LS2 and a ZF S6 650 Transmission, Am I crazy?

[JRhino]

Hello, I just wanted to get some input. I am graduating college in a few weeks and will be purchasing my first truck. I am planning on picking up a regular cab, short box, 4.8l, and a manual transmission. 4wd vs. 2wd is still up in the air but I am leaning towards 2wd for its simplicity.

My thought for using the zf transmission was so that I could hook up as much power as I wanted to it and not have to worry about the transmission breaking, I would keep my towing abilities where with a t56 I couldn't tow. I can also have excellent gas mileage on the freeway and also have great take off gearing.

I just wanted to see what others had to say. If you think I am crazy going with this transmission tell me why. I prefer if you have experience with it. I have yet to go test drive a vehicle with this tranny. Who knows maybe it just has poor overall performance and acts like a dog do to its size.

Thanks

[TXsilverado]

what are you planning of doing with the truck? are you going to race it, or do you plan on just pimpn' it.

[Hit Man X]

As I recall 1st gear is usless... like 6.XX:1. It's HUGE. I don't think it'd fit without some trans tunnel mods or a bodylift. They're also pretty spendy if you can get one.

Why can't you tow with a T56? It's a good close ratio unit... with 30" tires and a 4.88:1 you'd be around 2100rpm @ 70mph in 6th as it has 0.50:1 OD I recall.

[JRhino]

The problem with the t56 is the truck would be useless as a tow vehicle. I figure with the stock diameter tires and 2.73 gears in the rear, 70 mph in 6th (.76) gear would be 1,600 rpm and with 3.08 gears, 1800rpm. With 2.73 gears 2nd gear would still be useable as a starting gear on the street. But when it comes to having a little fun 1st gear at 1000rpm is about 5mph. The z51 packaged corvette goes 7.87 mph at 1000rpm with its stock rear end. Changing it to 4.10 gears is 6.56mph at 1000rpm.

I guess this transmission is a little to wide ratio. I just which there is geared in between the t56 and the zf that can take the power of 500 - 600 horses and not have a problem towing 5000 pounds when needed.

About the size of this transmission, everybody seems to think that this thing will be touching the ground. I guess I have not actually seen one of these things in person but looking at the transmission on this webpage http://www.thedieselpage.com/duramax/ZFS-650.htm it seems to me that the transmission doesn't fall but a couple of inches below the bottom of the bell housing. So, wouldn't that mean if the transmission was touching the ground, the oil pan on the engine should be too?

Anyway I am still evaluating my options and who knows by the time I actually get the money to get this far on my truck (2 years down the road), I will have some other tranny option to deal with. Maybe for now a tko would be a better option to solve my problems. The goal for this discussion for me was to figure out what I need to do so I am not purchasing extra services for something I am going to pull out later.

Thanks for the input

[JRhino]

Does anybody else have input on towing with a t56? 5000 pounds is all I need to tow on occasion.

[Hit Man X]

Go read up on the T56 F-bod ratios... last time I looked 1st was a 2.66:1 and 6th was 0.50:1 for the newer ones. You can get different gear sets from older ones. Lower 1st and taller 6th.

Regear the 10 bolt out back with the T56 and it's fine.

Remember you're trying to combine two different trannies for one purpose, a GIANT HD/Towing unit and a Racing unit in one...

There's no short throw shifter for the ZF, it's got an odd shift pattern, etc...

[JRhino]

doing a little more thinking.

original tranny nv3500 1st gear 4.02 x rear 3.23 = 12.9846.
t56 transmission 1st gear 2.66 x rear 4.88 = 12.9808.

70 mph is around 2000 rpm.

that sounds a bit more reasonable. and towing doesn't look like it will be that hard on the transmission with that rear gear ratio either.

[6gear]

I have 4.56 gears with my T56 and I turn 2000 rpm's at 78-80 mph with a 29.7" tire. I have put about 20K miles on this since the swap. If I was going to do quite a lot of heavy pulling I would go to 4.88 gears. Maybe some of this will help

[Hit Man X]

Or simply don't use 6th when towing in the T56. I think 5th is something like 0.72-75:1...

[RedHeartbeat]

You honestly don't want to tow a trailer in OD. You put mechanical levelage against the mainshaft of the transmission when in OD. GM, Ford and Dodge all recommend not to tow in OD. I destroyed a 5 speed pulling my boat in OD. I guess they know what they are talking about.