3.55 vs 3.73 Gears. Which are best? - Ford Mustang Forum
 
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post #1 of 11 (permalink) Old 04-03-2005 Thread Starter
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3.55 vs 3.73 Gears. Which are best?

I just read through 9 pages of an older thread in the tech section and it sure seems hard to understand people thought patterns on 3.55 vs 3.73 vs 4.10 gears.

At the stoplight torque gets you going. Horsepower - who cares. Torque is what makes a big block a big block and everything else just slower. As they say, there's no substitution for cubic inches. "More cubes" is generally due to a longer stroke. Why do you put a piece of pipe on a wrench to lengthen it to loosen a bolt? Because torque is torque. So if you want a 302 to compete, you put in gears which multiply and increase torque the the rear wheels in an attempt to get the levels available from a big block. Same thing applies to a rice burner. Sure you can throw nitrous in a Civic, but with four cylinders and a short stroke, the torque available means you better have a pretty lightweight car to comptete with. So again torque is torque.

So what gears to pick? In the other forum thread people seemed all concerned about running out of top end power or low gas mileage. The legal speed limit is 65 MPH. How many people are really going faster than say 120 MPH.

A stock 5 speed GT has a 3.35:1 first gear and a .68:1 fifth gear in the T5. With 3.73:1 differential gear you would have a 12.50:1 final drive "launching ratio" and an overdrive "cruise" final drive ratio of only 2.54:1. In other words with 3.73:1 diff gears how could you possibly claim to run out of motor - in OD you're not even hitting 2200 RPMs at 60 MPH! And as for gas mileage, I find it hard to believe 2200 RPM is killing your motor or sucking up that much more gas. Even with 4.10:1 how could you run out of motor?

I'm comparing these numbers to my '66 Mustang with 25" diameter tires, a 4 speed toploader with a 2.78:1 first gear and 1:1 4th gear. With a 3.50:1 rear diff gear, I'm looking at only a 9.73:1 launch ratio and a 3.50:1 final drive ratio. Not as much take off and worse gas mileage. Even with no overdrive the 3.50:1 ratio only put me at 4650 RPM at 100 MPH.

Lower gears only increase the power to the rear wheels so I don't understand how could these people be saying stick with a lower gear like a 3.55:1 because you'll lose power in the top end. That just doesn't make sense. More gear means more power multiplication! That's what makes a gear swap the biggest bang for your buck!

Unless I'm missing something here, I don't see the downside to 3.73 gears!!

The reason I'm asking these questions is that I just bought both a 3.55 and 3.73 gear set today. (Got a really good deal so I bought both figuring I could re-sell the one I don't use.) Can anyone explain to me any reason I would not put the 3.73 gear in!

Thanks!
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post #2 of 11 (permalink) Old 04-04-2005
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For a street car i agree with you that a 3.73 is most of the time better than a 3.55, but if you do lots of stop and go, your 1st becomes mostly useless and you will be shifting sooner, at least on a 5.0 with a T5. Thats why the most popular street gear ratio is still 3.55 for a 5 speed and 3.73s for most automatics and modular mustangs.

On the MPG issue, many of us mostly agree that theres little difference in MPG, on stop and go traffic a 3.73 will help you move the car, improving mileage, but on highway you will see a decrease. If you average your driving habits most probably will end up spending the same on gas.

Go with 3.73s

Rob Hernandez, AFM co-Founder.
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post #3 of 11 (permalink) Old 04-04-2005
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What about with supercharged applications? Would 3.73 be too much? Ive been holding off getting gears cause I am not sure which to go with. I was defenitely gonna go 3.73 before I got the sc but now Im not sure.

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Magnaflow catback,70mm throttle body,C&L plenum,Plasma ignition booster, white face gauges, billet fuel cap,
sct chip, Vortech v2-sq with fastrak intercooler, anderson powerpipe, 42lbs injectors, 255fuel pump,steeda full length subs, eibach lowering springs 1.5" and a new set of 18" by 9s up front and 18" by 10s in the rear.
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post #4 of 11 (permalink) Old 04-04-2005
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Quote:
Originally Posted by Learn-n-Burn
What about with supercharged applications? Would 3.73 be too much? Ive been holding off getting gears cause I am not sure which to go with. I was defenitely gonna go 3.73 before I got the sc but now Im not sure.

Well, it depends, if you want boost SOONER, a larger gear will help you get it, but if its too soon you might get tons of wheelspin.

My brother has a Vortech YR Trim in a 2K GT with a T56 and uses 3.73s, he's pretty happy with the setup. He gets boost at around 3k RPMs and the YR Trim is capable of delivering up to 20psi !! (he has now a 14 psi pulley), but thats him (around 500 RWHP).

He doesnt take it to the dragstrip, where i bet he will have a great deal of wheelspin ifrom 1st to 3rd gear.

In most cases a 3.55s will be enough for most people with SCs.

Rob Hernandez, AFM co-Founder.
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post #5 of 11 (permalink) Old 04-07-2005
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Quote:
Originally Posted by KK95GT
I just read through 9 pages of an older thread in the tech section and it sure seems hard to understand people thought patterns on 3.55 vs 3.73 vs 4.10 gears.

At the stoplight torque gets you going. Horsepower - who cares. Torque is what makes a big block a big block and everything else just slower. As they say, there's no substitution for cubic inches. "More cubes" is generally due to a longer stroke. Why do you put a piece of pipe on a wrench to lengthen it to loosen a bolt? Because torque is torque. So if you want a 302 to compete, you put in gears which multiply and increase torque the the rear wheels in an attempt to get the levels available from a big block. Same thing applies to a rice burner. Sure you can throw nitrous in a Civic, but with four cylinders and a short stroke, the torque available means you better have a pretty lightweight car to comptete with. So again torque is torque.

So what gears to pick? In the other forum thread people seemed all concerned about running out of top end power or low gas mileage. The legal speed limit is 65 MPH. How many people are really going faster than say 120 MPH.

A stock 5 speed GT has a 3.35:1 first gear and a .68:1 fifth gear in the T5. With 3.73:1 differential gear you would have a 12.50:1 final drive "launching ratio" and an overdrive "cruise" final drive ratio of only 2.54:1. In other words with 3.73:1 diff gears how could you possibly claim to run out of motor - in OD you're not even hitting 2200 RPMs at 60 MPH! And as for gas mileage, I find it hard to believe 2200 RPM is killing your motor or sucking up that much more gas. Even with 4.10:1 how could you run out of motor?

I'm comparing these numbers to my '66 Mustang with 25" diameter tires, a 4 speed toploader with a 2.78:1 first gear and 1:1 4th gear. With a 3.50:1 rear diff gear, I'm looking at only a 9.73:1 launch ratio and a 3.50:1 final drive ratio. Not as much take off and worse gas mileage. Even with no overdrive the 3.50:1 ratio only put me at 4650 RPM at 100 MPH.

Lower gears only increase the power to the rear wheels so I don't understand how could these people be saying stick with a lower gear like a 3.55:1 because you'll lose power in the top end. That just doesn't make sense. More gear means more power multiplication! That's what makes a gear swap the biggest bang for your buck!

Unless I'm missing something here, I don't see the downside to 3.73 gears!!

The reason I'm asking these questions is that I just bought both a 3.55 and 3.73 gear set today. (Got a really good deal so I bought both figuring I could re-sell the one I don't use.) Can anyone explain to me any reason I would not put the 3.73 gear in!

Thanks!
The only thing that concerns me is the running out of first gear. With stock 3.08 I need to shift at 20mph. Will 3.73 give 2nd gear a chirp and git? I have a 302w/T-5.
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post #6 of 11 (permalink) Old 04-11-2005
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i can't wait until i get to replace the gears on my new 95 gt. a friend of mine has an 86 SVO, and I'm a bit scared to race him (he's got 3.73's and I'm a bit inexperienced with a clutch).

what is the stock rear end in a 95? 3.08 or something?

95 Mustang GT / 89 Mustang LX 2.3
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post #7 of 11 (permalink) Old 04-12-2005
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3.73's is the way to go.
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post #8 of 11 (permalink) Old 04-12-2005
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Just had 3:73's installed:thumbsup

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post #9 of 11 (permalink) Old 04-13-2005
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3.73's are perfect for around town and highway..it's only a few hundered rpm more at 70mph. I think witha blower on a 5.0, you would be close to redline or just under in the quarter. I run 3.73's witha 125 shot of nitrous and I'm trapping @115mph...very close to redline. But for stock or lightly modified..3'73's. If it was just around town I would say 4.10's would really be awesome. As they say, don't fear the gear. lol
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post #10 of 11 (permalink) Old 04-13-2005 Thread Starter
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I'll throw in a couple technical questions to go along here.

Ford 8.8 3.73 and 3.55 gears sets - are they hunting or non-hunting ratios? Why do I ask? Determining this partially dictates how they are set up. Non-hunting and partially non-hunting are supposed to have "timing" marks on them. If you don't get them lined up they will wear quicker and will be noisier. I don't see any timing marks on the 3.73 and 3.55 I have but that may just be because the paint marks are worn off...

Second, these are used Ford gears. I bought them that way on purpose. They look like new condition and from what I've read from a couple sources they should be quieter than new.

Being that they are used, the pinion bearing is installed. It looks fine with no wear. I've had a couple technical people tell me I can leave the original race in the carrier and just put the pinion in with the current bearing - manufacturing tollerances are close enough today that they will match. Also, I've been told that Ford has tight manufacturing tolerances and if I keep track of the shims, I should be able to change gears without the need for a "high tech" setup - pinion depth will be good so all I will have to do is check backlash.

Anybody ever had any experience installing used gears?
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A friend of mine has the same mods as me except he has a x-pipe and equal lenth heads and 4.10 gears. His car is way faster than mine it cant be because of the E-headers and x-pipe right? I have good headers and h-pipe he should have the most about 12 horsepower over me. I think its the 4.10 gears he has. It is a big differents 3.55 to 4.10 if thats what is making him faster his car is a monster.


91 Mustang 5.0 with a K&N,headers, H-Pipe, flowmasters and 4.10 gears.
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