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TH400 rear end gear??????

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Old 07-20-2011, 12:35 AM   #1
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Default TH400 rear end gear??????

I am going to be switching rear end gears when I swap my m6 for a Th400. I am wandering what gears will be decent for the car. It is a H/C car with nitrous that will have a 28in tires if that makes a difference. I will be driving the car on the street and still want to take it to work on an occasion so it will see highway. I was really considering a 3.73 for the rear end or would a 3.42 be better. Let me know what you guess that have TH400's are thinking. Thanks Trevor
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Old 07-20-2011, 06:12 AM   #2
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a 400 is 1-1 in high gear-if your present trans (i dont know what an M6 is)
has a 1-1 gear, just drive around in that, its gonna be like a 400
3.73's, 28" tire, plus a stall converter, your gonna be reving up, a custom converter built to your specs. would help
there are some calc. out there to plug in your #'s, see what your RPM's would be, but they dont take into consideration to much converter slippage
having lived with these things for so many years w/o an OD trans, i can tell you i use nothing but a 4L80E anymore, lol
3.55's are a pretty good choice, but you really need the cam, converter, rear ratio to all be working together, not mismatched
ok, i have had too much coffee this morn, lol
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Old 07-20-2011, 08:07 PM   #3
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I have a 4.11 in my th400 car and hate it. Car tachs about 3500rpms on the freeway at 65. Its screaming. I am about to do a 4l80e swap. Drive your 6 speed in 4th for a little while. Thats 1:1 just like 3rd in a th400.
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Old 10-15-2011, 09:46 AM   #4
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how is it in the 1/4 mile with the th400 and 4.11 gear? does it run thru the traps ok or do you run out of gear? what kind of HP you making? I have a 4.10 and doing a th400 swap. i'm worried i'll run out of gear with the 700hp motor.
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Old 10-15-2011, 10:59 AM   #5
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depends on your rpms. I was turning 65-6800 going through the id say not a 1/4 set up. I did a calculation and it said top speed was 135, only about 30mph off LOL. I doubt converter slip could account for that... This is with a 4.11 gear/28in tire
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Old 10-15-2011, 07:14 PM   #6
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for 1/4 you need 3:73 or 3:90 depending on set up cam,nitrous or turbo
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