Rear end And Gears Question

Makdaddymac · Apr 3, 2008

I just recently swapped my aod to a t-5 and assuming i have the 2.73's....
but i was wondering if i had a posi rear end. cause only one tire hooks, i mean it could be worn out clutch packs but i dunno......i was going to go with 3.73's, but i was thinking would a stock 2.73 5 speed be faster than a stock 3.73 on the highway? or would it be a tie all the way up too an obnoxious MPH, im tired of puswa cars pulling on 5.0's on the highway, like from 60-80mph..... i think my VW GTI could take a 5.0 from a roll! but not off the line for sure. i was thinking 3.55's but i dunno and i know this topic is a dime a dozen, and ive researed it but im still at a loss. i really am just going to do gears, gasket repairs,intake painitng,pullies and be done for a while, i want to enjoy my ride, and play with some n2o on this stock block and when it gives up i'll go for serious neck braking power. so yah
keep the 2.73's
3.55's
3.73's
:SNSign:

SteedaGT9150 · Apr 3, 2008

your rear end prob needs a rebuild, that should fix the one wheel peel, and most people go with 3.73 for a 5 spd

bloopbloob · Apr 3, 2008

um *someone i know* had 273's before and the car topped out around 220km/h, with tons of rpm left on the table because the power wasnt there due to low rpms
3:73s will raise your highway rpms into a better power range. *theoretically*, with 373's this same car will still be pulling at 245km/h and only about 4200rpms. closed course (obviously).

1991notchbackLX · Apr 3, 2008

bloop: 'round here we use the english system!

but i put 3:73s in my 5 spd and it made a big difference, it will most definitely put you in a more favorable power range...as far as highway driving, my motor only spins at around 2100 rpm at 60-65 mph on the highway in 5th gear, only 4:10 or 4:56 are really troublesome and annoying for highway driving

5.0Torx · Apr 3, 2008

i just did some gear calculations. at 70 with a stock sized tire, the T5, and 2.72s, youre pulling just over 1600 rpm. Thats nuts. 3.73s would put you at just over 2300, which is a little high for my taste but thats my opinion.

Regardless, at 5000 rpm (right around the hp peak of a stock or mild 5.0), the 2.73s put you at 207 mph, and 3.73s at 152 mph. 152 mph top speed is much more realistic. with 2.73s, your top speed would be lower because at 152 mph with 2.73s youre pulling just over 3600 rpm, which is a solid 1400 rpm lower than the power peak.

To sum it up, 3.73s will raise your top speed over 2.73s, EASY. Unless you have about 800 rwhp.

Now over 3.55s?

with 3.55s, youre just under 2200 rpm at 70. and 5000 rpm puts you at 159 mph. I'd recommend this fi your 5.0 has or will get some decent mods. Wind resistance is exponential, so that extra 7 mph would come from a ~60 rwhp over a stock 5.0 (usually 190-200 rw).

Last thing i'd say is, hopefully youre doing all this top speed testing on a closed course. If you were standing in front of me telling me how you routinely go over 100 mph on congested highways i'd smack ya. Dont worry about absolute top speed too much. I'd worry more about how much fun you can have with the different rear gears, what kind of gas mileage / how much noise your exhaust is making at the different rpms. Either 3.55s or 3.73s would be a huge improvement over the 2.73s. 1600 rpm at 70 is like what the GM boys are pullin. Fbodies arent exactly snappy in sixth gear, so i cant imagine what its like with a .7L smaller motor, whose smaller displacement comes entirely from a smaller stroke(im talking about the LT1 here of course. Its amazing to me how many people dont know that the LS1 isnt a 350. regardless, i dont really feel like delving into any more detail on GM motors. just flame-proofing myself here)

So get that thing some gears!

Makdaddymac · Apr 4, 2008

well my first 5.0 had the 3.08's(factory 5speed). and i heard that the 3.08's to 3.55's isnt worth the time and money. and im trying to put my self in that old rocket(well at least ithought so) so i need something that is going to make me smile these are the fastest cars ive owned. well my gti is fast but not torquey.... so maybe 3.73's

Strype · Apr 4, 2008

Makdaddymac said:
well my first 5.0 had the 3.08's(factory 5speed). and i heard that the 3.08's to 3.55's isnt worth the time and money. and im trying to put my self in that old rocket(well at least ithought so) so i need something that is going to make me smile these are the fastest cars ive owned. well my gti is fast but not torquey.... so maybe 3.73's

Obviously whoever told you that had never done it before. I'd choose 3:55's over any set that I've had.

cenok is family · Apr 4, 2008

don't be a wuss. 4:10's rock.

Foxfan88 · Apr 4, 2008

if planning to stay stock or fairly mild a set of 3.73 or 4.10s would work great.

but if your plan on making some serious power. like 400+ the lower (numerically higher) gears become more of a hinderance than anything.

my car stock and with mild mods ran great with 3.90s it worked well with it. i added a supercharger and the power went way up and the 3.90s started making things silly. it would roast tires and gears went by too fast for my taste. it just gets out of its powerband and i have to shift too fast. i hope to swap to 3.55s sometime this year. with more power you dont need the help of low gears to get things moving fast (on the street)

for a pure drag car dial in the ratio to your peak HP rpm in your final drive gear. depending on engine size and RPM rang and tires and trans, it could be anywhere from hghwayish gears to super tall 4.56s. for instance a mild built big block would use a little higher gear (numerically lower) its operating range is much lower than that of a smaller say 302ci engine. the higher gear would keep the engine in its powerband better. throwing a set of 4.56s would kill it, it would be out of its power range. a smaller engine turning fast, like 7-8k plus can use a tall gear like 4.56s, since its NEEDS to be revving high to make its power, the tall gears will get those rpms up where the smaller / faster turning engine makes it power. and its not all dependant on engine size. its mostly RPM, i just used "big block" and "small engine" as examples.... super nice built bigblocks can turn massive RPM if you want. just alot of joe schmoe drag racers use stock bigblocks or mild where the rpm range isnt that high. just sort of a real world example

82CapriRS · Apr 5, 2008

3:55s are the best all around gear. i also had 2.73s stock an just changed them to 3:55s and i love them. good on the highway and good in the city. with stock motor an the usual bolt ons i ran 14.5@95 2.0 60ft on street tires. just changing to 3:55s with the same tires i ran a best so far of 14.0@98.5 with a worse 60 ft being 2.1. it could prolly run better times now but it spins more which im sure all you guys know about especially if the cars really stiff. we can thank the eibach sportlines for that lol. hope this helps an swap those gears!

Makdaddymac · Apr 5, 2008

well its def, 3.55 vs. 3.73's the other is too much for me, and knowing me i will go 3.73's cause the car is gonna be a stock drag-queen im just gonna slap on a nice 75shot and gears for my major mods,so that little extra will help

the 5speed swap,x-pipe,
and still need___>>catback,paint,rims/tires,engine gasket replacing and painting,gears,nos kit. i think i wil have enough money invested into my 5.0. and it will be able to have its hood open at car shows and spank some ls1's and new gt's

NIKwoaC · Apr 5, 2008

Top speed is really constrained more by engine performance and aerodynamics than it is rear end gear ratio, simply because transmission gears can account for differences in rear end ratio. That is why stock Fox cars are actually fastest in 4th gear over 5th.

Here's why:

2.73s in 4th (direct drive, or 1:1) yields a 2.73 total ratio.

3.73s in 5th (IIRC usually 0.68:1) yields 2.54 total ratio.

So the 2.73 car would have more mechanical advantage in 4th gear than the 3.73 in 5th.

BUT rear end gears are for acceleration, not top speed. Because they are nothing but torque multipliers, you need more traction to be able to utilize the extra torque they provide in lower gears, that is why some people complain that they don't work well with higher power engines. Just like anything else, you need parts to compliment the rear end gears.

mustangfan1990 · Apr 5, 2008

5.0Torx said:
i just did some gear calculations. at 70 with a stock sized tire, the T5, and 2.72s, youre pulling just over 1600 rpm. Thats nuts. 3.73s would put you at just over 2300, which is a little high for my taste but thats my opinion.

Regardless, at 5000 rpm (right around the hp peak of a stock or mild 5.0), the 2.73s put you at 207 mph, and 3.73s at 152 mph. 152 mph top speed is much more realistic. with 2.73s, your top speed would be lower because at 152 mph with 2.73s youre pulling just over 3600 rpm, which is a solid 1400 rpm lower than the power peak.

To sum it up, 3.73s will raise your top speed over 2.73s, EASY. Unless you have about 800 rwhp.

Now over 3.55s?

with 3.55s, youre just under 2200 rpm at 70. and 5000 rpm puts you at 159 mph. I'd recommend this fi your 5.0 has or will get some decent mods. Wind resistance is exponential, so that extra 7 mph would come from a ~60 rwhp over a stock 5.0 (usually 190-200 rw).

Last thing i'd say is, hopefully youre doing all this top speed testing on a closed course. If you were standing in front of me telling me how you routinely go over 100 mph on congested highways i'd smack ya. Dont worry about absolute top speed too much. I'd worry more about how much fun you can have with the different rear gears, what kind of gas mileage / how much noise your exhaust is making at the different rpms. Either 3.55s or 3.73s would be a huge improvement over the 2.73s. 1600 rpm at 70 is like what the GM boys are pullin. Fbodies arent exactly snappy in sixth gear, so i cant imagine what its like with a .7L smaller motor, whose smaller displacement comes entirely from a smaller stroke(im talking about the LT1 here of course. Its amazing to me how many people dont know that the LS1 isnt a 350. regardless, i dont really feel like delving into any more detail on GM motors. just flame-proofing myself here)

So get that thing some gears!

WOW I didnt know that a ls1 isnt a 350 hmmmm learn something new everyday

Makdaddymac · Apr 5, 2008

well if traction will be useless with 3.73's what fun are they, this is going to be a street car! so i dont want to be losing all my fun 10-50mph legal burst
so 3.55's also work good too huh??

cenok is family · Apr 5, 2008

i'd get 3.73's over 3.55's any day. traction won't be an issue unless you have some chitty tires.

Makdaddymac · Apr 6, 2008

well how come so many people b*** about not having traction
i dont know what to belive any more, i trust everyone here, but with so many dif. opinons its makes it even harder to decide, cause opinions are just to different

vote
3.73's

or

3.55's

dtlionsfan · Apr 6, 2008

I've tried them all and 3.55 is the best all around gear,hands down.

Makdaddymac · Apr 6, 2008

ive heard, my uncle told me that 3.73's could make you run out of engine on a quarter mile

85Vertible · Apr 6, 2008

t-5 street car: 3.55
AOD steet car: 3.73

Mustang5L5 · Apr 6, 2008

Makdaddymac said:
ive heard, my uncle told me that 3.73's could make you run out of engine on a quarter mile

That's what a set of taller DR's on the back is for

Rear end And Gears Question

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