Help with my tranny & rear-end experment

[benelliwang]

Hi guys,
I have a 6 speed C5, with Heads & Cam about 400 rwhp or so.

I swapped in a 3.15 rear-end after I shredded my 3.90 stage 2 set up. It works perfectly but I am having issues with traction control kicking in at highway speeds. The speedo is reading correctly since the speed sensor is in the rear-end. So I have to drive on the highway without the tracking control on. I am guessing there is something in the programming in the ABS sensor vs speed issue. There has got to be a table in the PCM that I can adjust. Anybody has an idea or two?

For those of you who question why I would slow my car down by using the 3.15 rear, it is because my car will be turdbo’ed this winter and I feel the 3.15 gear will be a good fit gearing wise. This is what I think of the 3.15 rear on a manual:

With my 6800 rpm redline, I can take it past 60mph in 1st gear.
On a 60mph highway roll, I can down shift into second and I would be right at my power band,
I would not have to shift into 4th in a ¼ mile run. That killed my time when I had the 3.90 rear and with 3.43 I had to bounce through the rev limiter at 7.2k rpm as I cross the traps.
The 3.15 rear-ends are cheap and easy to find, I can drop the tranny, torque tube, & rear diff assembly and put in a new rear in about a weekend now. 8 hours if I have a good help and I am in a hurry.
The down fall is that I can’t use my 6th anymore, rpm is way too low.
At the track I lost about 5mph from the gear swap compared to my 3.42 rear. I used to hit 115mph with the 3.42 rear and 5k rpm launch. I launched off the idle this time, didn’t want to blow out another rear too soon.
400rwhp feels quite slow now, this car would pull nicely with 550rwhp or so.
I will prove that theory shortly with a 100 shot and see what happens.

Here is the calculation I’ve found from somewhere if you are interested:
3.15 with MN6
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
6500 58 87 119 155 209 309
3.42 with MN6
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
6500 54 80 110 143 193 285
3.15 with MN12
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
6500 52 75 108 155 184 271
3.42 with MN12
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
6500 48 69 100 143 170 250

[Ouija]

I think what you are running into is a problem where TCS kicks in if the rear tires are more than a certain % off the fron ttire speed.

There's a thread about it on here some where. The end result was that the dealer wouldnt' unlock the sensors or somethign like that so the speedo had to be left off to keep the sensors happy.

I'm not 100% but it sounds like the same issue to me.