2.8 vs. 3.1

[McCool]

Hey guys,

I've got a Fiero with a 2.8 in it and I've been offered a 3.1 out of a 92 z24. I've was planning on buying another 2.8 on the side and rebuilding it over the course of a year but now that I’ve been offered this 3.1 I got thinking about whether or not it would be worth it to swap out the 2.8 for the 3.1.

So what I am asking is how does the 3.1 compare to the 2.8? I understand that there isn't much horse power improvement but does the 3.1 offer better mileage, is it more reliable? etc?.

Can the 3.1's power be increased with small/cheap modifications? Or is it a ‘what you see is what you get’ type deal?

I'm just exploring my options right now so any information would be great.

Thanks,
McCool

[GutlessSupreme]

Pretty much all you're looking at is a crank with a longer stroke. The power increase is so negligible that I'm surprised GM even bothered with it.

If you're going to buy a whole nother motor and rebuild it, you'd probably be better off finding a newer 3400. You can probably find one that ate the LIM gaskets and took the bearings with it for pretty cheap. It would be a much better starting point than a 2.8 or 3.1. this is just imho.

[Alxsmt]

if you choose to use the 3.1 heads you would have to do a bit of rewiring for the cav ecu, the distributer wont clear the intake plenum. you could use the 3.1 block and the iron 2.8 heads too, but that probly wouldnt be worth it (unless the engine is a steal).

you can get cams for pretty cheap, but it seems like thats about it as far as getting power from a 2.8/3.1 cheaply. maby swap iron 3.4 heads on it? i think its possable and u would get to keep the distributer and stock ecu (some1 will know for sure)

if you want a little more power and a direct bolt in engine maby you should consider the 3.4L iron head engine. if i rember correctly all you need to do is drill new holes for the starter(you can even buy a templete)

3400 i belive requires new mounts and the cav ecu. which if you dont mind doing would be a great engine, its what i plan to do with mine.

then there is the 3500... which is similer to the 3400 swap but requires an external crank trigger and a few other things i dont know about

and u also got the northstar, and other random v8s people like to throw into em

[Superdave]

If you are going to go through all the work to swap in a new engine.. go with something bigger and better. the gen2 3.1 is only 140 HP.. a 3400 is 185 HP from GM and responds very well to cam changes and other bolt-ons.

the cavalier computer and harness is a must, there are several chips out there programmed to run a stock 3400 on OBD1 as well...

[McCool]

the 3.1 offered to me is very very very cheap.

I don't have the money or the time to invest in dropping in an engine that will reguire modification to the car as it is now.

What are my options for increasing power on the 3.1?

[Superdave]

the 3.1 offered to me is very very very cheap.

I don't have the money or the time to invest in dropping in an engine that will reguire modification to the car as it is now.

What are my options for increasing power on the 3.1?

the gen2 3.1 won't drop right in, there isn't room to run your distributer with the aluminium top end.


you can stick in a Crane h260 cam and bolt on your old 2.8 top end but it's not going to be much of an improvement over stock.

[BillS]

The longer stroke of the 3.1 offers a welcome boost in torque, but that's all you'll see without doing other mods. There are intake and exhaust tract issues that are well worth addressing.

[2.8RS]

you can get cams for pretty cheap, but it seems like thats about it as far as getting power from a 2.8/3.1 cheaply. maby swap iron 3.4 heads on it? i think its possable and u would get to keep the distributer and stock ecu (some1 will know for sure)

All of the iron heads are the same so no boost in power from 3.4 heads.

[Alxsmt]

oh thats good to know.

[3100 MPFI]

1988 2.8 fiero is 135 HP, and 160 TQ. 1992 3.1 Cavalier is 140 HP, and 185 TQ.

First of all, the 3.1 does respond well to a cam, and if you go to the work to get the block into the car, in the future, you can look into doing the hybrid thing with 3100/3400 heads and intake.

The 3.1/3100 will be more rev happy than the 3400 if it is done right. I know this because the 3100 in my Cutlass Supreme would rev to 7000 RPM, but it was a built motor with high compression, hot cam, etc.

With the 3.1 MPFI, you CAN use the distributor if you swap the intakes around. I am talking to a friend in PM who has a 3.1 MPFI for his Fiero, and the 3.1 had the intake flipped around for the distributor. He was needing pics of my 3.1 MPFI so he can swap it back (he is going to run DIS in his Fiero).

I don't know why I like the 3.1 MPFI so much. I know there is more powerful alternatives out there, but for some reason, I have always had a soft spot (or a hard one for that matter) for the 3.1 MPFI and 2.8 MPFI (gen 2 2..

The 3.1 MPFI is a good engine, and in a car as light as the Fiero, it will have decent pull. It is also capable of extremly high gas milege if it is done up right with a custom chip. They are extremly reliable, easy to work on, and parts are cheap.

If you are getting the engine for REALLY CHEAP, or FREE, then I say you have nothing to lose. There will be some issues to work out, but that is part of the challenge that makes these cars fun to drive once you get it all worked out.