I was reviewing the gearing on the Boss compared to the GT500. It's an interesting comparison:

Boss 302:



GT500:
2.97 First
1.78 Second
1.3 Third
1.0 Fourth
0.80 Fifth
0.63 Sixth
Rear end gear 3.73:1 in my modified GT500

The transmission gearing is significantly different between the two cars. With a 3.73 geared GT500, how will they compare in how they drive?

What got me interested was calculating the top speed of 5th gear. In the Boss if you run a 295/30/18 Hoosier R6, you will hit the 7500 rev limiter at 156.19 MPH which is just above the factory speed limiter (at least with the black key). The problem is on the Boss you really can't effectively go into 6th on track because of a big dropoff from 1:1 to .65:1 and losing all your torque. In the GT500 at my 6500 rev limit, I am hitting 169 MPH at the top of 5th. At BIR with the mile long front straightaway you can get there.

Those of you that really understand gearing please chime in on this. I was hoping the Red Key increased the speed limiter, but looking at the gearing, it may be a moot point to a degree.

For kicks, the gearing limitation in 6th gear at 7500 RPM is 240 MPH. Unfortunately the HP and aero limitations come into play well before that limit

 

Interesting, have you compared the Boss gearing to a GT 5.0? I like the tighter ratios on the Boss.

 

I'm guessing 6th gear is not for racing and is a true overdrive designed to get the best possible highway mpg for the car.

 

I actually wish the gears were spaced just a little bit further apart. These are such strong engines, let them pull through the gearing just a bit more. These ratios will have you shifting quickly through the lower gears.

 

I doubt you'll be using 1st much on a track. For leisurly driving on the street you can probably start in 2nd and miss the skip shift altogether.

 

Can anyone with a gearing calculator figure out what speed 2nd gear will top out at the 7500 limit? This will be for autocross and with an 06 STi it was a huge gearing disadavantage because at the rev limiter it was going about 53mph in second gear so I was constantly bouncing the limiter on most courses. I'm hoping the Boss will be able to hit at least 60mph at the 7500 redline so I don't have the same issues with the short gearing. (At least until we find out if the Red Key bumps the limiter or not)

BTW in 07 SOA changed the Sti gearing so it would hit 60 + in 2nd gear which was awesome!! Also my 06 had to be shifted into 5th in the 1/4 and the 07+ ran through the traps in 4th gear.

 

Exactly....that's what I was thinking. That's why the GT500 gearing makes more sense to me. Of course the 7500 rev limit versus 6250 will help.

 

Would it be better to have wider ratios or a slightly higher rear end? I have a motorcycle background so I'm used to high revs and close ratios.

 

64.276 MPH at 7500 RPM in 2nd gear on a 26.1" tire. It will vary depending on your wheel/tire choice. For example on stock Pirelli's that are 28" tall you would hit 68.955 MPH.

Here is a calculator that you can use to play around with different tire sizes and RPMs: http://golenengineservice.com/calc/calcmph.htm

 

Most definitely. 2200 RPM at 75 MPH out in cowboy country and 1900 RPM at 65 MPH for you on the left coast

 

They are the same.

 

Thank you. If I can get it to hook up then the gearing is perfect for most of the venues I run. Hooking up being the tricky part. I am going to have a slight learning curve going from AWD with a Torsen front diff to RWD with the Torsen in the rear

 

275/40/18 FTW

 

I have a 2010 gt 500 and a Kenny 2.8 with other mods making 714 on 93 octane at @ 19 lbs boost I feel for that leaving gears at 3:55 will give blower a better chance to pull harder than 3:73 hopefully

 

3.55s are not an option on the BOSS unless you wanna shell out for it aftermarket.

Cloud9 I think your calculations are a little off. Also the Red Key should remove the top speed limiter. Furthermore, while the BOSS might not make any additional power above 7400, you should be able to run it up to 8000? (estimate) on the Red Key tune. I think I remember hearing the 302Rs redline at 8400!

Even if that's not an option, 157 with a 275/40 is pretty fast. You should still go to 6th gear if you need more speed...it will not pull much however as you already know.

Here is the BOSS/GT Gearing with a few different common race tire sizes (obviously the 6th gear figures will be unachievable):

 

Anyways here is the gearing spreadsheet if anyone wants to play with it. This was created by another TMSer, I simply added the 2011+ tabs.

 

I ran the same tire sizes you are using with the calculator I posted and came up with the same results. Not sure which calcs you are saying are off? If it's the tire size I'm using versus the dimensions you use in your calculator, that can vary by tire manufacturer. e.g. a 295/30/18 from Hoosier might be a different diameter than a 295/30/18 from Toyo.

 

Does anyone know if the transmission in the Boss is the same as in the GT, the 302S and the 302R.

Thanks,
Rickstir

 

I should have been more clear. I intended to say the street Boss vs the others mentioned above.

 

From what i understand the gearing in the trans is identical in all above mentioned cars