You know, even after hanging out on various boards since 1998, I still have some questions that I ponder... Like for example, some folks say that you should shift on nitrous lower than you do on motor. So say I shift at 6800 on motor, where would you shift on spray?

 

shift lower??? ****...how about add another stage!

But sometimes it doesnt HURT much to shift lower due to the massive TQ (and resulting hp) in the lower rpms....but IMO if you are dropping off that much in the upper rpms that shifting lower nets a smiliar ET then that means you have ALOT more room for juice in the upper rpms. John you may consider another 100 shot on a window switch that comes on after 5000 rpms...or by time if your traction limited.

 

I dont know about actually shifting lower, but your drivetrain will like you better for cutting the spray off about 200 rpms before your shift point. Depending on how far your rpms drop when you shift, maybe it would be better to short shift 1st gear to get back into your low end torque range. Give it a shot at the track, trial and error. after first gear i cant imagine a reason why you would want to shift lower on the spray.

 

I'm still running the stock bottom end so when I spray I will shift lower than I would NA. I have heard many people talk about this and the reason I am doing it is mainly because the nitrous adds more pressure and stress on your motor so I'm not going to spin it as high as I would if it was NA.

Now if I had a rotating assembly that would take it then yes, I would spin that thing high!

 

I did the same, my stock short lasted forever. But now i still usually shift a couple hundred lower, its problably just a old habit.

 

Shouldn't the shift point be determined bt the power curve? I would think you could look at a dyno pull and find where the power starts to fall off and go back a couple of hundred rpm and start there. Just a thought!

 

99 FRC

 

I understand where you are coming from, but the reason for shifting lower while spraying is because I am still on the stock bottom end. I'm already putting down 400 HP to the wheels on a stock bottom end, so spinning that thing high in the RPM's on the stock bearings is something that keeps me up at night.

 

I also shift lower than N/A...About 1K

 

Thats a good point for stock bottom end or drive train guys. just because you can make power to 6800 doesnt mean you want to rev it up that high. When it comes to longating the life of your car, you have to be a little conservative on your shift points.

 

unless the nitrous delivery is progressive based on RPM, the nitrous will always shift your best power curve down to a lower RPM range, so yes you run quicker by shifting sooner.

Exactly how much depends on the individual combo. Between 500 and 1000 RPM is very common.

 

I just shift to win. As long as I am ahead I am good to go and shift at a lower rpm, if its a closer race, I would just wait to about redline. Go Nitrous

 

It all depends on where it makes the power. I shift at 6800 on both motor and spray, and it loves it. The nitrous doesn't change the powerband of the motor(besides adding much more torque in the lower rpm's). If you make power at 6800 rpm on motor, you'll still make power at 6800 on nitrous(just alot more).

 

It doesn't shift the band lower. It makes more low-end torque, but doesn't kill off high-rpm power.

 

My reply was mostly for John. I can understand taking it easy on a stock bottom end for longevity. Also to clearify my earlier post, I was refering to the powerband on motor (should have specified I guess).

 

my opinion is to shift higher if the gear is short and lower if the gear is taller...

 

Agree with that. If you're trying to get your best time or you're losing, you're going to want to get everything out of it you can. I guess if you're just playing around, then short shifting is ok.

99 FRC

 

Short shifting first gear could very well result in a quicker ET. Think about ALL the torque you are making on the spray. but short shifting first you could get back into that big torque.

After that i agree with you and everyone else, shift it all the way up at the top of your power curve.

 

There is pretty much no use for me hitting the Nitrous in first gear, I spin bad enough as it is, the torque is too much for hitting it in first. From second on though that is a different story, I agree with what you are saying, and on a different note I need to get rid of these runcraps

 

Guys...shifting lower on juice is not going to save your bottom end any more than on motor. That is unless your worried about certain piston issues.

Most rpm related issues such as rod bolts have no affect with juice. Rod bolt failure happens when the piston changes direction with no load on the exhaust stroke.

Same goes for rod failure....unless you are talking cylinder pressure and the resulting load on the rod...but that has 0 to do with RPM. If you short shift you are actually staying in the higher cylinder pressure area as compared to the higher rpm when tq/cylinder pressure falls off. Its this higher cylinder pressure rpm range that is more likley to have piston ring land/rod failure due to cylinder pressure.

This is the entire reason for dual staging based on RPM. Maintain that cylinder pressure in the higher rpm.

The force from excessive rpm has very little to do with the force from excessive cylinder pressure.


As for short shifting for faster ET. You can somewhat calculate your shift points...but 9/10 shifting at or very near the same NA redline in an LS1 based motor will be the fastest ET on juice.
There can be some curcumstances that short shifting may help a bit...but IMO those are special curcumstance or setups that have issues such as improper gearing or a stall thats just not working good for the setup.

All this is assuming you have full traction at all times. If you are getting a better ET because of shortshifting to decrease tire spin then you should be addressing traction and suspension and not short shifting.