you leave the heads on the 2.8 block (since it runs and can be a backup) and then go to town on the heads you took off... and just get new valves for them. Just a thought... you have the spares... might as well start building it up so your car doesn't have to be out of commission for too long.



I might do a little bit, but the nice shiny heads are going on the 3400 haha
82-T/A [At Work] AUG 16, 03:13 PM

quote
Originally posted by 1985 Fiero GT:

I might do a little bit, but the nice shiny heads are going on the 3400 haha




Hahah... I don't blame you.