What is the highest compression ratio you can run without having problems with 91 octane pump gas?

 

11.5:1 just run colder plugs and hook up a det can and check for any kind of pinging.

 

What is a det can?

 

det is a detonation detecting can. compression ratio you can run varies with bore, stroke, cams , piston top design , etc
but b-series can usually see 12's compression with a good tune and cams to match

 

technically speaking having cams with a big enough lobe will lower the compression of the engine by opening the intake valves early (overlap) and closing the exhaust valves late. but there area lot of factors to determine this, load on the engine (transmission used and the weight of the car) and octane avail easily (cali at 91 or east coast at 93) not much but everything is a factor if you want the car to last and not just be fast for a little bit of time

 

but to say i've seen a lot at the 11 to 11.7 or so and live happy miles, on the higher end 11.5 - 12 would recommend some cams and a good tune to match

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EGvsEM &raquo;</TD></TR><TR><TD CLASS="quote">technically speaking having cams with a big enough lobe will lower the compression of the engine by opening the intake valves early (overlap) and closing the exhaust valves late. but there area lot of factors to determine this, load on the engine (transmission used and the weight of the car) and octane avail easily (cali at 91 or east coast at 93) not much but everything is a factor if you want the car to last and not just be fast for a little bit of time</TD></TR></TABLE>

No it wont, the piston bore, stroke and chamber determine static compression, all a bigger lobe will do is increase the volumetric efficiency of the intake and exhaust charges. It does not reduce compression.

Piston speed, chamber design, piston design, fuel delivery/octane used, and the temperature/density of the incoming air are all factors to consider in preventing detonation. Spark at the wrong time is also a factor, but this problem tends to be compounded by the variables above.

11.5 is a good number to be at, not quite radical, but still very streetable.

 

Where can I find said detonation can?

 

you have to make it.
look into ''chassis ear"

 

chassis ear? what the.. ?

 

it's almost like a sthethescopes(sp?) for a car...set of headphones and a probe so you can listen to the engine a little easier...if the motor was equipped with a knock sensor you can try to use that as well (count the knock count) make sure you get it tuned, and if your going over 11.5 get a set of cams to take advantage of the extra compression

 

how bad ia 12.5:1 compression on 91 octane to tune. Is that a safe ratio or should i shoot for lower?

 

it sucks only having 91 octane...sunoco 94 up here