3.1 stroking and piston clearance?

[johnc]

I noticed that my 2.8 pistons top out even with the edge of the cylinder. How do you use a 3.1 crank if the stroke is longer? On another post, somebody stated I needed higher compression pistons to make this work. Are they domed with valve clearance depressions, or what?

[v6h.o.]

the pistons for the 3.1L which you need, have the wrist pin higher up compared to the 2.8L piston.

otherwise yes, you'd have the pistons out the bore by quite a bit!

to turn a 2.8L into a 3.1L you only need the 3.1L: crankshaft and pistons.

is your engine an Iron headed engine or Aluminum?
if its iron headed, you need a set of Iron head 3.1L pistons. regular aluminum headed ones have a much larger dish to them thus drop the compression ratio.

[johnc]

Seems like the volume moved would be the same on both piston setups, but I am no engineer. My engine is from an '84 s10 and has iron heads. It has the one-piece rear seal. The engine is carb'd.

[614streets]

You dont need higher compression pistons to make it work , I was simply telling you to me the validity of going from a 2.8 to a 3.1 is "null" in my own opinion unless you increase the compression ratio. Again this is just a personal judgement of my own.

All you need are 3.1 Iron head pistons which were used in the camaro/firebird or the Izuzu rodeo 3.1.

[johnc]

I think you are right about the compression issue. I was thinking of using fiero heads if that would help. I want to stay with a low pressure fuel system, like the carb or tpi. Does this limit me to just the fiero iron heads?

[614streets]

The Fiero heads are the same as the ones found on your 2.8 so unfortionately that isnt the anwser. I spent some time searching for a 3.1 piston that would yeild 9.5:1 compression ratio but never found a production set. Going with the custom pistons is quite expensive as Im sure you know. Your best bet would be the pistons from a 3.1 camaro/firebird. The Izuzu Rodeo used the 3.1 with the iron heads as well but I dont know what pistons came in the IZUZU.

Also unfortionate is the fact that no aftermarket manifolds for the aluminum heads exsist and adapting a stocker to use tbi or carburetor is not feasable nor would its design cooperate with a tbi or carburetor.

If you can spare about $375 you could get custom pistons from Arias or Ross in a press fit to fit the stock rods, and request 9.5:1- 9.8:1 compression pistons . That would really make the 3.1 swap justifiable and powerful.

[614streets]

Well I did a little searching and the VIN Z pistons from the Rodeo may be the same P/N as the Camaro/ Firebird 3.1 units.


Last piston all the way down.

http://www.beckracing.com/slvpg66.htm

[614streets]

Yup its the same piston as the Camaro/Firebird 3.1

http://www.beckracing.com/slvpg23.htm

recess .106" deep.

If I recall the 3.1 in the Camaro gained 5 hp over the 2.8 . Dont recall the tq rating I think its about 10 more ft lbs. If that piston was a flat top and you used valves with no recess you would be in better shape. Well at least you can see some things on paper or on screen now and maybe do a bit more reasearching.
The valve swap is worth about a tenth or two of a point compression.

If I knew who manufactured my valves Id tell you I bought them off another person(stainless steel units). The underside of the valve doesnt recess(like stock valves) , its flat.