rmrtrex

Hey guys/gals,
Question for those of you that have bit the bullet and purchased a Tremec 5 or 6 speed. I currently have a BW Super T-10 and it runs pretty good with the exception of the highway where it is a little noisy. What do you all recommend a 5 speed with a close/wide ratio or a 6 speed. My car has a 3.08 rear end gear and it has about 370hp. Do you want first gear on your tranny to be 3.27 or opt and get 2.88? Also do you want 5th gear to be .68 or .72? I am contemplating upgrading my tranny. Do you really need a 6 speed since they are both going to end up on .72/.68 final gear or not? I would like a quicker take off, but I don't race my car. One of those things to want to have and not need than not have and need. Lol.

What do you all think?

cagotzmann

So take a C6 Corvette out for a test drive. Manual T56 with 3.42 rear gear.

This matches the tremec T56 close ratio transmission except for 5th, 6th

Tremec T56
1st 2.66
2nd 1.78
3rd 1.30
4th 1.00
5th .80 different
6th .63 different

Z06 1st gear - 2.66
Z06 2nd gear - 1.78
Z06 3rd gear - 1.30
Z06 4th gear - 1.00
Z06 5th gear - 0.74
Z06 6th gear - 0.50

My 78 Corvette started as a L48 auto, now runs a LS3-480 with a tremec T56 close ratio with a 3.36 rear gear.

I also have a 3.08 gear diff I used. Both worked very well together. 33MPG with LS3 & 3.08. And 5.5MPG at the road course. Worked great for street & track days.

427Hotrod

I'd say the TKX 5 speed with the 3.27 first gear with the 3.08's...and the .72 O/D. If you go to the .68 O/D you'll be down at a 2.09 final drive. It's not going to be happy there unless it's an incredibly mild engine. The .72 equals 2.21 which would is still a long gear for cruising.

I'm assuming this is an old school SBC with a carb?

JIM

Torqued Off

The C6 gear ratios are horrible if you drive in back roads at 50-60 mph….i know I have one, and it’s a constant back and forth shifting, with 5th gear bogging at 1400 rpm , or running at 2000 rpm in 4th. I would never recommend that transmission with that ratio setup.

When you seek these recommendation, you first have to decide how you will drive your car, what speeds, and what kind of roads, I.e. twisties or high speed highways…the best transmission and gear ratios, including what differential ratio is installed, is all based on that.

In my case, with my C3, a fifth gear would be almost useless except on longer trips on high speed four lane highways, which I avoid unless it’s the only option.

The conversion is not cheap. Make sure the change is actually useful, and not just a cool thing to brag about to your buddies.

Bikespace

A little noisy? It's probably not worth it. My 80 4-speed has 3.07 rear gears, and I just accept a bit of noise Or take the back roads, as @Torqued Off suggests, and as my car and I prefer. It seems we disagree on RPMs, though, as my car only sees 4th on the Interstate. If I blow up my B&W Super T-10, that car will get a Tremec Magnum 6-speed. But it works for now.

I have a TKX for my wife's 79, which has a 3.55 rear. I chose the 2.87 1st, 0.68 5th. This eliminates the awful TH-350, so it was absolutely worth it for that car.

Rescue Rogers

I had a 327 with a bit more horse and a 3:70 rear then a 4:11. I switched my M21 Gearing from the 2.2o:1 first to the M20 2.52 first and the car responded nicely. A small change but it was noticeable. Your very high rear gear is a big block gear because of the torque needed to get her going so I assume you have a big block.Edit Saw you have an L48...you definitely need more gear to get to the meat of your power band

My McLeod Muscle Car 5 speed is the daddy of the TKX. 2.95 first and .63 rear.....first is really deep and revs up fast...good for launching. .63 5th wasn't usable on side roads due to the lack of torque a small block has at low RPM. Very different on a big block....I can chug along at 1500rpm in 5th at 40 mph.... I also gained about 4 mpg highway since last years engine issues....overdrive bonus.
You definitely need the lower first and the higher rear and or a gear swap to more of a performance gear...3.70 rear diff is the most preferred for cruising and red light heros.
If you take your tranny ratio and multiply it buy your diff ratio you get your final drive ratio. Performance first gearing is north of 10:1... get as close as you can.

Torqued Off

Everything depends on the differential installed, and the ratios built into the transmission. Secondly....it depends on what YOU consider YOUR ideal of shift points and RPM's. It seems as though I am the rare individual who prefers NOT to shift at 5000 RPM. My shift points in my C6 and my C3 are typically 3000 RPM max, and I prefer the ratios to support that. The other factor is what engine you have, and how much torque it produces at what RPM. My concept of a good engine and transmission combination is an engine that has enough torque to accelerate the car rapidly WITHOUT requiring it be run up to 5000 or more RPM. Any engine that requires 5000 RPM or more to make the car accelerate is PATHETIC. A strong engine is one that does not require that to accelerate the car. Of course, again....that is my opinion, and typically not what you will hear from the racer boy crowd,....who typically likes alot of RPM and noise in their cars,...for some unknown reason. These comments apply to street cars limited to some speed close to the limits.....on a track...different story.

You choose what you want. I know I am outnumbered on this.

Rescue Rogers

If you achieve max hp and torque at 3000 rpm you are driving a diesel trucknor tractor...if you want to make those kind of assumptions about engines being pathetic over 5000 rpm you don't understand how torque is hp and that the equation crosses over at 5250 rpm. You are pretty much pointing out how little you know....sorry. you should take a competitive driving course and really enjoy your cars performance. Otherwise you should have bought a nice Cadillac..
And you are also confusing performance driving with daily driving...What you are talking about is torque which peaks below 5250 rpm generally and is multiplied by gear ratio

Rescue Rogers

So back to the OP...your final drive at .72 x 3.08 is about 2.21:1 and mine is .63 x 4.11=2.25 .1. This will drop your rpm depending on rear tire size to around 2750 to 2900 rpm at 80 mph...a lot quieter than beingvaround 3500 rpm.
I have a 28 inch rear tire and am at 2750 at 80 mph...slower I go the quieter it is. Back roads at 1500 rpm with my very loud pipes are easily tollerated as it is just a low rumble. Your small block probably won't like that but it will like a low first gear

Torqued Off

OF course, just as expected. The same old stuff. According to the forum mob,....if you don't drive a car on the street irresponsibly and like on a track....you are labeled as not understanding "performance". And this is why I put people on Ignore Lists, and have found this forum less than enjoyable. If you aren't a racer boy.....you are wrong. Typical BS nonsense from the same old crowd.

But what you, as well as many others, are missing, is that your big HP numbers REQUIRE that 5500 or more RPM to accelerate. Nobody can every understand the concept of increased torque at lower RPM's, and the effect it has acceleration, and I am sure this post won't change that. I fully understand HP and torque, as well as you do. HP is a mathematical equation. And HP matters if you are trying to attain a fast speed. Without high RPM,......and torque....you cannot attain top speed... because that DOES produce higher top speed.

But on the street, if you are going to limit your speed to something approximating the speed limits, especially in places like western PA, where there are very few straight roads, all that top end RPM means nothing. Therefore, more torque at lower RPM equals more acceleration....up to the speed limits you drive.

Your example of a diesel truck is perfect......as the new diesel trucks will pin you back in the seat...i.e. acceleration at very low RPM's...which is exactly where the fun is from 0-60 mph, and they do it all at low RPM. I see it all the time.....a diesel pickup truck at a stop light....light goes green, and the diesel pickup up launches and out accelerates everything else. And if the "race" continued......I am sure the Corvette would win the race at 180 mph........BUT WHO CARES? The acceleration is the fun, on the street. I fail to understand why people cannot comprehend this.

And I fully understand that if you want to run a car to 6000 RPM in first gear, then same in second.....great.....a bunch of noise and abuse to do NO BETTER than that diesel truck or my car. But by the time you get to shift to third.....you are at 70 mph. So its all noise and abuse for nothing. So I fully understand torque and HP. Bottom line.....take an engine cammed my way (selected by a cam expert Mike Jones) versus a racer boy cam........compare the torque numbers at 3000 RPM and at 6000 RPM. If the torque value at 3000 RPM on my cam is 500 ft lbs of torque, its exactly the same as 500 lbs of torque at any other RPM....because torque is NOT a calculation, its a measure of force, and the ONLY thing that moves the car. The racer boy cam will reach 500 ft lbs of torque as well.....but at a higher RPM, so that car has to get to that higher RPM before it makes that 500 lbs of torque, and not until then.....everything below that RPM is LESS THAN 500 ft lbs of torque. Pretty simple. Again....just to make sure you understand.......my point is ALL ABOUT discussing this within the SPEED that you will attain, and that means the responsible speed anyone should be driving on the streets and highways. ON a racetrack......different story.

But as usual, same old BS. I have said all I am saying.....cause I know I am outnumbered.....but the mob rule doesn't change my mind or the facts. And I really DGAF to post another post about it. So don't expect I will be reading any more on this thread, or responding.

Bikespace

My EV will do all of that, only even better, without burning a gallon of diesel every 6 miles. And it can blast down the interstate in silence. All without a transmission at all. And I can refuel my EV at my house, a cool capability once reserved for folks commuting by bicycle or horse. But that doesn't help the OP.

OP, I pointed out the difference of opinion on how to drive your car not to pick on anyone, but to point out that it matters how YOU drive YOUR car. A transmission swap to drop your RPMs on the interstate may matter more to you than it does to me. If you do it, also consider a differential gearing swap, too, to maximize the enjoyment of your car. I picked up a spare 3.55 iron diff, which will replace the 3.07 aluminum diff if that blows up before my transmission.

Here's a spreadsheet I made up comparing some of the options. The highlighted row is what others have suggested for your current 3.07 (3.08?) differential. The bolded rows are the two C3 setups I have now. All rows are for (stock) 27" OD tires.

Torqued Off

[QUOTE=Bikespace;1607789359]My EV will do all of that, only even better, without burning a gallon of diesel every 6 miles. And it can blast down the interstate in silence. All without a transmission at all. And I can refuel my EV at my house, a cool capability once reserved for folks commuting by bicycle or horse. But that doesn't help the OP.

Who GAF? An EV will never be a Corvette. And if you don't understand that, I can't explain it.

Tiger Joe

i'll go against everyone. id got 2.88 and .68.

2.88 and a 3.08 still gives you a first gear of 8.87, you like the way the car is now except high cruising rpm? thats probably the same 1st gear ratio as the Super T10

car will drive exactly the same, but drop rpm 1/3 on the highway when cruising. honestlly the ,68 or .72 is probably a negligible difference

stingr69

As someone who has done the exact transmission swap and has the same rear gear ratio.....you will prefer the wide ratio gear spacing and the least amount of overdrive.

Multiply the new transmission gear ratio in first gear x the rear differential gear ratio and see how close you can get to the ideal "10". That is the sweet spot. 3.27 x 3.08 = 10.07 ....perfect! Works for me.

The overdrive ratio needs to be the least amount you can get with a 3.08 differential. .72 is about right. It's what I have.

You want a broad torque bandwith engine if you want to cruise at highway speeds in OD. Think about wider cam lobe spacings. 110 LSA or narrower with lopey idle is not good here. Stock cams/engines will work well with this setup.

I have run this setup with my 383 and a 112 LSA cam and it is great. I'm going to try it with an LT-1 recreation next. Should be fine with the very wide power band.

If you call SST and ask them, I bet this is what they will recommend.

Seadoorider

Not much to add except I was at a decision point last year - my car is a 77 L82 with the M21 close ratio box, 3.70 axle. My engine is not original, 383 with roller cam, alum heads etc, still carbureted. I did not build this engine, but it seems to like some RPM, it’s not weak down low but it’s not a low RPM torque monster like my 89 L98 was either - payoff is much better power up top.

Anyhow, my transmission was pretty worn out but I decided to have it rebuilt instead of swapping for an OD. This was strictly a cost consideration, the complete rebuild cost a lot less than a new 5 speed and was straightforward keeping everything else the same. It works great but I’m in KS and there are a lot of long, straight roads. At 70 I’m turning close to 3500 which the motor seems fine with but it would sure be nice to have at least one OD ratio to calm things a bit and save fuel.

On the plus side, no downshift required for passing someone!

Z0Tex

@rmrtrex , If you are keeping your stock 3.07 rear gear, go for the 3.27/1st .72/5th "wide ratio" option. That will give you a bigger "kick" off the line in 1st gear compared to the stock ST-10 and still give you a useable OD for Texas freeways. If you plan on changing the rear to a 3.54 or 3.73, go for the 2.87/1st .68/5th "close ratio" option. The 1st-4th ratios of the "close ratio" TKX are damn near identical to the Super T10's that came in our 80's.

*edit* See the chart @Bikespace made in post #11. *edit*

I changed my rear gear to a 3.54 last year and will be going with the .68/close ratio TKX option this winter.

wvleon

I just installed the TKX wide ratio with the 3.27 gear with a 3.08 rear. Multiply the 3.27 x 3.08 and it gives you 10.07 gear which is perfect. I do not find any issues with the gear spacing or launch. My car is a 70 with a 467 so no shortage of torque. I spoke to Silver Sport and they convinced me to go this route and I have not been dissapointed.

OldCarBum

Everything has to work together to get the best bang for your buck!
First, I assume the engine is a sbc and not a bbc.
If it is a bbc then it changes everything because to bb torque is so much greater at the bottom end.
Depending on the cam specs, you want your cruising speed rpm to be within the power band of the cam.
So, if your cam’s operating range is from 2000 to 6000 rpm, you will want your highway cruising rpm to be a minimum of 2000 rpm.
With the 3.08 rear gears you want to get close to that perfect overall ration of “10” for first gear.
I would say that anything from the upper 8’s to 10 will work fine, but the higher the first gear ratio the quicker it will be off the line.
Another thing to consider is the actual rpm drop from 4th to 5th gears and the reverse when shifting down from 5th to 4th.

I went with the Tremec 5 spd with the 2.87 first and 0.82 fifth gears and 3.08 rear end ratio.
I also have a big low end bb torque monster so I’m not worried about first gear ratios and I did not want that huge rpm drop between fourth and fifth gears.

There have been many on the forum that have said they regretted going to a six speed because they rarely used sixth and the larger transmission case was really tight in the tunnel.

roscobbc

For me the 3.08 rear end with M21 and its 2.20 1st gear is almost perfect.........(well, almost perfect) truthfully the car could perhaps benefit from a higher ratio rear end (or o/d ratio)
With its BB engine's 450 ft/lb tq at a lowly 2400 rpm and max 606 ft/lbs at 4000 rpm any ratio lower than 2.20 would no doubt result in excess traction problems.
70 mph cruise at 2500 or so rpm is kinda OK but I'm sure a 1500 to 1800 rpm cruise would be far more relaxing. In normal driving torque is certainly king and there's little need to 'stir' the shifter too much.......unless I want to 'play' a little! What I probably need is the Tremec 6 speed but with OEM ratios as fitted to Camaro ZL1 with it's M21 like 1st to 3rd ratios (but overdrive 5th and 6th ratios) - but do I travel the miles to get maximum benefit?......not really!

leigh1322

You have an L48 and a 3.08 rear gear.
You basically have 2 TKX options. The WR 3.27/.72 seems like your best choice.
The 3.27 1st will give you a nice peppy 10:1 in 1st gear. Much better than your current 8:1 (2.64 1st S-T10?)
The .72 OD will give you a nice 2000 rpm cruise speed at roughly 70mph vs your current 2600.
The other CR 2.87/.81 trans does not work out as well. Not much difference in 1st over what you have now (8.1) and not much OD either.