188CORVETTE

I race a '99 FRC with 3:42
I've tried 4:10 too low!
does the 3:73 make much difference? The gears just seem to be too tall 3rd and 4th with the 3:42 especially where I drive (Infineon, Laguna)

Thoughts?

AU N EGL

MN6 with the 3:42 is the most popular

Even several of the T1 guys switch out the MN12 for the MN6.

Raise your RPM limiter to 6800 or 7000, Retune car for more low end tq.


Looking at gearing charts the 3:73 seems to make more sence, but then each track is different.

4:10s are just too low

Independent1

^^Would not recommend raising RPM limiter that high, unless you have done significant mods to motor. I think this was based on Z06 rpm range. The FRC redline is 6000 rpm and rev limiter is set at 6200 rpm.

If those are the only two tracks you race at why don't you use one of those rpm calculators to figure a better rear gear ratio for your car.

Here's one you might want to try.

http://www.juric.org/mopar/tools/topspeed.php


Another recommendation is to buy Carroll Smith's "Tune to Win", which has an excellent section on gear selection.

Be interested in hearing what you do, as I have a 99 FRC also that I want to take to HPDEs.

188CORVETTE

what is the final ratio fo 4th and 5th with my transmission? thanks for the reply guys!

AU N EGL

MN6 trans gear ratios:

2.66
1.78
1.3
1
0.74
0.5

Independent1

^^

If you want so more spec info on your vette suggest looking here. Might find it helpful.

http://www.corvetteactioncenter.com/...9/99specs.html

Pumba

Robert,

When I purchased my Z06 one of the first things I changed on it was the transmission. I swapped a shop my MN12 trans for a MN6 trans. In addition, I had Liberty Gear upgrade the internals, including a 9310 mainshaft, etc., and a custom 0.563:1 sixth gear. The following chart shows a comparison between my custom MN6 trans, with a 4.10 final drive ratio and a standard Z06 MN12 trans and a 3.42 gear. It assumes a tire with the same diameter as the stock C5 295/35ZR18 Goodyear.

I contend that the 4.10 gear is not the problem.

I am able to pull 161 mph in 5th gear @ 6,500 rpms.



.
The next chart shows the rpm loss with a 6,500 rpm shift point. As you can see, the 5th to 6th gear loss drops the rpms below the peak torque point with both the MN12 and the standard MN6 trans. With the custom MN6 trans the rpms stay above the peak torque point.

Gray Ghost GS

I went from the 4.10 to the 3.73 with my MN6 transmission for HPDE events on the road courses. Big improvement! Great combination. 4.10 gears require too much shifting and you hit the rev limiter way too fast. I typically run at VIR, Summit Point and BeaveRun. Going to Watkins Glen this September. 3.73 seems to provide a great balance for daily driver and track events.

AU N EGL

4.10s also seem to cause exseive trans, diff temps, Not to mention higher oil temps in the engine.

Your gearing also depends on the track you are running. Not that we can switch diffs as race teams do.

folsomlarry

Mark out at MSI in Roseville is a very experienced road racer. I know that he still works with a couple of the shops at Infineon helping to set up car for the tracks in our area. It will be interesting to see which gears you end up using, especially at Thunderhill which more of a high speed track than the other two.

Larry