Re: Distributor Timing Map/Curve for 65 SHP (365hp L76)?
Hill climbing or light acceleration detonation is possible when a spark advance map is optimal. It is sometimes caused by a "too aggressive" VAC. For the 30-30 cam, the typical idle is 10" @ 900, and it has an 8" VAC, so it just meets the Two Inch rule.
You say you have a 30-30 cam, but how do you know? How do I know? One thing to do is check normal idle vacuum with the VAC connected and the nominal 12* initial. If it's 10" Hg @ 900 that's a good inference that it has a real 30-30 cam. If it's higher you have something else. Measure it and let us know. Also, what valve clearance are you running?
Setting up an engine at the ragged edge of detonation is the best setup for fuel economy and performance when the available fuel octane is marginal for the CR. That's how I have all my cars setup, however, sometimes I experience a little transient detonation in hot weather.
If you have light detonation when climbing a hill, simply "drive around it" by shifting to a lower gear to climb the grade. If you can't live with that restore the proper initial timing and slow the centrifugal curve with some stiffer springs.
But I still have some suspicion about what you say is the configuration. There are virtually no reports of 365 HP detonation that I am aware of, otherwise.
I recently evaluated a local chapter member's 365 HP '65. The engine had been rebuilt by a PO and a mechanic had recently set the valve clearance to 365 HP specs. My testing indicated that it had the OE spark advance map and the 10" @ 900 idle was good evidence of a 30-30 cam, but we suspected the compression had been lowered with flattop pistons and a thick head gasket, which would drop the CR to around 9:1 - same as the advertised CR of the '71, LT-1, which was designed for regular unleaded.
I adjusted the idle mixture to get rid of some start-up stumble, set the total WOT advance at 39*, which would be about 15 intial and suggested he try a few gallons of 87 PON regular unleaded when the tank got low. He did and said it ran fine - no detonation, so now he can save about 5 percent at the pump.
The engine pulled fine from 1000 revs in top gear - not real strong for a big V-8 - but smoothly with no protest of any kind.
Duke
Hill climbing or light acceleration detonation is possible when a spark advance map is optimal. It is sometimes caused by a "too aggressive" VAC. For the 30-30 cam, the typical idle is 10" @ 900, and it has an 8" VAC, so it just meets the Two Inch rule.
You say you have a 30-30 cam, but how do you know? How do I know? One thing to do is check normal idle vacuum with the VAC connected and the nominal 12* initial. If it's 10" Hg @ 900 that's a good inference that it has a real 30-30 cam. If it's higher you have something else. Measure it and let us know. Also, what valve clearance are you running?
Setting up an engine at the ragged edge of detonation is the best setup for fuel economy and performance when the available fuel octane is marginal for the CR. That's how I have all my cars setup, however, sometimes I experience a little transient detonation in hot weather.
If you have light detonation when climbing a hill, simply "drive around it" by shifting to a lower gear to climb the grade. If you can't live with that restore the proper initial timing and slow the centrifugal curve with some stiffer springs.
But I still have some suspicion about what you say is the configuration. There are virtually no reports of 365 HP detonation that I am aware of, otherwise.
I recently evaluated a local chapter member's 365 HP '65. The engine had been rebuilt by a PO and a mechanic had recently set the valve clearance to 365 HP specs. My testing indicated that it had the OE spark advance map and the 10" @ 900 idle was good evidence of a 30-30 cam, but we suspected the compression had been lowered with flattop pistons and a thick head gasket, which would drop the CR to around 9:1 - same as the advertised CR of the '71, LT-1, which was designed for regular unleaded.
I adjusted the idle mixture to get rid of some start-up stumble, set the total WOT advance at 39*, which would be about 15 intial and suggested he try a few gallons of 87 PON regular unleaded when the tank got low. He did and said it ran fine - no detonation, so now he can save about 5 percent at the pump.
The engine pulled fine from 1000 revs in top gear - not real strong for a big V-8 - but smoothly with no protest of any kind.
Duke
Comment