What's with the TQ dropoff at low RPM's?
#1
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I've been doing a lot of head research. I noticed in one of the latest issues of GMHTP that it seems all the LS2 Dyno graphs had a TQ dropoff at low RPM's.
What causes this?
I got these graphs here... http://www.gmhightechperformance.com.../photo_25.html
![](http://aycu21.webshots.com/image/9980/2003331115404724330_rs.jpg)
What causes this?
I got these graphs here... http://www.gmhightechperformance.com.../photo_25.html
![](http://aycu21.webshots.com/image/9980/2003331115404724330_rs.jpg)
![](http://aycu14.webshots.com/image/8493/2003336898499985842_rs.jpg)
Last edited by bayer-z28; 12-26-2006 at 07:50 PM.
#4
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Originally Posted by 66deuce
i think it's how the dyno loads the motor.....
The 3000-4000 "hole" may be caused by the intake and perhaps exhaust tuning lengths as well as valve timing. You could "fill" in this hole to get more average torque/power but you might sacrifice a little peak hp. I guess it would depend on what your goals were. My guess is that most magazine tests look for the biggest peak numbers.
Note that the 30 lb-ft max "hole" was different for the different heads, but was still about the same rpm. Same intake, exhaust and cam if I recall the test.
In the 2006 Engine Masters Challenge, which is scored by (average torque + average hp) from 2500-6500, the winner was as much as 37 peak hp and only a few peak lb-ft down on the runner-up, but the averages were better. The runner-up had a big "hole" in the lower rpm torque curve.
If you replot the torque curve with the y-axis (torque) compressed to what you normally see on a Dynojet graph, you might not see so much of the "hole". Horsepower is calculated from torque and rpm, so the hp curve also dips, but less radically because the rpm is below 5252 where torque and hp numbers are the same. Note that little torque blips have a bigger effect on hp above 6000. Both engines had about 83-85% of peak torque from 2700 to 7000, which would make a killer street driver!
FWIW, this is the same reply to the same thread on another forum, which shall remain nameless.
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My $.02
#6
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That dropoff is very common with drive-by-wire LS1s and LS2s. There is a tuning fix. There's an entire thread about this in the dyno section from a month or two ago. Slowhawk knows how to fix the dip.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
![](https://ls1tech.com/forums/signaturepics/sigpic210_1.gif)
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
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#8
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Alot of times when ive seen this is with very powerfull racing heads, SB2.2's, splayed valve heads and so on, I would just about consider all LSX heads as production racing heads. I dont know why it happens. If you look at some of old school 23* stuff you dont see it as much. And alot of times you wont see it on an all out racing head as they dont test at that low of an rpm. just my .02 cents