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

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. 
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.