T56 vs 4L60E Comparison Spreadsheet

The following spreadsheet can be used for comparing the effects of Tire Size, Rear Gear Ratios and Engine Speed for the 4L60E automatic and 3 different T56 transmissions. I put it together when I was going through the rear gear selection process for a T56 swap and I would be glad to share it with fellow wagon lovers.

Below is a screenshot of the spreadsheet TAB with tables that calculate Engine Speeds at various Vehicle Speeds per gear for the different transmissions. Also calculated and graphed is Max Vehicle Speed for the entered value of Max Engine Speed per gear.


Another TAB has a set of tables that calculate Vehicle Speed for an entered Engine RPM per gear. It also has a set of tables that calculate Engine RPM for an entered Vehicle Speed per gear as shown below.


The cells that are highlighted in yellow are variables that can be changed by the user. These include Tire Size, Rear Gear Ratio, Max Engine RPM and Manual Transmission Option. The other cells are locked so you should not be able to mess them up .

The Manual Transmission Option allows you to enter the transmission that you want to compare ("1" for MN6, "2" for M29, "3" for M28 and "4" for an option so you can enter custom transmission ratios).

Send me a PM request with your email address if you want a copy of the spreadsheet. As I said above, I would be glad to share.

Anyone serious about getting the most out of their cars, need this chart. Don has done a great job. Have him email you an interactive version.

Spent the last 1/2 hour playing with the numbers, and also plugging in the values for the 4L80. Interesting in that in my case, the 6 speed would be useless unless I was pulling at least 4.11 gears.

Thanks Don

Bill

convert2diesel wrote:

Anyone serious about getting the most out of their cars, need this chart. Don has done a great job. Have him email you an interactive version.

Spent the last 1/2 hour playing with the numbers, and also plugging in the values for the 4L80. Interesting in that in my case, the 6 speed would be useless unless I was pulling at least 4.11 gears.

Thanks Don

Bill

plug in 4:88,s
then check out the 4l60e 3:73
close very close (final drive rpm)
Billy,. 4:88's would appeal to you,. the blue car witha stock motor and stock heavy flywheel,. with an lt4 style organic disc,.
will idle away from the lights in 3rd,...
just like driving an old pickup,. LOts of bottom end grunt,. LOts of mid range acceleration , in either 4th or 5th or 6th,. its not fusssy,.

Nick

convert2diesel wrote:

Anyone serious about getting the most out of their cars, need this chart. Bill

I appreciate the props...I'm glad that you find it useful.
Thanks,
Don

Nick:

Was the T56 ever used in any of the trucks? I looked up things such as clutches and hydraulic throw-out bearings and got totally confused as to clearances, flywheel thickness requirements and so on. It would be nice if we could find a direct bolt in replacement that will work with the diesel.

Also has anyone had any problems with the stock drive shafts spinning at the higher speeds? With the 4.88 gears, at 60 mph, the shaft will be spinning at about 2,200 RPMs. Alot of centrifical forces working here.

Seems to be alot more then figuring out how to mount an extra pedal. Still leaning towards a 4L80 but am open to the possibility of rowing gears again. Really only trying to get a couple of useful gears when towing the RV on the highway. The 4l60 can only tow in third and the spread between third and second is way too steep. The 4L80 will allow me to tow in fourth with third being available without running the engine up against its govenor.

Bill

convert2diesel wrote:

Nick:

if we could find a direct bolt in replacement that will work with the diesel.

Also has anyone had any problems with the stock drive shafts spinning at the higher speeds? With the 4.88 gears, at 60 mph, the shaft will be spinning at about 2,200 RPMs. Alot of centrifical forces working here.

Bill

well i have run the car down the highway at 100mph for a while,. no sweat,..
the t56 will physically bolt right onto the diesel,.same bolt pattern,. you might be able to talk a certain person i know out of their dual mass lt4 flywheel
(before wagon collector reads this) simple swap in your case,. its already been done,. toomany toyz had a caddy with a t56,. the v8 diesel shares the same space as an lt1,.
years back we used to rip out 6.2's and drop the 350 gas motor right in,. sits on the same mounts etc,. will even hook up to the head pipes,.


Nick

Not concerned about the engine, been there done that with the Roadmaster. Its the interface between the diesel and the T56. Would like to avoid the dual mass flywheel of the later 6.5 as they were troublesome, but rather use the stock flywheel for the 6.2.

My question was about the hydraulic throw out bearing thingy they keep talking about on the T56 aftermarket parts sites. Getting rid of the clutch fork and external slave makes a lot of sense, assuming the combo throw-out bearing, clutch slave will fit between the tranny and the engine.

Haven't looked closely at the Caddy's driveshaft but if I were to spin it twice its normal speed, I would still be concerned about balance. Not too worried but still better safe then sorry. Remember the Caddys shaft is 4 inches longer. 1/2 way to Florida is not the place to regret not doing it right.

Bill

convert2diesel wrote:

Not concerned about the engine, been there done that with the Roadmaster. Its the interface between the diesel and the T56. Would like to avoid the dual mass flywheel of the later 6.5 as they were troublesome, but rather use the stock flywheel for the 6.2.

huh?? interwhat? dual mass 6.5 flywheel?? huh?? did you read my post?

convert2diesel wrote:

My question was about the hydraulic throw out bearing thingy they keep talking about on the T56 aftermarket parts sites. Getting rid of the clutch fork and external slave makes a lot of sense, assuming the combo throw-out bearing, clutch slave will fit between the tranny and the engine.

why go that route? you're not going to drive the car like a boy racer,. so stock is more than adequete
inmho

convert2diesel wrote:

Haven't looked closely at the Caddy's driveshaft but if I were to spin it twice its normal speed, I would still be concerned about balance. Not too worried but still better safe then sorry. Remember the Caddys shaft is 4 inches longer. 1/2 way to Florida is not the place to regret not doing it right.

Bill

Perhaps a hi speed balance,. or a 2 piece shaft,. or an aluminum shaft,. (gm vans and pickup shafts are cheap at the wreckers,. cheap to get shortened IF necessary,.]
If i was doing your thing with the caddy towing etc, i,d re-tune the lt1 add a nice cai,. decent free flowing exhaust, bigger trans cooler, shift kit and 3:73's,.
be cheaper,. stronger and easier to get on the road,..
JM2C

Nick

Quote :

huh?? interwhat? dual mass 6.5 flywheel?? huh?? did you read my post?

Yes I did read your post. Seems the diesels chew up dual mass FWs at an alarming rate, so much so that GM went back to solid mass wheels in 97. I do know the bellhousing will bolt up, my question is what bellhousing is needed that gives me the clearance needed, if in fact I want to use the concentric slave as opposed to the fork system.

Quote :

why go that route? you're not going to drive the car like a boy racer,. so stock is more than adequete
inmho

Was under the impression it was stock in certain truck applications. Maybe I'm wrong, but combining the slave with the throwout bearing makes alot of sense to me. I do know the 6.5 guys have a few issues with the fork and ball system and the external slave.

Nick, its been over 20 years since I have played around with standard transmissions and alot has changed in the interim. I'm just trying to wrap my head around the various combinations and determine what would be needed to do the conversion. I like the idea of lots of gears and your original suggestion a year ago about using the T56 really got me thinking but I only want to do this once. Getting too old to be spending my weekends, grovelling around on the garage floor, pulling the car apart because I didn't do it right the first time.

Quote :

If i was doing your thing with the caddy towing etc, i,d re-tune the lt1 add a nice cai,. decent free flowing exhaust, bigger trans cooler, shift kit and 3:73's,.
be cheaper,. stronger and easier to get on the road,..

Your right but it wouldn't be as much fun, and besides, then I would be like everyone else .

The reality is the current engine has over 300 km on it and would have to be rebuilt anyways, so as long as it gets us south this year I'm happy. The other factor is mileage. Anyone who thinks gas is going to stay cheap should check out of Disneyland. The primary reason for the diesel is to get me my 40 mpg when used as my daily driver. Getting that with the LT1, and still having an engine that will haul the trailer would be a stretch. Diesel fuel just has more bang then gas (20% more). The trans stuff is just so I can tow the RV comfortably.

Bill

I had 4.56's in my Fleetwood with 26" tall tires and I did 100MPH stretches with no vibes from the stock shaft.

And Don, way cool chart!

I added a driveshaft speed calculation to the three tables.





PM your email address if you want me to send you an interactive copy of this spreadsheet.

http://www.impalassforum.com/vBulletin/showthread.php?t=233667

This came in handy when I was doing my calculations.