What RPM to shift at for best 1/4 mile trap speed?

[CMilViper]

I was just wondering what RPM you guys shift at when running the 1/4 mile when achieving your highest trap speeds?

Thanks

 

[Mike Brunton]

I've heard numbers all over the board, but I always ran it up to within a couple hundred RPM of redline. Worked for me. The other theory is that the motor makes torque down low so shift early, but I never experienced that to be beneficial.

 

[CMilViper]

Thanks Mike. Yeah, I have heard anywhere from 5500 all the way up to redline.

 

[Cudaman]

A lot of people, short shift first gear.

Cudaman

 

[genXgts]

hey Chris, I go 6K for 1 to 2, and then back off a few hundred for 2 to 3 and 3 to 4, I would say 5700-5800 for those two shifts. Have read as low as 5500 for the 2nd and third shifts, but have not went over 120mph at 5.5K.

121 on a stock car (filters, exhaust) with 6K into 2nd, and then 5800ish for the rest, good luck.....

 

[CMilViper]

Thanks Cudaman!

GenXgts...thanks man! That is the info I was looking for. Will try it next time out.

On my first time out, I was taking it all the way to 6000 on each shift.

 

[Snakester]

I was thinking of short-shifting 1st-to-2nd (maybe 5200RPM?)for the next time that I go drag racing. I've only taken the Viper out once, but I was able to shave off 0.3-0.4 seconds by leaving at 2000 RPM and feathering the clutch. But both times when I shifted to second the car spun badly and I had to back off of the throttle to regain traction.
Still, I got my two best times (and MPH) of the night.

Also after running a few quarters N/A, I'm going to try again with the N20 on (for the 1st time). I'd imagine that the 3.55 gears plus 160 Ft Lbs torque more, I'll have an even worse time getting traction in 2nd, so I had thought to shift even earlier (maybe 5000RPM) so that I hopefully don't overwhelm the stock tires badly in 2nd.

Does anyone have some dragracing experience with short-shifting? N/A or N20. I'm not concerned with getting a higher MPH as much as getting a lower 1/4 mile time.
And I'm likely only going to get one try with the N20 (if I do it right) because they're probably going to kick be off the track the first time that I get into the 11s.

-Dean.

 

[RSNAKE]

If you take it to a dyno you can calculate exactly where you should be shifting. I did this for my stock dyno run and for my modified. Completely stock, I got the most area under the curve by shifting at 6,000 RPM from 1st to 2nd, and from 2nd to 3rd. It was best to shift from 3rd to 4th at 5,800 RPM though. After headers, cats, cat back, it is best for me to shift at 6,000 to 6,100 in every gear. If you do the math you can convince yourself it is best to always ride back and forth over the horsepower peak. By figuring out what RPM your will drop to after the shift, you can then figure out how to stay moving back and forth over that peak. So long as the HP you are making after you shift is less than the HP you were making before you shift, you should continue to run higher RPM before the shift. When you get to the point where the opposite is true, you need to be shifting sooner.

 

[Snakester]

It certainly makes sense, And I have a few dyno runs done to determine where the power is made. Plus I have looked at the shift points with 3.55 gears to see where shifting at different RPMs would put me relative to peak power.

But shifting for peak power assumes perfect traction, and on my well used street tires, that's exactly where the problem comes in. I figure that I'm going to get some tire spinning, but last time that I drag raced, the two times that I hit 2nd hard, the rear completely lost traction, spinning until I backed off of the throttle.

And I'm pretty sure that adding 170 Ft TQ with the N20 is not going to make it less of a problem. So I figured that perhaps short-shifting would provide a little less power, but minimize the spinning somewhat until better traction was established.

But I'd love to hear from those of you who have tried short-shifting, and what you have learned.

-Dean.

 

[HOLD TYTE]

When calculating your shift points based off a dyno sheet don't forget to include your gearing multiplication. At first look I thought shifting earlier was better but once adding in the loss of power from going from one gear to the next it actually made sense in certain gears to pull higher.. as an example, you have a 1.3 in 3rd and a 1.0 in fourth.. you lose 30% gearing when you shift that gear. Try doing the math with the Dyno and considering your transmission and rear end gearing..

 

[Jack B]

You want to make the car work at the peak torque point, with the N2O the peak torque is about 3600 rpm, shifts should be at 4600 rpm's, dropping you back near peak torque after the shift. Your problem will be having to shift into 5th (with N2O) because of the 3.55's.

If you are not running ET's be ready for some excitement on the 1-2 and 2-3 shifts.