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Timing a 390

Started by Paul, August 10, 2019, 12:31:26 PM

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Paul

There are a lot of threads about timing. Wondering if anyone followed the shop manual for a 390 (59 cdv in my case) and set the timing to C? In my area outside Chicago the gas is 93 octane. Most threads advise advance for better performance. Anyone disagree with setting timing to C given the lower octane gas? Loved to hear some thoughts on it or advice?
I am trying to solve rough acceleration. Thx.
59 Caddy, Seminole Red with Dover White top

Big Fins

C= Top Dead Center. That's retarded of even the 5 degree base. With 93 octane fuel which is the standard premium fuel throughout the US you should be able to set your base at 10 degrees BTDC and the car should run beautifully and not ping.

At TDC it is probably a slug for performance and idle.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

35-709

1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Paul

So I set to 10 BTDC on the harmonic balancer. Yes, big increase in torque/horsepower. She feels like a much lighter car. However, not totally smooth and actually sounds like a truck. Very clunky sounding from the rear. Thoughts on why that would be? Any suggestions to correct that?
59 Caddy, Seminole Red with Dover White top

Big Fins

Go through the ignition from the points to the timing to the gap on the plugs. Then balance the air/fuel ratio and RPM. If you have one use a vacuum gauge to 'see' the inside of the engine. Well worth the few bucks that they cost.

These 390's are a very smooth engine.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

35-709

".... sounds like a truck. Very clunky sounding from the rear."??

Sounds more like a loose exhaust and/or a hole in the muffler or resonator.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2