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View Full Version : what compression for pump gas?


montyjcm
03-03-2004, 11:49 AM
Up to what compression can you run 91 octane pump gas? Would 10.8 work? Thanks.
UglyMotha™
03-03-2004, 12:12 PM
normally you can run a 10.8 on pump but in some cases you can get predetonation in the hotter tempatures
44oEX
03-04-2004, 08:52 AM
11:1 with no problems
rodenberg35
03-04-2004, 02:53 PM
the size of your cam would also make a diff. if you are running a larger duration cam you can get away with a higher compresion. due to the fact that preasure would be lost because the valves are open longer. this would only matter in a four stroke ofcourse. You should realy do a compresion check to see what psi you have.
ranger400ex1994
03-04-2004, 04:13 PM
ya i am kinda woundering the same thing? i am building a 416ex with either a JE or a wisco pistion port and polish head with either a hot cam stage 1 or 2. i was going to go with 10:8.1 for compression. would i be able to run 93octan with that compression?
hondafox440
03-04-2004, 05:04 PM
Originally posted by rodenberg35
the size of your cam would also make a diff. if you are running a larger duration cam you can get away with a higher compresion. due to the fact that preasure would be lost because the valves are open longer. this would only matter in a four stroke ofcourse. You should realy do a compresion check to see what psi you have.

I don't think so. The valves are closed during the compressing/combustion cycles. They HAVE to be.
jmpulse
03-04-2004, 10:55 PM
Originally posted by ranger400ex1994
ya i am kinda woundering the same thing? i am building a 416ex with either a JE or a wisco pistion port and polish head with either a hot cam stage 1 or 2. i was going to go with 10:8.1 for compression. would i be able to run 93octan with that compression?

10.8 shouldn't be a problem, I currently have the 11.5:1 in my 426, and if I keep it running with a correct jetting, it is fine. If it gets on the lean side, just a little, it gets uguly really quick!
hondarider2006
03-04-2004, 11:58 PM
next fall I was going to go with a 416, JE 10:8.1 piston, Hot cam stage 2....and some mild port and polish work. Now I know that 93 octane gas would work with this set up, BUT here we only have 90, would it work ok??