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Old Aug 20, 2013 | 07:42 AM
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Default Rear End Gearing

PT7675 turbo, shift points round 6400, 4L80E..

Was thinking a 3.50 gear area, or go lower with a 3.08 maybe?

On a 27inch hoosier, the 3.50s put me round 146mph, which I do not think it has the steam for, but would be nice to have an easy car to launch.
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Old Aug 20, 2013 | 07:59 AM
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With the 2.48 1st gear in the 4l80 I would not be scared to to with the 3.08 of course a lot of things come into play when choosing a gear ratio that you have left out. Weight of car? What are your goals for the car? Is it a street car or track only car? Converter?
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Old Aug 20, 2013 | 08:11 AM
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Weight is prob 3400 area, goals would be a quick street car, 3400 area FTI triple disk converter.
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Old Aug 20, 2013 | 08:48 AM
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You'd be surprised what your car will do at that weight. That is about what mine weighs and I went almost 137 mph on 10-11 lbs, shifting the 1-2 at 5300 rpm. I am running a 3.23 rear and 27.6 inch tires. I am going back to my 2.73 10 bolt as I killed the posi in this one. I hated the 2.73's with my Mickey's because my converter is way too loose, but I need to swap. I need to get it tightened up this winter.
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Old Aug 20, 2013 | 08:54 AM
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I love my 3.73's for street use and my car has no problem pouring on boost with that turbo, however I am hitting the traps on spring pressure(10psi) and hitting the rev limiter at about 135-138mph. I'm on about a 27 inch tire. I'm going to give it a little more rpm and switch to 3.54's which is the lowest I can go with an s60 so I hope that puts me in the mid 140's. at least that is what the calculators put me at.

Edit:my honest recommendation is to run it at the track and evaluate from there. Fwiw when I ran a half mile event I used OD in my 4l80e to hit 165mph(low boost) and it took it like a champ.
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Old Aug 20, 2013 | 08:55 AM
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Originally Posted by RedRocketZ28
You'd be surprised what your car will do at that weight. That is about what mine weighs and I went almost 137 mph on 10-11 lbs, shifting the 1-2 at 5300 rpm. I am running a 3.23 rear and 27.6 inch tires. I am going back to my 2.73 10 bolt as I killed the posi in this one. I hated the 2.73's with my Mickey's because my converter is way too loose, but I need to swap. I need to get it tightened up this winter.
......mine is an LT1....
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Old Aug 20, 2013 | 08:57 AM
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What gear do you have now?
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Old Aug 20, 2013 | 09:16 AM
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Originally Posted by willizm
What gear do you have now?
3.73s but the stock 10 bolt will be replaced with a new 9 inch and I need to pick gears first.

3.08s means for a great highway cruiser thats for sure.
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Old Aug 20, 2013 | 09:53 AM
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FWIW...

3.50 gear, 28" tire, 6 speed, 6500 RPM shifts

4th gear (1:1) will peg the speedo give or take a few mph actual speed. 5th will cruise 65 @ 2000 RPM and 6th will do over 90 @ 2k.
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Old Aug 20, 2013 | 10:18 AM
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I would go with the 3.08 if it was mine, with the 2.48 low you will still be able to 60 if you can make the steam.
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Old Aug 20, 2013 | 10:20 AM
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Originally Posted by Shownomercy
......mine is an LT1....
My bad. Kind of hard to tell that with no signature...
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Old Aug 20, 2013 | 10:22 AM
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Originally Posted by 68 SS
I would go with the 3.08 if it was mine, with the 2.48 low you will still be able to 60 if you can make the steam.
Ok then maybe thats what I will do.

Originally Posted by RedRocketZ28
My bad. Kind of hard to tell that with no signature...
if you don't mention you drive a LT1, people won't ruin thread with Lt1 hate. Sadly enough.

Can you go with too much gear, IE 3.08 or is it just gonna be slow off the line and then once it lites off, be fine?
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Old Aug 20, 2013 | 10:44 AM
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I agree, that is sad. Nothing wrong with LT1's IMO. Your car should run well.

I have not had the opportunity to run my car at the track with anything but the 3.23 rear end. I do know, that I could build more boost on the foot brake without pushing through the tires with the 2.73's. I will hopefully have some times with the 2.73's in the next couple of weeks.
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Old Aug 20, 2013 | 11:26 AM
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Originally Posted by Shownomercy
Ok then maybe thats what I will do.



if you don't mention you drive a LT1, people won't ruin thread with Lt1 hate. Sadly enough.

Can you go with too much gear, IE 3.08 or is it just gonna be slow off the line and then once it lites off, be fine?
3.08 will give you the ability to leave with more HP it all depends if you can get the wheel speed up and get on the tire (converter) it may take a few converter adjustments to get it right but when you do it will haul the mail.
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Old Aug 20, 2013 | 11:31 AM
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Originally Posted by 68 SS
3.08 will give you the ability to leave with more HP it all depends if you can get the wheel speed up and get on the tire (converter) it may take a few converter adjustments to get it right but when you do it will haul the mail.
Trans brake should help with that, I hope.

383ci so the turbo should be easy to lite off.
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Old Aug 24, 2013 | 04:52 PM
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Swapped in a spare 2.73 10 bolt today, builds boost rather fast compared to the 3.73 rear I had.

Def gonna go with a 3.00 ford rear now.
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Old Aug 24, 2013 | 05:08 PM
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I love my 3.08 with 4l80. Boost comes on quickly, and cruising Rpms are low. Best of everything.
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