2.8 vs 3.4

[GTRS Fiero]

What gives the 3.4 so much more torque that the 2.8?  Is it just the bigger bore?  Does boring and stroking a 2.8 to a 3.4 return the same torque and HP as a factory 3.4?

[Raydar]

The additional torque is provided mostly by the longer stroke. More leverage.
3.1s also have this advantage, somewhat. (2.8 and 3.1 use the same bore size.)
The 3.4's larger bore doesn't hurt any, though.

[GTRS Fiero]

Are both the 2.8 and 3.4 ”slow-reving” engines?  I've heard the 2.8 described as a ”boat anchor”.

[GTRS Fiero]

The engine ran very well. It would outright scream, for what it was. It had enough power to absolutely shatter a Getrag differential. (I also swapped the Getrag for the automatic, while I had it apart.) It really seemed as strong, although not quite as "torquey", as my 4.9.

With that said, I am contemplating a 3.4 DOHC for the "ghost in the machine". Simply because it will pretty much bolt in using stock Fiero brackets, I feel comfortable doing the harness and ECM, and I have a line on an inexpensive one, with a crapload of spare parts.
(The DOHC is reputed to be a lovely motor for a manual trans. A 3800 SC, not so much. But that's a whole 'nother topic.)

Yes, I read that the 3.4 DOHC is a great engine for the Fiero, as is the quad 4.

Doesn't the club's fastback Formula have a Getrag mated to the 3.4?  I thought Archie used the Getrag with his V8 swaps.  Surely the V8 has more torque than a 3.4PR.  Which auto transmission did you use, and how was it for reliability with the torque?

[Fierofool]

Touching on a few things Raydar said, the Grooms 3.4's were generally bored .030 over.  The first conversion I was involved with came from Grooms.  They wouldn't take a 2.8 as a core and in fact, did not rebuild 2.8's at all.  I believe they had a slightly higher lift cam in them also. 

Jasper was the same way.  No 2.8's as cores.  Grooms offered a warranty on their 3.4 when installed in a Fiero, thanks to the success that Ed Parks at The Fiero Factory had.  Jasper nor GM would, saying it was an improper application though GM would warranty it for the S10 with a carburetor. 

When I started searching for a 3.4 for a former member, GM was selling crate 3.4's.  Like Raydar said, they were to go into the early model S10's as a replacement for the 2.8 carbureted engine.  Mind you, an engine that was never carbureted to go into a carbureted truck.  They offered a 3 year, 36K mile warranty for this application.

GM wouldn't give me a warranty if it went into a Fiero because the Fiero never had a 3.4 and because the starter boss had to be redrilled for the left side.  GM crate 3.4's were selling for about $2700 plus core for a long block, valve covers, pan and timing set.  No timing cover. 

Jasper held pretty much the same reasoning for not warrantying it when installed in a Fiero.  They were a little cheaper.  Seems like they were somewhere around $2300 plus core.

Grooms quoted a price of around $1600 or $1700 plus shipping to Atlanta of about $75, I think.  No core.  Since it wasn't going to be installed by a certified mechanic, they would only offer an 18 month warranty, unlimited miles.  Turns out, the mechanic that installed it for us was a certified mechanic, but did Fiero work at his home.  The engine didn't need any warranty.  It's still running today after at least 10 years. 

[GTRS Fiero]

The 3.4 seems to have an entirely different sound from a 2.8.  The 3.4 idle sounds good, but not so much when the throttle is opened up.

When the engine is bored, doesn't it require more air?  Does the larger bore kill the top end?

Interesting spoiler.

[Fierofool]

It does have a different sound.  Even when exhaling through the stock Fiero exhaust.  A little larger pipe might help. 

I don't know what the top end is, but you've seen some of the videos filmed from my car.  In those, I often hit 4500 rpm.  I regularly run up to 4500, and I don't feel any drop out.  I've never knowingly pushed it past that.  I recognize what it sounds like at that rpm and without looking, that's where I let off or change gears.  At Road Atlanta, my top speed was 105.  Simply because I was too chicken to come off the long backstretch any faster and hit the chicane. 

I think, as some others, that the 3.4 can breathe very well up to the stock engine's limits.  The Camaro and Firebird throttlebodies were no larger bore than the Fiero's.  The real bottleneck is just that, the bottleneck between the throttlebody and the plenum.  Some have opened that portion up and gotten more out of the engine, without doing anything to the plenum, itself. 

The 3.4 is simply the most free horsepower you can get when you replace a broken or tired 2.8.  It costs just as much to rebuild a 2.8 as to rebuild a 3.4. 

I don't know that I'd bore a 2.8 beyond .040, but supposedly the 3.1 in the Formula Fastback is bored .060 over.  He believed the engine came from a FWD van.  Chosen because of the heavier block and cylinder wall castings and sleeve.  That car's been around for a while, so apparently it was a safe venture. 

[GTRS Fiero]

If you pushed the 3.4 past 4500RPM, what would happen?

Similarly, what would happen to the 2.8 if you opened up the intake and exhaust?  It already struggles for air.

[Fierofool]

I have no doubt that if I pushed it past 4500 rpm, it would be running faster.    Redline is same as the 2.8.  There's always room for error, depending upon condition of the engine. 

[Raydar]

If you pushed the 3.4 past 4500RPM, what would happen?
...

With a stock intake, it would just sort of make a lot of noise, but not much more power.
Once I did all the stuff with mine (still with a stock, rebuilt bottom end) I would regularly spin it to 6K. Took it to 6500 a time or two. Never floated any valves or broke any engine parts.
Keep in mind that the DOHC uses essentially the same crank and rods, and those will spin to 7K all day long.

The Getrag that I killed was... tired. But I beat the snot out of it, too.
Everyone used to post on Pennocks that they had weak differentials. I simply proved it, again.
This is the main reason that I have a New Venture T-550 (aka "Beretta Getrag") bolted to my 4.9. The later Getrags had sturdier differential assemblies. (There's also the hydraulic release bearing that eliminates the sometimes problematic slave cylinder. But that's a whole 'nother topic.)
I don't drive this one "easy", but I also do my best not to shock load it. To kill the Getrag with the 3.4, I had to wind it up, and then side-step the clutch. I kind of learned my lesson from that one. 

[GTRS Fiero]

To kill the Getrag with the 3.4, I had to wind it up, and then side-step the clutch. I kind of learned my lesson from that one.

What does side-stepping the clutch accomplish?  Spinning the tires?

[Raydar]

What does side-stepping the clutch accomplish?  Spinning the tires?

Holy resurrection, Batman!

But yeah. Pretty much. The shock breaks the tires loose.

It also breaks differentials, as I so skillfully proved.

[GTRS Fiero]

What can I say?  I go back and re-read topics.  Sometimes, I have new questions.

[Raydar]

No prob. I've seen much older threads (here and elsewhere) resurrected. I've seen some threads on some hifi/stereo forums that are still relevant to me, even seven years later.

[ron768]

As stated by Raydar:But yeah. Pretty much. The shock breaks the tires loose.

It also breaks differentials, as I so skillfully proved.      I have done this with the stock 2.8 with the stock 4 sp in my 85 2M6. I haven't posted alot about my experience with the 2.8 but I would guess that I have run a stock 2.8 about as hard as anyone. Yes, I broke a 4sp manual trans by dumping a lot of rpm's (redlined) in 1st gear. Cost me $379.00 back in 1988 to get it fixed. Car had just over 36 K miles and NO, Pontiac would NOT cover it(of course it was out of warrenty) . My 85's original 2.8 lasted til it had 179K miles on it and spun a rod bearing a couple of years ago. The motor in it now is a 3.1? rebuild. We are still working on getting the fuel/air ratio right, but it runs good. When stock, my car would run out to 123 mph on gps. I have yet to find out what this motor will push the car to.