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Charter Member
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Discussion Starter #1
I will be ordering my kit later this week. Doing the non donor appraoch and wondering what the gerneral suggestion or rear gears will be.

351W stroked to 408 ~500hp
TKO tranny
IRS
16" wheels

mostly for cruising on highway, but will play a bit too

I would like relativly low rpms in 5th gear, but I also want the quickness off the line!
Thanks
 

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Super Moderator
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29,434 Posts
3.55's or 3.73's would give you great acceleration, and still be driveable on the freeway.

2FAST
 

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FFCobra Craftsman
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849 Posts
I'm no-donor with FMS351. Bought the aluminum FMS carrier new. Only ratio available new is 3.73. Short first gear but there are several guys with 3.73 that love it. One of the guys swapped from the 3.73 over to 3.27 and after only a week switched back to the 3.73. It sounds like to me there is no right or wrong ratio, it just comes down to personal preferences.

I'm in the building phase so I can't really offer personal experience.
 

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Senior Member
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2,372 Posts
If you are running a 408 stroker. I would personally go with the 3;55 or maybe 3;27 With that kind of power, while the other guys are busy shifting you will be blowing past them!
Gearing is a substitute for lack of H.P.! :D
 

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FFCobra Fanatic
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1,038 Posts
I, too, am building a 408 with a Tremec. I am going with a 3.27 rear.

The reason is with this much power and being so light, you will blow past first too easily with any steeper gearing. First would become a useless gear.

With a 25.7 inch tire first goes to 46 MPH at 6500 RPM. This is nothing for the power to weight you have. Shifting to second takes you down to 4000 RPM and you shift again at 76 MPH.

Do you realize how much torque you will have at 4000 RPM? I figure over 500 ft. lbs.

And 2500 RPM in fifth is 86 MPH.
 

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Senior Charter Member
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540 Posts
from
http://www.thepontiactransampage.com/transgears.html

Ford Mustang 5.0l 5-spd manual1986-1988
3.35, 1.93, 1.29, 1.00, 0.68

1989-1994 5-spd manual
3.35, 1.99, 1.33, 1.00, 0.68

Borg Warner Close Ratio T-5
2.95, 1.94, 1.34, 1.00, 0.63 (0.80 optional)

Tremec 5-spd manual (aftermarket)
3.27, 1.98, 1.34, 1.00, 0.68 Model: 3550
3.18, 2.06, 1.39, 1.00, 0.65 Model: 3750S

A lot of guys say a 3.73 makes first gear useless but that depends a lot on what first gear you have. For example:
3.73 rear gear x 3.35 first gear(stock stang)=12.496engine revolution to tire revolution

3.73 rear gear x 3.27 first gear(Tremic 3550)=12.197engine revolution to tire revolution

3.73 rear gear x 2.95 first gear(World class T-5)=11.004engine revolution to tire revolution
This is what I have on my Hunter Cobra and I love the first gear. I used to run a 2.73 rear gear and it sucked

2.73 rear gear x 2.95 first gear(World class T-5)=8.054engine revolution to tire revolution

with the Tremic to get a simialr ratio use a 3.55 rear gear
3.55 rear gear x 3.27 first gear(tremic)=11.609engine revolution to tire revolution

using a 3.27 rear gear
3.27 rear gear x 3.27 first gear(tremic)=10.692engine revolution to tire revolution

before I changed out my 2.73 gears first gear felt like you were starting in second and it is actually almost the same as my second gear is now. The overdrive was useless and any legal speeds and 4th was useless unless you were on the highway. This is even with 275/40/17 tires which are much shorter than the 275-60-15 a lot of guys run on FFR's and other Cobras.

food for thought
 

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FFCobra Craftsman
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I am runnig a stroker from the engine factory 427w and one of the warranty requirements was to use 3.73 to 4.11 gears with the cam set up the engine came with.

I have the Tremec 3550 and a new Ford rear with 3.73's and first gear is a quick blink but 2,3,4 are pure fun if you get on the right pedal. With overdrive 5th is a charm for the highway...

I called Engine Factory to ask why those gears are better than others and the response was that the cam works best in the mid-upper RPM range along with that stump pulling torque down low but overall the gears they suggest have shown the best performance withthe engine..

They do this for a living so I am listening to them.. plus it gives me 1 year with peace of mind if I break the thing...

.02
 

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Senior Charter Member
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1,526 Posts
A guy in my area hopes to be finishing his Cobra in few weeks that has about the exact same setup you're describing. 408 stroker dyno'd at 451hp/482ftlbs. He's got 3.27s installed but hasn't driven it much. He's a good friend of Wayne's, so you can check back with he or I in a few weeks to see what he thinks of the 3.27s.
 

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FFCobra Craftsman
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784 Posts
Makeing a bit more than 500rwhp
and running the 3.27 gears..wouldnt have it anyother way..sill looking for traction..hrm...mayve a 2.73 and run 150mph in the quater..hehe

Phil
 

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I am a believer in steeper gears..3.73 being the max for me. With your set up I would go with the 3.55's. You should be in the 1900-200 range at 60mph with 26" tires.
 
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