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110/90 mix
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hacksaw1971 View Drop Down
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    Posted: Mar/18/2023 at 11:56pm
the math said i should have 9.75-ish on my comp. think i missed..... 93 pump ain't doing the trick. can only run 28 deg total with all the ethanol in it here. and it will be going up this summer.   so i got some 110 leaded ethanol free. 17.98 per gal.  almost 400 bucks to fill my 22 gal tank. but i can run the 36 deg she seems to like with no flat spot or pinging and good plug read.   if i was to run a 50/50 110 and 90 ethanol free from the pump do me any good? is there a mathematical way to figure out what the octane would be as i change the mix?
    thanks


Edited by hacksaw1971 - Mar/18/2023 at 11:58pm
its the little things that make the biggest difference
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Trader View Drop Down
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A place to start:
Are you running any vacuum advance? If you are, disconnect/plug it and and see what kind of total advance you can run.
Your mechanical advance may also be coming in too early. Typically you want all in at 3200 to 3600 RPM for street driving. But if the mechanical advance is starting to come in at below 2000 RPM with your SCR, recurving the distributor to have mechanical advance start later may also be were you want to start.  
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As a cheaper alternative I buy 100 octane low lead at the local airport and mix it 50/50 with BP Gold ethanol free and have no issues with my 12/1 TRW pistoned 70 390. AV gas here has been running between $6 and $7 a gallon.
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hacksaw1971 View Drop Down
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Originally posted by Trader Trader wrote:

A place to start:
Are you running any vacuum advance? If you are, disconnect/plug it and and see what kind of total advance you can run.
Your mechanical advance may also be coming in too early. Typically you want all in at 3200 to 3600 RPM for street driving. But if the mechanical advance is starting to come in at below 2000 RPM with your SCR, recurving the distributor to have mechanical advance start later may also be were you want to start.  
 i have no vacuum advance .... new springs and such has it coming all in at 3500-ish. had a  flat spot in the transfer spot in the carb.  but going to 13 deg base took that away.  i live 15 miles from a small airport and forgot all about 100 octane avgas. going to try that next. it unleaded but has no corn in it...
its the little things that make the biggest difference
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hacksaw1971 View Drop Down
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Originally posted by Judo390 Judo390 wrote:

As a cheaper alternative I buy 100 octane low lead at the local airport and mix it 50/50 with BP Gold ethanol free and have no issues with my 12/1 TRW pistoned 70 390. AV gas here has been running between $6 and $7 a gallon.


 thanks .. forgot all about that.   and i got a small airport just down the road...
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garland performce View Drop Down
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110 x 5 =550 90x5 =450         550 +450 =1000 divided by 10 = 100 octane
Also might look at a additive Called Race Gas have used it in several cars and have used it on the Dyno


Edited by garland performce - Mar/22/2023 at 6:22pm
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hacksaw1971 View Drop Down
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Originally posted by garland performce garland performce wrote:

110 x 5 =550 90x5 =450         550 +450 =1000 divided by 5 = 100 octane
Also might look at a additive Called Race Gas have used it in several cars and have used it on the Dyno
 thats what i was looking for ...  thanks.
its the little things that make the biggest difference
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Except you need to divide by 10 not 5 or you will have 200 octane.
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Originally posted by WesternRed WesternRed wrote:

Except you need to divide by 10 not 5 or you will have 200 octane.
As a former math major in college, I assumed it was new math.
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Originally posted by hacksaw1971 hacksaw1971 wrote:

 i live 15 miles from a small airport and forgot all about 100 octane avgas. going to try that next. it unleaded but has no corn in it...


 Are you sure about the unleaded part???? Right now I think unleaded aviation fuels are scarce. 100LL (low lead) is the most common av fuel.
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