What rpm do you shift your AT at...

from 1st to 2nd and from 2nd to 3rd under WOT? Do you let the trans shift itself or do you shift it?

 

In my 71 GS455 that ran 13.4's, I let the trans shift. It didn't have a shift kit, so it wasn't fond of me shifting manually.

It shifted around 5300 rpm.

 

Shifting myself reduced my 1/4 mile time from 13.17 to 12.75 in the 92 degree heat last week. Shifting itself at 4950 rpm's vs manually at 5700 rpm's or so.

You may try shifting 1-2 a little earlier than the 2-3 shift, could help as well...

 

6800

 

6800 also

 

Shifts itself @ 5700 with governor mods.

 

Are all of you guys using stock rods and crank or are you using performance rods???? Oh, by the way, I shift mine at 5,400 with an all stock bottom end.
Thanks,
Tony
81 Olds Cutlass
455 Buick Powered:TU:
11.71 et
1.575 60 ft.
:3gears:

 

5800-6000

 

Polished stock rod beams, oiling mods, main studs.

I doubt the guys shifting 6500 and up are stock.

 

If you want to find your optimal shift point, you can do this graphically if you have your engine torque curve. Plot driveshaft torque (engine torque times gear ratio) vs driveshaft speed (or vehicle speed) for each gear. Where they cross will be the optimal shift point. Back track to find what this is in engine rpm. If they don't cross, the optimal point will be redline rpm.

 

Interesting Scott. Could you show an actual calculation as an example? :TU:

 

The nice thing about the governor modification (although my GS455 didn't need them for the 5300 shift point) is the consistency of the shift for bracket racing.

Those of us who can't afford to be competitive heads-up, want the consistency for brackets.

Remember, it's all in the "package."

 

Seems like some people shift @ different RPM's for different gears. Any reason for that (ie 5500 into 2nd, 5000 into 3rd).

Larry, how did you modify your governor?

6800? Phew!!

 

I was told by Jim Weise that you should shift 200-300 above that point. Almost all engines that are not all out race engine cross over somewhere between 5200-5500 rpm.

 

6800 shifts
threw the traps at 7200

 

I have attached a pic. This could be easily done in XL. I used the torque curve of the 450 hp motor off of Jim W's site, except I added a 6000 rpm point to help lillustrate. This is for a 4-speed but could apply also to an auto, you would have to consider the converter slip. All shifts cross before the 6000 engine rpm point. Lets look at the 1-2 shift: If you shift at the crossover, the torque at the wheels is the same both before and after the shift. If you were to wring it out to 6000, then shift, the torque at the wheels drops after the crossover while still in first, then jumps back up after the shift. If you shift too early, the torque drops while in second, below what it is in first, then equals first and ends up above first.

This is why a torquey motor best benefits from early shifts; if it's real torquey, the tail end of the torque curve really falls off fast, you need to shift soon. A high-rpm motor is best at redline shifts; the head-end of the torque is down and the curves usually never cross, so you shift as high as practial.

 

ou: :eek2: :laugh:

 

6600 with the single 4, and 6900 with the dual 4's.

Most modified BBB street/strip BBB should be shifted at 6000.

All out race cars typically benefit from a higher shift point, as you have seen in the replys here.

You should shift 300-500 past the HP peak, the key is to get the motor in it's power range when the shift is completed.