[torsen] re: Piston ruminations

auditude at neta.com auditude at neta.com
Wed Oct 17 01:40:10 EDT 2001

Hey Scott,

Thanks for the feedback.  Some of the stuff I don't understand, 
such as the reference to 8.1, as far as prior unabused.  Would this 
be a custom motor, perhaps built out of a 7.8:1 MC-1 motor?  Does 
the knock table come into play only when there is detonation, or 
pinging, or does it come into play when the effective c/r is too high 
or something?

The part I guess I don't understand is if the MC-1 will be retarding 
timing before and MC-2 would be, assuming they had the same 
compression ratio.

Quite a while back, I remember someone asking if there was a 
problem running MC-2-boost levels in a MC-1 based motor.  At the 
time there was no response, but this post seems to be stating a 
clear opinion on it.

How does EFI make it possible to run higher compression pistons 
in a turbo motor?  Dumping more fuel to prevent detonation?  
Adjusting the timing much more faster and closer to the detonation 
threshold?  Well, I guess not that second part, since EFI doesn't 
mean ignition mods, just fuel delivery.



On 16 Oct 2001, at 21:52, QSHIPQ at aol.com wrote:

> There is plenty of meat on the MC head to mill and cc as necessary to get any 
> CR you so desire.  For the MC1, I'd look at no more than  8.1 to avoid going 
> to the lowest knock tables under boost.   The MC1 running the MC2 cr of 8.4 
> is too much.  A properly done (and prior unabused) 8.1 should be able to use 
> the stock timing belt. 
> Personally, I find the audi pistons to be pretty darn good ones.  Unless you 
> are going overbore or lightening, I'd leave the turbo pistons alone on either 
> the 10 or 20v motors
> SJ
> I also am curious to know what other options there are.  
> I would still like to get a higher compression piston than the MC-1's 
> 7.8:1.  I'm open to discussion about this.  I do not have much 
> technical knowledge about piston design either.
> I'm not crazy about the idea of additional piston slap than stock, or 
> increased likelihood of detonation due to a less desireable dish 
> design or location.
> My primary motivation for getting involved in this deal is to get a 
> higher c/r for my 4kstq project, so that off-line performance isn't so 
> bad, pre-boost.
> Thanks,
> Ken

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