Larry Herman

Here is a very unscientific look at it, but I think that it is very "real world". Keeping the revs in the power band is usually not too much of a problem on the straights, even with wide gear ratios. There is usually a corner or 2 though, that causes you to either be at redline before trackout, or run through the turn in the next higher gear with the motor below the power band. All of my experience with various cars and corners makes me prefer to have a shorter ratio gear box over more torque. When you have to be out of the power band in those situations, I have found that it is usually for much less time with shorter gears than with more torque. Like I said, not scientific, but very real world. YMMV.

mark kibort

Please, dont go there. It is riddled with major errors. the previous link was very good.

mk

Veloce Raptor

Mark, I didn't say not to shift at redline. I suggested instead that it did not make much sense to keep that motor constantly there by shifting a lot.

Big difference IMO.

Now, with the peakier Euro motors and the built out cammed prepared & WCTC spec motors, it does, but not the torque monster US motor in stock trim.

mark kibort

you are making it more complicated. just choose the gear that buys you the smoothest exit, while getting the most HP possible. if you are tracking out in 2nd gear at redline, so what. thats a good thing. you just used the max amount of HP available. if you cant put the hammer down through the curve, a taller gear is no problem. with wide gears, the choices are pretty obvious. the fact still remains. At ANY speed, if you want max acceleration, get the RPMs as close to max HP as possible.

shorter gear just shift the speeds in each gear up and down. There is no right answer, as it will vary at every single track. (if you could afford the luxury of changing before each race) Close ratio gear boxes allow for more time spent near max HP. more hp-seconds, the faster you will accelerate!

Mk

DaveM993

That about sums it up.

Mark -

"It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." LOL

DaveM993

But the linked vette article..which is good.. has a slightly different message - For max acceleration get the RPMs as close as possible to the max TORQUE point...which can be different than the point of max HP.

mark kibort

Can you find me one instance where you will have an advantage by shifting below redline, even in a US 3.2? You wont be able to because the HP curve doesn fall off at 7800rpm to a level BELOW 5500rpm. are you with me so far? If so , you will know the next thing i will say is that at 5500rpm you will always have a HP level far below any HP available at all the RPMs around 7000. This means. (because we know that acceleration is directly proportional to power) that if you have more Power at any vehicle speed, you will accelerate faster. This also implies that if you will accelerate faster you will have more thrust force available! Its pretty simple math. the reason i like to look at HP cuves vs vehicle speed, is that you can make shifting decisions very easily. looking at a falling torque curve can be difficult to decipher. You have to be pretty good at looking at a torque curve, to determine if its falling fast enough to have HP fall too. (remember, a falling torque curve is usually a flat HP curve)

So, if you have more HP available at ANY vehicle speed, you will have more TORQUE available at the rear wheels . Your US 3.2, even though the HP curve is falling at the high rpms, still has a much higher value than shifting to the next gear!

mk

DaveM993

I still like the adage...that I am sure I will screw up.

When you hit the wall...

TORQUE determines how far you go through it
HP determines how fast you hit it
Understeer/Oversteer detemines whether you hit front first or rear first

mark kibort

you found one of the first confusing messages of the article. (i had a list i forwared to the author about 12 years ago)

for max acceleration in any gear that is true. but, why in the heck would you care about max acceleration in any particular gear? downshift to the lower gear, get in the max HP range and accelerate at a much greater rate! again, at any speed, the fastest your car will accelerate, will be at an engine rpm that is as close as possible to max HP, not MAX torque. BUT, you have to choose a gear that allows this to happen.

So, Bruces article is riddled with mixed messages and incorrect statements.
I still have the list if you want me to PM you with it.

Mark K.

mark kibort

Nah, thats almost as bad as torque wins races, HP sells cars.

Its ALL about HP. HP determines how fast you hit, how far you go through it andt the torque at the rear wheels at any speed is determined by HP. Engine torque is almost meaningless, unless you tie a rpm to it. easily proved by the cars with 1/2 the engine torque, but the same HP as another car. They can accelerate as fast at any vehicle speed, as long as the HP curves are the same shape.

Mk

DaveM993

I did not find it confusing at all. Unless we have a CVT then of course you want to use as much of the HP band as possible. BUT your statement that the MAX. ACCELERATION (ie. ft/sec2 at a GIVEN point in time) occurs at the peak of HP is not true...it is at the peak of torque. It may be semantic thing since I suspect you are talking about max amount of WORK done, then yes HP is your bet. But acceleration is a measurement at a point in time. At least the way I was taught it.

mark kibort

you mean its better to have more HP??? because thats what Bruce says below in his article. gearing only alows you to more effectively utilize power available.

DaveM993

It was a joke...

DaveM993

Absolutely...I'll take more horsepower any day. (all that that means is I have more torque available at a given RPM and likely at the higher end of the range!!!)

EDIT - all he was saying is...at least my interpretation...is giving up low rpm torque for higher rpm torque is a good thing...

mark kibort

You see why I dislike this article????

Its not semantic at all. yes, a CVT would allow you to run at max HP and stay there to maximize acceleration, and that is not the point

Max accleration will occure at any vehicle speed, the closest you can be to max HP. (NOT MAX torque) as the article will lead you to believe.
this means, at any time you are at max torque you are at some vehicle speed.
if you downshift to a lower gear, you now are at a 40% greater mechanical advantage, but maybe only a 10% lower engine torque disadvantage due to 40%higher rpms. the net gain will be 30% more accelerative forces, WHY?????

acceleration= power/(mass x velocity)

make sense?

Mk

PS, i am not talking about the quantiy of work done, i am talking about the rate of doing work (i.e. HP).