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Discussion Starter #1
Getting ready to do my new rear end and playing around with some numbers.

My car is a 3320lb race weight SBF fox and dyno's a bit over 900 at the tires. Haven't made a clean full power hit yet but leaving on no boost and peak boost dialed back 6lbs it went 6.01 @ 121mph. Should have quite a bit more in it. Hoping to go 5.50's or 5.60's

Anyways, about the gearing. It's a 95% street car and I would really like to drop the cruising RPM. The car really doesn't hook at all on the street so I was thinking what would be the harm in throwing 2.73's in it?

The car has a TH400 and the final drives look like this...

First = 2.48 x 2.73 = 6.77
Second = 1.48 x 2.73 = 4.04
Third = 1.00 x 2.73 = 2.73

Just for comparison...this is what the finals would look like with a glide and 3.73's which seems to be a pretty popular combo.

First = 1.76 x 3.73 = 6.56
Second = 1.00 x 3.73 = 3.73

I would imaging I'm going hurt the 60' a little bit - but how much? What else should I consider?

Thanks!
 

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I ran a 3.08 gear in my car with a th400 and a 275 tire. IMO it hung on the converter a little more than I liked at slower speeds (35-50ish). I swapped to a 3.31 and it was way better I though. Not sure if that helps or not, but I don’t think the change would hurt ya.
 

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I was running 5.30s @ 133 in the 1/8th last year with 3.27 gears and TH400. I love it! Best of both worlds IMO...cruises nice on the street with not too much rpm, but also hauls decent to the 60' on 275s...1.27-1.30 range. I thought about going to a taller gear myself, like a 3.08, but I think it would put too much heat in the converter at lower speeds. If you are planning to send your converter out to be optimized for the 2.73s, then I'd say go for it and let it eat!!
 

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Discussion Starter #5 (Edited)
I appreciate everybody's feedback. The car had 3.27's in it last year and I really liked them. Now 3.73's and I hate them. I was thinking if the 3.27's were good then maybe the 2.73's would be even better since the car is making more power than it used to.

I have to get my rear rebuilt anyways...maybe I'll just throw the 3.27's back in.

As far as converter optimize though - yes, I'm blowing through it now. It came with the car and doesn't have any distinguishable markings on it. Any ideas who I could send it to for a restall?
 

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PTC will let you know if they can make it work for you or not. If not, sometimes they’ll give you a credit towards a new converter. Just send it in with a note to call you. Can’t beat that.
 

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What weight, and HP levels are you guys talking about with these ratios?
 

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I’m blown away with these ratios. Gone are the old days of the engine humming when you hit the highway. With the small cams turbo combos use and the torque you can make even at part throttle, you really can have your cake and eat it
 

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I was 3700 lbs or so when i was running my 2.73 26” tire and ~650-700 whp. It was just a pump gas first turbo car build. Went 9.8’s footbraking 1.49 60 ft. Never left on boost.

My 3.42’s with 28” tire is decent on the street. Reallly will be nice with 3.08’s. 1000+ whp overcomes anything, even leaving it in 1:1 3rd gear and romping on it from 45 mph roll
 

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Does anyone make new 9" gears taller than 3.0 ?

I want a set of 2.5 or 2.47 but theyre a bit difficult to come by lately in my neck of the woods even used. New I havent seen anything taller than 3.0 ?

Of course the other way to get more SLR with tall diff gears for a mostly street car, without going to heavier 4 speeds... is a low gearset for the t400, lower 1st and 2nd with 3rd staying at 1:1 for the highway.
 

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This is the same exact setup Im currently swapping my fox over to and replacing the tranny with a built 400.. I'm looking into a gear vendors OD for the 400 seriously and seems like a great option giving the 400 a .79 OD.. A lot of the drag week guys run them and theyre supposed to be bullet proof.. Ever look into that option with maybe a 3.00 or 3.25 gear swap?
 

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Do your homework on what the GV overdrive will really handle especially if you are considering engaging it under full power. There is a thread somewhere that details him destroying it several times. I guess everything has its limitations.
 

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Here you go.

 

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Strange. My buddies 598 nitrous car never seemed to have any issues with their gear vendors unit. Its been on 2 drag weeks i believe. I thought it didnt do anything under wot tho, only allowed overdrive at part throttle.
 
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