Pistons

[barks944]

Could I use slightly reduced compression ratio pistons from a Lux to make a ~9:1 compression ratio turbo engine?

 

[Tam Lin]

Lux? I thought the pre-88 924Ss had the lowest static comp.

 

[barks944]

They might be a better option then. I just thought as the lux pistons are > 9:1 compression I can removed a set volume of material to move them down to 9:1 compression. If the 924s pistons are closer to 9:1 it means removing less material, which I guess makes things a little easier. If they are already 9:1 then that would be ideal!

 

[barks944]

Seems like theres a lot of issues with removing material from pistons! The early american lux's ran ~9.5 CR but I think this might be a bit too high. I wonder what the stroker kits do to the compression ratio of the engine.

 

[TTM]

Hmmm I think Stroker kits usually include both specific pistons and rods.

 

[JamesO]

What about pistons from an 's' would they not lower the ratio?

 

[barks944]

I think the 944s is about 11:1 compression.

 

[JamesO]

Not with an eight valve head I believe. The 3L 16 valve pistons are dished for the 4 valves and would have thought the 2.5L would be the same. Lux pistons are flat with 2 valve recess, just an idea.

 

[barks944]

Good idea James I'll look into it.You running an S2 engine in your lux now?

 

[333pg333]

Are these forged?

 

[barks944]

Hmm not sure. What do ppl think of running 9:1 on a 2.5 turbo. My thoughts were that 8:1 gives the possibility of running very high boost but its not what I want to do with the car. 9:1 should let me run a decent boost level but make the engine better off boost, more efficient and give a quicker spoolup.

 

[JamesO]

Well in true form of the car the engine is a bit of a hybrid at the moment :-

968 bottom end
S2 flywheel and clutch
S2 head as currently the 968 head needs cams
S2 down pipe, 2.7 back box
968 intake and injectors
I would like to fit the 968 head but the cost of cams coupled with a refurb means not this year.

 

[333pg333]

To run 9.1 c/r you would need a way of controlling the ign map. Maybe if you got someone like Vitesse to write you a program based on your parameters.
Or go standalone.

You can buy a custom set of Wossner pistons pretty cheaply which would be designed to run in a turbo motor.
By the time you muck around with some sort of hybrid piston setup that may not work, it could well add up to a lot more than a set of proper pistons.

 

[barks944]

Got a plan to re-make the digital board in the motronic DME. Going to ask some clever bods I know on Monday if they would be up for making a prototype.