Yelo

how strong are the underdrive setups from Gear Vendors??......I know they hold up to diesel torque and trailer towing but what would happen if I used one on my truck to achieve better acceleration ??

I am swaping to 305/70-16's, I know I am going to lose acceleration from the taller tires and I was thinking of using an underdrive to improve the acceleration and performance around town and then once I am on the highway I can kick it off and still have decent highway RPM's, it seems that it would also be better than a higher-stall converter because there would be no motor spool-up time or towing restriction, it would also give me 8 gears to work with instead of 4 when towing my fifth wheel

I know the price is outrageous ($2695) but it may be worth it to me

Slowverado

it's not really 8 seperate gears really, it's like each gear is devided in half...like 1L/1H 2L/2H 3L/3H 4L/4H right?

Yelo

yeah...that's right
it's not quite in half though......it's more like a 22% underdrive for each gear

so...for a 4L80
1st is 2.48/3.02
2nd is 1.48/1.80
3rd is 1.22/1.22
4th is .76/.92

it almost makes a 4L80 into a 4L60 in terms of gear ratios

Slowverado

gottcha....you couldn't elaborate on how it works could ya? or maybe a link, this is kinda enteresting

Hit Man X

It splits your ratios by adding the 22% decrease to each one for the next gear... that will give you a ~1.93:1 1st when used not a 3.02:1. To make the best of this you should run 4.56:1 rear gears using both OD's and get a 2.46:1 OD. The 4.56:1 will make you accelerate faster and the double OD will keep the RPMs down.

I hope that makes sense.

GMC SKI

How Do you switch gears with the unit ?
Is it maual or computer operated ?
Driven by the computer would be good don't wanna be shifting so many gears

Yelo

Slowverado...... www.gearvendors.com

Hit Man X....I want to use it as an underdrive...not an overdrive (it can be used both ways....it all depends on how you order it), as an underdrive it creates a numerically higher gear (faster acceleration), as an overdrive it creates a numerically lower gear (lower rpm)

GMC SKI.....it is a push-button gear switch....let off the gas, push the putton. hit the gas...there is no lag when switching gears (less than 1 second to shift)

the unit replaces the tailhousing of the tranny on 2wd trucks and on 4x4's it replaces the front half of the housing of the transfer case....each unit is application specific so there is no need to lenghthen or shorten driveshafts or move transfer cases or mounts

Hit Man X

I didn't know you can order it to underdrive your gears! That's pretty bad ***, I assumed it was only to overdrive them.

Would it not be cheaper to install a 4.56:1 rear end gears, low gear set in the 4L80E and a mild stall converter to help get you out of your way? I'd say that could be done $2000 or so...

JamesB on FSC has a GV unit, you should PM him about it. He's cool as hell and will help ya out.

Yelo

the GV underdrive is in this case not just for performance unfortunatly, I want to use it for towing purposes as well....I tow a 9000+ lb fifth wheel a few times a year and a flatbed car hauler monthly, it would improve highway towing by giving me something in between 3rd and OD,

the lower gearset in the 4L80 was an idea but I haven't had much luck finding info on it....can ya help me with that ???....the 4.56's are out of the question because I already run 3000rpm's at 85mph....if I get any worse gas mileage my wife will divorce me, and the higher stall converter has me a little worried about tranny temps...I know Yank's TT2600 retains full towing capacity but heat buildup is still an issue when towing (more slip = more heat)

Hit Man X

Here is what I am thinking:

Go for the low geared 4L80E - http://www.tciauto.com/gm/gm_4L80E.htm (bottom of page)
Run a 4.56:1 rear axle
Go for the GV Overdrive unit.

With the GV in double OD with 4.56:1 gears that should make your OD now a .54:1, thus dropping your 85mph cruise speed from ~3000rpms to ~2300! That's nice. The lower 4.56:1 would allow you to haulass around town more (I mean tow better ), have that 3rd gear split for higher torque multiplication with lower RPMs, and have 2 OD's for the high speed cruise.

You could install a B&M supercooler with an electric fan on it that comes on at ~200* to keep temps in check, also I remember you saying you still run a 195* thermostat! Ever thought about a 180* or a 172* LS1 one?