bubbajones

Thanks. That's where most of the action is on this track.

I have no idea what that means.

I do open track days. No passing under duress. But I think I see your point that if passing at the end of straights were an issue, I'd rather be in the middle of 5th with a 3.73 than at the bottom of it with a 3.31. Whereas if there are a series of short straights that top near 90, then I'd rather be at the top of 3rd with 3.31 than in the middle of 4th with a 3.73.

Is that right?

Thanks.

Gene K

Ive done schools and open track days at Atlanta. Their were a couple of designated overtaking spots and of course it was the straightest fastest part of the track. If you cant pass their you must follow another lap. as you noted rather have the extra multiplication of 3.73 since you will most likely be in 5th at that point (Atlanta is a pretty fast track),

Normally gears ratios get closer as you go higher. 1-2 is a 51% Split (Increase in rpm if you down shifted), 2-3 is 44%, 3-4 is 28%, 4-5 is 32%. I believe what happened is the Ford engineers chose the 5.0 gear ratios to make the car as quick as possible at the Drag Strip trapping in 4th gear. This left a bigger step between 4-5 than 3-4. So if you gear the car to primarily work 3-4 you will not have as large an rpm drop between gears as if you gear it for 4-5.

If its primarily going to be a street car and 70-90 mph really is the major thing I would go with the 3.31. If it turns out to be wrong for you later you can always get them changed. You can find people that know what they are doing that will change rear axle gears fro $150 + parts if you shop for someone like a Moonlighting Ford Tech. That amounts to about $350 dollars ($150 Labor, $150 gears, $50 for lube,additive and sealer). Really you need to test drive cars with both 3.31 and 3.73 and see what you like (3.55 is rare on dealer cars).

VistaGT

How much quicker does the 3.73 make the 5.0?

I just drove a 3.31 geared 5.0 tonight and it wasn't very snappy accel

Timspony

3.73's for sure!!!

Gene K

So far no 3.73 car has run as quick as the 12.5 pass the 3.31 car made in showroom stock trim. I suspect the tires cant take advantage of the extra gear. I think a set of MT ET Streets and bumped rpm limiter will be needed to bring the 3.73 into its own. Mine spins at 20 mph in 1st if you punch it (3.55).

VistaGT

That's true, but from a roll lets say how much faster does the 3.73 geared car feel vs. the 3.31? I only ask because I feel, I hate to say it, dissapointed when I test drove the car tonight. I just thought it would blow me away and I think I hyped it up too much. Don't get me wrong-I can tell it's faster than my car by looking at the speedo......it just doesn't FEEL as fast. That and it's quiet! lol

Driver72

Gene, I don't recall seeing a fully stock 3.31 car do 12.5
I have seen 12.7's and 12.9's but not 12.5's
One car I saw did 12.4's on 3.31's at 115+ mph traps and that was with CAI and tune. Add DR's to that and he did 12.2's

As I've said from the get go (and I know you agree) I think the 3.55's will be the best overall for times. Will pull stronger than the 3.31's but not need the extra shift the 3.73's require and won't spin the tires into 2nd as much as the 3.73's either.

Driver72

Feel, I'd say it will feel much more snappy.
As for actual acceleration, well that's hard to say.
Look at it this way
Doing a 40-120 mph roll contest between two identical 11 GT's but one has 3.31 gears the other 3.73 gears.

Both will start off in 2nd gear.
But the 3.73's will END the run in 5th at below peak power.
The 3.31 car will go past 120 mph in 4th and be pretty much right at peak power at 120 mph (IIRC 4th gear tops out at 124 mph in a 3.31 geared car).

So again, the 3.73 car may accelerate through the gears faster and therefore FEEL faster, but it's going to require an additional shift.
And than from 111 mph to 120 mph it will be accelerating in a 1:1 gear ratio a thousand or so rpms BELOW peak power.
Whereas the 3.31 car will be accelerating in 4th which is more aggressive and between the same 111-120 mph, it will be right in the heart and peak of the engines powerband.

So to be honest, if anything the 3.73 car will end up slightly ahead due to it's slightly faster in gear acceleration, but from 111-120 mph when the 3.73 car is in 5th the 3.31 car being in 4th may actually gain some of that ground back. Until tests are done, this is my best guesstimate.

Again the reason I ordered the 3.55 gears.....best of both.

bubbajones

Thanks a lot. This is where I ended up after thinking about this over the weekend. This track is a 3-4 track for me in both a TT and an Elise. The Mustang has a lot more power than either of them, and the 3.31 will let me stay in 3rd (90+mph) where those cars were reaching for 4th.

We have a big fat straight (3/4 mile?) where I could see wanted 3.55 or 3.73 if I were racing, but that's where people will typically let off the gas and let you pass if you've been riding their tails in the past few corners. There are plenty of other places to pass as well, so it's not crucial in any event.

I also stumbled across a few threads here and elsewhere and the data seems to show that a 2011 3.31 in 3rd and 4th gear has the same total ratio as a 2010 with 4.10 rear end. I know the 2011 revs higher, but I gotta think it will be adequate.

To address someone else's question about "snappy" acceleration, I too didn't fell a lot of "oomph" in 3rd gear on a test drive, but I hit the rev limiter by accident on a 2-lane road, so it must be there. In my experience if you want "snappy" then a turbo (with lag) is the way to go. My TT feels pretty snappy, but it's not nearly as quick in reality.

Daniel60

3.73 not 3.55 If you get decent traction go with 4.10s. I hear these cars are better at traction then our 05-09s'