A locked 37 degrees worked best on the AFR headed 540 I had...ran it that way for years...:thumbsup:
Used a 6AL box and a crank trigger too for a very stable spark.

 

I run 37 degrees locked out as well for my AFR Headed 548.

 

I run a total of 40 on one of my 468s and 38 on the other with 22 intitial. Never cooked a plug and they don't detonate. Each engine is it own animal though.

 

41.5* on my 13:1 468 with AFR 305's which have been massaged.

 

Interesting as my motor showed a slight gain in MPH by running 34*. Honestly though, wasnt a whole lotta difference from either 32 or 36. This is a 9.8:1 502 with AFR 305's.

Bet the hotter motor with alot more compression will be much more sensitive, especially with some big domes. Only running flat tops here, which likely explains the need for a reduced amount of advance.

 

This might be of some help:
http://www.chevelles.com/forums/showthread.php?t=332882

 

I was just looking for a thread like this!
I just have my 540 on the road and I am finding I can only run 33 degrees total out of it. Any higher and it seems to ping on the highway when on the throttle. This only translates to about 13 degree of initial timing. I can change the bushing in the pro billet MSD distributor to get more initial but I would first like to know why I cannot get more total out of it. It runs through a 6AL box. 325 AFR heads, 10:1 compression, 93 octane, Champion C59C plugs, flat top pistons.
Thanks!

 

Oh yea.. and a hyd roller with 262/268 at .050 with 632 lift, Holley 950 cfm carb. When tuning I can pull 23mmHg of vacuum at about 1000 rpm.
I wonder if I am pulling vacuum at WOT and the vacuum advance is still active?

Along with running a vacuum gauge ,could you verify some of what you posted.
You idling at 1000 or just tuning there?
If at 1000 ,your probably into the mechanical advance.
Did you verify that TDC is actual TDC at the balancer/pointer?

 

Oh yea.. and a hyd roller with 262/268 at .050 with 632 lift, Holley 950 cfm carb. When tuning I can pull 23mmHg of vacume at about 1000 rpm.
I wonder if I am pulling vacume at WOT and the vacume advance is still active?

 

wonder if I am pulling vacume at WOT and the vacume advance is still active?

I am no BB guy but I would start there. Get a vacuum gauge and have it on the car for a few days. Map out the vacuum advance. Get a hand held vacuum pump and record when the vacuum can starts to pull in and also when it is all in. Also, have you verified how many degrees the can adds?

 

Yes, 23. You have to rev it some,1000-1200 rpm but the highest I got was 23. It settles at about 20 with idle at 900 rpm. If the idle goes down from there the vacume will drop significantly, like to 8, and the idle is poor.
The cam has a 114 degree LSA. This may possibly be allowing the motor to biuld more dynamic compression ration than the average performance cam with a 108 or 110 LSA. I am guessing this may be responsible for having some vacume at idle. This may also be contributing the the max of 33 degrees total timing since I am not bleeding off much pressure with a high overlap cam.
However... In other vehilces I have had, detonation from too much timing always sound like a popcorm popper, meaning frequent or constant popping noise. On this car, the popping was about one every second or so, very distinct seperate episodes of detonation. Is this more indicative of a single plug that may be heating up?

 

try another vacuum gauge............... there's no way I can see 20" of vacuum at 900 rpm idle and that cam, regardless of the wider LSA.

Jody

 

Locked out at 40* on a 496, ~10.5:1, 260/266@.050 SR, running on propane. May bump it a couple degrees more next time I feel like messing with it.

 

Thanks for the input guys :thumbsup:

 

I will borrow another gauge and see what's up with the vaume.

What are the symptoms and causes of unburnt fuel getting to the hot headers? I drove it more this weekend and maybe I am hearing some ignition of fuel in the headers when I nail it?..