RickBetterley

My electronic dash has shift indicator lights, which I find pretty helpful, especially with my short gears.
There are 5 levels of lights; the fifth and highest is generally set at red line (which is 6800 in my 993).
Any suggestions as to where to set each of the lights?
Thanks

mnorek

Rick,

I suggest you dyno your car and see where the meat in the powerband is (Bill Pfister at Eurotech in Framingham has a nice DynaPack chassis dyno). I set the lights to start with the beginning of good torque, the end, then start of HP, then the end, then holy *&%^, time to shift. It's a useful tool when playing with lines and lap times.

Michael

RickBetterley

Hi Mike
That's what I like; a good, reasoned explanation that acknowledges the *&%^ inputs as well.
Seriously - thanks for the suggestions. I will try it in the cold and damp at WGI Monday.

Bryan Watts

I generally try to set the last light a bit before redline so that I have time to shift when I see the light. I prefer to use it as a shift light rather than a tachometer. I generally set the first or second green light somewhere around where I'd like to shift if I'm short shifting and taking it easy.

924RACR

I drive on a very short and busy track; as a consequence I rarely have time to watch all the lights light up, pretty as they are. So instead, I set my top light to be at my desired shift point (6000rpm - redline is 6500 IIRC), and the bottom light to be at the bottom of my powerband (should be 3000rpm, based on stock curves). So I know if I have no lights lit, I should downshift (rare, only when avoiding major on-track incidents, etc). More importantly, I know I can just floor it till I see the lights blinking, then shift.

ngoldrich

Rick,

FWIW -

on my MXL Pro I have been running for several years I have the following shift lite config-

My rev limiter is currently set at 7200

Lights are:

6800
6400
6000
5600
5200

Not sure they are optimal, but have worked well for me...

Norm

Geoffrey

To determine the optimal shift points, you'd want to plot your torque curve with the final drive ratio in each gear to determine the torque drop at each shift which will vary depending on gear.

RickBetterley

That sounds like a great idea.
I, um, don't know where to start. I have a spreadsheet with RPM in each gear, and torque curves from the owners manual (engine is stock, though gears 3-6 are changed; the spreadsheet is for the current gear set). Should I set the shift lights to fire at the peak torque for each gear, then the top light at redline?Thanks; I appreciate your help, as well as the suggestions from other responders.

Geoffrey

You can create a spreadsheet with the gear ratios and torque from a dyno, then use the speed and axle torque calculations to determine the axle torque at various and from there you can determine the % drop or gain. Here is a chart for an engine and gears. You can see that at some RPMs, shifts actually INCREASE axle torque. Negative numbers represent an increase in axle torque.

RickBetterley

I knew you'd have this kind of help for me. Sending PM.
How's the weather down WGI way? I have 2 days with Kojote Monday/Tuesday. I think the weather will be sub-optimal.

Geoffrey

You'll have to check the weather channel, I'm more near LRP (50min west) and we have snow on the ground again.

Premier Motorsp

Geoffrey,

Your chart seems to indicate that for best performance with this engine/trans combination one should shift at the highest permissable RPM.

I have found that this is true for almost all normally aspirated Porsche racing engines.

Would you concur?

Geoffrey

No, I would not agree 100%, but that IS what the graph shows. For example my 3.8l engine pulls cleanly to 7800 which is my redline and 6k is peak torque. However, I have a 800rpm drop between 5 & 6. When you are at those speeds, there is a lot of drag on the car and short shifting 5-6 at 7100rpm gains more mph than wringing out 5th to 7800 and shifting to 6th on some tracks. I see this with my data logging at WGI back straight AND Mosport for instance. Now, it might be possible to lay fault with the gearing and say that the gears are not appropriate for the car, but that is the specific reason why I geared 6th so close to 5th. You can try it yourself in May

And, the more I think about it, it is more than the torque drop, it is also the outright axle torque available, so there may be reasons (such as described above) where short shifting the car may be beneficial. Luckily with the MoTeC ADL you can program the shift lights specific for each gear.

I used the above chart to estimate the gearing for my car when I was building the trans. I, unlike you, don't regear my trans for each track, you run your cars more like a pro does and is probably a better approach than a generic gearset like I have.

Greg Smith

Good work on the gearing/trq chart. I did the same thing a few weeks back, althought it wasn't quite as easy to read as yours, but it made sense to me.

On the Aim Pista can you set the multi stage shifts lights so they change depending on what gear you're in?

Geoffrey

No.