I have a 69 350HP with a 6,000rpm redline and a 4.11 rearend. I am in desparate need to install a 6-speed tranny so I can cruise more comfortably at highway speeds as 4,000rpms at 80mph is well...just ain't much fun.

I am totally clueless as to why I should match up my rearend 4.11 & 6,000 redline and tranny gear ratios....can somebody tell me why?

I see that both the T-56 and richmonds have the option to run slightly different gearing combos. Which ratio set should I use with thoughts of being able to cruise very comfortable at 70~90mph and also have maximized my 1/4 mile (0 to 100mph) performance numbers?

I want to keep the 4.11 rearend. I am trying to somewhat rebuild my 350 drivetrain into a very streetable daily driver...yet deliver the goods when I need them if that makes any sense that I can have both at the same time.

I will be dropping off the car with a mechanic next week to have this mod done while I am away for 4 weeks on business and would like your all input on what ratios would work best.

 

I think your gear ratios are more to do with your camshaft and compression than the redline, you don't want to be at redline all the time, do you?
How is the motor built? it is built for low down torque or high end horsepower? What range is the cam designed to work in?
If the cam is designed to work from 2000 to 6000 then your cruise revs should be just above the low end of the cam, say 2500.
To get off the line, the first gear multiplied by the diff ratio should give a value of 10 so for the 4.11 rear end, First gear should be about 2.4:1.
then you should have an even spread of gear ratios up to 4th at 1:1.
The T56 has 2 OD gears (about .78 and .5 from memory)
Don't know what the richmond box has in it but at .5 OD, the equivalent ratio for the diff is 2.06 and you are spinning at half the revs you were in 4th. So if you were spinning at 4000 at 80mph then you will be sitting at 2000 in 6th. The engine may not have enough torque to pull this easily and you will find the motor likes 5th (3120rpm) better than sixth for 80mph. Sixth may be useless for normal driving and a 5 speed with a .68 OD may be better suited for cruising at 80mph (2720 Rpm)
As I said, it all depends on the motor.
Hope I have been of some assistance

 

Ditto RHD

 

Many thanks...I now am beginning to see the light. Unfortunately I just bought the car and have no idea what cam is in the motor. All I know it was an original 350HP that was rebuilt to a 9~9.5:1 compression and a mild cam.

I was thinking about doing the 6-speed first and then tackling the intake and cam on the motor, but maybe now I am thinking I should do it the other way around or all at the same time?

I would like to setup the motor for 2,000~6,000rpm performance.

Also why would I want to target a torque multiplication factor of 10 for the first gear? Is it because anything above that factor would just spin the tires?

 

LT1 T56 with .5 OD is what you need. You'll make plenty of power to control your speed in 6th with those gears and that engine.

 

Would it cause a lot of problems running the T-56 with a final overdrive of 0.62 versus 0.5? I don't mind running the slightly higher rpm (2,480 vs. 2,000) while cruising @ 80mph but I would sure enjoy the slightly better gearing for acceleration. Would running the motor at its current setup at 2,500 versus 2,000 create any cruising driveability problems?

 

Hi

The T56 with .62 6th gear is lower rated as the T56 Viper with .50 6 th gear.
The 4 first gears are for power acceleration, the overdrives are for highway cruising.
I have the T56 with .50 in my 68 BB with 3,70 rear end and 6500 red line and realy love it, but am thinking about installing a 4.11 rear end.
The overdives realy knock down the RPM , so 4.11 should be perfect.

Günther

 

"I am totally clueless as to why I should match up my rearend 4.11 & 6,000 redline and tranny gear ratios....can somebody tell me why?"

I'll take a stab at this: When setting a car up for drag racing, you want to go through the traps in your top gear at red line. You want to maximize your gearing without having to lift at the finish line.

This has nothing to do with driveability and probably isn't too applicable to a six speed (unless you want to row through all six gears in the 1/4 mile). Even if you were a hard core drag racer, you might pick fourth to give you red-line at the traps and use fifth and sixth for your cruising gears to get to and from the track.

I run a T-56 with the .62 OD and 4.11 gears in a '66 vette. I am very happy with the combo....4.11 gears and the ability to cruise comfortably at 70.

 

The 0.62 OD is probably fine for your motor, what I was trying to say was it may not have enough torque to be happy with the 0.5 OD and if the compression has been lowered and the cam reduced to a "mild" specification this is probably true. Be aware that raising the compression and putting a bigger cam in will increase the max outputs of torque and HP but will also move the curves up in the rev range. you may end up with exactly the same amount of torque at 2000 rpm, but more up further.
the TPI fuel injected motors have more low end torque which makes the 0.5 OD easier to live with.

The 10 multiplication factor just works well(with our size wheels and power). If the multiplication is too high you end up with a granny or crawler first gear and if it is too low you have to slip the clutch to get moving, like trying to start on a hill in third.
My 1st gear is 3.25 and my diff is 3.7 giving a multiplication of 12. First is a little short for my liking and if I went to 3.08 diff it would give a multiplication of 10 exactly. It does make it easy to get off the line but you are into second straight away.
As Cris said
"When setting a car up for drag racing, you want to go through the traps in your top gear at red line. You want to maximize your gearing without having to lift at the finish line."
The 4.11 gearset (and 4.56) were considered drag setups as you were close to redline in 4th as you crossed the line. Not good for economy but then you knew this
(BTW, Muncie 1st 2.2 x 4.11=9.042, 2.2 x 4.56= 10.03)

 

thanks for the info...very very helpful with me learning. I think I am going to go with the tranny ends in a OD of around 0.62 versus the 0.5.

I found this calculator on the net (see link below) that allows me to calculate my speed vs. rpm vs. tranny vs. rearend gearing so I can get a close idea of what rpm and mph I will be running at. I entered the figures for both versions of the t-56 and came up being in 4th gear at 100mph is about 5,100~200 rpms which is just about maximizing my first 4 gears to redline just as I finish the 1/4 mile which is what I think I need to accomplish to get the most benefit out of some good 1/4 times assuming I run a trap speed of about 100mph.

http://www.geocities.com/z_design_st...ion_z28_6.html

 

okay....time is fast approaching and here is where I am at with me needing to decide quickly. The shop can do either the t-56 or ROD 6 speed tranny. they recommend the ROD 6 for the vette and the t-56 for the camero....don't really know why?

from researching all the past posts (many) here is what I have concluded:

ROD
1. can be difficult to shift, but seems to be solved by using a light weight flywheel that allows things to sync easier and faster versus heavier stock according to one post I read
2. can be loud....what can be done about this? I don't want anything louder than my stock M-20.
3. only 1 overdrive with multiple gear ratio selections to make things easier to match up my 350HP & 4.11 rearend and with only 1 overdrive that means I can match more gears up for better 1/4 acceleration
4. seems like some really like the ROD with no problems and others have had their issues with them such as breakage, noise, shift hardness
5. think the ROD is a little more expensive than the t-56
6. might be more difficult to the ROD serviced if need be? don't know exactly


T-56
1. seems to shift smoothly
2. is quiet
3. limited to gear ratios and 2 overdrives so I guess with 2 overdrives I lose some acceleration benefit that I get from the ROD
4. seems like there are minimal complaints with the T-56 not seeing a post about breakage, noise, or shift hardness
5. think the t-56 is a couple $100 cheaper
6. my thoughts are it is easier to get serviced due to other applications in use


For those with experience with either of the issues mentioned or the ROD can you please comment asap as I am dropping off the car late this week and need to decide by Thursday/Friday which way to go.

I like the way the ROD's are setup with only 1 overdrive & OD of 0.62 thereby getting better (I think because of 5th 1:1) acceleration, but my main concern right now with the ROD is the noise.

I think the t-56 would work out great also with my 4.11 rearend and final OD of 0.62....same as the ROD, but I would give up some acceleration numbers (I think).

all comments and suggestions welcomed and I will try to find out Wednesday why the shop recommends the ROD vs. T-56 for the vette vs camero thingy.

 

I'll never hear the noise of the ROD over the symphony of the sidepipes...

 

that there is funny and hopefully I pickup a 2nd C3 to do just that.....side pipes, yet unfortunately I am trying to build to be somewhat civilized since I already have another loud beast.

Here are the gearing ratios & max mph using 6,000 redline and 4.11 rearend that I have narrowed down to between the two tranny's

T-56 Ratio=2.97 ~ 2.07 ~ 1.43 ~ 1.00 ~ 0.80 ~ 0.62
T-56 MPH = 40 ~~ 57 ~~ 82 ~~ 117 ~~ 147 ~~ 189

ROD Ratio=3.01 ~ 1.88 ~ 1.46 ~ 1.18 ~ 1.00 ~ 0.62
ROD MPH = 39 ~~ 62 ~~ 80 ~~ 100 ~~ 117 ~~ 189

My final drive ratio is the same along with my 1st gear ratio for all practical purpose is the same. The 2nd to 5th gear ratios have me thinking. After doing all the math speed vs. rpm vs. gearing calcs the T-56 seems to be the more practical route. The advantage (I think) goes to the ROD in minimizing 1/4 ET due to the 4th gear 1.18.

 

The LT1 T56 has a .50 6th gear ratio. The ratios you mentioned I believe are from an LS6 Corvette. To my knowledge that trans won't work for you.

 

I like my ROD. I've never heard of a noisy ROD, but I have of Richmond rear end gears. If you take the time to set up the linkages properly the ROD shifts smoothly with the Red Line 75W90NS gear oil. I have the 3.28 first and .76 sixth using my stock 2.87 rear end. Stays in the powerband between gears with no slump. The ROD probably installs more easily in the vette. You may have to trim your tunnel somewhat but there are no mods as far as the shifter coming up in the stock location. Also the Long (brand) shifter is one of the best on the market. Your crossmember mod will be the biggest challenge although yours would be easier than mine was. Any transmission will break whether it's behind a 200hp or 1000hp motor. I'm not really convinced in some torque ratings that I see. I have driven several T-56's and a couple of Keisler units but I prefer the ROD myself.....but that's just my opinion. One of these days I'm going to take the time to learn how to post pics of my car here.. Good luck!

 

Damn....I new I probably missed some little detail like the wrong tranny. Here are the new figures using the correct tranny ratios.

T-56 Ratio=2.66 ~ 1.78 ~ 1.30 ~ 1.00 ~ 0.74 ~ 0.50
T-56 MPH = 44 ~~ 66 ~~ 90 ~~ 117 ~~ 159 ~~ 235

ROD Ratio=3.01 ~ 1.88 ~ 1.46 ~ 1.18 ~ 1.00 ~ 0.62
ROD MPH = 39 ~~ 62 ~~ 80 ~~ 100 ~~ 117 ~~ 189

M-20 Ratio=2.52 ~ 1.88 ~ 1.47 ~ 1.00
M-20 MPH = 47 ~~ 62 ~~ 80 ~~ 117

Now I really like the other T56 vette ratios that I had listed earlier that I did not realize would not work. Now I do need to reconsider a lot of things including replacement of my 4.11 rearend. Uggh!!!! Now I am liking the ROD ratios the best given my current setup.

 

Just to confuse you some more, I'm 90% sure that you could swap out the gears. Meaning buy an LT1 trans and put the LS6 T56 gears into it. I can find out for sure if I talk to my neighbor about it. He was talking about doing that to his.

But I don't know why you'd wanna give up that .05 OD especially with 4.11s. That'd be perfect in my opinion. And with the LT1 T56 and 350hp you probably won't have to shift out of 4th in the 1/4 if you can push that redline.

 

There are choices for ratios in the ROD. I just went throught the same set of calculations this summer. I built an excel model that compared tire diameter, final drive, and trans ratios of my current setup and the potential new setups. Plotted RPM's in gears with road speed and went out with my current car and found the RPM's that the sound was good.

Remember you need to take in to account the tire diameter as it has a noticable effect on final drive.

 

okay....I have officially decided to go with the Richmond. I spoke with the shop which installs both the T-56 and Richmond and they said they prefer the Richmond because it is a little easier to install than the T-56 but can do which ever I prefer.

We are going to install a light weight flywheel and make sure the shift linkage is adjusted properly to make the shifts smooth and quick. They told me that I will hear the tranny a little during idle compared to my M-20 but the difference is minimal. When driving it will not be any noticeable difference in sound compared to stock. I hope this to be true that using a light weight flywheel, correct tranny fluid, and adjusting linkage will give me many years of trouble free enjoyable smooth & quick shifts. I will post a followup when I get my car back hopefully before the end of the year as I am having a ton of other work done to it also.

Lastly...we or I should say me am working on selecting appropriate tranny gears. The mechanic is also working up some ratio combos for me to consider. I plan to adjust the 350HP motor to have its power band between 2,000~6,000rpms with a 4.11 rearend and tire size of about 26.5~27" tall with the thoughts of eventually running something like a 275/40/18 rear tire that is 26.7" tall on some TTII's.

I think want cruising rpms on the freeway @80mph around 2,500rpms (just above the cam powerband) so I think the OD should be around 0.62....correct?

I am not sure how short of a first gear I should use...I heard that the torque multiplication number should be around 10 so next objective will be to space the ratios out evenly I guess.

Thanks all for you help....much appreciated coming from a new person who really does not have any grease under my finger tips yet.

 

Hello -

I see you're agonizing over the choice of a 6 speed. I would love to speak with you about installing a 6 speed in your C3, since this is the type of thing we do dozens of time per day.

The T-56 is the better choice and you can get the close ratio version (2.97 1st, .8 5th, .62 6th) with a shifter position that fits your Vette and a mechanical speedo. The Camaro version has the wrong shifter position and an electronic speed which are probably some of the reasons why your shop recommends you not use it.

You can also achieve your acceleration and cruising goals with one of our re-engineered Tremec TKO 600 5 speeds. It will save you $$$$ and bolts right in without ANY mods to you car.

Please give me a call Friday 423-773-9789

Robert - The Driven Man
Keisler Sales