ModifiedC5

If my dyno run indicates that my max hp occurs at 6300 rpm and my max torque occurs at 4800 rpm? My shift light will wire directly to the PCM. Also, should I be setting the shift light at a point in advance of the ideal rpm to account for any delays or differences in reported rpm vs. actual rpm?
TIA!
:seeya

ModifiedC5

anyone? :confused:

6Speeder

If you peak at 6,300 I'd set the light to flash at 6,200. You'll end up shifting at 6,400 or higher in first. If you end up hitting your rev-limiter then lower the rpm for your light. That's where I'm starting with my light. my limiter is set for 6,600 rpm. :steering:

vetterdstr

6200 is good

vetterdstr :cheers:

Timmy's C5

Just wondering here. Since acceleration is more a function of torque than horsepower in drag racing, might it not be better to shift earlier nearer the peak torque figure. Wonder if somebody has plotted the hp vs. torque curve and found the ultimate shift point for the ¼ mile?

scool93535

Yes there is a site. The key is maintaining maximum area under the TQ curve. For a stock LS1, all shifts should occur at redline, (6000 rpm). The advantace of a shift light is it will indicate when 6K is reached without having to guess where the actural RPM is Vs the lag between the engine and tach.

:cheers:

ICULUKN-C5

5850 for a LS1
6250 for a LS6

Arthur6

When you shift, you want the engine in the meat of the torque IN THE NEXT gear, so shift at 6200-ish

Rays Vet

Just to pass some info, a guy on ls1.com raised his rpm by 300 rpm over were the car would shift on it's own(in 3rd) and knocked off .20 tenths in the 1/4 mile.

C5 Tweaker

To confirm my theory, I did a detailed G-Force vs. MPH vs. Gear analysis. The data was based on dyno results from my 430 RWHP heads/cam car with 5,800 fuel cutoff.

The results show that the g-force graph for each gear does not intersect the next - thus the ideal shift point is just before fuel cutoff.

To compensate for reaction delay, ideally your shift light should come on at a different RPM for each gear. This is due to the very different rate of RPM increase in each gear. If you adjust it to be ideal for 3-4, you Will bump the limiter on 1-2, etc. With a single RPM setting, there must be a tradeoff.

The new G-Tech Competition meter has a neat shift light built in. I have requested that they add a feature to allow a different RPM setting for each shift point. Fingers crossed...

Timmy's C5

Good work C5 Tweaker.
Just as I thought. Picking a point for the shift light to come on is not as simple as it seems. I would like to see your graphs. Also, I think that timing is critical. Maybe by staying in the lower gears longer than required by your graph would indicate you could eliminate a extra gear shift near the end of the ¼ mile and thus save time (maybe at the expense of top speed). It is time rather then speed that wins drag races.

Allgonoshow

I was just reading a dyno+track test on light vs heavy flywheels.(beer with me now) In the test to see which was better to have for drag racing. Lighter for acceleration, or heavier for the purpose of using the extra stored energy to increase the torque load after the shift. With the 2 cars, a 12 and 10 sec car, they found that when the lighter setup came up in the rpms quicker the shift was slightly delayed. It was 150rpm after the rest of the shifts with the heavy flywheel. (they spent a couple hours with the cars practicing dyno racing making sure all shifts where consistant). They found that the extra 150 rpm made up for the lose in torque rite after the shift for that 6 or 7 tenths. The more power the car had the more it increased over the heavy flywheel. So...after reading that I would suggest setting it at the point just below where u would bounce of the limiter in first. Then as stated above, dont react to the light as fast as u would in the next gears do to the loss in rpm acceleration. Should keep u closer to the limiter and give you that extra stored energy from the flywheel turning faster to move u out faster rite after the shift.

Hope this helps. Just read it during new years party.

lost

Check out this link, has a program to do just what you want, where you input gear ratios and dyno #s to give you best shift points..... http://www.prestage.com/carmath/dynochart.asp

C5 Tweaker

Timmy et al,

Maybe my earlier post was unclear. The ideal shift point is AT fuel cutoff. You cannot stay in any gear longer than ideal without bumping the limiter (which can bounce lifters in some configurations - not good either).

Here is the graph. As the ideal shift point is where the lines intersect, and the lines do not intersect, the ideal point is at fuel cutoff.

Enjoy...



I see the auto-resizing sucks - sorry...



[Modified by C5 Tweaker, 8:29 PM 1/2/2003]

ModifiedC5

thanx for all the replies.
lost, that is a great site. Based upon my dyno, it calculates that my best points to shift are at 6500 for 1-2-3 shifts. 6400 for 3-4-5-6 shifts. Now for real world reasons (not an expert shifter, rpm lag, room for error, etc) I'll probably set my shift light to somewhere between 5800 to 6000. Sound reasonable?:skep:
:cheers:


[Modified by ModifiedC5, 7:50 PM 1/2/2003]