What is the theory that goes into determining where to set shift points at. I know that track time will tell all but....

Based upon DD here is a HP and torque info

DD HP 527-587 @ 6000
DD TQ 539-562 @ 4500

Based upon the info I have the powercurve is partial to 5200 to 5400 shifts.

The worst incrementals were from 2 runs with a 5600 rpm shift point.

Is that strange??

also what kind of 60 foots should I expect? I am at 1.69 with 8psi in the hoosier QTpro 31x18.5x15 slicks with 4.11 gears It was the same as with the 4.56 gears last time out. I improved by 2 mph and .02 sec with the new gear set but I cant help this feeling like I am overlooking something major and leaving alot on the table!!!

60' 1.693
1st incr 3.172
330' 4.865
2nd incr 2.685
1/8 7.550
MPH 91.05
3rd incr 2.30
1000' 9.849
4th incr 2.010
et 11.859
MPH 113.36


Thanks
Milan

The theory is to use trial and error at the dragstrip until the quickest ET is achieved. Generally, shifts take place over peak HP by 300-500 RPM.

typically it is 10% over peak HP. however you're using DD2k numbers which may or may not be accurate.

BTW, when i refer to the shift point, i'm refering to the actual point at which it shifts, NOT WHEN THE LIGHT FLASHES, since in my case i pick up 600rpms on the 1-2 from when the light flashes until the trans shifts, and 400rpms on the 2-3.

I took the time one time to run my big motors torque and hp peaks through Drag while also varying tranny gear ratios and found that by shifting say 300 above the hp peak, I created a best sim. transmission!

I forget just what the gear spread ended up being compared to my M-20, 3.31's and 26.5" tall tires but it was a bit different AND did improve my sim. drag race by a decent amount!!!

I think I had to vary each gear in the tranny separate until it optimized to the final lowest ET run!!

And it did take quite a while of playing around to do it to.... Fun at the time..

I don't know if Drag has an iteration subroutine in the latest version like D2K does or not, but if it did, the time spent to do this would be just letting it crank until it stopped like D2K does..

pdq67

PS., I figured that a race Top-Loader 4-speed tranny with a splined clustergear shaft and individual clustergears would be ideal to use for creating an optimized 4-speed if you have the money!!

interesting all replies hinge aroung HP. If it it torque that moves the car, why not shift around torque peaks?

Thanks again
Milan

Might try this:

http://www.bgsoflex.com/auto.html

Has some good info, including optimum shift points.

Cheers-

Rob

interesting all replies hinge aroung HP. If it it torque that moves the car, why not shift around torque peaks?

Thanks again
Milan

i dont appreciate the sarcasm.

What people don't realize is that hp is a function of torque. NOT the other way around..

It's just that a LOWER RPM torque motor has such a low rpm OPERATING range whereas a hp motor has it's torque curve moved over to the right on the rpm scale!!

Example of a torque motor being a Diesel!! Just shift the sucker alotta times!! That's how the Big-Rigs pull their big loads....

I have said this more than once!!

A 427, L-88 motor is a HIGH RPM torque motor!! Both it's curves are moreso over to the right with the hp curve generally going up, WAY UP!!! Same way with the little Z-28 motor!!

Roundy-round motors are HIGH RPM torque motors!! How else can you account for their torque peaks being past 5252 rpm???? The super speedway ones that have power curves like 754hp at 7150rpm and 628t at 5850 rpm sorta deal!!! (Just an example!!).... Some ricers are like this too!! That's why they are a bit-h to stay up with up top unless you are running a high rpm 302..

It's been said that "If you make torque where you want to, hp will follow right along".. No truer words spoken, imho..

pdq67

What sarcasm?

What sarcasm?

My thoughts exactly. What sarcasm?

Don't think there is any??

pdq67

I agree. It's a good question and far from sarcasm.

It's desirable to make shifts at an optimal RPM so that on the gear change the engine falls back to an area of high torque. You're shooting for a minimal shift recovery time. Each combo is different so you'll have to experiment.

That is actually a really good question and a good topic of discussion. Here's why you use peak HP rpm when picking shift points . . .

Torque is a measure of applied force (think of a TQ wrench), HP is a measure of work that is accomplished over a period of time. So while TQ is important (the more the better) HP is actually more applicable when talking about acceleration (and shift points).

So in the context of our discussion, max HP is the max amount of work being done -- so you want to keep your engine operating as close to peak HP as possible during a run. Best ET's are typically achieved when the engine is shifted a couple hundred RPM past peak HP.

Knowing peak TQ and using it to pick converter stall RPM or launch RPM is just as important as determining shift points. Typically, best launches (and ET's) are had with a converter that stalls just at or slightly past peak TQ.

Once again, I am not saying TQ is not important . . . I am saying it is just a different measurement than HP and applies to other things . . . just not so much shift points.

PS. and I think Freiburger did an awesome write up on this a few months ago.

i think i understand whats being said here,but i have an honest question.its in relation the the age old 327 vs. 350 debate...if hp is a function of torque,shouldn't a 400 hp 327 and 350 both make the same amount of torque,just the 327 at higher rpms?i see really nasty 327 combos making like 370 lb/ft peak torque while a relatively mild 350 making 400+ lb/ft torque..again not trying to step on anyones toes just trying to learn and understand a bit better..what am i missing?

Think of it like this. If you shift 200-400 past peak HP your RPMs drop roughly into the middle of the torque curve to push the car faster up the RPMs to the peak HP. I think I said this right.

You need to remember that torque is created by displacement here..

A bigger motor naturally makes more power, it's that simple until you get into the "cubic money" deal..

Another very good thing to consider is that stroke dictate's cam selection moreso than bore b/c a longer stroked motor with the same length rod will close the intake valve slightly lower in the compression stroke, and this means that a stroked motor can accept a longer intake valve closing duration, (i.e., bigger cam), then a shorter stroked same type motor. And this creates more power for the same engine operating characteristics.

D. F. is going to hopefully vary rod length in his follow-up article AND I for one AM really looking forward to what he comes up with......

pdq67

pdq67

First let me say that no sarcasm was intended!

Back to the topic. So if The shift points higher up that the torque curve are not as productive as lower shift points closer to the TQ curve. is it fair to say that there is a problem inhibiting peak HP production?

Thanks
Milan

I can see the debate tables are setting up now on this subject. Hopefully, there will be plenty of snowballs in reserve. I'll watch...........

I, myself, depending on OEM engine design, will shift about the torque peak. This is the force used to get the mass moving. Then, I will use the hp to go for mph.

One big problem for peak HP production is the restrictions of moving air through the engine. The second biggest problem is lack of monies to remove these restrictions.

Like climbing a hill. If you fall down the hill it is easier to get back to the top if you just fall a little ways down instead of a long ways down.