What shift points for max excelleration ?

[White 68]

From my dyno sheet I,m making max hp/torque at 5500-6000 rpm ....I,m running stock gears ....At what rpm should I be shifting to get the most excelleration ? ...Thanks :steering:

[bhamvett]

I say 5900!

[BiZ]

From your graph I would shift @5700. You start loosing power after that. Headers and exhaust would change that to ~6800


[Modified by BiZ, 3:38 PM 7/27/2003]

[xlr8nflorida]

From your graph I would shift @5700. You start loosing power after that. Headers and exhaust would change that to ~6800


[Modified by BiZ, 3:38 PM 7/27/2003]

5850 :lol:

What is the correct shift point for my car?

[BiZ]

What is the correct shift point for my car?

Would need to see when the power starts to fall off. When the power falls off you start slowing down.

[USAZR1]

You normally want to shift gears around 500rpm above the power peak. For a relatively stock 375hp LT5,that would be somewhere around 6400-6500rpm. For a relatively stock 405hp LT5,that would be around 6700-6800rpm.

[xlr8nflorida]

Thanks Clint :cheers:

[xsmph]

it all depends on the power curve. What you want is to shift at a rpm so when you grab the next gear you are making the same hp at the new rpm as you were when you left the gear before.

Looking at your graph lets figure out the best shiftig rpm from third gear to 4th gear.

Your car drops 23% in rpms from going from third to fourth. this is calculated y dividing the trany ratios (1/1.3)

So if you shift at 5500 rpms our of third gear , you will pick up 4th gear at 4235 rpm.

At 5500 rpms you are making peak power of around 330 rwhp. So if you shift you will pick up 4th gear making 250 rwhp at 4200 rpms.
So why would you want to come out of third making 330hp to grab fourth and make 250 hp?

What you want is to ride the curve and equalize the hp numbers on each side of the power peak.

In your case 6500 rpm would give the desired results.
310 hp at 6500 in third and and after the 23% drop you grab fourth at 5000 rpms making again 310 hp..
hope this helps



[Modified by xsmph, 6:39 PM 7/27/2003]

[White 68]

Thanks for all the suggestions ....Julio thats the info I was needing ....I knew the rpms dropped and wanted to stay in my peak.....You guys are great thanks ;;;;Now out to do some testing ;;;;; :)... :steering:

[BlackWidow#2]

it all depends on the power curve. What you want is to shift at a rpm so when you grab the next gear you are making the same hp at the new rpm as you were when you left the gear before.

Looking at your graph lets figure out the best shiftig rpm from third gear to 4th gear.

Your car drops 23% in rpms from going from third to fourth. this is calculated y dividing the trany ratios (1/1.3)

So if you shift at 5500 rpms our of third gear , you will pick up 4th gear at 4235 rpm.

At 5500 rpms you are making peak power of around 330 rwhp. So if you shift you will pick up 4th gear making 250 rwhp at 4200 rpms.
So why would you want to come out of third making 330hp to grab fourth and make 250 hp?

What you want is to ride the curve and equalize the hp numbers on each side of the power peak.

In your case 6500 rpm would give the desired results.
310 hp at 6500 in third and and after the 23% drop you grab fourth at 5000 rpms making again 310 hp..
hope this helps

[Modified by xsmph, 6:39 PM 7/27/2003]

:iagree: :thumbs:

[Bans25]

:iagree: With xsmph, you want the average (during a run) to be as high in the curve as possible, don't worry about shifting at the peak.

[BiZ]

What is the % drop from 1st-2nd and 2nd-3rd. Most of us don't run 3rd and 4th out too much. Will this change the shift RPM?

[The Lurker]

If you had a 368 you could change those numbers. Plus, how nice would a beautiful blue powder coated engine look in that beautiful blue ZR-1? Not that I would tempt you.... Remember, in September my time is full time... not that I woul tempt you... The slime mobile was looking pretty nice today.. ran nice too... Yours could too... Not that I would tempt you...... Bbbbbwwwwwaaaaa haaaa haaa haaaa... Seriosly... well take care of the wife... we'll tell her you will take her on a lovely vacation after it is done... :D Nice meeting you today... even though I smelled like a goat..

[White 68]

Jim it was good to meet you and chris ....that 368 sure did look and sound nice ..great powder coat and color ..test ride was even better :).....September isnt too far off maybe I,ll hit the lottery by then and you can start a 415 in quasar blue powder coat of course :lol: ...Well atleast a P/P headers/exhaust if I dont hit it big;;;ha ha ...Talk to you soon :cheers:

[xsmph]

Biz, here are the % drops in rpms...

First to second gear you get 1.8/2.66= .67 or 33%. Actually you will multiply your leaving rpm in first gear times .67, and you get rpms in second gear.

Second to third = 1.3/1.8 = .72 or 28%

Third to fourth = 1/1.3 = .77 or 23%

Fourth to Fifth = .75/1 = .75 or 25%

Now, go and Test!! :D


[Modified by xsmph, 6:42 AM 7/28/2003]

[xsmph]

On another note, some people use the TQ curve to figure out shifting points. After all TQ is what accelerates the car, and Hp is just a mathematical conversion.
However, if you use the TQ curve the gear ratios in the trany have to be used in the "rwtq" number in order to get accurate results.

For Example:

In the Dyno above, at 6500 rpms your rwtq in the graph is 250 ft-lb.
This you must multiply times "1.3" which is the third gear ratio on our example. So now you get a 325 ft-lb of TQ at the wheels ( not counting rear end ratio as it is the same in all gears) in third gear at 6500 rpms.

You shift to fourth and come down to 5000 rpms. Rwtq now is 325 ft-lb.
Now you will multiply this times your trany ratio in fourth, which is 1:1.. or just "1", and you get the same rwtq at the wheels as in third at 6500 rpsm.

This is actually how is figured out, but doing the HP curve gives the same results without having to multiply times trany ratios....

[95ZR1#418]

:iagree:

Bob