Re: 13-1/2 to 1 compression ...on the street?

Steve wrote:
> 
> M.Burns wrote:
> > Looking at a nice Pro Street car with 13.5 to 1 compression pistons. 
It
> > apparently has been at some statewide cruises, rod runs, etc, so I
know it's
> > been driven. My question is, what kind of fuel must the owner be
running for
> > the engine to survive. Heard claim that by retarding the timing
somewhat,
> > pump gas with octane booster works(?)  Race fuel?  Any ideas  (...from
guys
> > familiar with similar cars or situations). Thanks
> >
> >
> 
> It depends on a lot of things. How radical is the cam? If its a HUGE cam
> with a ton of overlap, then the actual compression pressure might be
> manageable enough to live on pump premium with a mild octane booster.

explain to me how overlap and not IVC will effect low rpm cylinder
pressure?

> Same if it has aluminum heads with polished chambers- that will reduce
> octane requirement, but as deposits build up as the engine is run the
> octane requirements can creep back up.
> 
> But at 13.5:1 (assuming that it was computed correctly, most people tend
> to over-estimate the true compression when they build an engine) then it
> would be pretty hard to make it live on pump gas.
> 
> Retarding the timing is a band-aid, and not a good idea. It makes the
> exhaust valves run cherry-red hot all the time and can cause valve seat
> recession and burned valves.