Wide or close ratio transmission gears & why.

[Samckitt]

What looking at the new T56 Magnum transmission, it comes in 2 different sets of gear ratios.

2.66 1.78 1.30 1.00 .80 .63
&
2.97 2.10 1.46 1.00 .74 .50

The car weights about 3400 lbs, motor will be a 6.2L L92 & the rear is 3.42:1.

The 6 speed auto behind the L92 has the following gear ratios:
4.027 2.364 1.532 1.152 0.852 0.667
I image the rear is deeper ratio & sure it weighs a lot more.

Which would be better to choose, & why?

Thanks

[Samckitt]

No suggestions?

[6spdcamaro]

I would go with the close ratio. With a 3:42 the wide ratio 6th (.5) would be useless, depending on your tire diameter.

[Jim Nilsen]

Wider ratios always give you more overlap in the gears and is way better for track use. Close ratios for dragracing just don't do it for me.

If you give up that low 1st gear you will really notice the take off performance drop.

[garys 68]

Wide ratio. The L92 has a great torque range. 0.5 OD with 3.42 will be usable on the highway. It's the same combo corvettes and some f bodies used with a smaller LS1 motor. And with $4/gal gas on the way, milage and comfortable driving will be a plus.
The 10.xx overall first gear is great for acceleration, it's what I'm using for my 6.0 LS in a 68 corvette.
My $0.02

[Samckitt]

I had been debating going to 3.73 or 4.10 rear. So with WIDE ratio & that I should be good.

[The WidowMaker]

Wider ratios always give you more overlap in the gears and is way better for track use. Close ratios for dragracing just don't do it for me.



interesting. i always thought that you wanted a close ratio box for the road course. tremec even calls the close ratio tko a "road race" version. the rpm drop is less and it keeps the motor in the power band a little more. could you explain the "more overlap" portion?

i did away with my never driven tko 600 (2.87) and was deciding between the 2.66 and 2.97 magnum as well. after reading about some guys having issues with too much power and a low first gear, i was thinking about the 2.66 to keep from starting in second like some of them were doing.

[Cannon]

yea close ratio is ideal for road racing cause it gives more gear selection for different speed corners but for a street car you want the 2.97 1st with .5 overdrive great on the street and gives great drag strip acceleration and not really a big disadvantage for road racing when you gain so much street manors. and if you want to tighten the gears up more then get some 4.10's in the rearend.

[andrewb70]

I had been debating going to 3.73 or 4.10 rear. So with WIDE ratio & that I should be good.

I would go with the wide ratio and keep the 3.42s to keep the driveshaft speed down.

Andrew

[The WidowMaker]

the main problem i have with the wide ratio is that the 6th gear is not useable unless you have a tame motor. with 3.42's and a 27" tall tire, the close is 75mph and the wide is 94mph at 2000. you would have to drop down to 1600 rpm to be at 75 with the wide ratio.

since i sold my 600, ive been trying to make the same decision as well. what leads me to the close is that most every stock tranny that was in these cars had a first gear pretty close to the 2.66. not that i should be basing my decision on 40 year old gear selections, but i never thought that my 430hp gen I small block had any issues with the th350. i did have a converter that helped though. now with 600+, i dont think the 2.66 will be an issue.

his 3.42's may be the difference. i have a ratio of 9.9 and his is 9.1 with the 2.66.

[theRG]

Why the T-56, a wide ratio .64 TKO-600 5 speed has a gear spread that is only slightly wider than the T-56 close ratio. Most street driven 6 speeds and even alot of those track driven can't properly utilize all the gears and I myself am a fan of the 5 speed over the 6 speed and would only go to the 6 if I needed another gear. I am a fan of using the rear gear ratio and not the trans ratio to keep the car in power range and inversely if street driven cruising range, so a compromise is usually the case.

Also, if you're planning on much road course driving the small gear spread of the close ratio is in all but rare circumstances the pretty standard choice.

[garys 68]

Another possibility is a Richmond 6 speed. You can pick your 1st and 6th gear.
http://www.richmondgear.com/07pdfs/RG21.pdf
When I dropped a 6.0 LQ9 in my 68 vette, I chose the 0.76 6th Richmond because I was worried a 0.6x OD of most 5 speeds would be too much gear with a 3.08 rear. I was pretty conservative, the low end torque and drivability of the SFI LS motors is amazing. The L92 with VVT should even be better.
Keep in mind that even a 5500lb escalade with an L92 runs down the hiway, 70mph, at 1700rpm and gets 20mpg.

[67CamNKC]

If 10.xx is the most desirable overall gear (3.42 x 2.97=10.16) , would a 12.xx not be usable (like 4.11 x 2.97 = 12.21)?

[AMC Racer]

With T56 Magnum you can custom order with the OD gears of your choice. So if you want to go with the 2.97 box for your 3.42 gears, you can get the dealer to fit the 0.80 or 0.75 5th and 0.63 or 0.50 6th if you choose (see below & check the link for details on "Mix & Match" OD gears - pg.8). The 2.66 / 0.63 with 3.73 - 4.10 gears is a good choice with a stout cam that is more peaky and doesn't have much low end.
https://static1.pt-content.com/images/noimg.gif
http://www.ttcautomotive.com/English/onlineorder/pdf/TRMC_R3_0210_198.pdf
P.S. Neither of the standard Magnum gear sets are really close ratio. Close ratio would be e.g. the 2.29, 1.60, 1.21, 1.00, 0.85, 0.76 ... good for a 7000 rpm engine.

[Samckitt]

Was also debating going with the Mast L92 SS cam, they claim up to 550 hp at the flywheel. Not sure where the power band is though.

[Ron.in.SoCal]

interesting. i always thought that you wanted a close ratio box for the road course. tremec even calls the close ratio tko a "road race" version. the rpm drop is less and it keeps the motor in the power band a little more. could you explain the "more overlap" portion?

i did away with my never driven tko 600 (2.87) and was deciding between the 2.66 and 2.97 magnum as well. after reading about some guys having issues with too much power and a low first gear, i was thinking about the 2.66 to keep from starting in second like some of them were doing.

Scot - got you thinking about this, huh? :)

Tim - I consulted a number of experts on tihs subject and your commnet above is exactly what they all reccomended. CR for road race applications. I'm running a similar motor (and HP) as Scot and am looking for 'in the powerband' performance. One question I did not get answered is if I were running peanut AutoX, would the 2.97 1st be better matched w the .80/.63 5th/6th??

[Samckitt]

Yeah I am thinking about it now. I am terrible at making decisions sometimes. One minute I am leaning towards the wide ratio, then next minute the close ratio. AHHHHH

[6'9"Witha69]

Close ratio. Huge RPM drops are never good, in Drag or Road racing applications. Wide ratio is good for street vehicles. Deep firsts to get off the line using less gas and allow fewer shifts driving around town.

[The WidowMaker]

Deep firsts to get off the line using less gas and allow fewer shifts driving around town.


thats the thing though, they arent "that" much different. both still have a 1:1 4th and thats most likely what i will cruise with on the street. so both require 3 gear shifts.

below is kind of hard to read, but the numbers are based on the OP's 3.42 and a 27" tall tire. the first column is obviously the RPM, but then the next 6 numbers are pairs of 1st 2nd and 3rd of both trannys. it shows me that there isnt a huge difference between speeds at a given rpm. now, how they would actually feel while driving i dont know. im not sure if you would notice the 6 mph drop in 3rd at 3000 or not.

2000 16 18 22 26 32 36
2100 17 19 23 28 34 38
2200 17 19 25 29 35 40
2300 18 20 26 30 37 42
2400 19 21 27 32 39 43
2500 20 22 28 33 40 45
2600 21 23 29 34 42 47
2700 21 24 30 36 43 49
2800 22 25 31 37 45 51
2900 23 26 32 38 47 52
3000 24 26 34 40 48 54

[Samckitt]

Here is a dyno graph from a motor & cam that I am debating. This is what MAST sent me on the L92 SS cam, but using a different intake so he said numbers are a little lower.

https://static1.pt-content.com/images/noimg.gif

[andrewb70]

I would keep the 3.42 gears and do a .80 5th and .63 6th. Again, this is aimed at reducing driveshaft speed. With the 2.97 first gear and 3.42 rear gears you will have a little over 10:1 in first overall. That's perfect.

Andrew

[LUACE]

Since you can ‘Mix & Match’ 5th and 6th, it creates about 8 different set up options with the close ratio and wide ratio options. Can someone break it down using the following categories:

1. Best performance in autox-
2. A little of both- autox performance and Street-
3. Best for Street use-

[Samckitt]

I would keep the 3.42 gears and do a .80 5th and .63 6th. Again, this is aimed at reducing driveshaft speed. With the 2.97 first gear and 3.42 rear gears you will have a little over 10:1 in first overall. That's perfect.

Andrew

What are you saying, go with the wide ratio one but replace 5th & 6th gears to the .80 & .63 ratios? How is that reducing driveshaft speed? Going 100 mph the driveshaft speed will be the same for .63 ratio 6th gear as it will for .50 ratio 6th gear, just be a different motor RPM.

[andrewb70]

What are you saying, go with the wide ratio one but replace 5th & 6th gears to the .80 & .63 ratios? How is that reducing driveshaft speed? Going 100 mph the driveshaft speed will be the same for .63 ratio 6th gear as it will for .50 ratio 6th gear, just be a different motor RPM.

What lowers driveshaft speed is keeping the 3.42 gears. You had mentioned earlier about possibly going to a 4.10 gear and using the close ratio t56. I am saying stick with the 3.42 gears which will keep the driveshaft speed down compared to the 4.10s, but you will still have a similar 1st overall gear ration.

1st gear overall:
3.42x2.97=10.16
4.10x2.66=10.90

6th gear overall:
3.42x.63=2.15
4.10x.50=2.05

See what I mean?

Andrew

[Samckitt]

What lowers driveshaft speed is keeping the 3.42 gears. You had mentioned earlier about possibly going to a 4.10 gear and using the close ratio t56. I am saying stick with the 3.42 gears which will keep the driveshaft speed down compared to the 4.10s, but you will still have a similar 1st overall gear ration.

1st gear overall:
3.42x2.97=10.16
4.10x2.66=10.90

6th gear overall:
3.42x.63=2.15
4.10x.50=2.05

See what I mean?

Andrew
Gotcha, gotcha. I thought you were trying to say the 5th & 6th gear change would change driveshaft speed.

[The WidowMaker]

any update?

[chicane67]

I'd go with the 2.66 first, .80/.63 close ratio and 3.42's myself.

Before 5 and 6 speeds became the norm... I always felt the 2.43 first super T-10 with a 3.42 was THE most fun and productive combination for a true street car. It will keep the engine in the true power band and the shift recovery point will stay right in the torque curve much better than with a wide ratio.

But what do I know ?

[JEFFTATE]

I'd go with the 2.66 first, .80/.63 close ratio and 3.42's myself.

Before 5 and 6 speeds became the norm... I always felt the 2.43 first super T-10 with a 3.42 was THE most fun and productive combination for a true street car. It will keep the engine in the true power band and the shift recovery point will stay right in the torque curve much better than with a wide ratio.

But what do I know ?

Exactly !
You know a lot Tom ..

[AMC Racer]

This may be of interest. If drag racing is important, may want 3.90 or 4.10 gears to use 1st through 4th assuming the LS pulls > 6500 rpm ... depending on tires. With 3.42 gears, 26" tires the 2.66 box will likely work with 1st through 3rd (118 mph @ 6800 rpm in 3rd) ... with the 2.97 box, likely need to shift to 4th to get mph so 2.66 box may be quicker (107 mph in 3rd @ 6800 rpm with 2.97 box). Just cruising ... well, your call.

https://static1.pt-content.com/images/noimg.gif

[chicane67]

Good point on the 3.90's... I also agree. A 2.66 .80/.63 with 3.90's would be a great combination for an 'all around' use type build. Good low speed torque multiplication and the double OD makes up for the stuff on the open road.

Something to mention... any time you go over a .75 OD... the efficiency falls off exponentially.

I guess my case is somewhat odd (?!?)... as I am using a 2.29 first .85/.76 with a 3.25 rear and a second third member set up with 3.90's. The 3.25's are for general use and the B'ville boogie... and the 3.90's are for road course and auto-cross type abuse.

Not that I have spent any time thinking about this, but I wrote an extensive excel sheet that covers all available transmissions and final drive gear ratios along with tire diameters... all just to stare at the computer screen and haggle out the finer points of what finite increments do to rpm drops and shift recovery points, for working rpm and mph.

Good times...

[rob07002]

Just installed a T56 Magnum with the 2.66 first and .63 6th with 4.10's and a 26" tall tire (285.35.18) and so far really like this combo. Good off the line acceleration and I cruise at 2400 and 75 mph on the highway. Just about doubled my fuel economy too!!

[Roadrage David]

Ok guys for project ""Road Force one"" that im working on, we are going for a tranzilla t56 clutchless 6 speed, our rear ratio is 3.42 engine wil be a 475 ci 730 hp engine wityh 4 inch stroke 7200 rpm!.

now we are finally going to use the vari lift system( V-Tec) that we have lyng around for the last couple of years.this system has a rokker ratio of 1.18 below 3500 rpm and switch to 1,67 ratio at 3500 rpm, this obviusly means a longer eurlyer torque curve of about 5000rpm!!!.

with this sytem you kinda have 2 diferend cams profiles overlaping etchoder in one set up and 2 diferend valve lashes. the car wil be 80% all out road racing and 20% street driving.
This system makes it able to run a 20* bigger cam but stil keep the same streetbebilety of a smaller cam .

Now my question is How do i aprotch the gear ratio chooice of the transmission ???.
I know i have more and eurlyer torque at 2000 rpm in sted of the torque setting in at 3500 rpm , with what this cam normaly produces.

And that i wil be able to come out a 2e gear corner with torque set in eurlyer ecetera. any thoughts on what gear artio would be best for the transmission??.torque wil be around 700lbs 730 hp 7200rpm 27 inch tall tires 13 inch wide(slicks) in the rear 25 inch tall tires 11 inch wide front, car wil weigh in at around 3000/2900 lbs