how much compression compaired to what gas to use??

R

rebelwalker

just wondering how you rate pump gas compresion up to race gas? my stock compresion was around 150 psi now its closer to 200psi ive been mixing 1/2 race gas and 1/2 93 oct. was hoping its enough. at what point do you change from 93 oct to mixing race and pump to having to run straight race gas?

thanks in advance
 
sjetrider

sjetrider

615 Freeriders are addicted to T1 madness.
Location
in the 615 (Nashville)
rebelwalker said:
just wondering how you rate pump gas compresion up to race gas? my stock compresion was around 150 psi now its closer to 200psi ive been mixing 1/2 race gas and 1/2 93 oct. was hoping its enough. at what point do you change from 93 oct to mixing race and pump to having to run straight race gas?

thanks in advance
Click to expand...

I would run:
full race gas at 200 comp. & up
Mixed from 185 to 200
93 oct. from 185 down
Just my theory.
 
Powder

Powder

( o Y o )
Location
Cleveland
Shonuff said:
As a rough estimate, your octane should equal at least half of your compression.

185psi = 91 octane
200psi = 100 octane
Click to expand...
At stock timing and in reference to a twin.
180 psi on a tripple you might need like 98-100 octane
 
Last edited:
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
Depends on bore size, dome shape, squish, engine use and load, ignition timing, and, last but not least, compression.

It's not that easy.
 
kskip

kskip

X
What was said before, whatever your compression number, run an octane number at least half of this..
You get above 200 compression it gets dicey,,,also, if you are right on the edge with these numbers you may back a degree or 3 on your timing to be safe...
Depends on your WOT length of times, how hard your pulling as far as prop pitch goes,,it goes on and on....
kskip
 
Speedfreak

Speedfreak

Location
So. IL
Just run it on pump gas and then if it blows you know that wasn't enough... That was my theroy with an old 650 I had I kept lowering the octane untill I was on 89 or 90 octane with 230 PSI compression.

I was told that with my ported 200 PSI compression motor that I can't have any WOT burst over a couple seconds on 93 pump fuel but I might mix it 50/50 for a while untill that 6.50 a gallon gets old then I will cut it back to pump fuel and hope for the best
 
yama_freak615

yama_freak615

MIA
Location
Middle Tennessee
Speedfreak said:
Just run it on pump gas and then if it blows you know that wasn't enough... That was my theroy with an old 650 I had I kept lowering the octane untill I was on 89 or 90 octane with 230 PSI compression.

I was told that with my ported 200 PSI compression motor that I can't have any WOT burst over a couple seconds on 93 pump fuel but I might mix it 50/50 for a while untill that 6.50 a gallon gets old then I will cut it back to pump fuel and hope for the best
Click to expand...


:bigeyes: :bigeyes: :bigeyes:


i would deff run race if i was close to 200, i was worried about it when i was at 185
 
Speedfreak

Speedfreak

Location
So. IL
Speedfreak said:
I was on 89 or 90 octane with 230 PSI
Click to expand...

Yea I know it was crazy but the ski was only $250 and loaded with parts and I couldn't part it out while it was running. But it never blew so I sold it for $300 the next year. There was a reason I was testing it not becasue I have so much money I wanted to see what would happen
 
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