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Rear end ratio

Discussion in 'GM Powertrain' started by msm1889, Aug 20, 2007.

  1. msm1889

    msm1889 New Member

    I have just finished putting a Whipple Supercharger on my 02 5.3 Tahoe. The car runs great but frankly not my expectations! I think it's heavy car and I'm considering changes to the axel ratio. I have 3:73 on and looking for 4:10. I need help on couple of things:
    - How much Improvement should I expect in take off? I know it's not high way gears but my car is used alot in city driving and off road.
    -Do I need to match the same ratio to the front end, i.e both 4:10 in back and front? or can I just change the rear ratio and keep the stock front?
    - What other mods I can put to improve the performance? I have already put Headers and cat back, High flow induction but i would not touch the boost to keep the car street use!

    Any Help, thoughts or ideas are appreciated Guys.
  2. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    first of all, this does not belong in the member introductions area, it belongs in Powertrain issues. secondly, you must keep the same gear ratios in the front and rear, and switching out a differential's gear ratio can easily cost 300+ to just replace one diff, much less a front and a rear. You probably wouldn't see too much in the line of difference between 3.83s and 4.10s on takeoff. You will see some, but I don't think you'll see as much as it seems you're looking for, you'd have to go with really high gear ratios (at the cost of top end speed).
  3. msm1889

    msm1889 New Member

    Thank you, I guess first timers make mistake! I will pay attention next time but thank you again for the reply.
  4. CaJuN625

    CaJuN625 New Member

    Don't take it hard

    Don't let the "wrong place" comment get under your skin. Maybe this person just hadn't had his morning cup of coffee before they replied.

    Anyway, yes, both front and rear as you were told. If you only did the rears, imagine the problems when you went to 4wd the first time and the fronts tried to turn different rpms than the rears?

    You'll find it costs about $250-$300 in labor alone to switch gear ratios on the back. The fronts can cost up to TWICE as much because of the IFS not allowing the gears to be removed with the housing attached to the frame - unlike the rear-end. You can get new gears for $160-$500 a pair (you'll need two sets, obviously) that should have all the bearings and spacers and such that you'll need for the swap. It's not something you want to do yourself, though, as it's something that takes ALOT of practice to get right. You might get lucky doing it yourself, but ... the risk is WAY too high, in my opinion.

    It amazes me that the 3.73 gears aren't to your liking. I've got 3.42s in my Tahoe and under the right circumstances, she'll take off like a bat out of hell. No, she's not a Camaro or Mustang, but for 3 tons of steel and a small block ... wow.

    I'd turn my resources to a custom tune for your computer, personally. It seems to me you're missing something ... if you've got a supercharger and STILL aren't happy. Keep in mind, you don't have a big block, you've got a 327 on a vehicle that's twice as heavy as the original cars these engines were put into : Corvettes and Camaros and the like (2800-3400 pounds). Even so, you should have about 375-400 at the flywheel, now, so you should have noticed SOMETHING. Definitely get the computer reprogrammed to understand WHAT it's got and HOW it should react. Money well spent.

    Good luck.
  5. TrailLeadr

    TrailLeadr Epic Member 5+ Years 1000 Posts

    I have to agree with Cajun on the tune.
    Don't worry about Crawdady, we'll have him whipped, and flogged later.:slap:

    BTW: Welcome to the club. Keep us posted on whatever you decide to do.:great:
  6. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    sorry if I came off the wrong way, it's just a pet peeve of mine I need to get rid of. I didn't mean to scold or be angry at anyone or anything of the sort. Tuning the PCM does sound like a good next step. I wanna get some bolt-ons done before I order my chip, then again, PCMforless does offer reprogramming to new specs for just $50 bucks... (did I get some brownie points for the plug TrailLeadr?:rules:)
  7. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    From experience (I own a supercharged Tacoma and a Turbocharged Toyota truck, and recently sold a supercharged Suburban) I can tell you that if you havent had the computer and engine tuned for forced induction your missing out on a lot of potential performance.

    Yes gears should be matched from front to rear, you can be off by less than 10% between front and rear but its best to get the same ratio for both axles. 3.73 to 4.10 is to much of a difference. The only trucks I can think of that run a different gear ratio front to rear are dedicated mud trucks that use a smaller tire and lower gear ratio up front so they can keep the front tires spinning to steer the truck.

    Additional Mods:
    Index the plugs
    Bigger plug wires
    Different plug settings (you may be able to run a hotter plug with the Supercharger)
    Upgrade the manual valve body in the transmission
    Or a performance built transmission

    You off-road this truck, what size tires are you running? This could also be some of your lack of performance issue.

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