390 ci timing question

Pscarlato

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What vehicle(s) do you drive?
1959 coupe deville
Hi, new to this forum and happy to be here. Can anyone give some guidance on timing for my 59 coupe with a 390 engine. I switched from ported vacuum to manifold vacuum. I set initial timing to 5 BTC as per the book. Mechanical timing adds 20 crank degrees and it hovers around 25 degrees BTC. Seems to run fine. With vacuum advance canister hooked up it adds about 12 crank shaft degrees so it ends up at total timing of 36 degrees at about 2500 or 2800 rpm - somewhere around there. Given it’s a high compression engine (10.5:1) and it’s a big heavy car, does this sound right? I see posts all the time saying it can go up to 40 or more degrees total advance. I want to avoid detonation. Running 93 octane. Any guidance on this timing would be helpful. Thank you.
 

5one9

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What vehicle(s) do you drive?
2007 Magnum SRT8, 1957 F100
I’d run 30-32 before vacuum advance. You should be able to bump initial up to 10 or 12 without bucking the starter, which would get you there.
 

Caddylackn

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When I ran my '61 with the 390 as a daily driver back in the 90s. I set it to factory spec, then backed it off a few degrees. I could only get 91 octane. I used to run a bottle of cheap octane boost per tank sometimes, as it helped. Later I found out the cheap octane boost I was using was just kerosene. After that I ran about a pint to a pint and a half of kerosene per tank. It really helped on detonation going up those big Seattle hills. I believe the kerosene didn't raise the octane of the gas, but did slow down the combustion rate of the mixture to help with pre-detonation. I also ran a petronix ignition, which helped, and those ol' splitfire spark plugs, which were the rage in the 90s. I have gotten up to 15 mpg on long trips, not bad for a big block boat designed in 1961.
 
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