I tend to find using the HP charts are more intuitive (for me) than looking at
torque numbers that are rolling off at odd rates.

So can we agree that using the HP peak is just as effective...or do I have to
lay a beat down on someone?

 

As Jim said they are linked, I never look at them seperately. HP is just the WORK function of TQ. Thats it. I honestly cant say that you have to look at both and a HP vs. TQ discussion is utterly pointless.

I guess it's just how you think really. This thread should be more on how you think than what you think of, cause obviously that **** ain't working.

Bret

 

I don't know if that's a put down, or a clarification?

In any case, from the beginning of this thread, several people were saying
torque peak.

Some of you were saying HP peak...and some said a combination of other things.

This was never meant to be HP vs. TQ, but it ended up that way. I wanted
to talk about acceleration, and I've been satisfied with points made.

Now, we're on the TQ vs. HP hype and I'm going to go out on a limb and say,
you don't need to consider torque AT ALL when figuring shift points.

I say, it's all in the HP numbers/curve because as you (Bret) state, it's
mathematically linked.

To further my statement, look at this torque graph. Pick your shift point:

http://gmthunder.com/tino/c292h3.jpg

If HP encompasses the region of where the engine is doing the most work,
then not shifting to AT LEAST the HP peak in EACH gear is pointless.

 

I think you're the only one who believes that's still an issue for discussion.

No one is saying "don't hold the gear until or past the horsepower peak", and I've mathematically and visually shown why you do so. The fact remains that g's of acceleration peak with the torque peak and fall off afterward and have a 1:1 relationship to the shape of the torque curve. That is not debatable.

 

Bottom Line F=MA
More F = More A

More A = Lower T to travel S

nuff said

Thanks for the graphs Jim, they're perfect.


Steve

 

That's not what I had interpreted from your graph. When I saw the intersecting
lines cross before the HP circle, it looked like shifting before the HP peak.

(reference: http://home.gci.net/~jimlab/images/M...eleration2.jpg )

All I wanted was a clarification - I've never seen a graph like that before.

No argument here.

I don't believe I've agrued that fact. It was more a question to understand
why my Z28 continued to accelerate with more force after the torque peak.

Jon believes my converter continues to multiply torque after the MFG rated
RPM. I'm happy with that answer as it explains what I feel and see on the
G-Tech graphs.

I think we can lock this thread now...maybe throw it away and burn it too!

 

Excellent job, Jim!

Notice how the area under the red line, torque to the wheels, is maximized when you shift at the intersections. Any other shift point produces a vertical line segment from the shift point (mph) in the lower gear to the same mph point in the higher gear and "area under the wheel torque curve" is lost. It's that "area" that accelerates the vehicle.


"Crystal!"

 

So, correct me if i'm misinterpreting this discussion, saying that the most practical way to find optimum shift points is by using a dyno? Do a pull in each gear, graph wheel torque vs speed, overlap all curves on the same graph, then look for intersection points... sound correct?

BTW, picked up the latest Engine Masters mag, Bret made some comments about nitrous vs superchargers on pages 39-40 if anyone isn't aware. Great read!

 

Tino,

Yes you use HP to pick shift points.

My post a long while back about using the most RPM you can or producing the most TQ you can at the highest RPM point states that.

I would say go get the Skip Barber Racing School Book "Going Faster" They give a great explaination on where to shift in a car if this stuff is all too much.

The drag racing programs are basically giving you the shift points. A little study of them will show that you ALWAYS shift after HP peak in any motor, and usually few hundred RPM beyond that.

The only reason I am making any comments here is because I wonder if you really don't get this concept at all (since you have all the tools in front of you to get it) or you just like obsessing about this? These are rules that don't change, you can know exactly why they are the rules or you can accept them and then use and exploit them for your benefit. I sure know I do when designing motors, if I can get more RPM into a setup I do it, because more RPM means more gear, which means more TQ at the rear tires.

Bret

 

Bret,

No, I'm not obsessing. I was just very confused by what my feelings and scan
data showed with the Z28 acceleration properties.

This thread started because I've always wondered why people would say the
car accelerates according to the torque curve, yet my car would throw me
back harder from 4500 - 6000 RPM, than 3000 to 4500 RPM.

At any point during my testing, I did not realize the torque converter would
multiply torque beyond 3000 RPM holding a steady speed in first gear.

Then I wonder why the mulitpication didn't show up on the dyno graph?

So, none of this discussion from page 1-4 really sunk in, until Jon (OldSStroker)
mentioned the possibility of torque multiplication.

After that, I dropped the acceleration force discussion.

Then, Jim was nice enough to post a few graphs and explain shifting. I agreed
with the math, but I was confused by that shifting graph. It did not seem
to coincide with his description of torque because the shifts fell before the
yellow circles (which indicate HP peak).

Now that we've cleared that up, I'm done with this discussion. I never meant
to seem persistent; it's tough for people like you to understand because
I don't work on engines everyday, nor do I have the education that most of
you have. Until yesterday, I've never looked at a shifting graph in the form
that Jim posted.

I'd rather beat something to death and understand it totally, than preach a
bunch of sh*t all over the internet, or with auto enthusiasts and look even more foolish.

Sorry if I got under everyone's skin, but I feel good about putting this behind
me finally.

 

torpe is a myth, there is no such thing..........

 

Egad! A member of the Anti-Archimedes Society has surfaced. I thought we finally eradicated all of them.

(This is on-topic, BTW, but a bit obtuse.)

 

Come on, everyone knows torque is a myth...it's backpressure that accelerates you!

Jim,

Here's something that will make you happy. I figured out how to read your
graph.

It's the green lines that show the shift points, not the orange arrows (what
I had originally interpreted as the "path").

http://gmthunder.com/tino/jimlab.jpg

Thank you for showing this concept, it's a cool visual of the math!

 

Hell, I still don't understand it. My car is a manual and it too, breaks the tires loose RIGHT BEFORE redline. Pretty stock, so I know the peah TQ is way lower.

 

That's because you were looking at the horsepower peak for the next gear, not the current gear.

Nope, apparently it's still eluding you.

The orange arrows you added do (roughly) show the optimum shift points. You do not shift at the horsepower peak for maximum acceleration. The blue and yellow circles were for reference only, to show where the torque and horsepower peaks occur in relation to the optimum shift points.

Forget the red line and look at the graph without it.
http://home.gci.net/~jimlab/images/M...celeration.jpg

Note that the curves for 1st gear (dark blue), 2nd gear (pink) and 3rd gear (yellow) do not intersect with the line below them representing the next higher gear. This indicates that you would accelerate fastest by holding 1st, 2nd, and 3rd gear to redline.

Note that the 4th gear line (light blue) does intersect with the 5th gear line (purple) about mid-way between the last two data points (7,500 and 8,000 rpm in this case). The optimum shift point in 4th gear is therefore about mid-way between those two points, or about 7,750 rpm.

Note that the same thing happens in 5th gear (purple) where it crosses the 6th gear line (dark brown). Again, the optimum shift point would be about 7,750 rpm, not the horsepower peak of 7,000 rpm.

Got it now?