All knowing CF community (LOL), looking for some thoughts on transmission choice.

Currently, I have a 350 backed by a Tremec 3550 (ratios 3.27/1.98/1.34/1.00/.68) with a 3.36 rear. So, first gear multiplication ratio is right at 11:1 and overdrive is 2.28:1.

The project right now is a 496 big block with a 3.73 12 bolt rear. Looking for about 550-575 hp/tq with a 6000 redline.

I did purchase a T-56 Magnum from Hurst Overdrives and it is sitting in the garage. I got the close ratio version which has ratios of 2.66/1.78/1.30/1.00/.80/.63 . First gear multiplication ratio with this setup is 9.9 and overdrive is 2.35.

There is also a wide ratio version of the T-56 with 2.97/2.10/1.46/1.00/.74/.50 gears. This works out to first gear multiplication ratio with of 11.1 and overdrive is 1.86. Too much overdrive for a carbed big block.

Another option that I have explored is the TKO-600 (2.87/1.89/1.28/1.00/.64). First gear becomes 10.7 and overdrive is 2.39. Of course you do have the big drop between 4th and 5th.

You can also change the 5/6 gear ratios in the T-56. In that case, I would swap to a wide ration 1-4 and get the .8/.63 5/6 setup. No idea on the price but could be expensive.

I do know that the TKO will be much easier to install with the plethora of kits out there.

Just looking for thoughts/opinions as I work through this. Got two weeks or so till my heads show up and then everything will start coming together.

 

I have a lot to say about this but not much time to type it. I'm on my way out the door. I have had the TKO in mine and currently have an 06 GTO T56. The gear ratios if I'm not mistaken are 2.97 1st and the 6th is around .62. Rarely use 6th but on the highway but 5th is great around town. Stick with the T56 over the TKO if at all possible.

 

Gordon,

Appreciate the input. I really wish that Tremec would sell a T-56 Magnum with the 2.97 first/.63 OD combo. I am looking at options on how I could do that but the best right now is return my current T-56 to Hurst, get the wide ratio and then pay more money to get 5th and 6th gears changed.

 

I chose the T56 close ratio with 4.11 12 bolt for my 383.
10.93 to 1 first
2.59 to 1 6th

 

Voted for pie, but from the choices above I'd go with the first one. Curious, why didn't you include the Richmond 5 w/OD?

 

I had a vette with a ZF6 .50 OD. It just didn't cut with a hot rod LS motor when combined with a low 3.00 ratio rear. Switching to 4.10 made OD usable

My present TKO600 .64 is a bad deal because of the jump from 1.00 to .64 and now with 3.55 rear end it is a freeway only gear.

Big 496's with lots of TQ do not need lots of gears. Shifting takes time. Problem number 2 for your is rear gear change. That is another $1000 or more operation.

When you have enough TQ I would vote 5 speed and a .82 OD and keep the 3.36 rear for now and see how you like it. Where you live what is the real life max practical speed that you will ever see? Then figure out if .82 and 3.36 with 27 inch tall tires works for you.

 

I like pie too.

 

Not in the polls but a Richmond 6spd ROD would match up good with that 3.36......

 

3.36 is gone which is why no Richmond 6 speed (only one OD gear).

Decided to get a 12 bolt rear and only ratios available are 3.73 and 4.11 and so I went with the 3.73. Why the 12 bolt? Was going to do a Super 10 bolt rear but the supplier that makes tool steel 30 spline spiders has stopped making them. Tom's Differentials had a very limited supply and anything new is being made with powdered metal offshore. So, I decided to splurge on the whole 12 bolt setup and do the BBC swap at the same time. I did the full 12 bolt conversion with 30 spline inner and outer axles and 1350 U-joints, 1/2" wheel studs and trailing arms rebuilt.

I honestly believe that by this time next rear, it will be impossible to build a quality 12 bolt rear for the C3.


The rear is being built in CT by the same guy who did my steering box. He is active on the digital site.

 

I was starting to think that as well but talking to the rear end builder, I decided to stick with 3.73 for the BBC.

I found myself looking for a gear between the 1.00 4th and .68 OD that I currently had. So I think that this T-56 will work well. Just second guessing myself on the first gear multiplication ratio.

 

havea stout sbc with the 2.66 low T56...believe me you dont need a deeper first gear its perfect. had the same trans with a 3.08 and 3.73 also.
The 5th and 6th gear option is nice. It will cost more but be worth it.

Your BBC will pull it no problem. I can "just " pull 6th witha 260@.050 cam
4.11 gear 26 in tire
IMO 6th is almost too tall. great shifting trans though!

 

I voted for T-56 close ratio. I just did a TKO600 .64od swap last year, and while I am very happy with it, I wish I had done a T-56 instead. To be perfectly honest, part of the reason I did the swap was to get better gas mileage. The only place I can use the od is on the highway, on the city streets the rpm drops too low for me to use it at anything under ~50mph. If I had a .80 5th gear I could use it on city streets and see in increse in mpg there too, and use the .63 6th for the highway.

 

Snap!, same as me

dave

 

Now that see your choice the tranny would work even better with a 4.10

My .64 was very nice with a 4.11 The extra .80 would be nice in the 6 speed

 

I'm just a little curious on the "spider gear story" as the Super 10 bolt uses the same spider gear set as a 12 bolt Chevy differential. How can they supply the gear set for a 12 bolt housing and not have the same set for a 10 bolt housing?

 

I installed the TKO 600 with the .64 5th and a 3.73 rear and wished I installed the T-56. I'm used to my 96LT4 with the ZF Trans and a 6th gear. That is till I ran the numbers and found that the the total ratio from 1st to OD is about the same between the to. In my 96 I rarely use 5th I generaly go straight to 6th. I intend to go to a 3.36 or 3.21 Rear gear and that should make things the way I want them. The T-56 has one more gear,weighs 30lbs more and is harder to install. That 6th gear makes it woth it to some but not all.

 

The T-56 6th gear is really nice for long highway cruises, but pretty worthless otherwise. Understand there's lots of floor carving involved, getting these into C3's. I've had two T-56, 3.42 axle late model LS Vette's, with the latest being an LS7. Sure is nice cruising at 70 mph, seeing 25-26 mpg in a 500+ hp car. My buddy with a 79' L-82, 3.70 axle car, installed a Keisler TKO kit, and was plug and play, with no floor carving. It's a 0.68 od 5th, which isn't the T-56's 0.50 od 6th, but quite an improvement on the highway, considering the ease of install. As for the mentioned Richmond. Heard these are pretty crude units in operation, compared to the smooth/quiet shifting of the TKO.

 

Absolutely correct, it takes a large amount of fab to get the T-56 to fit into a C-3. The T-56 does have superior shift feel and torque handling capacity, but it's also much newer technology. I would say that in most cases the TKO is up to task for general purpose driving and ease of install. Additionally, the 6th gear ends up giving the car pretty long legs, and unless you are on a long stretch of deserted freeway, you most likely won't use the 2nd overdrive very much.