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Discussion Starter · #1 ·
For those who have installed a t56 in your chevelle what did you put in for rear end gears? I am about to have my 9 in setup with a new posi and can't decide what gears to put in.
 

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I have the close ratio t56 with the .63 6th gear and have a 3.31 rear. You need to be at 60 mph or so to use 6th, and that puts me, with the current rear tires, at around 1400-1500 rpm.
 

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I have a low reving 454 BBC and I installed a T56 magnum with .63 6th gear. With the 3.31s it was extremely enjoyable to drive and cruise around with. Because I have such a mild engine, it was able to cruise on the highway at 1500 rpm with ease.

I then switched to 3.91 gears and it picked up about 4 tenths in ET, and is still very good. It burns through 1st and 2nd gear much easier now on the street. I use 5th gear much more often than before. Highway cruising isn't quite as nice, but its still a million times better than not 3000+ rpm days.
 

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I WISH....I had that close ratio gearset, have a GM LT1 T56.

Op what kind of powerplant do you have, max rpm, cam etc.What is your driving style are you conservative, a lugger or dont mind hearing the engine a lil?
In town driving or lots of open road stuff?
1 thing I learned the hard way $$$ yrs back is gear for the cam NOT some ideal fwy rpm deal.

I run a 4.11, 26 inch tall tire.

This site has some fun calculators to play with. 6th is more of a steady cruise gear not so much for acceleration esp if you have the tall GM .50 OD

 

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Figure out what gears you have in your trans, what tire size you have, then use this calculator to help you determine which gears to go with. It's not just the rear gears, it's your tire height that plays in to the final drive ratio.

I have a "high" revving LS motor, have 3.73s and currently running 25" tall tires. Got stupid lucky with a trans from an 05 GTO, (TUET2066), 0.56 6th gear. I can throw it into 6th at 40mph and it's happy all day long, 2k rpm @ 70mph.


Here's the different T56 gear ratios over the years:
 

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Discussion Starter · #9 ·
I didn't realize how many different trans ratios there are in these things. I looks like I need to figure out what O/D I have in 6th and do more math.
I am using an ls1 with a small cam and don't kreally know what power it really makes yet.

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The tag on my trans is on the passenger side, hanging off bolt on tailhousing. Hopefully yours is there so you can find what ratios you have. I used that blocklayer site to also help me understand my upshift/downshift mph while driving/racing. It's a great calculator.
 

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Figure out what gears you have in your trans, what tire size you have, then use this calculator to help you determine which gears to go with. It's not just the rear gears, it's your tire height that plays in to the final drive ratio.

I have a "high" revving LS motor, have 3.73s and currently running 25" tall tires. Got stupid lucky with a trans from an 05 GTO, (TUET2066), 0.56 6th gear. I can throw it into 6th at 40mph and it's happy all day long, 2k rpm @ 70mph.


Here's the different T56 gear ratios over the years:
That chart is not complete fwiw but it may just be addressing earlier front engine/rear drive applications. Late model Camaro SS w/6-spd have a 3.01 first gear ratio and most newer Z06/ZR1 Corvettes w/6-spd or 7-spd have a 2.29 first gear - not sure about the newer Ford offerings. I have a G-Force Street T56 with 2.71/1.79/1.30/1.00/0.89/0.75 ratios and my rear gear is 3.55.
 

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That chart is not complete fwiw but it may just be addressing earlier front engine/rear drive applications. Late model Camaro SS w/6-spd have a 3.01 first gear ratio and most newer Z06/ZR1 Corvettes w/6-spd or 7-spd have a 2.29 first gear - not sure about the newer Ford offerings. I have a G-Force Street T56 with 2.71/1.79/1.30/1.00/0.89/0.75 ratios and my rear gear is 3.55.
Late model Camaro/vette run TR6060 transmission.

 

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Sorry, my bad! I tend to lump them all into the same category as they are an updated/newer version of the T56. My G-Force T56 has a newer T56 Magnum case and extension housing but the 9310 alloy main shaft retains a Viper 30-spline output shaft (as opposed to the Magnum 31-spline) configuration. Triple cone synchronizers through out. Does that make it a "Frankenstein T56"?
 
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I have 3.42s with a close ratio T56 Magnum. If you do the calcs, back in the day a good combination was a close ratio muncie with 4:11 gears, so 4.11 x 2.20 = 9.042:1 for an overall first gear ratio. Or a wide ratio muncie with 3.55 gears so 3.55 x 2.56 = 9.088:1 for an overall first gear ratio. With a close ratio T56 the calc goes 3.42 x 2.66 = 9.092:1 for an overall first gear ratio. That keeps the lower gears more usable.

At 1900 rpms in 6th with a 26.67 tire I'll be running right at 70 mph so that's a good rpm for cruising. Also, if I can get it to hook up, I should be able to be close to top end for 4th gear through the 1/4 mile.

Lastly by using the 3.42 gears you keep the driveshaft RPMs down to reduce the chance of hitting the critical speed for the driveshaft.

It depends on what you're going to use the car for, engine configuration, etc. Mine goal is a good road car, with some autocrossing, and a drag race every now and then. I am still building my car so this all theory, but the math works. My target for the engine is 900hp at the crank from an LS based 396 that has a positive displacement supercharger.

Use the tremec calculator and it'll give you some ideas.

 

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Discussion Starter · #15 ·
I have 3.42s with a close ratio T56 Magnum. If you do the calcs, back in the day a good combination was a close ratio muncie with 4:11 gears, so 4.11 x 2.20 = 9.042:1 for an overall first gear ratio. Or a wide ratio muncie with 3.55 gears so 3.55 x 2.56 = 9.088:1 for an overall first gear ratio. With a close ratio T56 the calc goes 3.42 x 2.66 = 9.092:1 for an overall first gear ratio. That keeps the lower gears more usable.

At 1900 rpms in 6th with a 26.67 tire I'll be running right at 70 mph so that's a good rpm for cruising. Also, if I can get it to hook up, I should be able to be close to top end for 4th gear through the 1/4 mile.

Lastly by using the 3.42 gears you keep the driveshaft RPMs down to reduce the chance of hitting the critical speed for the driveshaft.

It depends on what you're going to use the car for, engine configuration, etc. Mine goal is a good road car, with some autocrossing, and a drag race every now and then. I am still building my car so this all theory, but the math works. My target for the engine is 900hp at the crank from an LS based 396 that has a positive displacement supercharger.

Use the tremec calculator and it'll give you some ideas.

this is what mine will be for. I am working for a good highway cruise and figure all the rest of the gears will work out from there. My whole town is 25 mph with 3 35 mph streets only thing higher is going to wally world we have 55, So if i never use 6th here that will be good and 6th for out on the interstate.
 

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Discussion Starter · #16 ·
I pulled trans out to check which 6th I had. It has the .50 do it looks like 3.42 will be the answer.
6th Gear will get me 81 mph at 1800 rpm. What fo you all think of that choice.


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Is it a T56 Magnum wide ratio (i.e. 2.97 first, .50 sixth)? Also as others have posted what cam are you running? I assume you're using 26" diameter tires for 81 mph calc..

It looks like you'll be at 1550 rpms at 70 so I'd want to make sure the cam is settling down by that point. It's a balancing act to make sure first isn't a stump pulling gear or sixth is unusable.

With a small cam in an LS1 it's probably a good ratio. It's similar to a wide ratio muncie with 4.11s in first gear. If you ran around a 3.90 with a 2.97 you'd be similar to a a set of 4.56 gears with a wide ratio muncie. I had that setup many years ago in a '68 camaro. You row through the gear pretty quick but sure helps the launch when you're down on power.
 
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