Supercharge or gear swap?

[ASTAR]

Ok so I Love my new Hummer but the mileage sucks (I knew it would so no biggie) and the power is lacking. I went from a 700hp/1400ft lb tq Dodge diesel truck to this and man, what a difference. I am not expecting to have a hot rod like my Dodge was or the tow master it was either but....
Something I can't deal with is the lack of being able to hold 4th gear on the freeway at speed. If I am doing 70-75ish and there is the slightest incline, it slows down (cruise on or off) and then downshifts to 3rd to hold speed. Its constant. I have 38" tires on it now and I know that made it much worse. I did the small engine upgrades (see signature) but it still sucks badly.
Ultimately, I would like to gain seat of the pants power and can't decide how to do it. I was thinking about putting 4:88 gears in it but wonder what will happen to my fuel mileage. It was around 11.5 before lift and now around 9 with the lift/tires. Maybe a supercharger (yes I have been searching) but the transmission scares me. I don't want to dump another 10 grand into this thing between the upgraded tranny and supercharger itself. What will the MPG do with a supercharger if I did though?
I also tow about 7k once or twice a month. Not a big deal but if I hit a hill, whoa, it hurts. The MPG drops hard and the power is seriously deprived.

So whats the word from the masses?
I figure I can install the S/C if I go that route and maybe I can talk GM into helping out some with a tranny if I smoke it? Maybe? I'd also return the Airaid and Hypertech if I supercharge (money back) since it's only been on for about 2 weeks. Gotta Love Summit!
If I do the gears, I'll have to have them done as I don't know how to "set up" gears.
Seems the gears would be a lot cheaper and more warranty friendly but will I feel the power again? Will I have horrible MPG since RPM's will be higher in O/D on the freeway at 75mph? I'll also be keeping the Airaid and Hypertech if I re-gear.

Any input is appreciated, I can't deal with this downshifting!!! HELP!

Thanks.

[KenP]

You're complaining about mileage, lack of power and inability to hold OD on a grade. Put the 4:88's in and you'll have that times 2.

Install the SC with a proper programmer and that will really help. But that also will bring other problems with it.

PM these guys:
HUMMERcustoms.com/TAZ
or
HGW

[rocketw19]

i would suggest the magnuson super charger with the stock program. adds alot of power but still dependable no tranny problems for me. they have after market guys settin up super programs to get the most out of there trucks but i have no clue how reliable they are. or if the factory warranty is still there. gas milage is gonna suck no matter what but you should of know that already. my milage droped from 10 to 8.3 do to me pressin harder on the gas peddle i like the fell of the SC.

[Screeper]

I have 38 inch tires and did the gear swap to 4:88s which I highly recommend. I am very pleased with the result. I think your MPG will improve as you are pushing a lot or tire and gear with that tranny in your current set up. I used a hypertech programmer to correct my speedo and got it right on, although I had to play with tire size as it only went up to 4:56. I recently went up against a non lifted factory tired 05 and pulled on him to 55 where he started to come back but seat of pants was a huge improvement. I dont downshift at all at 70 and only occasionally at 75. At eighty I am spinning 2500rpm exact. My mpg went from 11.7 before the lift,tires and gears to 10.2 after. The mpg goes to hell after 70 mph. I am obviously a fan of gear swap. The torque strain on the tranny and engine pushing those tires with a supercharger as got ot be immense. I think the heat and wear have got to be an issue. If your looking for pure fun, and not mechanical longevity, I dont think you can argue with a supercharger.

[KenP]

Our mileage went UP after getting the SC from the 10s to the 11s.

Screep, with the 4:88s, you're turning a higher RPM across the entire band. I don't understand how you could get BETTER gas mileage.

I do see the truck performing better.

[Screeper]

It comes down to how hard the engine is working and where you are placing your torque curve for optimum fuel economy. Imagine your transmission got stuck in third gear and you were driving in the city. The engine would be straining constantly to get the truck moving. You would have to be hard on the gas and most of your MPG would go into the converter to generate the torque need to move the truck. Big tires have the same effect as taking away your first gear. Changing the gears allows the engine and transmission to not "see" the size of the tires. My 4:88s with 38 by 15.50 tires in gears 1 through 3 pretty much have the same rpm range as factory. Anouther way to look at it is like a bicycle. Imagine you and anouther rider are about to go up a large hill on mountain bikes (resistance) You both are equally strong and the bikes are identical with the exception that your bike is stuck in its top gear. The other rider can drop into his lower gears and pedal much more easily. When you reach the top of the hill the other rider is fresh whereas you are exhausted. Your bike would have been the best and required the least energy for long long flat rides but stop and go or up hill it required the most energy. It basically comes down to allowing your engine and transmission to work at the RPM where it is most effective. I am no expert so I hope this is somewhat understandable if not a bit wordy.

Al

[KenP]

Iunderstandwhatyouaresayinganditseemstomakesensefr omstrictlyalogicalstanding.
Imjustnotconvincedthatforhighwaydrivingitwouldhelp butaroundtownitdoesmakesound
logical.

[HUMTECH]

Here's my take on it. Add more horsepower and torque but don't increase skinny pedal input=better fuel milage, engine doesn't have to work as hard to accellerate and maintain speed. Lower your gear ratio all you have done is increase your ability to accellerate, maintaining speed now requires higher engine rpm=lower fuel milage. Add larger tires with the gear swap, maintain somewhat stock ratio will still give you lower fuel milage cause now your just turning more mass unless you have light weight wheels and tires. Add weight and lower your milage, really it's quite simple.

[PARAGON]

Originally Posted by HUMTECH

Here's my take on it. Add more horsepower and torque but don't increase skinny pedal input=better fuel milage, engine doesn't have to work as hard to accellerate and maintain speed. Lower your gear ratio all you have done is increase your ability to accellerate, maintaining speed now requires higher engine rpm=lower fuel milage. Add larger tires with the gear swap, maintain somewhat stock ratio will still give you lower fuel milage cause now your just turning more mass unless you have light weight wheels and tires. Add weight and lower your milage, really it's quite simple.

you could put hydrogen in the tires

[KenP]

Originally Posted by HUMTECH

Here's my take on it. Add more horsepower and torque but don't increase skinny pedal input=better fuel milage, engine doesn't have to work as hard to accellerate and maintain speed. Lower your gear ratio all you have done is increase your ability to accellerate, maintaining speed now requires higher engine rpm=lower fuel milage. Add larger tires with the gear swap, maintain somewhat stock ratio will still give you lower fuel milage cause now your just turning more mass unless you have light weight wheels and tires. Add weight and lower your milage, really it's quite simple.

Makes sense. But NITROGEN in the tires would be cool.

[PARAGON]

Originally Posted by KenP

Makes sense. But NITROGEN in the tires would be cool.

liquid, no doubt

[KenP]

Originally Posted by PARAGON

liquid, no doubt

No doubt.

[Screeper]

Your right about not helping at highway speed 75+. The tranny compensates for the gears up to about 80 mph where it goes downhill real fast. As I said I am spinning 2500 rpm exactly at 80 mph. I dont remember remember what it used be factory and I am curious. The gains are all 70 mph down. If I cruise at 70 I get 10.7 solid. The truck leaps off the line and is much more enjoyable around town. I also had to tow three Harleys on a 20 ft flat trailer and was glad I had the gears as it towed better then when stock and the tranny did not get as hot. Phil helped me out with the gears and it was not too pricey compared to the supercharger. I also filled my tires with helium which cut a good two pounds off the weight of each tire.

Al

[ASTAR]

Screeper, what did the gear swap cost you and who did it? Is there a carrier break to go to 4:88's (did you have to use new carriers)?
How bad does the mileage drop off after 70? I drive I-5 a decent amount and 70 is the limit. If I drive 70, I get run down by big rigs!
My good ol Dodge, cruising at 90 on 5 and getting 16mpg.
Oh well, the Hummer is like nothing else!

[Screeper]

I dont remember the cost right now but it is on this forum somewhere from when I actually had the job done. It was very reasonable and phil will give you great price on the gears and also make sure you get the right ones. All you have to buy are the gears and a bearing kit as they are bolt in. As for driving over 80. I just went to Orlando and was in more of a hurry then worrying about a few bucks. I think I had the cruise set at 85 and was getting 9.0 going into the eights on the small inclines they call hills down here. I know my avarage for the whole trip was 9.5.

[ASTAR]

With the cruise set at 85 does it stay in 4th gear? Mine will not hold 4th with cruise going over 75. Barely holds doing 70. And the mileage is horrible doing 75-80 (like 7-8mpg) in 3rd gear!
Why did you not put 4.56's in it? I think that would bring it closer to stock, no?

[Screeper]

I spin 2500rpm at exactly 80 mph. I am curious what a factory H2 is spinning at the same speed. I wanted to do just a little more then stock to increase the torque getting to the road and offset the weight of the rims and tires. Around town its better then stock. As I said before at 75 it cruises perfect with decent mpg. I guess at 85 mph on 38X15.50 tires I should not complain about 9.0 mpg. Your down shifts sound like they are being caused by the engine revving to low and needing to get back up into its torque curve. I think there are some people on the forum who did the 4:56 and wished they had just gone to the 4:88s. The difference between the factory 4:11 and 4:56 is not that great.

[ASTAR]

Cool, thanks for the reply.
Yeah, the truck just can't pull a decent speed in 4th with these gears but if it goes to 3rd, it holds whatever I want, the mileage just suffers immensly!
I'm going to go with 4.88's then. Now to find a good shop locally that I trust to do the job!

[Screeper]

Good luck. I think you will be happy. Feel free to PM me if you have any questions.

[mowdoc]

Hey Screeper,

I checked this morning and my stock 06 was turning 2300 at 80 mph in 4th with the converter locked.

I doubt I'll ever go to larger tires but if I had 38s on I would be looking for 4.88 gearing. I think anything less would be too much load on the tranny.

I have considered getting the Maggie blower but am waiting to see what other problems develope after supercharging is done. It would sure be nice to drive up a grade and keep the damn converter locked. I love my H2 but GM needs to take a closer look at shift points and downshift requests on this rig. I was spoiled by a maxed out DuraMax diesel before the Hummer and I tow a lot. The D-Max would pull a hitch in half in 5th gear while this Hummer can't pull itself up a slight grade without downshifting. Like I said, I was spoiled by the diesel. I do love the Hummer, I just wish it would stay in high gear more.

mowdoc