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Hello,

Can somebody tell me what's the best sprak timing for the following engine

- 4 bolt block
- closed chamber 4V heads
- stock crank
- stock rods with ARP nuts & bolts
- pistons 0.030 over
- Comp cam 290HR (LSA 110, IC 106, lift 0.588, 230 @.050)
- 1,73 rockers
- Holley 750 sec vac
- Holley strip dominator, 1/2 inch spacer
- 1 7/8 primairies
- engine pull 9.5" vacuum idle
- ratio 10:1

This are mine thoughts:
17* initial
20* mech. total 37*
10* vacuum

Greeting

Frank (Holland)
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you can experiment with initial & total timing individually, set the initial to 17* and see if it has any hot re-start issues. then set the total to 37* drive it, i doubt you'll notice any drivability issues, the question is whether it likes more or less?

the real trick is finding the rate that the advance comes in, the rpm when the springs are fully stretched to the stops and mechanical total timing is achieved. too fast & you'll get ping / knock / detonation, too slow & you'll be 'leaving power on the table'

your altitude makes a difference, a fast curve that works at 4500' elevation will not work at sea level

you may want a very slow curve
humaxxx, while the above suggestions probably will be good starting points, the optimum curve will be individual for each engine. And if you don't try to find that optimum curve, you'll lose out on HP and also risk pinging. Allow me to recommend my book on the topic. Or if you want, being a fellow Pantera'isti, I'll be happy to send you that section of the book that can help you find the optimum curve.

Regardless, always start conservative, less advance produces less HP, too much advance produces a boat anchor...
I copied the chart below from George's Cobra Jet thread. I would guess the VE of your engine with the Holley Strip Dominator is less than 90% at 4000 rpm, but better than 80% at 6500 rpm. That's just my guess based on comments about the performance of single plane intake manifolds.

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quote:
Originally posted by humaxxx: I heard that i must be all in at 2700-2800rpm


sounds a little on the fast side to me, for your elevation.

did the source that 'heard it to you' disclose their elevation?

at sea level your engine will develop more cylinder pressure than it would at higher elevation, higher cylinder pressure means more tendency to experience ping, knock, detonation, damage to your engine

do you know what pistons are in your 351C?

aftermarket hypereutectic pistons are very fragile and will not survive tuning experiments with detonation

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