need help figuring out shift points

[mrQQ]

Hello,

first of all, i'm really sorry if this is a boring question, or if this has been answered a zillion of times already. God knows, I've read tons of horsepower vs torque, and optimal shift points articles, and i'm still lost.

Basicly, most of them tell me, that torque and wheels is what moves the car. So thats engine torque combined with gear ratios etc. That's all fine.

Though.. they also say that it's not best to shift at peak torque. Cause you have to take into account to what RPMs will you drop, and all that.

That's all fine.. but.. how does horsepower come into all that?

For example my 323F has:

Peak HP: 87@5200 [metric system]
Peak torque: 125@3100

So what does that give me? If I try to shift @ 3100, i'll be running in low HP zone.. while if i try to push to 5200, wont I be overreving and losing torque?

As for my gear ratios, they are:

1: 3.3
2: 1.83
3: 1.31
4: 1.03
5: 0.83

Final: 4.105

I seem to understand the meaning of both HP and torque, but I still have no clue whatsoever of how do they both fit into "optimal" shift points..

Thanks for any help!

[Mr. Luos]

A dynograph is a good start. It all depends on how many RPM's you drop each time you shift.
With the dynochart, you can get a decent idea how the curve looks, and at what RPM's your motor is likely to pull the strongest.

Mine....take it until the cam drops off. Old set-up, right at red-line, 6200. New set-up....past redline, 6600.

[mrQQ]

i dont have dyno readings, but i found this on the net, it should be something like that

[mrQQ]

So about that RPM drop - where do i aim it to drop to? max power, or max torque zone? It can't really be max power cause I cant push it that much, and if aim it to max torque, then, again, where does power come into play here?

[Mr. Luos]

I can't see anything on that dyno sheet.

I would just play with it. Get used to what feels best. Track time is the way to really find the shift points. Just change it a little and see how it does.

[mrQQ]

surely i can "feel" stuff about the car, but being who i am i want to know the theory behind it - e.g. WHY it is the way it is.

[Mr. Luos]

When you shift, you are looking for an good starting point for your next gear.
You want to be in the powerband for your next shift.
The way your HP peaks right at the end there, I would say that would be your shift point. Since the HP doesn't drop down, might as well use it.

[500]

Here are some numbers to chew on.

gear-----6000 rpm---mph/1000----rpm after shift----rpm drop

3.3-------33 mph------5.5

1.83------59----------9.83----------3357-----------2643

1.31------83----------13.8----------4275-----------1725

1.03------106---------17.6----------4715-----------1285

.83-------131---------21.8----------4862-----------1138

These numbers are not going to be exact. I needed a tire dia and just used 25" to get the program to run.

[mrQQ]

But if I shift into, say, 4.8k rpm, that's way below my peak torque, and it has dropped alot, won't that hurt my acceleration?

that's what i don't get - i can't have both torque, and HP peak, and everbody seems to say different which i should look for

[JekylandHyde]

Shift point information:

http://www.lingenfelter.com/shiftpoint.asp

http://www.allpar.com/eek/hp-vs-torque.html

http://realbig.com/miata/miata/1995-12/910.html

[mrQQ]

first link doesn't work

[500]

This guy does not have a clue about how a water brake dyno works. Do a www search on stuska to learn more.

From Allpar site:
Incidentally, water brake dynamometers get a direct measurement of power by measuring the increase in the temperature of water flowing past a propeller spun by the engine under test. You can solve for torque if you know engine RPM.

[500]

What you need to do is run your car on a chassis dyno . It would help to know what sort of rpm limit the factory put in the ignition. You want to know what your power curve does after the power peak. If it drops off dramatically then you are really constrained. If it is more of a gradual drop then you have more options.

You will probably want to rev the motor a bit higher in first [ compared to 2nd, 3rd.... ] before making the first to second shift. The gearing is low enough that the engine will accelerate past the power peak pretty quickly in first gear and this puts the rpm higher when you engage 2nd. There is such that huge RPM drop on the 1st to 2nd shift that you need to compensate for if possible.

In the higher gears it will be better to shift just barely beyond the power peak. The motor won't be accelerating at such a fast rate and trying to rev it much beyond the power peak will most likely cost you time.

Get some graph paper and plot out the horsepower curve and then play with the above numbers to see what difference shifting at different rpms makes in the hp at the rpm the next gear is engaged.

[UncleBob]

I know this is a really old post, but I'm amazed how much bad info there is here.

HP is the name of the game. You always shift after your peak HP to create the highest average HP. If that dyno is what your engine is like, then you want to shift at redline regardless of gear, since it peaks pretty much at redline.

[90redgt]

that's what i do. My peak torque is at like 4800rpm, but HP peaks at 6200rpm. I shift right at 6200. Basicly torque is your take-off power or "low rpm power". Horsepower is your "top end power". Always shift at max HP not max Trq.