More advanced initial timing if using Lower CR Pistons ??
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Racer
Joined: Aug 2001
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More advanced initial timing if using Lower CR Pistons ??
On my engine rebuild which should be completed next week, i decided to go with 9.6 CR SpeedPro Pistons instead of the 10.8 CR Pistons i had in there. Im wondering if i will be able to advance the timing more , before detonation occurs, using the lower CR Pistons (while still using the same premium 103 octane pump gas) ???
What is the answer to that question ?
Thanks, RR
What is the answer to that question ?
Thanks, RR
Race Director
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Re: More advanced initial timing if using Lower CR Pistons ?? (Rumpity Rump)
Theoretically a less dense mixture burns a bit slower, so a lower compression ratio would indicate the need for a bit more total WOT timing, but there are other variables. SBs that make peak power in the 5500 to 6000 range generally make the best power at about 36 to 38 degrees, but varying timing two to three degrees from optimum will only reduce power about one percent, which you can't feel SOTP and it's within the run to run variation of the best dynos.
Duke
Duke
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Re: More advanced initial timing if using Lower CR Pistons ?? (Rumpity Rump)
As Duke posted, there's a point where more advance only hurts power and more isn't always better. Just because it doesn't cause pinging doesn't mean it's good. A lot of low compression engines still won't ping even with WAY too much advance. The only real way of knowing if your timing is optimum is to make direct comparisons at different settings. Keep in mind that best performance doesn't always come from the highest peak power but, instead, it comes from making the most power throughout the entire the range that the performance is being measured. The more power that you have below the curve, the faster the car will accellerate to it's peak.
Race Director
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Re: More advanced initial timing if using Lower CR Pistons ?? (Vetterodder)
Just to add to the above. The best situation would be to tune/time it on a dyno. The track is the next best place. If done at the track, tune for the MPH numbers and NOT the ET. The MPH is a better indicator of the overall horse power. Good luck.
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Re: More advanced initial timing if using Lower CR Pistons ?? (CFI-EFI)
Also, whatever you end up with for max timing, you will probably need to set up the curve to get it all in pretty early. Lower compression engines are pretty "lazy" and the increased initial timing and quick rate, plus limiting total advance really can wake one up.
Don't be afraid of 16-20+* initial timing.
But I gotta ask...
If you can get 103 octane gas and are willing to pay for it, why did you go with such low compression? Man... I'd be thinking 11.5-12.0+ with that stuff.
Jim
[Modified by 427Hotrod, 3:23 PM 6/24/2002]
Don't be afraid of 16-20+* initial timing.
But I gotta ask...
If you can get 103 octane gas and are willing to pay for it, why did you go with such low compression? Man... I'd be thinking 11.5-12.0+ with that stuff.
Jim
[Modified by 427Hotrod, 3:23 PM 6/24/2002]
