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Switching from 3.89 to 3.00 gears...

Old 09-02-2015, 03:02 PM
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musnicki
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Default Switching from 3.89 to 3.00 gears...

My car is a 67 Mustang with a 9" rear, TKO-600 with .84 5th gear, tires are 26.1, and 3.89 gears. Currently I max out at around 75mph at 3100rpms. Kinda rough on the FE 428/7.0L that I have in it, especially after doing a few 1500+ mile round trips across the USA in it. I just moved to Germany and the cars here are crushing me on the highways here. The average speed, when the speed cap is lifted, is about 180kph/120mph. I have coil suspension all around and dropped it to the ground already but my rear gears are whats holding me back...It handles great at 135mph, it's just that I can't sustain that speed for hours at a time (if you're doing the math, that's 5500rpm). I have disc brakes x4 already, so stopping isn't a problem. I hate BMWs, Audi's and Merc's non-stop passing me...my poor American pride :'(

Does anyone here run a big motor with low low gears, like 3.10, 3.00 or 2.90...how much take off speed will I be giving up?

Thanks,

James
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Old 09-02-2015, 03:04 PM
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Booger...finish your Fastback.
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Old 09-02-2015, 04:49 PM
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69mach1377
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What is the 1st gear ratio on your tko?
.84 OD is not much either.
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Old 09-03-2015, 12:57 AM
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1st gear is 2.87.
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Old 09-03-2015, 06:48 AM
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fastbackford351
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Just this last weekend I FINALLY got off my cheap *** and upgraded the 8" pumpkin from the factory 2.80 peg leg to a 3.25 trac loc. I didn't go higher because I still have the C-6 and didn't want ungodly RPM's on the highway. I figured the 3.25 would be a good compromise and I have to say that I'm pretty tickled with it. It has, obviously, more oomph off the line while keeping the revs at an acceptable level on the open road.

I have always run a small block and even with the 2.80 in it I had plenty of pull off the line for any driving condition Hell, even with my 2.80 and a small block I was able to do great one-wheel squeals with minimal effort so with a big, healthy FE, you'll be just fine and be able to scald the hell out of your tires.
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Old 09-03-2015, 09:46 AM
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69mach1377
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Yeah, big block torque should have no problem with a rear ratio change. But your OD may still prevent easy cruising at high speeds, the math is easy enough.
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Old 09-22-2015, 09:19 PM
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Originally Posted by musnicki View Post
Booger...finish your Fastback.
Damned you!! And your big block!! I picked up a engine stand this past weekend, and started collecting my Post 911 MGIB for college.. Soon, my friend, soon!!
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Old 09-22-2015, 09:22 PM
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Would it be easier to change the gear set in the trans to something like a .64 like the AOD? I know nothing about the TKO, but it would probably be worth looking into.. ?
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Old 09-23-2015, 07:11 AM
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Chromeshadow
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https://www.gearvendors.com/

You could add this, seen these on a few classics
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