This may be just a stupid idea. a couple of weeks ago, I was swapping heads on a front drive 3.1( no spark plug threads in one cylinder). I used the head off of a 2.8(also front drive). The bore size is the same, even the cast in part number on the head was the same. the 3.1 pistons, however, had a much bigger dish than the 2.8 pistons. No doubt to keep the same compression ratio with the longer stroke. So-to the point of this post- if you want higher compression from your 3.1 you could use 2.8 pistons, right? I once used a 2.8 ring to replace the top ring in a 3.1 that had the moly flaking out and causing low compression. that car is still running with 277000 miles on it. Just a thought- maybe a stupid thought, but one nontheless. oh, by the way, anyone need a set of 2.8 pistons? Free to good home!

 

The only difference between the 2.8 and 3.1 is the crank, called a stroked crank. compression is the same.

 

are u sure those dishes are to change compression? or are those the dishes to allow proper valve clearence on the front wheel drive version of the 2.8L/3.1L. Our rear drive 2.8L's and 3.1L's are equipped with a flat topped piston setup, becuase our engines do not have the same heads as their front wheel drive counterparts which have splayed valves, and require the dished pistons.

 

don't know about the compression on the front wheel drive cars but on our cars it's 8.5 to 1 and is the same on the 3.1 and 2.8

 

actually 8.9 : 1

 

for FWD applications, I have heard from a guy that by putting 2.8 heads on a 3.1 block, compression is raised. I don't know how true this is.

 

From some reading on the 60*V6 motor that I have done, GM put really small chambers in the FWD heads because of the splayed valve arrangement. I think that it was both for clearance and for lower compression that they used the dished pistons. I do know that you can't use the heads on any RWD engines. In any case, using those pistons in a RWD 2.8 or 3.1 would probably give you compression rivaled only by that of a Briggs and Stratton lawnmower. That's just my $.02 worth.

 

I think you can use the splayed valve Gen II aluminum heads on a Gen I motor, as long as you use the Gen II pistons. I started to look into that, when I was making a price sheet for rebuilding my motor, but never followed up further. Seems if I was to tear the motor down anyway, changing the pistons wouldn't be a big deal... it'd be either buying 2.8 Gen I pistons or 2.8 Gen II pistons, and with luck, cost would be the same. But then there's the question of whether Gen II pistons can be pressed onto Gen I rods. Did we ever find out "for sure" if a Gen II crank is the same as an '87-up Gen I crank?

 

I'm not sure about the crank but the Gen II heads would not work on a Gen I motor -- even with a piston change. The reason is due to the location of the intake ports on the cylinder heads. Gen I heads are siamesed; Gen II heads have the ports equally spaced. Now if the intake manifold/plenum could be made to work -- we'd be home free

 

i'm not to interested in doing a swap like that, but now you've got my curiosity going around in circles. If you were to use the Gen II styled intake plenum and manifold, along with the fuel rail, would it be compatiable to be hooked up with the computer that's alraedy in our car? Just curious on that, i'd think that it would. So therefore, a f-body would end up switching heads, pistons, intake manifold, plenum, fuel rail, just in order to get the more "modern" technology. Was there any performance gain between these GenI and GenII motors? just curious now.

 

Well yes and no... It would work in theory HOWEVER due to the plenum design on FWD cars, we cannot mount the distributor in the motor. So the intake would either need to be modified so we could use the distributor or... convert to DIS ignition which would need a computer swap.

According to the GM performance book the splayed valves did liven up the acceleration a little

 

plus the entire manifold/plenum is assbackwards on the FWD motors.........the throttle body is right over the tranny's bellhousing..................if somebody wants a FWD 3.1 core to play around with, i know where to get 4 for free, but you need to come pick them up where i work

TomP, your local, want one?

 

I might......

 

Thanks '91Teal, but I've gotta pass... my father would kill me. Right now I've got two axles, two front bumpers, two fenders, and the rear 1/2 of a Firebird in the backyard. You should see the basement! Could I make off with just the heads? (I have two pair of 2.8 heads in the basement, I don't think anyone would notice a third pair! )