Different 3.4l piston/head compatibility (Page 1/7)
1985 Fiero GT AUG 10, 01:11 AM
I was reading recently about the 3400 SFI engine, and how the iron heads bolt onto that, giving you a factory looking engine with much stronger and more reliable bottom end. I hear people need to use different pistons to get good compression ratios though, as the aluminum heads have smaller combustion chambers. From what I can tell, there are 3 different options, original 3400 pistons which give about 7.7:1 compression, 3.4 DOHC pistons which give 9.7:1 compression, and one I've not heard anyone mention, the 3.4 pr pistons? I hear people put the DOHC pistons in the 3.4pr for higher compression, so would 3.4pr pistons in a 3400 block with 3.4pr (Fiero iron) heads=regular 8.5:1 compression?

Of all of these, what turbo boost levels would be achievable in a daily driver format, how would each effect power, and longevity, compared to unboosted but weaker 2.8s?

My thought is maybe the factory 8.5 is good for factory (3.4l) power off boost, with ample headroom for boost that the 9.7 wouldn't have.

I'm not specifically looking to do any of this immediately/ever, but I think a boosted 3400 block would make the most power with the best reliability of anything with the Fiero intake, as it is stronger and more reliable than the 2.8 and 3.4, and being boosted reduces/removes the issue of the restrictive intake/heads.

Edit: I'm aware factory intake and heads are bad, I'm not asking about how good they are, I'm asking about pistons and their correlation to safe boost in a relatively reliable turbocharged motor.

[This message has been edited by 1985 Fiero GT (edited 08-10-2024).]

jelly2m8 AUG 10, 03:56 AM
I am going to be REAL with you here. First. The most proven and agreed bottle neck of the 2.8 is the upper intake manifold. If the Fiero 2.8's intake manifold is it's biggest restriction , how the f/k can it feed a 3.4? 2nd quite a few 3.4 bottom with 2.8 Fiero intake manifolds end up for sale, there is a reason, they Do Not perform better, they are a disappointment.

If you want to do a 3.4, do the Entire 3.4, Intake manifolds included.

The 2.8 Fiero's intake is it's biggest let down, the 3.4L F-body using the same head at a higher HP absolutely proves this.

[This message has been edited by jelly2m8 (edited 08-10-2024).]

1985 Fiero GT AUG 10, 06:38 AM

quote
Originally posted by jelly2m8:

I am going to be REAL with you here. First. The most proven and agreed bottle neck of the 2.8 is the upper intake manifold. If the Fiero 2.8's intake manifold is it's biggest restriction , how the f/k can it feed a 3.4? 2nd quite a few 3.4 bottom with 2.8 Fiero intake manifolds end up for sale, there is a reason, they Do Not perform better, they are a disappointment.

If you want to do a 3.4, do the Entire 3.4, Intake manifolds included.

The 2.8 Fiero's intake is it's biggest let down, the 3.4L F-body using the same head at a higher HP absolutely proves this.




I am not talking about the Firebird 3.4, I'm talking about the minivan 3400 that comes with aluminum heads, etc, there's a difference. Also, with the use of a turbocharger, a restricted intake would become much less apparent, only issue with turbos is that the 2.8 and Firebird 3.4 are weak, and will blow up, from what I've read that is not so with the minivan 3400, they can handle some power. Granted without a turbo, it would end up being maybe 165-70hp (along with the mods I've already got on my 2.8), but with forced induction, that number can rise a lot, restricted intake or not. I'm not thinking seriously of this at this time, just gathering some information, seeing what others have done, and asking what the best pistons would be for reliable boost.
82-T/A [At Work] AUG 10, 08:58 AM

quote
Originally posted by 1985 Fiero GT:
I was reading recently about the 3400 SFI engine, and how the iron heads bolt onto that, giving you a factory looking engine with much stronger and more reliable bottom end.



Based on everything I've read, the 3.4 PR engine is significantly stronger than the 2.8 block. The wall thickness is nearly double in most places, and there are a few other improvements in just the block itself, even if dimensionally it bolts everything you need / want from the stock engine. I personally love the 3400... I've driven several of them (as completed 3400 motors) in cars like the Alero and GrandAm back in the day. The power was fantastic (I mean, relatively speaking), the torque curve was excellent, and it was an all around incredibly smooth motor. But I think compared to the 3.4PR motor... my thought is that the only real benefit would be the fact that the 3400 has a roller cam. This also (I think) limits off the shelf aftermarket camshafts that are available. But I'm not aware of the 3400 SFI having a better bottom end than the 3.4 PR.



quote
Originally posted by jelly2m8:

I am going to be REAL with you here. First. The most proven and agreed bottle neck of the 2.8 is the upper intake manifold. If the Fiero 2.8's intake manifold is it's biggest restriction , how the f/k can it feed a 3.4? 2nd quite a few 3.4 bottom with 2.8 Fiero intake manifolds end up for sale, there is a reason, they Do Not perform better, they are a disappointment.

If you want to do a 3.4, do the Entire 3.4, Intake manifolds included. The 2.8 Fiero's intake is it's biggest let down, the 3.4L F-body using the same head at a higher HP absolutely proves this.



Full disclosure, I've never driven a 3.4 Fiero, but I've heard that even with the stock intake, they provide a significant improvement in low to mid-range power. Obviously, that can be subjective. I see you have 2m8 in your sig, so ... hahaha... you've got 2 more cyls. That said, I do think the 3.4 PR is an excellent swap for someone who wants the most power they can get, while keeping the car looking as totally stock as possible.

That said, if I was totally unconcerned with looking stock, I'd say the 3400 SFI motor is a huge improvement overall in drivability compared to the 3.4 PR. I absolutely love the 3400 / 3500 V6 motors. They are really fantastic engines. And the 60 degree layout already is a huge advantage over other engines because it's more naturally balanced (a reason why many Ferrari motors choose a near 60 degree splay for their motors).

But yeah... I'm building a 3.4 myself, and doing so for the purpose of keeping the car stock, but getting as much power from it as I can. I just want to relive my high school / early adult years so to speak... in a car that still sounds / looks / feels like the car I had in high school did (which incidentally, is the exact same car... just been in storage for 13 years).

I've not really driven the car, honestly... since 2007, and even then, it wasn't very long trips. I had a 2.8 and built it out to a 3.1 with a hotter cam... and at 4,200 rpms, it would just smack you in the face how the performance would drop. For my engine (not to make this about me, but for the sake of all these things), I already have EVERYTHING accounted for and improved... EXCEPT the neck of the intake. That is the only thing I've not addressed. It's already been bored out by Darrel Morse back in the day, but the neck is still too narrow... I HAVE to do the DAWG mod... I just cannot weld in aluminum, but I may ask someone to do it.

I think it was CVXJET or SleekFiero who did an excellent write-up of the DAWG mod.


EDIT: (not specifically to Jelly 2m8), but one of the best benefits of either engine, so long as you have the correct ECM running it... is Sequential Port Fuel Injection. This makes a HUGE difference in driveability and performance in the lower RPMs. I spent an unreasonable amount of time reading up on it, and trying to determine if it even matters, and with the exception of wide open throttle above ~3,200 rpms, SFI provides dramatically better engine performance... with more lower-to-mid horsepower and better fuel economy. The difference of course being that SFI squirts fuel directly before the valve opens for the next valve in the firing order, where as batch just squirts everything on the left side of the motor, and then everything on the right side of the motor, with fuel pooling above the valve. It tends to waste more fuel. All of that said, above a certain rpm (I think it was roughly a little above 3,000 rpms), it starts making no difference at all because it pretty much becomes more or less the same thing.

But something I definitely want to try to keep when I convert to a 3.4 PR on my Fiero.

[This message has been edited by 82-T/A [At Work] (edited 08-10-2024).]

ericjon262 AUG 10, 10:00 AM

quote
Originally posted by 1985 Fiero GT:
Also, with the use of a turbocharger, a restricted intake would become much less apparent, .



this is false, the engine may make more power, but that doesn't mean the issues are gone, it now means your IAT's are higher, and the amount of boost you're making isn't as effective at making power.

the heads and intake are 90% of what makes a 3400 swap good, and a firebird 3.4 swap bad.

------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

I invited Lou Dias to trash me in my own thread, he refused. sorry. if he trashes your thread going after me. I tried.

1985 Fiero GT AUG 10, 10:10 AM

quote
Originally posted by ericjon262:


this is false, the engine may make more power, but that doesn't mean the issues are gone, it now means your IAT's are higher, and the amount of boost you're making isn't as effective at making power.

the heads and intake are 90% of what makes a 3400 swap good, and a firebird 3.4 swap bad.




Of course the issue isn't gone, I said it is less apparent, as in naturally aspirated performance hits a wall at a certain rpm, forced induction removes the wall, whether it's the maximum power output per psi of boost, or whatever, I don't care, I think it would be the most powerful of any 60*v6 with the stock intake, without sacrificing reliability to much/at all compared to the 2.8.

I am not asking for advice on intakes. There are dozens of threads talking about that, and I've read more about it than I care to have. I am asking about different pistons in a 3400 block with Fiero heads and intake, which are better for boosted power and reliability. I am not set on doing this, just thought of something I haven't seen anyone ask before, and figured it might help someone/give me a project in future.
1985 Fiero GT AUG 10, 10:16 AM

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


Based on everything I've read, the 3.4 PR engine is significantly stronger than the 2.8 block. The wall thickness is nearly double in most places, and there are a few other improvements in just the block itself, even if dimensionally it bolts everything you need / want from the stock engine. I personally love the 3400... I've driven several of them (as completed 3400 motors) in cars like the Alero and GrandAm back in the day. The power was fantastic (I mean, relatively speaking), the torque curve was excellent, and it was an all around incredibly smooth motor. But I think compared to the 3.4PR motor... my thought is that the only real benefit would be the fact that the 3400 has a roller cam. This also (I think) limits off the shelf aftermarket camshafts that are available. But I'm not aware of the 3400 SFI having a better bottom end than the 3.4 PR.





I know the 3.4 is stronger than the 2.8, but the 3400 has a structural oil pan, extra webbing in the camshaft area, etc. the 3.4pr is a improved gen 1 block, the 3400 is a gen 3 60*v6, even if strength is the same, oiling will be better, and blocks are easier to find and in better condition, all of which make me think it would be good to turbo, to work around the restrictive intake/heads of a Fiero.
82-T/A [At Work] AUG 10, 10:22 AM

quote
Originally posted by 1985 Fiero GT:Of course the issue isn't gone, I said it is less apparent, as in naturally aspirated performance hits a wall at a certain rpm, forced induction removes the wall, whether it's the maximum power output per psi of boost, or whatever, I don't care, I think it would be the most powerful of any 60*v6 with the stock intake, without sacrificing reliability to much/at all compared to the 2.8.

I am not asking for advice on intakes. There are dozens of threads talking about that, and I've read more about it than I care to have. I am asking about different pistons in a 3400 block with Fiero heads and intake, which are better for boosted power and reliability. I am not set on doing this, just thought of something I haven't seen anyone ask before, and figured it might help someone/give me a project in future.



I'm probably not stating anything you don't already know... but generally, overall lower compression is more ideal if you intend to boost your engine. Higher compression pistons essentially limit your ability to boost the engine since that's essentially what the turbo / supercharger is intending to do.

On the topic of the 3400 vs 3.4, I think the 3400 block is going to be more refined, just not sure if there's really going to be much of a power benefit since the 3.4 block is already built way better than the 2.8 block is. I think it comes down to which one is cheaper. I don't know how easy it is to bolt on stock Fiero parts to the 3400 (as in, brackets, etc.), or if perhaps you want to simply just use the 3400 stuff (assuming the brackets from the 3400 will bolt to the 2.8 heads). It would be interesting to see. Again, I know I'm repeating myself, but I really like that engine. I'd love to see a 3500 engine, as-is, installed in a Fiero and see how it performs with some basic improvements (stock cold-air Fiero intake, high-flow exhuast with some shorty headers, and perhaps a mild roller cam). I'd be willing to bet it would sound amazing, and perform fantastic.
1985 Fiero GT AUG 10, 10:32 AM

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


I'm probably not stating anything you don't already know... but generally, overall lower compression is more ideal if you intend to boost your engine. Higher compression pistons essentially limit your ability to boost the engine since that's essentially what the turbo / supercharger is intending to do.

On the topic of the 3400 vs 3.4, I think the 3400 block is going to be more refined, just not sure if there's really going to be much of a power benefit since the 3.4 block is already built way better than the 2.8 block is. I think it comes down to which one is cheaper. I don't know how easy it is to bolt on stock Fiero parts to the 3400 (as in, brackets, etc.), or if perhaps you want to simply just use the 3400 stuff (assuming the brackets from the 3400 will bolt to the 2.8 heads). It would be interesting to see.



Fierosound has a write up on this engine, some others do as well, from what I can see, it is basically bolt on, engine mounts are the same, etc. requires similar work to the 3.4pr (that requires starter holes, I think the 3400 requires some dremeling of an engine mount) I know lower compression is better for boost, fierosound built his as naturally aspirated, so went with the DOHC pistons, he's since supercharged it, noone else I've seen has built one specifically for boost to start with, the 3400 pistons would give extremely low compression ratio (maybe to low?) the DOHC pistons are definitely to high, I've never heard anyone mention the 3.4pr pistons, which should give 8.5:1 like a factory Fiero or 3.4pr engine (maybe? I assume they are compatible, but that's another question to be answered). What are the pros and cons of 7.7:1 3400 pistons versus 8.5:1 3.4pr pistons, how much power off boost, how much boost is safe, and power on boost?

As for price and availability, I just found one for 500cad in my area, no 3.4 Camaro engine within 750kms of me

[This message has been edited by 1985 Fiero GT (edited 08-10-2024).]

82-T/A [At Work] AUG 10, 11:24 AM

quote
Originally posted by 1985 Fiero GT:


Fierosound has a write up on this engine, some others do as well, from what I can see, it is basically bolt on, engine mounts are the same, etc. requires similar work to the 3.4pr (that requires starter holes, I think the 3400 requires some dremeling of an engine mount) I know lower compression is better for boost, fierosound built his as naturally aspirated, so went with the DOHC pistons, he's since supercharged it, noone else I've seen has built one specifically for boost to start with, the 3400 pistons would give extremely low compression ratio (maybe to low?) the DOHC pistons are definitely to high, I've never heard anyone mention the 3.4pr pistons, which should give 8.5:1 like a factory Fiero or 3.4pr engine (maybe? I assume they are compatible, but that's another question to be answered). What are the pros and cons of 7.7:1 3400 pistons versus 8.5:1 3.4pr pistons, how much power off boost, how much boost is safe, and power on boost?

As for price and availability, I just found one for 500cad in my area, no 3.4 Camaro engine within 750kms of me




That's all a really good point. I think 7.7:1 is pretty low... I don't think you'd be happy, and I'd question, quite frankly, how the engine would perform on the street... especially having to deal with stop and go traffic. But at 8.5:1 compression, that's really not so far off from the 8.9:1 compression.