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Discussion Starter #1
Hi guys. I am hoping for some help, please. I've been googling and looking at calculators etc and I am just torn what to do about rear end gears in my GT and those calculators dont tell me exactly what I am looking for... sorry :s

A little About me and the car. The car sees the track twice a year. However... it is also just a nice weather toy with a great 6th gear for hwy cruises so...

Currently I am centrifugal vortech supercharged at 650whp the car weighs approx 3250 with a teksid aluminum built motor etc... again the car makes power between 5600-6200rpm. I have the T56 with the tall 2.66 first gear. I am running a 28" Mickey Thompson Street R sticky DR with 3:73 gears out back. I've been down the track 2 different days with little seat experience paying most attention to launches , boost guage and AFR guage as well as staying straight and perhaps watching the guy in the rear view mirror lol j.k. I can not pin point my rpm while crossing the line, sorry. However... I am NOT all the way through 4th. Best slip is an 11.02 @ 127mph with a 1.7 60' with a bad 1/8th mile of 95mph and a 6.8 sec. I am wondering if the 3:73's with the bigger tire and T56 is dragging me in the 1/8th

Which gears would be best to wake up this centrifugal supercharger and turn the 28" tire with the long 2.66 T56 transmission.

I dont want to swap tires.... I like how the 28" fits in there and they were already expensive enough. Plus I hook better with those 28's over a 26"

Any help would be appreciated guys I may also up power to around 700 or so. But I am hoping to order gears soon
 

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I would leave your set up. It sounds good as is. If u start hooking up be prepared for breaking stuff like axles. 28" tire 3.73 gears are the best all around combo. If u like the way it looks even better.
 

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4.10:1 and don't look back.
 

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I messed with a calculator a bit and I agree with the 4.10 gearing.
Puts the car at ~130mph at the top of 4th gear at 6400rpms (Assuming you'd shift here given your power band)

What do you normally shift at?
 

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Discussion Starter #6
Hi guys. Thanks for piping in. The rear end is built pretty tough with 31"Moser Axels, C -Clip eliminators and an Eaton centre section. Clutch is a spec III plus capable of some good tourque. The tranny is built as well.... I'm just working at putting down the power now. If I were a roots or twin screw type blower I realize the hit out of the hole would be a lot harder and 3:73 would be best ? But the centrifugal doesnt hit as hard with less chance breaking things. I was hoping to find someone with some real life experience or someone who can actually use the calculator... I looked on line a d there are many variations that just leaves me guessing still.
Power is made between 5900 and 6400rpm with a slight climb from 5900 to 6400.
 

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IMG_0459.jpg Real life experience with a 28''x4.10. On a good day 127, on a better day 129. Same car just a different motor. In your RPM range. With a 4.30 you'll be over your rpm range unless your car is capable of running it out the back door with a little bit extra. On a 1/8 mile track it would flash my shift light right at the stripe @ 6500 at the top of 3rd @ 96. I wouldn't worry about axles. You'll be just fine in that department. BTW nice car!
 

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Discussion Starter #8
Thanks for the reply Mr
2 step. Nice car with big boots yourself. 😉 I am intending to be a quarter mike contender... but looking at my 1/8th ? That's where I was thinking gears would help. I am at 127mph now in the quarter with the 3:73 @ 11.02. I just want that little extra but, I am also stepping g up power a bit from 650 to potentially 750 or 800. I just want to.make the right gear choice before I spend $. Thanks for your input Mr.
 

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A 4.10:1 gear will have a softer hit on the tire compared to a 3.73:1. My car has a P/D S/C with a 4.10:1 gear and used to have a 3.73:1 gear. It is easier to get the car to hook out of the hole with the 4.10:1 gear. It sounds counter intuitive, but it works. I even used the 4.10:1 gear with a 26" tire with no issues. Just need an engine that can carry the rpm with that set up. I am going to go to a 4.30 gear because my car is a 1/8 mile car. With 3.73 gears and a 26" tire I had no issues running the car all the out through the 1/4 mile. With 4.10's and a 26" tire I can get to 1,000 feet before I run out of rpm. With the 28" tire and 4.10's it allows me to run all the way out in the 1/4. Going to a 4.30 gear or so should optimize my 1/8 mile package but still let me run it out to a 1,000 foot or so. If I let the car go for the full 1/4 as it now sits with the 4.10 gears I would blow right through the 8.5 chassis cert, and going to a 25.5 cert would set me back $4-5K+or so. I don't want that expense right now so I keep it contained to 1/8 mile stuff.
 

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Discussion Starter #11
Thanks for the experience Saleen 414. Even with a 26" tire hey ? And you're running the T56 6 speed tranny ?

I am leaning between the 3:91 & the 4:10's... tough decision. But I think I need to ditch the 3:73 's
 

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I have a street car,same gear box that you have. 28'' bias ply tires (Hoosier QTP 28x11.50)
My fox is a little lighter and a little more power,i use a 3.90 gear.

For the track a 4.10 gear set will work for you. On the street with radials,is a whole other story.
 

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Discussion Starter #13
JB Books. Thanks Mr. Also a good real life advice. Thanks man. Honest. Maybe the small incrimint from 3:73 to 3:91 will be enough to wake this car up and help my new to me Ysi centri blower get into the rpms more respectively? Yeah for the highway we have the super tall .5 6th gear... but I just dont want 4:10's ripping tires everytime I wanna get on it in town... I still wanna plant my foot in it and proper forward. I didnt want to play a guessing game on ratios and tires... it's nice to hear others feed back on real life experience. I am at 650whp now probably going to be 750ish with the new blower and tune.
Any other advice is much appreciated
Thanks
 
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