Author Topic: Unmodified L78 guys.. what are you running for octane?  (Read 2799 times)

boomer632

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Unmodified L78 guys.. what are you running for octane?
« on: March 09, 2023, 08:33:03 PM »
Guys with the 11:1 L78 what octane are you running? How about any lead additive or octane booster. I think the station that carried Turbo Blue wont be carrying it this year so Im looking for advice. Other than a Pertronix Flamethrower distributor, my L78 motor is how it came from factory.  Not really interested in messing with timing at this point.

Any thoughts?
« Last Edit: March 09, 2023, 09:04:37 PM by boomer632 »
69 SS NOR 06A 711 57 57 X66 L78 M22 BU

usa1ti

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #1 on: March 09, 2023, 08:42:24 PM »
The last 2 12.5 to 1 427s I have built I ran on 93 octane premium. 1 was open chamber GM aluminum heads 1 was closed chamber iron 840s. The 10-15% alcohol seems to cure a lot of compression issues. I still take a little timing out and don't run a lot of advance. My 302 runs fine on it also.
Todd, East TN

plumL78

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #2 on: March 09, 2023, 11:01:19 PM »
93 in my z28's and my L78 no additives just a little less timing

x66 714

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #3 on: March 09, 2023, 11:41:01 PM »
I don't have a L78 but in my 302 I run 1/2 110 & 1/2 93. Works good....Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

cook_dw

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #4 on: March 10, 2023, 03:13:07 AM »
25/75 of non-ethanol 91 and 110 Renegade Racing fuel.  Splash of groovy grape to make it smell good.  It runs fine on straight 91 but it like the mix better with timing all in at 38*

rare396bronze

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #5 on: March 10, 2023, 04:35:15 AM »
Groovy Baby!

RikerZ28

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #6 on: March 10, 2023, 01:44:09 PM »
My L72 with 11.0:1 ratio 840 cast iron heads I use 50/50 unleaded non alcohol premium 92 and 100LL Av gas. Timing all in at 38* 
1969 Z/28 02D X-33 / L72

lynnbilodeau

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #7 on: March 11, 2023, 12:24:27 AM »
I am lucky to be close to a municipal airport that will sell to the public.  I have an LT-1 spec motor in my 69 Z right now with 11.5:1.

I run 100 LL.

Kelley W King

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #8 on: March 11, 2023, 03:52:00 AM »
My L78 runs ok on pump 93 but it does diesel some when you turn it off. Mix in a gallon of two of purple gas and it sures does run better and no dieseling. I don,t run it too hard since with stock size tires it likes to break them loose at any speed. Stock except headers.
69 Z28 RS Scuncio Hi Performance
69 SS L78
67 SS Chevelle
64 Corvette
66 GTO Tiger Gold
77 Trans Am Special Edition

sixt9x33rs

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #9 on: April 09, 2023, 06:11:20 PM »
There is a great article in April Hemmings American Muscle Machines about dieseling. Per the article the dieseling is caused by carbon build up on the top of the pistons or excessive high idle or both. Ray Bohacz says to soak the pistons with GM Upper Engine and fuel Injection Cleaner. There is a lot more to the details about doing this so read the article before soaking anything. Ray says that this process will cure your dieseling problems.

Good luck
'69 RS Z/28 65B, 711 Flat hood no spoiler, endura, 4:10 43K miles
69 X77 Z/28 69 69 711 Original Paint Unrestored (Sold)
'69 X66 Convertible 69B 712 auto, (Sold) 44K miles

Pacecar

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #10 on: April 09, 2023, 10:49:19 PM »
I use aviation gas. 100 octane. $5.29 per gallon

DuWayne Ladner

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #11 on: April 13, 2023, 04:46:31 PM »
Just had my CE L78 completely re-done, bored .60 over. My engine builder says I should be fine running 93 octane.

maroman

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #12 on: April 13, 2023, 05:44:18 PM »
I love the color. If I had to have a '69 I would want that combo.
Doug  '67 RS/SS 396 auto I know the car since new

David K

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #13 on: April 13, 2023, 11:21:26 PM »
Looking good with those "ZL1 Hubcaps ".🫣🫢🫣😀😆

MO

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Re: Unmodified L78 guys.. what are you running for octane?
« Reply #14 on: April 14, 2023, 05:27:55 AM »
Agree, great color combo.

I'm surprised to hear so many can readily get Av-gas. I use to buy it from a small airport, but they stopped servicing anything non aviation. I was told because of EPA issues.