[Kunz]

Hi there

As it is wintertime in Switzerland, the roads wet or icy, very bad conditions to drive a supercharged 968 CS with semislicks, I have some time to think about possible projects.

Something that runs it's circels in my head for a long time now is the following:
- Sleeving the 968 block ( for ex Darton / SFR)
- doing so increase displacement to 3.1 - 3.3l
- doing so increace compression to 11.6-11.8
- maybe add a big intake-plenum and exhaust work
- tune it
- combine it with a short final drive (for ex 4.25 from Californiamotorsports)
- let it rev...

I know some members might have done this at least partly. Are there any experiances on that? I would also like to know what Tim of SFR could tell us about that, also Fox944 which showed us a short vid once of his preped car.

Thanks!

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[flash]

over-sizing has been done - i don't have any reports on how well

increasing compression has been done, and pete at RS Barn can fill you in on that

pete can also tell you all about what an intake plenum would do

as for changing the drive to a shorter one, i've thought about this one too - while it would be simpler to just change the ring and pinion to achieve the goal, i would not recommend doing that - 1st or 2nd gear are already less than perfect - if you are pumping up the engine, the extra loads on those gears will certainly take its toll - besides, they are already very low - i get the idea behind wanting to push 3-6 down, but i would do only those gears, and not lose 1-2

something else to think about is piston speed - larger displacement means lower piston speed limits - i haven't done the math on it yet, but you may not be able to "let it rev" like you want with larger displacement - i will be crunching those numbers soon though, as i think i ultimately want a 3.2 myself

fun stuff though

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[Kunz]

Thanks for your answer, Flash!

As the larger displacement would come from more bore and not more hub I thought rev it to 7200rpm should probably be possible.

As for the intake plenum that SFR and RSB sell I have never found anybody that really uses it and can speak out of his own experiance. All I ever did hear was "it will..." or "it should...". Personally I think there could really some gains to be made. Even if the stocker might have some advantages I am not very happy with it; it makes the engine react "not typicaly" on upgrades.

The box: It obviously all depends on how you use the car and where you live. As it might be OK for you in the States it is far to long for my taste and the roads I move the car; curvy and up'n'down. Sure, the car is not slow (esp with the SC) and the relativly long gears calm the ride but still waiting for the next shift is so boring...

Interesting you thinks about something like that as well; please keep me / us on the run if you ever should start with it...

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[flash]

while stroke has far more of an effect, there is still one from bore size too - the physical speed is not affected by bore, but the frictions and pressures are - there is a volume limit that any cylinder can effectively compress - i'll do the math though and see where the rev limit is on that - the valve train limit is probably the real issue, and unaffected by bore, but still at about 8k

pete has a new manifold he just had made - he hasn't posted anything about it, but showed it at the recent gathering at his shop - i'm sure he would be willing to discuss that

i totally agree about the gear ratios - my only concern is the already weak 1-2 set

i'll definitely keep everybody in the loop, as i am going to have to do something with the box anyway

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[flash]

just for giggles i did the piston speed calc - at 7500rpm it's 4325fpm (it's 3864 at stock 6700 redline)

that's pretty darned fast, considering the modern standard max is 3500 and the old standard was 2500 - - it takes some really fine work to get 4325 - without some extra work, i would not go beyond that for long and expect to keep the cylinders intact

the modern high performance max is now about 5000 - that would equate to a redline of 8670, but you can figure on very short life at that rate

i still haven't gotten to the pressures and frictions math - that will take more time - i'm way too old to remember how to do that and will have to look it up

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[firefish]

Thick walls make for good power. It's probably money better spent to deal with the head issues, cooling and making sure that you don't start blowing head gaskets (thus allowing more boost), than trying to get an extra 500 usable rpm.

The idea of a sleeve is interesting, although it is more appealing as a way of getting a rounder and more stable bore.

I assume that we aren't talking about n/a's right?

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