[s-cars] Question about compression ratios and tuning

[Mihnea Cotet]

Mike,

The ADU cams are definitely different. The exhaust cam has more lift and 
duration and the intake one is 10 degrees off compared to an AAN/ABY.

Boost profiles are about the same between an ABY and an AAN, but the ADU 
has more, as it has a larger turbo... an ADU actually runs about what the 
maximum reliable boost is on a stock ABY/AAN motor/turbo.

As I'm definitely not a motor builder, I can't really say what a reasonable 
variation in CR is, so I won't try to say anything...

Cheers,

Mihnea

At 09:16 3/02/2004 -0700, M Pederson wrote:
>See previous re: dynamic CR.  Do your ABY/ADU and AAN all have the same
>cam(s)?  Same boost profiles?
>
>Maybe one of these variable might explain the advance levels, and or suggest
>that at the edge of the envelope, one might want to have their chips "set"
>for the peculiarities, even on a mass production line, of the inevitable
>variation that probably occurs from motor to motor, head casting to head
>casting.
>
>What do motor builders consider a "reasonable" or acceptable variation in
>head cylinder volume ~> hence CR from cylinder to cylinder in the same
>motor?
>
>Mike
>
> > -----Original Message-----
> > From: Mihnea Cotet [mailto:mik at info.fundp.ac.be]
>
> > Pistons and head combustion chambers are actually the same between 3B,
> > AAN,
> > ABY and ADU. The only difference in CR between an ADU and an AAN/ABY is
> > the
> > head gasket, the metal item is thicker and lowers CR by about .3:1. How do
> > I know? The knock limits aren't at the same advance levels on a full
> > RS2-equipped ABY than on an ADU. Just a few degrees, but that's enough to
> > mess things up for those who do "generic" chips.
> >
> > HTH,
> >
> > Mihnea
> >