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Avgas
What octane should I run
- Thread starter MOPARMAGA
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At 11 to 1 or less = I run C11 but it is more expensive
for some crazy reason.
Higher compression than that I run C12.
The timeslips will tell you what your car prefers.
However, different fuel often takes a bit of experimentation
with Jetting and timing to optimize you combination.
But it is not a big difference.
But I won a class race in stockagainst another 340 at Denver Nationals
by .0001 true margin, bracket racing is not near as critical.
for some crazy reason.
Higher compression than that I run C12.
The timeslips will tell you what your car prefers.
However, different fuel often takes a bit of experimentation
with Jetting and timing to optimize you combination.
But it is not a big difference.
But I won a class race in stockagainst another 340 at Denver Nationals
by .0001 true margin, bracket racing is not near as critical.
Last edited:
I ran that for a while on the Dyno. It's only 100 octane but it is 1/2 the price. But it didn't hurt the engine
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Its only 200 psi right? The static comp is ultimately meaningless as its comes down to when you close the intake valve as that's when you start to compress the mixture.
Yep, 72 degrees abdc
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Read this thread:
SOME HOLLEY CARB TIPS - Page 8 - PY Online Forums - Bringing the Pontiac Hobby Together
The engine dynoed was built to run Sonoco 112 BUT it made more power on Avgas because of the lower cylinder pressures UNTIL the rings finally ran themselves in and the cylinder pressure increased requiring the 112.
"AV-gas is a consistant fuel that is the same everywhere in the world and its the same all year and it evaporates easily inside the engine to create a good homogenous mixture throughout the cylinder. Av-gas has just about the highest energy content of any petrol, racing fuels or not. Race fuels are made from av-gas. Av-gas is the stuff to use. I dont understand why people wont tune to run it. It tunes to run nice at light load to keep cylinder condition correct for changes to WOT. Its easier to idle on the line with it. It is far more forgiving of a bad engine combination than street unleaded is. Its cheaper than race fuels."
SOME HOLLEY CARB TIPS - Page 8 - PY Online Forums - Bringing the Pontiac Hobby Together
The engine dynoed was built to run Sonoco 112 BUT it made more power on Avgas because of the lower cylinder pressures UNTIL the rings finally ran themselves in and the cylinder pressure increased requiring the 112.
"AV-gas is a consistant fuel that is the same everywhere in the world and its the same all year and it evaporates easily inside the engine to create a good homogenous mixture throughout the cylinder. Av-gas has just about the highest energy content of any petrol, racing fuels or not. Race fuels are made from av-gas. Av-gas is the stuff to use. I dont understand why people wont tune to run it. It tunes to run nice at light load to keep cylinder condition correct for changes to WOT. Its easier to idle on the line with it. It is far more forgiving of a bad engine combination than street unleaded is. Its cheaper than race fuels."
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TT5.9mag
Two atmospheres are better than one
Interesting, I’d recommend the exact opposite. Start with 112 and get a baseline tune up in it then strip away octane until the power starts to go away, that’ll give you your limit. I’d rather start with too much octane. On the dyno the fuel price is what it is. But you’ll know what your engine wants.
TT5.9mag
Two atmospheres are better than one
On the dyno I bet that thing would run full load, full timing on pump 91 with 130-140 deg coolant temps and cold intake air. In the car I wouldn’t chance it. Until I did some testing. But I would test and I would try.
Thanks that great information.
Keep this in mind. Many vendors will try to pass off unleaded 108 as leaded 110. Just something to bear in mind.
Okay, I was wrong again lol.
I have 110 sonoco at the pump. Or I have av gas at the pump (airport).
Everything else is in 5 gallon cans or 55 gallon drums.
Basically I just need to make up my mind.
Thank you all for your input. I appreciate you all.
I have 110 sonoco at the pump. Or I have av gas at the pump (airport).
Everything else is in 5 gallon cans or 55 gallon drums.
Basically I just need to make up my mind.
Thank you all for your input. I appreciate you all.
AV gas has altitude additives in it that your engine doesn't need. Just a little FYI.
Interesting, I'll have to check that out.
TT5.9mag
Two atmospheres are better than one
Get 5 gallons of sonoco 110 and 5 gallons of 91-93 whatever is high test. That will get you through your dyno session. 11.6:1 with 260@050 on intake and aluminum heads doesn’t need some crazy high octane number. Start rich with low timing and 110 and keep inching up on the tune up and adding pump gas to the mix. You’ll find your safe tune up and octane level. Then you get to put it in the car and do it all over again.
It's 12.8 now [email protected]
TT5.9mag
Two atmospheres are better than one
How the F…. did I miss that?
Will do, thanks !
33IMP
Well-Known Member
That is a very valid testing procedure alternative.
MM has MUCH more motor than me, only a 500hp iron head 440, 10.5, and I definitely can run on Cali 91, but since I now have access to AZ avgas, I toss in a couple gallons per tank, cause I can. And avgas in AZ is cheaper than Cali pump 91.
Straight avgas or E85 might be a perfectly good alternative to race gas. Diagnosis time.
I can't write out sentences properly, I went back and edited the 1st post
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Its only got 200 cranking psi.
TT5.9mag
Two atmospheres are better than one
No you did just fine. I remembered the cam change but I still wrote it wrong. I just completely looked past the compression increase.
Tim said hi .
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