Ozark Mountain Region SCCA

Can you change the rear gear in ESP? I can't find a thing about it in the rules.

Sort of. All you can do is update / backdate to another car on the same line in the rulebook.

Therefore the question is, what other gear ratios were available on the '05 - '09 Mustangs? You could swap to those (if any).

Bullitt comes standard with 3.73 (actually, standard with the entire GT500 rear). I think the 3.55 is the GT "optional standard", with 3.21(?) the "standard".

The FR500 cars have a plethora (how many is a "plethora", exactly?) of ratios available, but I don't think they're "legal" cars for SCCA. If they were, they're probably NOT on the same line.

I need to take a ride with you Scott and see the difference in the 3.73's.
I never have been to happy with the 3.55's that I have.

Couldn't you just run a shorter tire on race day to get the same effect?

The Huff wrote:I need to take a ride with you Scott and see the difference in the 3.73's.
I never have been to happy with the 3.55's that I have.

Any time, my friend. Any time.

craigb wrote:Couldn't you just run a shorter tire on race day to get the same effect?

And what if you run the shorter tire with the shorter gears?


A quick exercise in Math and self-flaggelation with a Stupid Stick:

This year I plan to run Hoosier 285/30-18's (24.7" dia, 77.7" circ, 740 revs/mi) as opposed to stock-size 235/50-18's (27.3dia, 85.6" circ, 815 revs/mi) for some events on the B.

The TR3650 has a 3.38:1 first gear (some sources say 3.34:1), 2.00:1 second, 1.32:1 third, 1.00:1 fourth, and 0.67:1 fifth.

I was mistaken earlier about the standard GT rear-ratio - it's 3.31:1 with the optional at 3.55:1 (and Bullitt @ 3.73:1).

The Bullitt also has a higher rev-ceiling (6550rpm vs. the standard GT @6200rpm).

If I didn't screw-up the math someplace:

Standard GT 6200rpm limit w/235's in 2nd: 3.31=75mph; 3.55=70mph; 3.73=67mph. Bullitt w/3.73=71mph.

Standard GT w/285's in 2nd: 3.31=69mph; 3.55=64mph; 3.73=61mph; Bullitt w/3.73=65mph.

What does it all mean?

Other than I probably still can't drive the car for shyte, and going to the shorter tire loses 6mph at the rev-limiter in 2nd gear - Hell if I know.

So, bullitt, you must be some sort of engineer. I'm going to school here in Rolla and the guys I hang out with do that sort of mathmatical magic for fun

fordfocusguy wrote:So, bullitt, you must be some sort of engineer. I'm going to school here in Rolla and the guys I hang out with do that sort of mathmatical magic for fun

Pour some beers down me, I get stupid-into the bench racing thing. As if I needed the beer to get stupid.

craigb wrote:Couldn't you just run a shorter tire on race day to get the same effect?

Scott has the right idea, shorter tire and gear. I already run a shorter tire but my 2nd gear just feels slow.

Scott, Have you had the Bullitt at the drag strip? I ran a 14.0929 at 99.91mph. That would also tell us how the 3.73's run against 3.50's.
That was before my intake and tuner though. I can't tell any difference in power with this tuner. I did set the redline to 6500, that doesn't help much in autox, but should help a bit at the strip.

I doubt that a change in final drive ratio - given the time/expense/aggravation - will help you much on an autocross course. The problem with the '05-'09 Mustangs is weight and the spacing of gearbox ratios...you're in third gear and feel like you need to be in second but second forces the revs too high and unsettles the car....or you're in second and want to shift to third but you know the revs will fall off too much.

Changing the rear end ratio is only going to move these problems to another part of the course or to a different course on another day.

Drag racing is a different matter...higher (numerical) gears definitely improve performance.

Ted Wells
Satin Silver "05 Mustang GT

Justin, I'll add some of the info from my car if it'll help you make a decision.

So we know you have a 3.55 rear gear with the following trans ratios....

Bullitt2954 wrote:The TR3650 has a 3.38:1 first gear (some sources say 3.34:1), 2.00:1 second, 1.32:1 third, 1.00:1 fourth, and 0.67:1 fifth.

My car has a 3.42 rear gear (no upgrades available) with the following trans ratios....

2.66- first, 1.78- second, 1.30-third, 1.00-fourth, 0.74-fifth and 0.50-sixth.

From that it appears that you already have a healthy gearing advantage in comparison to my car.

I don't know where that 3 valve motor likes to run but it was my impression that they put out similar power numbers to that of a lightly modded LT1 (like mine).

Here's a very recent dyno sheet (post tuning) from my car....


Anybody have a dyno sheet for the '05 - '09 Mustang?

I know you want to get faster. You know how my car runs. Hopefully this will help you determine if your car would benefit from the gears.

I really don't know enough about how Mustangs drive to offer an intelligent suggestion.

Thanks for the info. I guess for now, I'll keep things the way they are.

Just 4 more weeks and we'll be autoxin!!!!

Ironhead wrote:Anybody have a dyno sheet for the '05 - '09 Mustang?

I found this one from C&L - they've got stock numbers, and also plots from the install of their Cold-air Intake.

http://www.cnlperformance.com/images/C&L_Racer_Dyno.jpg

OK, I have no idea why the "img" tags will not display the image. F-it.