[Roger25]

Hi i ready to fire up my freshly built 77 pontiac 400 w72

What sould be my initial timing

Qjet freshly rebuilt
9.5:1 comp
6x-4 head
Dougs headers
Crower cam: iNT/EXH - Dur @ .050” Lift: 210°/221° RR: 1.5/1.5 Gross Lift: .422”/.446” LSA: 112° RPM: 1300-1500 to 4800 Redline: 5300

Thank for the advice

[Kenth]

Welcome to the Forums!

I would start with the factory 16° initial setting.

This will result in max 34°-38° total centrifugal advance @ 4400 rpm with the original distributor.

HTH

[steve25]

Since your breaking in a new Cam it would seem would go with 18 to 20 degrees.

This will make the motor less likely to stall and run hot during the 20 minute Cam break in period as your getting other things sorted out.
Be sure to prime the Carb with fuel tru the air horn vent until the accelerator pump is seen to work well.

If this is the original Carb that was previously running on the old motor then turn up the idle speed screw by one full turn .so that you have 2200 to 2400 rpm taking place .

Note that the the motor is at #1 TDC when you see #6 Exh valve opening.

Also if you have the good full size balancer and you measure around from the timing notch another 2 1/8” that should check out at 38 degrees or so with the vacuum advance disconnected and plugged.

[nUcLeArEnVoY]

Factory initial timing for W72 motors for most years was 18 degrees, but you're making higher compression. Maybe bump it back to 16 degrees and take it from there?

[78w72]

I have a .030 bored 78 W72, with original .030-40 shaved 6x heads at ~9:1, mild comp XE cam, and Cliff built Q-jet to match the specs. I set the initial timing at the factory 18° and run a stock timing curve distributor.... no issues with detonation or hesitation etc in any situations, the engine runs excellent on 87 gas but I usually run 89 or 91 if I plan to race it or run it really hard.

I would start with the stock setting initial cam break in, then when all the bugs are sorted out see how it runs at the stock setting & go from there.