rx7learner

Does anyone have any tips for shift points and methods. I'm new to racing my 7, and I know I've got some decent power but I think I'm not shifting right.

IE. I made a left in front of a small Ford econobox thinking he would be a spec in my rearview mirror after hitting 3rd, and he blew passed me. Hurt my feelings! But I think I just wasn't shifting right.

Should I be raising my RPMs and popping my clutch everytime I shift in each gear?

aussiesmg

iTrader: (1)

You hold the gear for as long as it makes power, every car is different as to where this is, so hold the gear until you feel the car stop pulling fowards. In corners select a gear that wont force you to shift while in the corner.

trochoid

iTrader: (6)

Haha, most pickups now days are faster than a stock 7 anyway, it's called progress.

Popping the clutch, if I understand what you are meaning, will lose time. Try flat/speed shifting, i.e., not letting off the go pedal between shifts. This can be hard on the syncros, moreso if they are worn and grind during normal shifting

The power curve, stock, tends to start falling off around 6200-6500 rpm. The critical part when shifting is which part of the powerband does the next gear change put you in. Best way to find out is to make timed runs, varying the shift point until you find your fastest time.

purple82

This question comes up often on this board. Basically, you want to keep the most torque to the wheels. This is a fairly simple formula of engine torque, gear ratios, friction estimate, and wheel diameter plotted out for each gear ratio and engine speed. Then you can determine at which engine speed for each gear you should shift to get the most torque to the ground. It's not necessarily the same engine speed for each gear!

If someone has the gear ratios and a plot of the stock 12a's engine torque, I will make a spreadsheet to finally answer this question.

purple82

OK, here's my engine and gear ratios. You can see that there is a small benefit to shifting from 1st to 2nd on my car at about 37.5 MPH. Otherwise, I should run to redline in all the other gears.

mr_ouija

Easy way to tell if you're shifting too slow/late...

After you shift, if you're slammed back into your seat, it's either a late or slow shift. As power drops off (shifting too late in the RPM range) your body won't be stuck back in the seat as much. After you shift, you'll be back in the power band and you will get slammed back into the seat. Optimally, you'll be shifting right at or slightly before the peak of the power band, and shift into the lower side of the power band, and quickly pull back to the peak.

There's more to it than that, and it's not perfect by any means, but that is the basic idea of it.

Buffumguy1

LOL, you got to love this board. Great spreadsheet purple82, not so much because I wanted to know the info, but because someone went to the trouble to find it out for a fellow 7 owner.
rx7learner I feel your pain. I ran neck and neck with POS early 90's accord. I wanted to lead him bad, but the 12a just did not have the poop. Luckly he did not lead me either.

Midwest 7's

iTrader: (4)

is your 7 stock? sound like you need exaust and intake/carb. shift a second after that 7k redline buzzer goes off, just make sure your engine has good and approriate oil. premix your gas and drive the **** out of it.

purple82

Common misconception, it's the torque to the wheels which includes gearing. It's not just engine torque, and notice I don't say anything about power.

dean23

my car doesnt have a redline buzzer... that or if it did it doesnt work anymore, but that i wouldnt belive... haha

rx7learner

Not stock... Street Ported with RB header & exhaust, Holley red pump, mech secondaries, 2nd gen coil, no rats nest, only driving the ac compressor, 195/50/15 Tires.

That graph was awesome and the info is great. Thanks...

I think my stock nikki carb and intake is holding me back as well... but I'm not sure how much??? See that RB has a 12A intake and holley carb kit for about 700$. If having a stock intake & carb loses as much HP as what I lose when I cut my A/C on (I still have it because my car is a DD in Tampa) then I need to invest in upgrading the intake & carb becuase my car is a SLUG when I cut the AC on.

purple82

The plot that I made is for my S5 13b engine only. It's based on my latest dyno run. It will be different for every engine and gear set.

rx7learner

Do shops that provide DYNO's produce graphs like that? (Post above hit before I finished... thanx....)

Since torque can be felt maybe I should go through each gear multiple iterations watching the tach and note what RPM the torque goes flat for each gear. Which would give me a general idea of shift point, but the other factor is the performance between the max torque shift points.

For example if you hit max torque in 1st at x rpms, and in 2nd at y rpms, how long did it take to get from x to y? Would it have been better to extend x; even though it defines the max torque in 1st, because it shortens the time between x and y (we can call that factor z).

Even though max torque points play part in the formula, how would someone identify the z factor?

purple82

They take your gearing into account and give you one curve of the engine based on that gearing.


You should be concerned with vehicle speed, not engine speed. When you shift, the car stays at about the same speed and the engine speed matches what the gearing dictates. That's another one of the reasons why just looking at a dyno for shift points doesn't help you.

Unfortunately, you're not going to be able to tell the best shift points by just driving around. You could do a series of timed acceleration runs and get close to it that way, but you'll need to mathematically figure it out to get it for sure, as I have done.

darthrotary

lol at the redline buzzer. i totally forgot my car had one. i could tell my engine was gonna go at any day so i was driving like a granny. when i got my rebuild, i decidided to do alittle heavy shifting after the break in period and i totally forgot about the buzzer and it scared the **** out of me and i missed 2nd gear like a ****!

purple82

I had an error in my wheel force spreadsheet. Also we're now looking at rear wheel torque instead of force. Now things are a little more interesting as far as the best power shift points, but not much more interesting as redline is still about the right place to shift.