[Lloyd-TX]

Good info, Cliff - thanks!

Later,
"455HO" Lloyd

1972 Formula 455HO; Lucerne Blue; 12.96 @ 104 MPH @ the '03 PSN's; 12.50's or bust this year!
1970 GTO 455HO; Palomino Copper
1972 GTO 455HO; Sundance Orange

[toddmoll]

I see everyone is after the vacuum advance or total timing. What carburetor are you using? and has it been setup for your engine? Many q-jets had a lean part throttle, this is how mileage was increased. Holleys almost always come out of the box too lean on both ends for a performance engine.


Todd.

[Kenth]

A lean mixture does not ignite as easy as a rich mixture and will not make the engine ping, just loose power.
A too rich mixture will make the engine ping.
Cylinder peak pressure should occur at 14 degrees ATDC, and that´s when the combustion should be finished.
That´s why there are different ignition advance curves depending on combustion chamber shape, compression, fuel used,amount of fuel used, rpm´s and so on.
If you have a too rich mixture it will burn off faster than necessary (before 14 degrees ATDC)and creating ping.
Excessive oil consumtion will also create ping.

[buwalda]

To PMDracer

Yes, the 4" to 17" range of vacuum is for the Crane adjustable #99600 unit that fits the GM HEI.
As the cam gets bigger in duration, the spring in the stock vacuum advance unit will probably be too stiff to work properly with the lower vacuum of a large cam. This is when the Crane unit works well.

[PMDRACER]

Geoff -
Thanks for the reply!
Looks like my problem is my Crane vacuum advance can is defective. Testing with 2 different mityvacs, my Crane only changes it's opening point from 7 to 9 inches of vacuum.

Again, thanks!

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. [email protected]

The point to life isn't necessarilly the decimal.