Nascar 9:1?

[Corey L. Cole]

Michael D. Porter wrote:
> 
> Russ Highton Jr. wrote:
> >
> > In regards to the "cheaper nascar engines" with 9:1 compression.  Are you
> > sure?  Last I heard they were running 18:1 to compensate for a vacuum
> > condition caused in the intake at high RPMs from the restrictors.  Am I
> > wrong?
> 
> I would suppose an 18:1 CR is a bit beyond the pale, Russ. At that CR,
> the heat of compression would likely cause spontaneous detonation of any
> NASCAR-legal fuel. That's very close to diesel engine compression
> ratios, and the cetane rating for gasoline of any type doesn't come
> close to that of diesel fuel. Even methyl alcohol-burning diesels are
> running about 15.5-17:1 ratios. The lower compression NASCAR engines are
> probably compensating for intake restrictions by maximizing flow at
> usable rpms and so concentrating on volumetric efficiency, not
> stratospheric compression ratios. Higher compression ratios help, but
> after the limit, they hurt.
> Cheers.
> 
> --
> My other Triumph doesn't run, either....

'Tis true, in Winston Cup, they do run at 17-18:1 CRs.  There was an
article
a while back (actually, a 2 part article) in Circle Track and Racing
Technology by Smokey Yunick discussing the technical feasibility of
going to
unleaded gas.  They ran dyno tests of engines from 9:1 to 14.5 to 1, all
on
the unleaded equivalent of Turbo Blue.

Not only do they run ultra high compression, but they also run cylinder
specific compression ratios to compensate for fuel distribution problems
caused by the restrictor plates.
-- 
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