DragStuff

Is a 800rpm drop ok or should it be more for a glide from 1st to hi gear? I shift at 7200 and it drops to 6440 or so. That on a 250 shot of nitrous. I thought it should drop lower.

the power curve of the motor dictates how much drop we want on the shift, but 800 is ok as long as you do not run out of rpm before the finish line

It rpm's at 7240 or so out the back with a .078 nitrous jet set up. The reason I'm asking is we tested with a .082 nitrous set up this past weekend. When it wasn't spinning the tires in hi gear it was spinning in low. It's a 275/60/15 DR tire. I can tell that it will rpm out the back once hooked all the way down the track a lot higher than with the smaller jet. Like around 7400 and up. Would it be better to have just a little tighter?

Might consider a taller rear gear than tighter converter on those tires...

John_Heard wrote:Might consider a taller rear gear than tighter converter on those tires...

It has 4.30's in it now. 4.10's?

No wonder...

Uh, I'd drop down to 3.7 range - what tranny do you have and what 1st gear?

PG with a 1.80 low gear. I would think that going to a lower gear in the rear would cause the converter to be loser with maybe even less rpm drop.

It will, although it might not be as much as what you'd expect.

I'll let Marty explain more as he's the expert on this subject.

How is this?
And can someone explain the humps in 1st gear?

The smaller humps are tire spin. The first big hump where it rolls over is the converter locking up.

So at the the end of the big hump were it starts to go up is were the converter stalls at?

And the little hump, are they caused by the car porpoising?

Yes that first one is the converter loading the engine down. Also notice in 2nd gear it's a nice smooth line - that means it was hooked. I don't see spin at the shift in the engine rpm, if you had driveshaft rpm data, you can see that better.

I wouldn't call that proposing, when it does that it's very easy to spot, very cyclic looking.

This gragh is on the .078 nitrous jet set up. I did not get a good pass on the .082 nitrous jet set up.

have you dynod the motor? where is peak hp? I like to keep as much gear in the rear end as possible so you may need to tighten the converter. In a perfect world we would just drop the first gear in the trans from 1.8 to 1.5 and leave the rear end gear alone and tighten the converter. Problem is there is no such thing as a p/g 1.5 planetary. Are you 1/8 mile or 1/4?