Pump gas compression

Its more about compression ratio than compression, although a higher compressoin ratio means more compression and compression is power. Divide the head volume into the cylinder volume and you get a number typically between 7 and 15, meaning the compression ratio is between 7:1 and 15:1. Depending on the engine and the altitude, once you reduce the volume of the head chamber and raise the compression ratio, you need to go through a process almost like jetting and reading plugs to determine the octane needed to prevent detonation and get the most power from the engine. If you use a fuel with too high an octane for the engine's needs, you loose power, to low and the engine will detonate to death. It takes a long time to get it right and its frustrating and expensive. I have built a couple of mod engines but really just did what I was told to do. There are guys on this site (MrViper for one) who can give you a more complete and accurate explanation.
 
generally speaking...all things right on...135 will be safe...140 to me is getting into the danger area..
riding in area's where old gas (gas loses octane with age) or other negative fuel factors make detonation more possible...
remember that higher compression without sufficient octane to prevent detonation will raise temps and higher temps will raise chances for detonation...can be a viscious circle..
 
What do you intend to do to the engine? If you just cut the head to raise the compression, I think you are asking for trouble. You will raise the compression by reducing the head chamber volume but the head design must include appropriate squish design. If the squish is good, IMO, you can approach 150# on premium fuel. There are some very experienced engine builders on this site that may chime in with some specific advice for you.
 
modmax is correct..squish is very important...150 must be at higher elevations?not at sea level day in and day out especially with our U P gas!

I thought I was the only guy able to run 1375 deg egt's and 157 lbs of compression at sea level on pump gas and not burn down..lol..( a little special sauce saved me)
 
Years ago, I had an engine built by altitude engineering in Taos New Mexico. They bored a 1994 600 to 700, ported it and reworked the head. Compression was 150# at 1800 ft. I ran it successfully on pump premium. Boy did it work good. Back then the Poo XLT's were having there way with the vmax sleds. Not this one. Of course I never bothered to tell anyone it was a 700.
 
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