# ‘69 Ram Air III 400 timing



## Roqetman (Aug 31, 2015)

Does anyone with a ‘69 RAIII 400 have a solution for running pump gas without spark knock? I’m having to add a couple gallons of 112 octane race gas per tank full of 93 octane/ethanol to prevent detonation. Initial timing is set at 14 degrees btdc, 34 degrees total. At this setting vacuum is 15, if I go below 14 degrees the vacuum drops which effects power brakes negatively. If I go above 14 degrees the vacuum at idle improves but I’m afraid that will create more detonation. The engine is original 389 bored .030 over = 395 ci, mid-range cam, GM HEI ignition/with no vacuum advance, headers, 750 Quadrajet, mid-rpm power cam, Th400 transmission. It goes like a scalded dog but I’d like to know what timing or distributor curve would give best performance on 93 octane w/o adding race gas. I tried octane boosters, they were a waste of money.


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## Old Man Taylor (May 9, 2011)

You can't really work around the CR I expect you have. Your only choice is to use some kind of Octane booster, as you are doing. If/when you rebuild the engine you will need to drop the compression ratio.


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## O52 (Jan 27, 2019)

You can always add a hydraboost power brake system Then dial down your timing.


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## PontiacJim (Dec 29, 2012)

You will NOT be able to get the pinging out due to the high compression. I went through this with a member who PM'd me. Did everything known to man to include swapping cams, adjusting carb, getting engine temps down, adjusting timing/curve several times. Got the pinging reduced, but not gone. He had to still use an octane additive. Lowered compression is the only answer.


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## Roqetman (Aug 31, 2015)

Yeah, that’s what I was afraid of 10.75:1 CR with 93 octane doesn’t jive to good.


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## Old Man Taylor (May 9, 2011)

I had the same problem with my '70 GTO. It broke a ring and ring land, and a piece of the ring got caught under the head of the #1 exhaust valve.


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