3.55 or 3.73?

[scrappydoo1888]

Hi Gang! Just need some help/opinions with deciding on which rear gear would be best for my below application....3.55's or 3.73's? I currently have 4.10's in there which were installed pre-supercharger era lol but now feels too much for the street I find.

A little background.... I have a 2005 Mustang GT convertible with an intercooled Whipple supercharger/Steeda 10-Rib pulley set-up pushing out 525hp at the rear wheels and 485ft/lbs. Full suspension, Brembo Big brake kit, stock 5spd. transmission with Exedy Mach 500 stage-3 clutch, and all the other normal bolt on goodies.....

With my Engine HP output and transmission what would you guys choose? This is a daily summer driver only and doesn't see the track.

Thanks,

Steve

 

[Marble]

I say neither and get good tires. A good drag radial with some stiff sidewall and let it rip.

But if you must, there isn't much difference imo between the two choices.

 

[skwerl]

I had 3.73 gears on my supercharged Bullitt and dealt with the same issues. I could downshift and smoke the tires from 50mph. always had to be wary of too much throttle because the tires would spin so easily.

With that much power I'd say 3.55 gears would be your best choice. Or you could run a bigger pulley on your blower and back off on the boost, but what fun is that?

 

[stkjock]

What brand/model tire and size is on the car now?

 

[JG-1]

I personally enjoy 4.10 gearing on an 800 hp blown Mustang on E85. I’m running 19” 305 Michelin Pilot Super Sports and have traction issues but the car is very fun.

 

[ChewyR]

I have ran 4.10, 3.73, and 3.55 with my supercharged 3v tr3650. I really liked 3.73 at the 475 rwhp level. 3.55s now with 600+ rwhp. If you think the 4.10 are way too much then do 3.55, if you think 4.10 are just a little to much then you will be happier with 3.73.

 

[JeremyH]

Plus one on what tires you have. Keep that in mind when you choose a gear. Often its cheaper to lower effective gearing with taller tires which in turn will have more contact patch and traction. Or if you got a buddy with taller tires to feel out before picking a gear. The formula is simple, current height divided by new height times final drive ratio equals effective drive ratio.

So for example 26" ÷ 28" x 4.10 = 3.80

 

[scrappydoo1888]

What brand/model tire and size is on the car now?

I have Nitto Extreme Perrformance NT555 255/35ZR20 all around. They are a good summer tire but I can smoke them way too easily with the gearing I find.

 

[stkjock]

That’s a 27” tire. So going to a 28” wouldn’t cut the effective gearing much.

However going to a 28” tall drag radial will make a world of difference for traction.

 

[scrappydoo1888]

The crappy thing is I originally had 3.55's but swapped them out a couple years ago when I installed Comp Cams Mutha Thumpr's which needed the 4.10's to run right. Didn't think I would have the funds for a supercharger this soon. Oh well I will have 4.10 gears for sale in the spring lol

 

[stkjock]

The crappy thing is I originally had 3.55's but swapped them out a couple years ago when I installed Comp Cams Mutha Thumpr's which needed the 4.10's to run right. Didn't think I would have the funds for a supercharger this soon. Oh well I will have 4.10 gears for sale in the spring lol

that's a new one one me.... sounds like your tune was the issue, not the gearing.

 

[scrappydoo1888]

that's a new one one me.... sounds like your tune was the issue, not the gearing.

It was a bit of both for sure! (Bama email tune) After the supercharger install I got it dyno tuned at Dasilva and everything is way better. Just too much power with that gearing for the street. Is that actually a bad thing though? lol

 

[skwerl]

The McTune was the issue, not the cams. Glad you got a real tune finally.

 

[07 Boss]

If you're still running the cam I would keep the 4.10's and learn how to modulate the right foot. Planting it to the floor doesn't take any skill. Why tune it down? I run 4.10's with my Whipple but i run a 28.8" tire which makes it effectively a 3.93 ratio. Anyways I'm currently running NT05's and I do have to say it kinda sucks, though maybe a tad better than the triple 5's. I've run a few summer street tires and a bunch of drag radials and I just cheaped out last time it came for tires. Never again. MT Street Radials are the best out of all of them. Or the Street SS if you need a little more tread. That's what I will be running next in a 305/45/18.

 

[01yellerCobra]

I have Nitto Extreme Perrformance NT555 255/35ZR20 all around. They are a good summer tire but I can smoke them way too easily with the gearing I find.

That's your biggest problem right there. Those tires aren't great at all. The normal 555's are basically rocks. I ran the G2's for a bit and my little pullied eaton would spin them through 3rd without trying. Get a real tire and you'll be amazed at the difference.

 

[1950StangJump$]

If you want to do this right, go to Tremec's website and use their calculator. Use a constant engine speed, e.g. 2000 RPM, and start with your 3650's ratios and current rear end -- then look at the MPH for each gear. Then, you can mess with the ratios by choosing other transmissions and rear ends and compare what the MPH would be. That way, you can decide whether you want shorter or longer based on how the car feels with the current setup.

I have a Kenne Bell blown 08 with the 3650 and 3.55 rear end. Since mine is street only, I was less concerned about hookup and more concerned about the car being a blast. With that attitude in mind, I find 1st gear great, but 2nd and 3rd way, way too long. Feels like the car just doesn't go when I goose it while cruising around in 2nd or 3rd at lower RPM (e.g. 2000).

I was going to swap in a Magnum anyway. So, I did some Excel charts showing what the speeds are in comparison to different Magnums and rear ends. Long story short, I just ordered a Magnum XL with the 2.97 gear and will be putting in a 4.10 rear. This will keep my 1st gear almost identical to the 3650 with the 3.55, but make 2nd and 3rd much shorter -- exactly what I wanted. The final gear (6th) will be just a little shorter than the current final gear on the 3650 (5th).

In the future, I plan to forge the motor and turn up the boost. I will certainly go back to a 3.73 or 3.55 rear gear then.

Take a little time to do lay the numbers out and compare them against what you feel in the car now. A little research now will do you good.

 

[RoushStage_3]

Hi Gang! Just need some help/opinions with deciding on which rear gear would be best for my below application....3.55's or 3.73's? I currently have 4.10's in there which were installed pre-supercharger era lol but now feels too much for the street I find.

A little background.... I have a 2005 Mustang GT convertible with an intercooled Whipple supercharger/Steeda 10-Rib pulley set-up pushing out 525hp at the rear wheels and 485ft/lbs. Full suspension, Brembo Big brake kit, stock 5spd. transmission with Exedy Mach 500 stage-3 clutch, and all the other normal bolt on goodies.....

With my Engine HP output and transmission what would you guys choose? This is a daily summer driver only and doesn't see the track.

Thanks,

Steve

Since your car is maxing much power cause of the supercharger and it’s not a centri go with the longer 3.55 gears since the main point of steeper gears is to get you in the power band quicker and your power is probably pretty linear you won’t need to be forcing it. Let the 500whp do the work for you lol. My roush supercharged stage 3 cane factory with 3.55 gears..... if roush is doing it then there’s probably something to it


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[1950StangJump$]

The car having 3.55 gears was probably just the luck of the draw when Roush received X number of Mustangs from Ford to convert.

The problem I see with the 3650 is that 1st gear is really short, while 2nd and 3rd are really long. I suspect the 2nd/3rd induces folks to want the shorter gears, only to make 1st feel borderline unusable when you add power.

 

[PonyBoy]

I have a fairly stock 2010 GT 5-speed right now with the staggered Bullitt/Mickey Thompson tire set-up from American Muscle. I love the look, handling and traction. I find that I don't even want to bother with first gear many times - unless I'm on an incline. I don't know if that is bad, but most of the time. Anyone else skip first?

Also - if I'm just cruising around, I find after first gear, I can upshift without the clutch. It sounds like it's a terrible idea, but it doesn't seem to harm anything. Any transmission guys out there have any thoughts?

 

[46addict]

I never skip first. And skipping first from a standstill puts unnecessary wear on your clutch. If you feel the gears are too short, you can start in first and skip to third, but I would never start in second. I had 3.73 gears with the 3650 on a Procharged car making 430whp and that was a good combo. If traction wasn't an issue I would have liked to try a 3.90/4.10.

I now have a TR6060 with a 2.97 1st and 3.73s in the rear and it works out better in the higher powered car. The effective ratio in 1st is the same as having 3.31s with a 3650.