Holley 600 vac sec with non CC HEI. How will changing the secondary spring affect the vacuum advance on the distributor? My thinking is that if the secondaries open sooner (lighter spring) there will be less vacuum to advance the timing.
Also do the aftermarket advance weights allow more total advance than the GM ones.
I am getting about 100 RPM worth of pinging at WOT at about 4300-4400. It decreases a lot if i disconnect the vac advance, but not completely.

 

I probably shouldn't answer this, since I don't have a VS Holley. But, by the time vacuum has dropped enough to open your secondaries, the distributor isn't getting much vacuum.

I've never gotten satisfactory results using the Mr Gasket HEI advance kit. It's supposed to allow more total timing, but I've only seen poorer advance curves using it. I've stuck to using lighter springs and setting the total timing only (ignoring the initial timing, just living with the stock weights & cam).

You might have a vacuum restriction that is keeping the vacuum advance in longer than it should at WOT. Can't say I've ever seen it, but sounds possible.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

IT might change advance a tad..but not really enough to be worth worrying about. I wouldn't mess with the VS spring at all actually. I did, spent forever messing with it..tried every spring in the kit at least once...and just ended up back on the stock spring.

 

It will in theory take away a bit of timing. However, the amount that you're worried about is miniscule and if you were looking to squeeze out the little bit of HP you'd get from that you would need an adjustable vaccum canister. It all depends, I changed my secondary spring and it was much better than stock. If I were you I wouldn't worry about it because chances are it is the stock canister and probably leaks being it's 20 years old (unless you bought a rebuilt unit).

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

 

84 FTA called it right. I replaced all of the components of the old HEI except the cannister. My car has always had an off idle stumble which i hadnt been able to get rid of despite trying everything to the carb(adjustments, jets, accel pump cams, PV's and 2' springs) and timing including advance springs. Turn out that i have had a leak in the vacuum advance cannister. The new one "cured" my off idle stumble and the transient pinging at 4300. I am expecting to get better gas milage too. This car never did as well as i thought at part throttle cruising, this may explain it.
BTW the Mr gasket advance set is a POS!!!! the weights have about 30-40000 miles and they have worn into each other. One was actually riding on top of the other a bit. I filed them smooth until i have a chance to get new ones. Does GM sell OEM replacements?