What octane should I run?

[hotrodaj_2]

I have 155lb of compression when I kick it over. I guess the compression rises alot when engine is running on the pipe so I'm not sure what octane to run.

premium pump gas --- what compression
100 octane gas ------ what compression
110 race gas ---------what compression

I have a 240 kit with a L.A. Sleeve and wiesco piston. All other internals are stock. Is that ok compression for a engine with a kit? Whats stock comp.?Whats the most comp. you can get?
Thanks

 

[blasterdude14]

not sure what the most comp you can get is but im pretty sure at that comp you need to run at least 93 octane

 

[motoman9911]

Compression doesn't change with RPM's if that's what you're thinking.

 

[yb200]

i have 150 psi and i run premium 91 oct

 

[Brute71]

Compression doesn't change with RPM's if that's what you're thinking.

on the contrary, it actually does. One of the builders explained it in another thread on here. When the bike is on the pipe, you are getting more fuel/air mix in the combustion chamber (packing) causing an increase in compression while the bike is on the pipe.

I would try just some 91-93 octane premium pump gas for now and see if you get any detonation (pinging). If you do, try out a higher octane gas. If 100 octane seems to fix the issue, you can run a 1/1 ratio of 110 race gas to 91-93 octane premium to get the same octane as the 100 for less money. There are tons of guys around here that do that for their race bikes.

 

[Kennedy_Power]

Compression doesn't change with RPM's if that's what you're thinking.

Actually peak cylinder pressure does increase with engine speed... From a engineering stand point peak pressure occurs after TDC around 17-22 crank angle. I know this for a fact doing combustion and calibration work during my day job. A gas engine is about 120bar of peak pressure at full power and a diesel can be pushed to 220 bar..... 1 bar=14.6PSI
You do the math, lots of pressure per square inch

 

[xjma]

Well of course the pressure in the chamber is going to increase after detonation!!!! If it didn't, you wouldn't be going very far.


Run the highest octane you can get your hands on! With just a 240 kit you should be fine with premium 91. Higher octane doesn't hurt though.

 

[blasters/banshees]

I run 93 in all my quads and dirtbikes

 

[4cfed]

93 octane ( or what ever your highest premium fuel at the pump is) nothing less even at 100 psi

anyhting and everything iv owned 2 or 4 stroke gets premium unless it my daily driver

 

[phragle]

actually, running to much octane will rob a little power.. however higher octane will for lack of a better way of describing it, run a little cooler in an aircooled motor.

 

[Joey_Stacks]

I put 93 in everything I own truck trike quad MC's all of it get 92-93

 

[motoman9911]

Actually peak cylinder pressure does increase with engine speed... From a engineering stand point peak pressure occurs after TDC around 17-22 crank angle. I know this for a fact doing combustion and calibration work during my day job. A gas engine is about 120bar of peak pressure at full power and a diesel can be pushed to 220 bar..... 1 bar=14.6PSI
You do the math, lots of pressure per square inch

I'm not learning sh*t in school.

 

[brandoz28]

why do you think you think that most nitrous guys burn down around peak torque? cylinder pressure

 

[Kennedy_Power]

why do you think you think that most nitrous guys burn down around peak torque? cylinder pressure

Lack of fuel.. Most of the time that's the issue....

 

[royalt67]

Lack of fuel.. Most of the time that's the issue....

Yep, nitrous will lean you out in a heartbeat.

 

[brandoz28]

Lack of fuel.. Most of the time that's the issue....

too much fuel will kill it faster than too little.......that being if you're pulling enough timing.

 

[hotrodaj_2]

Thanks for the help. I tell you what I did before I asked the question on here. I bought premium (91 in calif.) and added a good quality 104 octane boost to get close to 100 octane. I'm deathly afraid of it pinging and wasting a piston on the 91. Is a good quality booster ok to run or do you half to mix race gas with premium to get 100 or is 91 ok to run. (155lb compression)

 

[blasterdude14]

Thanks for the help. I tell you what I did before I asked the question on here. I bought premium (91 in calif.) and added a good quality 104 octane boost to get close to 100 octane. I'm deathly afraid of it pinging and wasting a piston on the 91. Is a good quality booster ok to run or do you half to mix race gas with premium to get 100 or is 91 ok to run. (155lb compression)

I would say mix race gas and premium just to be safe, 91 and 104 would be good

 

[stephen12091985]

octane booster doesnt really do nothin.it barely puts ur octane up