Had a question on compression

[fast superjet chase]

Hi every one i had a question on high compression im running a full mod 760 in my superjet its fully ported head pipe reeds you name it. it is done my question is that im at 183psi per cylinder at 5900 feet and was wondering if i need to be running race fuel or not im am right now but man its breaking me. so if any one out there knows for sure please let me know.

 

[Mark44]

You do not need race gas. I run 200 PSI and use premium fuel at 185 I would probably run mid grade.

Mark44

 

[fast superjet chase]

With a 760 big bore and being ported whats the cut off when you have to start running race fuel

 

[Mark44]

I would start race fuel over 200 PSI some people more some less depends how you ride. I don't do wide open runs for more than a couple seconds.

Mark44

 

[sqwidget]

So even even though my head says at 180psi I should be running 98 octane, but I can run premium and still be okay?

 

[CoreyLKN]

You do not need race gas. I run 200 PSI and use premium fuel at 185 I would probably run mid grade.

Mark44

Really you never have any problems? I thought anything over 185 or 190 need race fuel. What size domes are you running?

 

[stanton]

You do not need race gas. I run 200 PSI and use premium fuel at 185 I would probably run mid grade.

Mark44

very generalized statement.
i wouldnt run anything less than premium.

 

[Mark44]

p

Really you never have any problems? I thought anything over 185 or 190 need race fuel. What size domes are you running?

701 bored a couple times over don't know the exact CC. Been using premium 91 for years. In Katie's 185 PSI motor we use regular 87. Never an issue.

33cc ada domes on ported motor .045 squish.

Mark44

 

[fast superjet chase]

my 760 is 2mm over with 35cc domes and wicked arm pulling force.

 

[Speedfreak]

My 5mm stroker was built by Art at Jetworks and was built for high compression. It is bored to 86mm and runs right at 195 psi and I was told that I didn't need to run anything more than 91 octane. So I don't. Plus I run MSD enhanser to the timing is advanced.

It is all in how the motor is setup to run. A stock motor will handle a crap load of compression as long as you don't do WOT runs. I ran 29c domes in my 01 ~ 230 psi compresion on pump fuel and never had a problem.

If you don't push the threashold you will never know where it is. I kept leaning the motor out and upping the compression but sold it before I found out what "too much" was.

 

[fast superjet chase]

i love running wide open throttle though

 

[suva]

There are more variables than compression, porting being one of them. I ended up with some deto at 160psi 89 octane @ 700ft with aggressive race porting.

 

[fast superjet chase]

Ya my port job is real aggressive and 183psi im sick of running race fuel

 

[SUPERTUNE]

Well... put some 37cc domes in if you like pump fuel cost.

 

[SUPERTUNE]

If your running stock carbs you could experience some detonation from being emission (lean burn) carbs.
Aftermarket dual 46's would be a good choice and then you can most likely leave the domes @ 185 lbs.

 

[fast superjet chase]

im running dual 48mm black jacks.