calculating gear ratios based on torque curve
 

ok, if the purpose of a tranny is to keep the engine at peak torque. what's the calculation for choosing gear ratio's based on X torque between say 4-5k? I have a low boost setup on a stock sohc zc and I'm trying to figure out the best tranny. I've never taken this thing to the dyno, so I have no idea when it's actually making max toque, but if I did. I've seen a lot of calculators that tell you the mph, but I don't see the relevance, if your not adding your torque curve to the equation?
I'm not sure what's even available as of gears for singles if you knew this, but there's a couple FD's and of course tires to mess with it.

hell, some engineers came up with the numbers on stock engines......

Re: calculating gear ratios based on torque curve
 

There are a lot of considerations that go into choosing gear ratios. Traction and other dynamics go into as well.

For a purely output based calculation though It's based on the horsepower production, not torque.

The calculations involve integrating the horsepower curve and finding the rpm range that produces the largest integral, which is simply the area under the curve.

Re: calculating gear ratios based on torque curve
 

Zuh? If you look at torque or look at horsepower, your conclusions will be exactly the same. Everything else I agree with, but I don't see why you can't get a valid analysis looking at torque over an rpm range.

Re: calculating gear ratios based on torque curve
 

CRX Si has the best 1-4 ratios, maybe add a 3.083 1st.

FD does NOT effect the rpm gear split between shifts.

You whill find most NA motors have a 2000 rpm powerband, you want the 2-3-4 gears to keep it in that powerband.

Re: calculating gear ratios based on torque curve
 

No they will not. Torque is not a unit of energy. The area under the horsepower curve will show maximum energy production.

For lower torque made at higher rpms, if the horsepower is higher, then you can always take advantage of gearing to make more torque at the output.

Re: calculating gear ratios based on torque curve
 

MADMAX, you'd better reread your post :)

Re: calculating gear ratios based on torque curve
 

you are gonna want to look at your torque and figure out where you make, say 90% of peak, and if that is an acceptable range to have a gear last. find out how long that lasts and then get the gears that will split that much.

hp dont mean jack ----, 200ftlbs at 4000 has the same acceleration as 200ftlbs at 6000

Re: calculating gear ratios based on torque curve
 

100% wrong and only assumes the same gear ratios. This conversation is about ideal gear ratios.

Let assume a 1:1 gear ratio on the 200ftlbs @ 4000 (152hp). That's 200ftlbs to the wheel at speed Xmph. For the 200ftlbs at 6000 (228hp) at the same speed Xmph you are going to have a 1.5:1 gear ratio, which now translates into 350ftlbs at speed Xmph. F=ma buddy. Simple physics. Higher force (torque) equates to faster acceleration.

See why horsepower is what matters in this type of calculation? You can always have a better gear ratio with higher rpms. The whole premise to revving higher and making torque at higher rpms.




Quit being a moron bone. I know exactly what I said.

Re: calculating gear ratios based on torque curve
 

what i was saying is that if your motor puts out a flat 200ftlb curve from 4000 to 6000, your rate of acceleration is going to be the same (actually goes down with increased air drag). so if you got a solid 2000rpm of flat torque and its your peak then you would get gears that do a 2000rpm split and shift at 6000 every time.

Re: calculating gear ratios based on torque curve
 

2000 rpm powerband.........I wonder.......maybe........a D15.......will it?

Attachment 18553


Now couple that with my "perfect" 1-5 gearing, look at the gear splits :)
1st 0000 7000 35.39
2nd 4801 7000 51.60
3rd 4959 7000 72.84
4th 5544 7000 91.97
5th 5766 7000 111.66

Re: calculating gear ratios based on torque curve
 

BTW, What is Horsepower?

T * T

Re: calculating gear ratios based on torque curve
 

The amount of power one horse puts out :1

Re: calculating gear ratios based on torque curve
 

Now you've proven that you don't know what you are talking about and are a complete fool. Shifting at 7000rpms does not yield maximum acceleration.

You should've run that motor out to 7500 to see were horsepower really drops off. Stopping at 7000 was foolish. The most area under the curve would've been at around 7200-7300 shift point.

It's area under the horsepower curve, NOT the torque curve. Even though the motor makes less torque at higher rpms, it makes more power which takes advantage of gearing.



Power = torque * acceleration

Again, torque is not a unit of energy. Torque without revolution is worthless. Horsepower is a unit of energy. Even though you may have less torque at higher rpms, the are under the horsepower curve is greater, thus higher acceleration.

Re: calculating gear ratios based on torque curve
 

Your calling me an idiot with this simple statement........

Understand what tq curves and HP curves are. FIRST know what HP is in relation to TQ. I'll give you a simple number

5252.5252525252

Why should have I tried taking my motor out to 7500 rpms when it was falling on it's face? I was shifting at 6500-6600 for best ETs. The power loss was known, part of a problem with Crome. But even without that issue HP was falling off and TQ went south to Mexico.

Please just anwser the ONE major question.

What is HORSEPOWER?

Now, I've discussed gearing with Gale Banks (who started my gearing madness in 1983) and have talked on the phone with John Lingenfelter about the C&D 40th Vette, also with a SCCA National Championship last year and other little wins. From drag racing Honda side of things, best is a low 11 sec pass D16 before getting booted for no cage. Maybe I have a CRX 4th gear into a 5g WHITE HB going 10's, but no vids lately.

I'll stop now, 6 pack almost gone.........

.......your thoughts about reving out the motor beyond it's limits/power curve is a simple reason little D's end up walking DOHC VTEC B's due to drivers trying for 9 MILLION RPMS in a torqueless motor.

Re: calculating gear ratios based on torque curve
 

Yes they are one one number away from each other, BUT that makes all the difference when integrating the curve to find the most area over the rpm drop.

HINT: When you integrate a curve, line, or any function, you find the area underneath.

Go look up what integrating is. Here, crude but nonetheless helpful: http://en.wikipedia.org/wiki/Integral



Going off of what you are saying, if a motor makes a constant 100ftlbs of torque between 0 and 8000rpms, you could just shift anywhere, cause the torque is the same and the area under the torque curve is the same and the car will be the fastest no matter what.

See where it matters now? Obviously horsepower will rise and the higher up, the more area under the curve. It's because horsepower shows energy production, torque does not. 100ftlbs at 4000rpms is less energy than 100ftlbs of torque at 8000rpms. The latter allows lower gearing and makes 200ftlbs of torque at the same speed as the subsequent output.


It's like only using current to calculate energy usage. You can't do that without electromotive force (voltage). This is why units are what they are in world. Torque is not a unit of energy. Horsepower is however.

Re: calculating gear ratios based on torque curve
 

Madmax is right. I was wrong. I wasn't thinking things through.

Re: calculating gear ratios based on torque curve
 

:y :y

But torque is the only thing that matters. As long as you have 5 bajillion ft.-lbs of torque at 0.0002 RPM, that is all that matters.

:P

Re: calculating gear ratios based on torque curve
 

If Horsepower is torque over a period of time then explain this

"It's because horsepower shows energy production, torque does not"

A) Step away from the train driver handbook
B) Do some real world testing or atleast research it.

Torque moves mountains, HP wins bench races.

Re: calculating gear ratios based on torque curve
 

It's this statement that shows how truly ignorant you really are.



You just did. A constant amount of torque does not indicate how much energy is being produced. You need to know rpms to calculate power.

Power is torque over time.

Re: calculating gear ratios based on torque curve
 

ok so that dyno sheet is your car right?

go get a stopwatch and get in 3nd gear and floor it at 4500rpm and hit the stopwatch untill you get to 5500

then do that same thing from 5500 to 6500

i guarantee that it is almost the EXACT same time.
yes at higher rpms you are doing more 'work' but the engine is not pushing against the wheels any more then it did at lower rpms, its just pushing at a higher speed.

Re: calculating gear ratios based on torque curve
 

Yes you are exactly right, but like I mentioned earlier, this conversation was started about choosing gear ratios for maximum performance.




But, what you have pointed out is what I said earlier. Shifting at 5500 will make the car slower, because power under the curve is less than shifting at 6500. I mean you guys are answering your own questions about this using real world examples.