Foo Cat

Here are the instructions for the yellow jacket. The example given is for 4.77 gears, which has a setting of 28.

instructions for yellow jacket calibration

Wisconsin S2k

not to mention the 4.57's are stronger than the 4.77's. IMO that's more of a downgrade. even price alone dictates that.

Wisconsin S2k

gearing alone dictates about an 11.5% change.



to the OP, my suggestion is to remove the yellow box, and use one of the other methods to dial in your speed. 80mph is too high of a speed to properly calibrate IMO, since tire flex is going to skew your results.

I suggest this. Set your yellow jacket to an 11% correction factor. (assuming you have stock tire diameter?) then drive next to another S2k that is going exactly 60mph and talk to each other on the phone and see what your speedo reads when you match his speed.

the other option is to do the 1 mile at 60mph technique and then do the cross multiplication.

xviper

That is how I did mine. I had myself paced by a police car two different road speeds, BUT this was only to confirm what I already knew.

Listen to what Wisconsin just posted. Anyone who puts gears in the car should do the following if possible:

1. Before installation, confirm the exact ratio of gears you are putting. COUNT THE TEETH. This is so easy I am confounded by why people don't do it.

2. Once you confirm the ratio by counting teeth and you know you got what you paid for, do the math and find out what the % change is from the stock gearing. Use this number to dial in the correction on the speed compensator. So far, this is pure physics and math. If you do this, you will have dialed in the change for the gears and your speedo and odo WILL read as it did before.

3. Now, if you want to correct for any errors that were (and are) inherent in your particular car, THEN confirm this by the other methods described here. Be it known that when you do this, you will have also dialed out ANY error that was in the speed measuring device of the car that was there before, including any error induced by a different wheel/tire configuration. Most digital, speedos can have an error of 0% to over 2%.

PilotSi

I guess I'll have to pace someone then. But the problem with counting the teeth is that I got mine prebuilt by Hardtopguy, so it makes it kind of hard to count

xviper

I would hope that HTguy's installer does this prior to every insall. (That's why I said "if possible".)
But like I said, if you have 4.57s, dial in 11.46% and you will have fully compensated for the gears. Then all you need to do is confirm it and dial out the naturally occuring error, is you so desire.

twohoos

You gotta do what billman said; that's the only way to be absolutely sure which gears are in there (without taking 'em out and counting teeth!). All the GPS/tire diameter/speedo stuff introduces too many error sources. Plus this only takes a couple minutes, while the GPS thing will keep you occupied forever finding level roads, measuring tire deformation, calibrating speedos...

If you're gonna meaure something, *measure* it!

gfacter

I am going try the Billman method.

FYI I just got back from a another track day at Summit Point (main course) where I have done more that 25 events.

I adjusted the jacket to 21 just to see the difference, on the way up 4000 rpm in 6th was 65-66 MPH.

On the track I was redlining 5th at 120MPH,

With the 4:10 gears I never could redline 5th at this track both with and without the supercharger. The max Speed I have even seen there NA was 125, and 135 supercharged.

Billman250

Get out the yellow crayon sounds primitive, but it's foolproof.

WyattH

to HTG.
Interesting thread. I just installed my 4.56 pumpkin, and will now set my yellowjacket.