Total timing and timing curve recommendation

[supr78nova]

Looking for a total timing recommendation for my combo. Also what would be a good timing curve for this combo?

Approx 9.4:1 CR, ~15" vacuum @ idle
350 goodwrench short block
Vortec heads modified for increased lift
comp cams XE268 cam .477/.480 lift
holley 650 vac secondary
stock HEI distributor
2 5/8 full length headers w/2 1/2 exhaust

TH350 trans
3.42 gears


I recently purchased a piston stop to first verify true TDC, a degreed balancer cover, adjustable pointer, and an HEI recurve kit.



Any help would be appreciated,

Dan

[Shuboxchevy]

Dan,

I have a similar setup as you. L31 block with vortec heads. XE270 hyd roller cam. 9.4:1 CR. I was having pretty good luck with 10* initial w/ a 24* curve that was all in at 3000 rpm for a total mechanical timing of 34* advanced. I was also running a 18* vacuum curve that was all in at 8 in HG. I had pretty good luck with it and it may be a good starting point for you.

If anything, you may need a couple degrees less timing then what I was running since I was running the wrong length spark plugs previously.

Hope that helps.

[Seattle_Mike]

Above sounds about right for your combo. Read the plugs too...the best indicator of what's going on overall.

[kane]

just experiment, don't be afraid of more initial. My car is the same except I have more compression and it runs best with 18 initial and 32 total. I suggest you return the recurve kit, and buy the crane adjustable vacuum advance kit. It comes with the vacuum canister, and springs the recurve the mechanical advance.

[supr78nova]

Kane,
I forgot to mention that I do already have an adjustable vacuum advance canister installed.

As a general rule what would be the max total timing for my vortec headed combo? I know that vortecs require less total timing than older heads because of their more efficient chamber design amongst other variables, I'm just not sure how much total timing would be too much.



Dan

[kane]

I don't have track times where I've played with the timing, but from reading I just heard they run good around 32-33. Maybe drivewfo will chime in. But I will say, my car runs better with 18 initial. The idle is better, it's more responsive, starts right up, and runs cooler.

[Shuboxchevy]

Kane,
I forgot to mention that I do already have an adjustable vacuum advance canister installed.

As a general rule what would be the max total timing for my vortec headed combo? I know that vortecs require less total timing than older heads because of their more efficient chamber design amongst other variables, I'm just not sure how much total timing would be too much.



Dan

If it detonates... that's too much timing. :thumbsup:

52 total timing (initial + mechanical + vacuum) is ballpark for a SBC. Subtract a few degrees and that's about max for your vortec.