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Jun 15, 2011 | 10:26 PM

Clubby99

Thread Starter

Burning Brakes

Joined: Jan 2011

Posts: 954

Likes: 2

From: San Jose CA

Racing Fuel

I always wondered how my car would run with proper octane gas. In California, I have never seen octane higher than 91.

Today, I saw racing fuel (100 octane) at a pump at a Union 76.

Sells for $6.99 a gallon.

Could I mix 50% 89 octane and 50% 100 octane and get 95 octane gas?

Will this damage my car?

What would happen if I used straight 100 octane?

For SF Bay Area guys: Union 76 on Woodside in Redwood City.

Jun 15, 2011 | 10:36 PM

81pilot

Drifting

Joined: Aug 2009

Posts: 1,635

Likes: 8

From: Enid Oklahoma

In order for anyone to answer that question you need to give the engine specs, especially compresson ratio. Not all Vettes need high octane fuel. A simple rule of thumb is to run the lowest octane you can with no predetonation. Without starting an octane discussion, it is always better to run an octane that does not allow knock than one too high that builds carbon. Knock equals bad, but too high is of no benefit at all, just paying more money for the fuel.

Jun 16, 2011 | 12:40 AM

Mike Ward

Race Director

Joined: Jul 2001

Posts: 15,892

Likes: 42

Your profile says that you have a 1972. If it's stock, it will make full potential power on anything better than lamp oil.

'Racin' gas' would be complete waste of money.

Jun 16, 2011 | 12:49 AM

Mick71

Melting Slicks

Joined: Nov 2010

Posts: 3,363

Likes: 32

From: Bowtie, Pennsyltucky

St. Jude Donor '13-'14-'15,'21

Quote:

Originally Posted by Mike Ward

Your profile says that you have a 1972. If it's stock, it will make full potential power on anything better than lamp oil.

'Racin' gas' would be complete waste of money.

I tried a couple gallons of 87 just to try it and my stock '71 270hp ran fine. No ping or dieseling at all. Save your $.

Jun 16, 2011 | 08:55 AM

Joe Buck

Racer

Joined: May 2004

Posts: 315

Likes: 0

From: North Richland Hills TX

Off hand, is there a rule of thumb for compression ratio and racing grade octane???

I myself have 10.5:1, have wondered if it would help...

Jun 16, 2011 | 09:34 AM

gbvette62

Race Director

Joined: Oct 2000

Posts: 12,679

Likes: 3,130

From: Shamong, NJ

Quote:

Originally Posted by Joe Buck

Off hand, is there a rule of thumb for compression ratio and racing grade octane???

I myself have 10.5:1, have wondered if it would help...

"Back in the day", most cars with 10.0:1-10.5:1 compression ratios, ran fine on premium. Cars with higher compression, had the option of using 102 octane Sunoco 260. My cousin had a 62 409 Impala with 11.5:1 pistons, and it was only happy with 260 in it. He had a friend that was a pilot and when he raced it, they would go get some aviation fuel for it. I don't know if it made a real difference, but he still swears it did.

As far as an octane "rule of thumb". I would say that as long as you don't get "pinging", under hard acceleration, you should be okay.

Jun 16, 2011 | 03:46 PM

RMVette

Race Director

Joined: Jan 2001

Posts: 16,221

Likes: 118

From: Matthews NC

I run 110 octane racing fuel in my '70 with 11:1 (L46) and my compression may be a tad higher with the block decked on the rebuild. Granted mine is not a daily driver and only goes on short trips and to car shows so spending the +$5.00/gallon is not a problem. I used to run 100 LL aviation fuel which is about the same price but when I found a gas station that sold the racing fuel I changed due to it being easier to purchase.

BTW...mine loves the 110 octane!

Last edited by RMVette; Jun 16, 2011 at 03:57 PM.

Jun 16, 2011 | 07:51 PM

Manuel Azevedo

Burning Brakes

Joined: Jan 2007

Posts: 1,057

Likes: 4

From: Concord Calif

Quote:

Originally Posted by Clubby99

There is NO HP in a higher octane fuel than the compression and timing you are running needs to not detonate. The higher octane could allow you to run more lead if you are a bit retarded (timing that is!! ) then you could feel a difference from the timing increase but not directly from fuel! If one is running in the neighborhood of 14 degrees at idle and say 36 all in around 2250rpm and you have no pinging than any higher octane fuel will only show a decrease in power! If you see an increase in power by using a higher octane fuel than required by your compression and timing you have a problem in jetting for sure! that was just covered up a bit with the fuel!