New Member
Aug 9, 2005
Is it worth running a 50/50 mix of 110 octane race gas and 93 octane pump gas in a built up 1969 351W? When I got the car it would ping on only 93 during WOT but with this mix, no ping and I can basically put as much timing in it as I want to. I have a stock dizzy but pulled the points and I'm running a Pertonix set up. It also has a holley 750 carb. Is this fuel mixture safe and what is the optimum timing set up initial and total? I can or can not use vac adv., doesn't matter to me since I am not looking for fuel milage, I'm looking for HP.
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Performer intake
750 Holley
Small cam

Sounds a little mismatched IMO.
The compression and carb go together, then a small cam (without knowing specs) and such a VERY mild intake go together.
The problem is that small cams and intakes can magnify the ill effects of high compression, as opposed to complimenting each other.
In the meantime no pinging with too much octane is better then pinging with not enough-

Definately run the higher octane fuel until the pining is sorted out.

It may be that taking 3* out of the timing will stop the pinging and result in MORE horsepower than running the higher octane fuel with more timing. Although with 11:1 and stock iron heads, he might be stuck with race gas no matter what the timing is.
I don't agree, with the right cam 11 to 1 and iron heads is very possible. My 68 Merc's 390 was fine with stock iron heads (C8AE-H, good quench heads as are the 69 Windsors) and 89 octane gas. Just what is this "small cam" anyway? Pinging could also be the result of too hot plugs and a too lean fuel mixture. And too much timing can do damage too, even with the right octane, you're basically putting more stress on the rods, pistons and bearings trying to compress the fuel mixture that's starting to ignite. Try running straight 93 again, but pull off the timing till it stops the pinging, then get back to us on what that is.
Who don't you agree with? I personally said he might be stuck with race gas. I know it's possible to run 93 octane with iron heads and 11:1 but at this point it can go either way.
I don't agree, with the right cam 11 to 1 and iron heads is very possible.
That is kinda what I was getting at.
Usually mild cams build cylinder pressure which in turn magnifies the effects of high compression and in the end, hurting performance.
You can run high compression and iron heads with great results if your cam has the right overlap to bleed off some pressure.
Mild cams are often even specifically designed to boost cylinder pressure.
If you mix one of these cams engineered as such with high compression, there is almost nothing you can do to stop ping short of changing one or the other component.
Or run diesel fuel... :D