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3.73 OR 3.55?

pufferfish

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i need to replace my factory 3.73's because of excessive backlash and i have been toying around with the idea of taking the opportunity to change the ratio. only get one shot at this so i need to be sure about it. i have been satisfied with the 3.73's on the street (although it does make 1st gear largely useless), but since adding the short hoosiers to my track days, i think there might be too much gear. i was thinking 3.55's might be a better option. also, funds permitted, the shop has offered to put in a T2 for me without additional labor if i buy it from them (+$589). i don't have an issue with my traction loc, but Ford put the T2's in for a reason.

i did look for a T2 equipped rear from a wrecked boss, but apparently they are being well cared for, so there are none in circulation.

i just can't decide, so help me out!
 

NeuRon

2012 500A #1626
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On the street, and with any mods, I think the 3.55 is good. I tend to start from 2nd gear a lot of the time and mine is stock. Still plenty of wheelspin occurring in the top half of the tach. ;)
 

steveespo

Lord knows I'm a Voodoo Child
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Steve
I run 3.55s in my car with a Torsen T2 and I feel it is the best combo if you have torque. Since your GT is running stock manifold you have a better mid range than a stock Boss. I run Boss Intake and long tubes so I have the best of both worlds, the car will pull the slightly taller gear. I have found that the 3.55 with stock tire height gets me a little more use out of 4th gear at some of my favorite tracks without having to shift up to 5th close to the braking zone. For tighter tracks like Summit Shenandoah I plan on using 650 mm tall rear tires that effectively give the car a 3.73 ratio. Also you have a little better throttle control coming out of corners because the power on 'hit' is a little softer in the lower gears, I can get the tail to rotate on power but am not so afraid of shocking the tires into a big slide.

Steve
 

zzyzx

Steve
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1st is useless in pretty much any situation where you need to launch quickly. Combined with 18" wheels and the smaller rolling diameter, it's even worse. I'm still on 19s, and a 27" rolling diameter and I think 3.55s are the way to go even for 19s. For autox specifically, you'd end up with a better launch (if needed, depending on course layout), and an improved top speed in 2nd gear (which really counts).

3.55s would have dropped my times last weekend by a good 5/10ths sec since I was all over the limiter in 2nd in multiple places on course.
 

steveespo

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zzyzx said:
1st is useless in pretty much any situation where you need to launch quickly. Combined with 18" wheels and the smaller rolling diameter, it's even worse. I'm still on 19s, and a 27" rolling diameter and I think 3.55s are the way to go even for 19s. For autox specifically, you'd end up with a better launch (if needed, depending on course layout), and an improved top speed in 2nd gear (which really counts).

3.55s would have dropped my times last weekend by a good 5/10ths sec since I was all over the limiter in 2nd in multiple places on course.

+1 On This :)
 

Grant 302

basic and well known psychic
I'd make that exact switch for my GT. Torsen and 3.55...

Unless you are planning a build or tune that will bump your RPM limit up, I find that 4th runs out too quickly with short tires say 25.6" to 26.3" tall. I would keep 3.73s if running 26.9" to 27.7".

Side note: If you are keeping your engine *mostly* stock, I recommend the ProCal tuner. Everything on my GT feels more Boss-like with regard to throttle response and engine braking. Compares very well to the silver key feel...
 

pufferfish

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i am glad to hear everyone is backing up what i thought would be the best gear choice. i am going to schedule my appointment asap!

grant, i burned the warranty 3 months after purchasing the car, beginning with tune and cai! i rev to 7500, so i do get to extend my gears as much as possible, but i really could have shifted into 6th on vir back straight last month with those short hoosiers. i think they are 25" tall? i don't ever want to have a need to go into 6th on track. i don't trust the transmission to handle power in 6th.

another plus of the 3.55's is they inherently have less tendancy to whine. i am really looking forward to hearing less from the rear. the coasting death rattle i am getting from all this backlash is really disturbing. it scares people!
 
I am going to swap gears at some point for the 3.55 myself. Running Conti slicks at about 25 inches really adds to the 3.73, in fact with these tires and the 3.55 I would be about the same as factory tires and 3.73's.

Sounds like a different crowd here when I asked about the same thing last year everyone thought I was crazy.
 
I was told that the Boss's used at "The Track Attack" use a 4:10. I've always thought it would be fun to try a Boss with 4:10's or even 4:30's. It seems the high revving 302 would love either of those gears. I agree that 1st gear wouldn't be of much use though.
 
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seca954 said:
I was told that the Boss's used at "The Track Attack" use a 4:10. I've always thought it would be fun to try a Boss with 4:10's or even 4:30's. It seems the high revving 302 would love either of those gears. I agree that 1st gear wouldn't be of much use though.

I'm fairly certain that the Track Attack Bosses have the stock 3.73.

When I went, someone in our group asked what exactly was done to the cars vs a stock Boss, and it was fairly minimal. Track Key, exhaust plates out, roll bar, harness, two piece brake rotors, different brake pads/fluid, different tires, and I think that was it. I may be missing one or two minor things but gears definitely were not on the list.
 

pufferfish

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YellowBoss said:
I am going to swap gears at some point for the 3.55 myself. Running Conti slicks at about 25 inches really adds to the 3.73, in fact with these tires and the 3.55 I would be about the same as factory tires and 3.73's.

Sounds like a different crowd here when I asked about the same thing last year everyone thought I was crazy.

never in the history of the mustang has there been the right combination of parts and performance to NOT want the most gear possible. guess it just took time for the culture to shift into a different mindset about these cars? im guilty of it...i would have told you it was crazy a year ago too! 3.73's were the "compromise" between economy and performance before 2011.

i had not done the calcs on the effective ratio with the shorter tires, but your assessment sounds right and fits my goals. i just need to scrape together some more cash for another set of 18's for the street so i can have the same acelleration, ride height and speedo calibration. BUY SOME TOW HOOKS PEOPLE!
 
What is involved to change the ratio of the stock Torsen rear end and what would the approximate cost be? I think that even for street use a higher gear (lower number) would be beneficial.
 

Justin

Save the dawn for your dishes!!!
GottaBoss said:
What is involved to change the ratio of the stock Torsen rear end and what would the approximate cost be? I think that even for street use a higher gear (lower number) would be beneficial.
That varies greatly depending on where you get the work done. gear set can be had for 150 plus three qts of fluid. Throw in a master bearing kit for new bearings around 100 bucks. Dealers charge outrageous prices to swap gears and they generally suck at doing gears from my experiences. I do my own gear swaps if you have the tools and some guidance its not that bad.
 

pufferfish

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the tools are the big issue. need a press with a bearing puller. need an internal bearing remover slide hammer thingy. need a dial indicator with a magnetic base. thats about $600 in tools. then you have to know what parameters for tolerance and gear pattern and how to correct them when they are out of tolerance.

i am a big proponent of diy and having every tool to do it, but in this case, its best left for the experts...and they aren't at most dealers or most shops. the shop i am having it done at actually sub-contracts it out to a real pro. more shops are doing that because it is specialized work and your average SAE certified wrench-turner shops hire are not specialized enough to do it.

i have done it in the past and it isn't rocket science, but if you aren't REALLY good at it, the risk is high to end up wiping out a set of gears, bearings or just deal with gear whine and clunking. i would rebuild and automatic trans before i would change gears out again. just my .02

by the way, the labor i am paying is $650.
 

Justin

Save the dawn for your dishes!!!
pufferfish said:
the tools are the big issue. need a press with a bearing puller. need an internal bearing remover slide hammer thingy. need a dial indicator with a magnetic base. thats about $600 in tools. then you have to know what parameters for tolerance and gear pattern and how to correct them when they are out of tolerance.

i am a big proponent of diy and having every tool to do it, but in this case, its best left for the experts...and they aren't at most dealers or most shops. the shop i am having it done at actually sub-contracts it out to a real pro. more shops are doing that because it is specialized work and your average SAE certified wrench-turner shops hire are not specialized enough to do it.

i have done it in the past and it isn't rocket science, but if you aren't REALLY good at it, the risk is high to end up wiping out a set of gears, bearings or just deal with gear whine and clunking. i would rebuild and automatic trans before i would change gears out again. just my .02

by the way, the labor i am paying is $650.
I just buy new bearings so I don't have to mess with taking the old one off the pinion. But as far a the other tools I found that a plastic PvC pipe and A bfh gets most bearings on. You are right though unless you have someone there to teach you don't do it yourself. Took me A few times with a good friend that had done hundreds of them to help me get it down.

He owns a small Mustang shop still only charges 150 to do a gear swap. I tell him to charge more but he refuses to lol
 

pufferfish

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Justin said:
I just buy new bearings so I don't have to mess with taking the old one off the pinion. But as far a the other tools I found that a plastic PvC pipe and A bfh gets most bearings on. You are right though unless you have someone there to teach you don't do it yourself. Took me A few times with a good friend that had done hundreds of them to help me get it down.

He owns a small Mustang shop still only charges 150 to do a gear swap. I tell him to charge more but he refuses to lol

...but the shims are pressed between the bearing and the pinion gear. if you have never had to pull the bearing back off to reshim, you are the luckiest person alive!

he should definitely charge more. a properly installed ring and pinion with a full bearing and seal kit takes pros 3+ hours. book time is 5 hours. charging that little implies he is doing the old "use the same shims that came out of it and put it back together" method. not saying he is, but it gives the impression of cutting corners.
 

Justin

Save the dawn for your dishes!!!
pufferfish said:
...but the shims are pressed between the bearing and the pinion gear. if you have never had to pull the bearing back off to reshim, you are the luckiest person alive!

he should definitely charge more. a properly installed ring and pinion with a full bearing and seal kit takes pros 3+ hours. book time is 5 hours. charging that little implies he is doing the old "use the same shims that came out of it and put it back together" method. not saying he is, but it gives the impression of cutting corners.
no he and I have a honed out bearing. Get it right take it back apart install new bearing done. He doesn't cut corners. Just had 20 years experience....
 

pufferfish

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whoh, whoh! this is new to me! do you have the bearing honed or do you buy it that way? i have never seen it as an option. honestly, that and the crush sleeve nonsense are the 2 reasons i stopped doing this myself!
 

Justin

Save the dawn for your dishes!!!
pufferfish said:
whoh, whoh! this is new to me! do you have the bearing honed or do you buy it that way? i have never seen it as an option. honestly, that and the crush sleeve nonsense are the 2 reasons i stopped doing this myself!
you make it use a dremel to make it just big enough to slide on and off by hand. Then the crush sleeve just make it tight enough to take the slack out while fitting it all up. Then use a new one for final install. He taught me lots of tricks.
 

pufferfish

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Ah, I see. I don't trust myself to dremel out a concentric hole in hardened steel. No offense, but I wouldn't trust any dremeled out bearing job. Now a drum brake cylinder hone might be a better alternative. It would take an hour or two to get the .002" out of the inner race diameter, but it would be a guaranteed concentric hole.
 

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