[footjoy]

I have never raced on a dragstrip but with all the reading I have done about heads and horse power and torque I was curious do you shift at peak HP or peak torque.?

Thanks
Greg

[slowbird]

Most serious race cars/engines never even see peak torque, its way to low in the rpm range. Most shift 200-500 pass peak hp

[Scott Stoneburg]

I think its best to leave the line just below or at peak torque. And shift a few hundred rpms above peak HP like Slowbird suggested

[Steve C.]

In discussion don't forget to address converter slip if automatic trans.

There are also others out there....

http://www.gtsparkplugs.com/GearCalc.html


http://www.wallaceracing.com/calc-rpm-drop-shift.php


.

[dammen8]

My 535 made peak at 7500, I have the shift light come on at 7850, typically my shift is completed between 7950 and 8100 depending on how much I anticipate the shift or how much I miss it by...just seems to be where my car is the quickest...

Chad

[slowbird]

Originally Posted by dammen8

My 535 made peak at 7500, I have the shift light come on at 7850, typically my shift is completed between 7950 and 8100 depending on how much I anticipate the shift or how much I miss it by...just seems to be where my car is the quickest...

Chad

What does your rpm fall back to and what was you peak torque rpm?

[Stan Weiss]

How far past peak HP you should shift also depends on how fast or slow your HP drops off after peak HP. The problem I see with many dyno tests is that they never make a pull high enough to get a good idea of how the HP carries after peak.

Stan

[Steve C.]

" I see with many dyno tests is that they never make a pull high enough to get a good idea of how the HP carries after peak."

Good point. With that in mind for interest I looked at the dyno sheet for my previous 462 engine. It was more street than a race car situation but we did run it competitively on occasions. The peak power RPM was at 5800 and it made 580.2 HP there. At 5900 RPM it was 578 HP and at 6000 RPM it was 572.9 HP and here the dyno pull stopped. For racing we had a 6000 RPM shift chip installed on the shift light. It was shifted at this 6000 rpm, 200 RPM over peak power. That said by the time one sees the shift light come on and you react to it I have no clue how much higher the RPM actually was. Both second and third gear were at the same 6000 RPM. Maybe not scientific but it worked out ok.
Best Performance was 10.88 at 124.28 mph. In the heat and depending on track conditions it might be low 11s.

But this was bracket racing and very important the car was capable of being pretty consistent.

Example at the Pontiac Southern Nationals in the heat...

Time Trail Runs:
11.099
11.098
11.081
11.084
Afternoon eliminations:
11.085
11.160 (out ! )


.

[John Langer]

Originally Posted by slowbird

Most serious race cars/engines never even see peak torque, its way to low in the rpm range. Most shift 200-500 pass peak hp

I leave within 4 ft/lbs of my highest torque value on my dyno sheet.

[slowbird]

Originally Posted by John Langer

I leave within 4 ft/lbs of my highest torque value on my dyno sheet.

I should have said except on launch most never see or come close to peak tq rpm. That a better statement?

[dammen8]

Originally Posted by slowbird

What does your rpm fall back to and what was you peak torque rpm?

As you know I got very few passes on this combo... this is one of my n/a passes..

[dammen8]

Originally Posted by slowbird

What does your rpm fall back to and what was you peak torque rpm?

This was one of the couple bottle passes

[dammen8]

Originally Posted by slowbird

What does your rpm fall back to and what was you peak torque rpm?

Sorry for all the posts... here was my dyno sheet...

But so far with my very limited number of passes (7 total) the time slip has shown 990 hp ... based off of Wallace racing's site.

[John Langer]

My converter flashes within 4 ft/lbs of peak torque on the hit and falls back within 21 ft/lbs of peak torque after the gear change. I shift and go thru 500rpm over peak hp but my junk isn’t peaky at all and doesn’t drop off fast.

[slowbird]

FWIW My junk from peak tq rpm to 4tq down is 300 rpm and 20tq down is 700rpm. But rpm wise my setup never sees peak tq rpm except briefly at launch. I do need to do a lot more converter testing but im going through 700rpm pass peak hp.

[Lee]

Originally Posted by footjoy

I have never raced on a dragstrip but with all the reading I have done about heads and horse power and torque I was curious do you shift at peak HP or peak torque.?

Thanks
Greg

Shift about 600rpm SOONER than you think is "optimal" for a couple of runs.

Then, make another pass where you shift about 200rpm higher.

Look at the results. If you ran quicker, then raise the shift points another 200. If you ran considerably slower, then try even lower than where you started.

Some motors will TANK a few hundred rpm past peak HP, while others will have a rather flat HP curve past peak. I've had cars that ran quickest when shifted just past peak HP, but had one that peaked HP around 6200 but ran best shifted just before 7000.

Also, not all tachometers are actually accurate. Some are off by a few hundred RPM. Experiment, and find out what works best for YOUR combo.

[Half-Inch Stud]

Originally Posted by slowbird

I should have said except on launch most never see or come close to peak tq rpm. That a better statement?

I'd double-down to say "iszat before or after the TQ Converter?".

Wish we had TQ Converter behavior when loaded into a water brake.

[Stan Weiss]

Originally Posted by Half-Inch Stud

I'd double-down to say "iszat before or after the TQ Converter?".

Wish we had TQ Converter behavior when loaded into a water brake.

Mark,
Shouldn't you be able to look at the TC behavior on an axle inertia dyno? You should be able to adjust the load to simulate vehicle weight and then be able to run a simulated 1/4 mile run minus aerodynamic drag.

Stan

[Half-Inch Stud]

@Stan I think a base pull would need to be done in 1:1 DRIVE to be most informative on the Engine & Converter capacity.

Then however there is a valuable performance inspection during the upshift: MANY Converters lose the power transfer (fluid momentum loses functional sense) during upshift, or TQ Multiply mode. Plain speak MANY Converters cannot efficiently go from 1:1 fluid lockup to TQ Multiply from a quick upshift.

I truely believe the ECM has the best Converters in the field due to strong acceleration through the upshift. Yet i suspect 10 Converters could be built and maybe 3 perform (i dunno). The Parts and assembly stack has to be perfect - repeatably.

-->Do we have such DYNO with converter macros, somewhere in PA?


Not sure an inertial car-chassi dyno has been built to be close to relevant, to allow "rowing the gears" for a real result.

[70GS455]

When you have dyno info, the answer is simple. Plot driveshaft torque or hp (either one gets you the same answer) in each transmission gear on the same plot. Where the curves from the plot cross over that of the next highest gear, that is the optimum shift point. If the curves don't cross, shift point is engine rev limiter rpm. That ensures you deliver the maximum hp for the run

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