TKX vs T56

[DentalDart]

Care to shed some light on why someone would choose 1 over the other?

Is one more comfortable to drive? Or more fun to drive?

If you start explaining gear ratio numbers I will not know or understand anything you’re saying so say it is stupid people terms like you have to shift out of first fast, your car loses power when shifting into last gear.

Photo for fun… 70 degrees and sunny in SW Missouri for Christmas.

 

[340sFastback]

T56 has better gearing and two over drives. But T56 is around 50 pounds heavier, a bit larger in size, and a bit more expensive. TKX is very good trans

 

[72bluNblu]

I mean, beyond the extra gear?

The TKX still requires tunnel and crossmember work, but substantially less than the T56 needs. My rationale for the T56 was that if I was cutting and welding I was cutting and welding. I was comparing to a TKO though at the time because the TKX wasn’t a thing yet. While the TKX takes less modification it’s not like the car stays stock.

The T56 magnum (aftermarket version) is good for 700 ft/lbs of torque, so, 100 more than the TKX if that matters.

The T56 is also widely supported, I know there’s a couple different versions though and not everything interchanges. But some of the production models are pretty beefy and there’s a lot of support. The TKX is based off a T5 so there’s lots of production on the T5 as well, but the production T5’s aren’t that strong and I don’t know how useful any of the production parts are for the TKX. Either way if you’re not beating hard on the transmission the aftermarket support might not matter too much for either one.

With the T56 in my Duster I have the .80 and .63 overdrive gears. Even with that set up, 4.30’s and 27” tall tires I typically only get into 6th on the freeway. Most of the time I’d manage just fine with only a .8. But it is nice having the extra gear and I probably wouldn’t have gone to 4.30’s if I didn’t have the .63 as well.

 

[DentalDart]

T56 has better gearing and two over drives. But T56 is around 50 pounds heavier, a bit larger in size, and a bit more expensive. TKX is very good trans

I don’t understand the gearing. Most of my shifting will be up to 60 mph on side streets, not much freeway driving, maybe 10-15 minute freeway drives every couple of months.

The OD of the 56 I’ve read mixed reviews, people saying 6th isn’t usable unless going 70+ mph or on long drives?

 

[340sFastback]

I don’t understand the gearing. Most of my shifting will be up to 60 mph on side streets, not much freeway driving, maybe 10-15 minute freeway drives every couple of months.

The OD of the 56 I’ve read mixed reviews, people saying 6th isn’t usable unless going 70+ mph or on long drives?

There are two T56s one wide ratio and one close ratio. Then the torque curve of engine and rear gear ratio come into play. So 6'th isn't usable means the trans and rear gear aren't matched to the engine. So yeah if someone doesn't have a clue what they are doing when they built their car we can have cases where 6 is not usable.

 

[DentalDart]

There are two T56s one wide ratio and one close ratio. Then the torque curve of engine and rear gear ratio come into play. So 6'th isn't usable means the trans and rear gear aren't matched to the engine. So yeah if someone doesn't have a clue what they are doing when they built their car we can have cases where 6 is not usable.

Ok so say the engine is a 470 or 499…. 3.55 rear gears… idk if those are the best gears but it’s a set I was thinking…

 

[1WildRT]

5 speeds = really good acceleration from a dead stop to over 90+ MPH
6 speeds = really good acceleration from a dead stop to over 140+ MPH

6 speed is considerably bulkier requiring more tunnel modification....

Both are extremely fun....

 

[DentalDart]

5 speeds = really good acceleration from a dead stop to over 90+ MPH
6 speeds = really good acceleration from a dead stop to over 140+ MPH

6 speed is considerably bulkier requiring more tunnel modification....

Both are extremely fun....

This is perfect. I’m never going that fast lol

 

[72bluNblu]

Ok so say the engine is a 470 or 499…. 3.55 rear gears… idk if those are the best gears but it’s a set I was thinking…

With a 470 or 499 you’ll have more than enough torque to use 6th gear and drop the rpm’s down for extended freeway use. Run some 3.91’s and a T56 with a .63 6th.

Keep in mind that the production T56’s are usually the .50 6th, so even lower rpm’s at speed, and those are what modern Challengers run with Gen III hemi’s. And Camaro’s, etc.

 

[340sFastback]

My setup is 414 small block stroker 500 hp and 500 tq, T56 close ratio 2.66 first gear .63 six'th gear, I had 391s but dropped down to 373s when Dana got swapped in, 27 inch tall tire. Its basically like a close ratio 4 spd with two over drives. When I up shift through first 4 gears RPMs don't drop much keeping engine in max torque curve. Higher speed roads 5'th gear cruising. I can cruise on highway 70-80 mph engine is quiet can pull steep grades no down shifting needed. Its basically no compromise ANYWHERE speed wise. All the acceleration tire burning fun through first 4 gears and ultra comfy high speed cruising. The 6 speed is much better then I had expected so glad I did it.

You are not going to get as close of gear ratios in a TKX which means bigger RPM drops on upshifts less tire burning fun. So the TKX is a compromise compared to a T56 which does not give up any performance either low or high speed driving. To me if you want the best in terms of gearing for acceleration AND high speed cruising the T56 out shines the TKX.

 

[Car Nut]

I personally prefer the TREMEC TR-6060 over the T56, if you wanna cut it up, go big or go home. Handles way more torque and horsepower. If you want an easier install, you can’t go wrong with the TKX. When I drove the 6 sp. new Challenger, I hardly ever used the six speed.

 

[72bluNblu]

I personally prefer the TREMEC TR-6060 over the T56, if you wanna cut it up, go big or go home. Handles way more torque and horsepower. If you want an easier install, you can’t go wrong with the TKX. When I drove the 6 sp. new Challenger, I hardly ever used the six speed.

The TR6060 is internally similar to the T56 Magnum, which is the aftermarket version. That’s the 700 ft/lb rating, it’s not better than that. And I believe the 6060 has the .50
6th. Maybe not but the challenger has sub 4 rear gears in some of its trims so unless you’re doing 80+ on the freeway 6th won’t be super helpful. But just don’t run that rear gearing, problem solved.

 

[340sFastback]

I personally prefer the TREMEC TR-6060 over the T56, if you wanna cut it up, go big or go home. Handles way more torque and horsepower. If you want an easier install, you can’t go wrong with the TKX. When I drove the 6 sp. new Challenger, I hardly ever used the six speed.

Ppl keep making statements hardly used six gear without any specifics. Some T56 have .5 six some have .63 six, some engines more low end torque, different rear end ratios, different height tires, diff weight cars ect ect ect. Saying you hardly used six gear means eng trans rear not well matched. It does not apply to correctly matched setups AT ALL!!

 

[72bluNblu]

Ppl keep making statements hardly used six gear without any specifics. Some T56 have .5 six some have .63 six, some engines more low end torque, different rear end ratios, different height tires, diff weight cars ect ect ect. Saying you hardly used six gear means eng trans rear not well matched. It does not apply to correctly matched setups AT ALL!!

Yeah it’s not a problem with the transmission!

That’s why I run 4.30’s. My 340 is stock stroke and it’s a little high strung for a commuter so I keep it above 2k rpm’s unless I’m literally just rolling downhill. But lots of modern set ups are set to cruise down to like 1,500 rpm.

It’s also one of the reasons I didn’t get the .50
6th version of the T56 magnum, I was gearing it to cruise at ~2,500 rpm not 1,500. And I wanted the close ratio’s anyway.

The 2nd gear was the other thing I looked at, I wanted to run 2nd from ~30-60mph without dropping out of the powerband, because that would mean most AutoX courses would be 2nd gear and very little shifting. It makes 1st a little short but that makes the higher strung 340 easier to deal with in slow traffic anyway.

 

[1WildRT]

So, more gears keeps your engine in a tighter operating range... Great... Why did I build an engine with a wide torque curve? I like winding out the gears, Every time you shift your loosing acceleration between the shifts...

The reason modern cars have six/seven/eight & even ten speeds is fuel economy & emissions...

Most guys are happy with a four speed but have to compromise either at take off, highway speed or wide gear spreads.... Five gears is enough to keep the engine in a reasonable range from zero to a hundred MPH...

Not saying there's anything wrong with more gears, just saying it's not necessary....

 

[72bluNblu]

So, more gears keeps your engine in a tighter operating range... Great... Why did I build an engine with a wide torque curve? I like winding out the gears, Every time you shift your loosing acceleration between the shifts...

The reason modern cars have six/seven/eight & even ten speeds is fuel economy & emissions...

Most guys are happy with a four speed but have to compromise either at take off, highway speed or wide gear spreads.... Five gears is enough to keep the engine in a reasonable range from zero to a hundred MPH...

Not saying there's anything wrong with more gears, just saying it's not necessary....

Having an old car to drive isn’t necessary either.

Sorry, I’ve run my car with a 4 speed and a 6 speed and you can pry my 6 speed from my cold, dead hands. By far the best upgrade I’ve done. Even including updating the suspension into the current century.

And you can shift wherever you want, I wind out the first 4 gears just like I would if I had a 4 speed. But then I have two more gears to cruise so I can hang out with modern cars on the freeway without screaming away at 4k rpm’s. And yeah, I’ve had 5 speeds too and the 6 speed is absolutely an upgrade from that too. It doesn’t have to be just an “economy thing” if you set your gear ratio’s properly to your powerband and how you drive your car.

 

[DentalDart]

Don’t need a fighting match. I just want to be able to fun shift through gears without feeling bogged down and then cruise on the highway. Seems like it can be done with both, is the extra gear worth 1-2k more?

None of my cars are manual and it’s the one thing I wished the gts convertible was…. But those aren’t for sale so I think I should make the swinger manual. That’s it.

 

[mopowers]

Most guys are happy with a four speed but have to compromise either at take off, highway speed or wide gear spreads.... Five gears is enough to keep the engine in a reasonable range from zero to a hundred MPH...

That's a great way to put it.

 

[72bluNblu]

Don’t need a fighting match. I just want to be able to fun shift through gears without feeling bogged down and then cruise on the highway. Seems like it can be done with both, is the extra gear worth 1-2k more?

None of my cars are manual and it’s the one thing I wished the gts convertible was…. But those aren’t for sale so I think I should make the swinger manual. That’s it.

When I priced out my T56 magnum it was about a grand more than the 5 speeds available at the time. The fabrication is more extensive but it’s all the same stuff, it’s not like you can install the 5 speed without tunnel work and a modified crossmember.

And I’ve had 5 speeds before, the T56 was absolutely worth the extra investment. Better transmission, better gear splits, just better all around.

That's a great way to put it.

If you haven’t actually run a 6 speed in a classic car, sure.

If you set up your gearing correctly and actually drive your car it’s a huge improvement compared to a 4 speed.

 

[DentalDart]

When I priced out my T56 magnum it was about a grand more than the 5 speeds available at the time. The fabrication is more extensive but it’s all the same, it’s not like you can install the 5 speed without tunnel work and a modified crossmember.

And I’ve had 5 speeds before, the T56 was absolutely worth the extra investment. Better transmission, better gear splits, just better all around.




If you haven’t actually run a 6 speed in a classic car, sure.

I will call SST next week and try to get details on a quote for the T56 as well and also gearing. The sales person was saying “most mopar guys do the tkx for less modifications unless going for high horsepower or an extra intermediate overdrive gear around town.”

I don’t do much cutting, welding, body work or anything like that. I was hoping to have the shop who’s doing the body work do the quick swap but maybe I’ll have to give it a go.

How do people choose between SST and American Powertrain? Anything I should ask specifically?

 

[72bluNblu]

I will call SST next week and try to get details on a quote for the T56 as well and also gearing. The sales person was saying “most mopar guys do the tkx for less modifications unless going for high horsepower or an extra intermediate overdrive gear around town.”

I don’t do much cutting, welding, body work or anything like that. I was hoping to have the shop who’s doing the body work do the quick swap but maybe I’ll have to give it a go.

How do people choose between SST and American Powertrain? Anything I should ask specifically?

I’m not really surprised from a sales perspective, but it’s not that different as far as modifications go. You still have to cut the tunnel and you still have to cut and modify the crossmember. If you’re doing a bunch of welding adding a few more inches of weld doesn’t make that much of a difference. You’re probably doing 85% of the work either way and you have to do all the same prep. If you’re tearing the car down that far and have the skills to do one you can do the other.

And if you or someone else wanted to return the car to “original” specs for some reason it would take the same work either way. You’d need to replace the crossmember and the whole tunnel section to undo either install.

I’ve purchased parts from both SST and American Powertrain, I haven’t had issues with either business. But I didn’t buy a kit from either one, I bought the transmission from Summit (supplied by American Powertrain), and collected everything else I needed for the swap myself. My whole T56 magnum install is here, including my entire parts list

My "new" '74 Duster- or why I need a project like a hole in the head

 

[TT5.9mag]

I’ve only dealt with American Powertrain so this is not a comparison, but they were fantastic and I only have good things to say about them. I didn’t buy my T56 magnum or most of the parts from them, and they still were great.

 

[DentalDart]

@72bluNblu what do you use to cut the floor boards? Angle grinder? Plasma cutter?

 

[TT5.9mag]

Angle grinder? Plasma cutter?

Yes, with a thin cut off wheel.
And yes when large cuts are needed and cleanliness or accuracy is less important.

 

[DentalDart]

I have a tkx crossmember already and I have a car I can cut into to practice on….

https://www.holley.com/products/discontinued_product/parts/67520001