Join Date: Aug 2001
Location: Lawrenceville, PA, USA
Sure are a lot of timeing questions.
First, does anyone know of a book on tuning the GM HEI?
Second, what determines total mechanical timing in the distributor? Is it the weights or the springs or a combination of both?
The reason I ask:
I bought a new HEI from a race shop. The initial setting had light springs. Advance started at 900 rpm and gave a total of 18* by 2300rpm. I thought this was a little too quick plus I couldn't get the timing to go back to static at idle. It was sticking at 20* @1200rpms.
So I took it back to the shop. They put it on a machine and free'd up the mechanism. It was sticking a little. They also put in another set of springs.
Now the advance starts at 1200rpm and ends by 3000rpm BUT I only have 12* of advance!!
I took the dist. apart and put in a set of MR Gasket Silver springs. The advance started at 1500rpm and ended at 3300rpm. BUT still only 12* of advance.
What would be limiting the * of advance? Should I change weights? The weights from the race shop and the Mr. Gasket weights look identical.
'79 Z28, 4spd, 3.73 10 bolt, 350 4-bolt .030 over with stud kit, 10:1 Compression, Keith Black Flat Tops, Comp Cams Magnum 294 Solid Cam .525 lift, 63cc Heads, Stainless valves, hardened exhaust seats, guideplates, Summit Needle Bearing Roller Rockers 1.5 ratio, Offy Single Plane Intake, Holley 650 Vac. Secondaries, Stock HEI (for now), Headers 1 7/8" primaries, 3" Collectors into 2 1/2" exhaust with "H" pipe and Turbo Mufflers.