NG horsepower upgrades

[Dave Glubrecht]

As far as sensible cr, just a wild reference point.  The Yamaha YZ400f  is
12.5:1  I do not know how much the cam affects the dynamic, but this is a
motor that runs on regular pump gas (better on premium)  through a
carburetor with no knock sensor AFAIK.  Biggest complaint is kicking it to
life.
     Dave G



----- Original Message ----- 
From: "Hoffman Anthony J A1C 552 CMS/MXMVC" <Anthony.Hoffman at tinker.af.mil>
To: "Quattro List (E-mail)" <quattro at audifans.com>
Sent: Friday, August 27, 2004 4:45 AM
Subject: RE: NG horsepower upgrades


>
> >>>my cam will be my 272, I will not be using equal length headers, and as
> for cr of 12:1, sounds a bit high for my liking for reliability, what is
> everyones opinion on a >>>sensible cr?
>
>
> First, the dynamic compresion ratio varies with the cam. In other words,
at
> low speeds, because of the overlap of a larget cam, the cylinder doesn't
> fill as completely. This efectively lowers the CR at low RPM's, which will
> reduce the tendency to preignite. There are several other factors, the
> biggest of which is the size of the piston. The larger it is, the better
the
> heat dissipation is. On a VW 1.8 with 3.40 pistons 10:1 is about the limit
> for the street on 91 octane. My 351 Ford has 4.030 pistons, and it runs
> 10.5:1, no knock sensor, no pinging ever even on 85 octane (huge cam,
> though).
>
> Just some info the chew on,
> Tony Hoffman
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