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I’ve got our 1970 back on the road after the PO had it sitting for 26 years. in our first post here I said it’s a 1973 455 with #13 heads and people were nice enough to let me know she’s got too much compression for pump gas. Another thing working against us is that the accell distributer is stuck in the intake and it’s got 20 degrees of timing at idle and 40 at 3000 RPM. I know I’m screwed and should be changing heads but it’s not in the budget right now.

What would be the best option to keep it from pinging under loads? Mix of 110 and 93? 93 with an octane booster? E85? I’m going to try to get the distributor able to move and lower the timing to 12 and 32 but will that be enough to run only 93?

Thanks.
 

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My old 67 with 670 heads would run just fine on the old 91 octane, back in the late 80's through the 90's, and when money was tight a mix of 5 gallons of 87 topped off with12-15 gallons of 91, it was fine. With that said and ethanol in today's fuel...I'd think a good brand of octane booster with today's 91 or 93 and you'd be good to go. BUT, you have to get the timing right or all bets are off.
 

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I’ve got our 1970 back on the road after the PO had it sitting for 26 years. in our first post here I said it’s a 1973 455 with #13 heads and people were nice enough to let me know she’s got too much compression for pump gas. Another thing working against us is that the accell distributer is stuck in the intake and it’s got 20 degrees of timing at idle and 40 at 3000 RPM. I know I’m screwed and should be changing heads but it’s not in the budget right now.

What would be the best option to keep it from pinging under loads? Mix of 110 and 93? 93 with an octane booster? E85? I’m going to try to get the distributor able to move and lower the timing to 12 and 32 but will that be enough to run only 93?

Thanks.
Fix/Ditch the distributor first and go from there. Make sure you have a distributor with a vacuum advance can. But, that won't do it because compression will be too high for pump gas of any kind and is really more on the line of a race engine combo.

Then, with the #13 heads having 72CC's, you will be either adding an octane booster or mixing race gas. You may have close to 11.0 compression. You will need at least 100 octane, maybe more.

Best bet would be to install another set of heads with bigger combustion chambers or rebuild the engine with dished pistons.
 

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Fix/Ditch the distributor first and go from there. Make sure you have a distributor with a vacuum advance can. But, that won't do it because compression will be too high for pump gas of any kind and is really more on the line of a race engine combo.

Then, with the #13 heads having 72CC's, you will be either adding an octane booster or mixing race gas. You may have close to 11.0 compression. You will need at least 100 octane, maybe more.

Best bet would be to install another set of heads with bigger combustion chambers or rebuild the engine with dished pistons.
THIS, ^^^^, 100%. Use a slide hammer if you have to to pull the distributor. Fix that first. No matter what, you will need 100 octane fuel to stay out of detonation. E-85 is alcohol and would require major fuel system changes. Agree with installing the 101cc heads and driving it.
 

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6X heads are very decent and can be bought on the cheap. For a little bit more, you can get a pair that is already refreshed and ready to go. I'm running a set of Nitemare stage II on mine. They are fantastic. If your engine is more of a stock build, a pair of their stage I would probably be more than enough.


I don't work for them, just a happy customer.
 

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My 65 with stock 10.75:1 compression I run 93 with Hapco lead replacement additive and get no pinging. While not ideal a $75 gallon of additive treats 200 gal of gas..

I have about 36 degrees total timing, 8 initial with manifold vacuum advance. I would try backing your timing off or installing a limiting bushing so you can keep initial advance up but limit total.

How hot does your car run - mine is about 195-200, and I have it jetted a tad rich which also helps.

I would think if you can try a couple of things like above you should be able to get it to work ok.
 

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Mixture and operating temps really, really matter where I live, in hot, arid central CA. Particularly since all we can get is ethanol-laces gas, which runs too lean in a factory calibrated carb and boils off at 140 degrees. A slight rich mixture and a running temp below 200 are a huge help. My 9.3 CR '67 400 will ping on 91 octane on a 105 degree day under a load. It needs more octane in those conditions.
 
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