Explanation of optimum timing inside...
04-22-2004, 12:56 PM
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Explanation of optimum timing inside... By Klauss at innovate. May explain why I was making max power toward 11.5 AF.
http://www.innovatemotorsports.com/f...=1389#post1389
Most engines develop max torque (equal to max power for a given rpm) when the peak pressure point (ppp) in the cylinder is about 14-19 deg ATDC. The important thing to know is that this value is INDEPENDENT of engine load and rpm, but dependent on engine geometry like bore/stroke relationship, rod length and so on. The point of ignition advance is to time the onset of burn such that the ppp is at the sweet spot. If your ignition is too advanced (even without ping), you are earlier than the sweet spot (with normal mixture). By richening up the mix, you slow the burn so you hit the sweet spot again (rich mixture burns slower). But of course you produce less power, but the max that can be achieved with the ignition setting. I would try to retard a bit and see if you can't make more power with a leaner AFR.
http://www.innovatemotorsports.com/f...=1389#post1389
Most engines develop max torque (equal to max power for a given rpm) when the peak pressure point (ppp) in the cylinder is about 14-19 deg ATDC. The important thing to know is that this value is INDEPENDENT of engine load and rpm, but dependent on engine geometry like bore/stroke relationship, rod length and so on. The point of ignition advance is to time the onset of burn such that the ppp is at the sweet spot. If your ignition is too advanced (even without ping), you are earlier than the sweet spot (with normal mixture). By richening up the mix, you slow the burn so you hit the sweet spot again (rich mixture burns slower). But of course you produce less power, but the max that can be achieved with the ignition setting. I would try to retard a bit and see if you can't make more power with a leaner AFR.
04-22-2004, 02:00 PM
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This gets almost to the fundamental question, which is:
where is peak power made on an LS-1, given two
degrees of freedom (fuel and spark) - what AFR and
what spark advance (w/ RPM)?
The majority seem to end up somewhere about 12.8-13.0:1
and "whatever spark she'll take", from what I observe. But
to exhaustively map this out, would be some swell science.
For somebody with unlimited free dyno time anyway.
where is peak power made on an LS-1, given two
degrees of freedom (fuel and spark) - what AFR and
what spark advance (w/ RPM)?
The majority seem to end up somewhere about 12.8-13.0:1
and "whatever spark she'll take", from what I observe. But
to exhaustively map this out, would be some swell science.
For somebody with unlimited free dyno time anyway.
04-22-2004, 06:38 PM
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I didn't intend to run that much, but on the dyno in 3rd gear, I was low enough load to move up the timing chart. I didn't realize I wasn't really changing timing the day I was tuning, as I was doing everything right below the actual load cells I was in. I intend to try more than just third gear to make sure I tune different load points. (if time allows)
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04-30-2004, 01:19 PM
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By traditional SBC or even SBF standards, yes. But I can't think what else explains I make max power at 11.5:1 with a proven reliable wideband unit. Do you have dyno testing on the LS1 motor that bears out that optimum power is past 29 ?
05-02-2004, 04:31 PM
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ive dynoed about 100 ls1 fbodies. Not saying that max power is necessarily higher then 29 degrees, but saying that many cars with 29 degrees timing have not needed to run that rich NA for max power. Ive NEVER seen a NA motor run its best at 11.5
Not that it cant happen, ive seen stranger. Ive made max power with a wideband reading 14.7:1 at peak torque, 28 degrees timing, no knock. Not garunteeing that the proven relible wideband wasnt in question though
Not that it cant happen, ive seen stranger. Ive made max power with a wideband reading 14.7:1 at peak torque, 28 degrees timing, no knock. Not garunteeing that the proven relible wideband wasnt in question though
05-02-2004, 04:46 PM
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I appreciate the insight. My next dyno is scheduled with a better dynojet facility. I'm adding another bung to the other bank of my exhaust & will have the dyno operator's wideband to compare to mine. Have you seen a typical max timing level for a TR224 cam only car/2001 up type heads ? My wideband is dead on at stoich/14.7/part throttle and the exhaust/O2 is pretty black with WOT set in the 11s.... V. interesting and will certainly report back. I would think to run peak power at 11.5 would much too much timing... we'll see.
05-04-2004, 07:12 PM
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I will. Dyno date tentatively scheduled for May 19th.. Midwest supposed to ship my converter back tomorrow.
I posted this elsewhere, but do you dyno in other gears to tune different loads? Especially since the dyno will be a bit lower load than the street?
Dean
I posted this elsewhere, but do you dyno in other gears to tune different loads? Especially since the dyno will be a bit lower load than the street?
Dean
06-06-2004, 07:52 AM
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Viper, 4th makes sense. Where did you find optimal timing and/or AF?
Update- bottom line, the car was actually close to optimum as I left that first dyno. I made peak power around 12.5 on the new dyno facility's pre-cat wideband and in the 28 degree range of timing. (The innovate kit read more like high 11s... still not sure which is more 'accurate')Even more interesting, within a 4+ degree range of timing and 10% range of fuel richness, I made no greater a range of power than about 8hp. Kind of surprising. For anyone that wants to see the actual files/graphs at various fuel and timing points, let me know.
Update- bottom line, the car was actually close to optimum as I left that first dyno. I made peak power around 12.5 on the new dyno facility's pre-cat wideband and in the 28 degree range of timing. (The innovate kit read more like high 11s... still not sure which is more 'accurate')Even more interesting, within a 4+ degree range of timing and 10% range of fuel richness, I made no greater a range of power than about 8hp. Kind of surprising. For anyone that wants to see the actual files/graphs at various fuel and timing points, let me know.
06-06-2004, 10:35 AM
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Originally Posted by Sunset01
Viper, 4th makes sense. Where did you find optimal timing and/or AF?
Update- bottom line, the car was actually close to optimum as I left that first dyno. I made peak power around 12.5 on the new dyno facility's pre-cat wideband and in the 28 degree range of timing. (The innovate kit read more like high 11s... still not sure which is more 'accurate')Even more interesting, within a 4+ degree range of timing and 10% range of fuel richness, I made no greater a range of power than about 8hp. Kind of surprising. For anyone that wants to see the actual files/graphs at various fuel and timing points, let me know.
Update- bottom line, the car was actually close to optimum as I left that first dyno. I made peak power around 12.5 on the new dyno facility's pre-cat wideband and in the 28 degree range of timing. (The innovate kit read more like high 11s... still not sure which is more 'accurate')Even more interesting, within a 4+ degree range of timing and 10% range of fuel richness, I made no greater a range of power than about 8hp. Kind of surprising. For anyone that wants to see the actual files/graphs at various fuel and timing points, let me know.
This is something that concerns me about these
wideband sensor products. Their operation depends
on some initial calibration and most appear to have
no "auto-cal" procedure or means of determining
whether the unit has drifted out. I think I saw one
that did have field-calibration or autocal features.
It would be a bummer to throw down $400 for a
wideband unit, thinking you're buying accuracy
and then spend your life mistuning your car with
a bad instrument.
Any wideband users / owners know about their
units' long-term accuracy, how it is ensured, and
how trustworthy the scheme appears?