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help on Rear end ratio for AI 5.0


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I just received my Novice Permit at Summit Point in Nov. Ran my first race there. What a gas.


My car is a 91 LX 5.0 with a 347 stroker and a 3.73 rear. I find myself rowing a lot of gears around Summit and VIR. I am changing the rear this winter but cannot decide on whether to go with a 3.55 or a 3.27. At Summit, I ran out of 4th at about the tower and had to go to 5th which is worthless in a T-5. I think I have the torque to handle a 3.27 which would give me a top speed of 140 at 6000 rpm, as opposed to 129 with the 3.55's. Top in 4th with the 3.73's is 123mph.


My torque should be about 345 ft/lb at the rear wheels.

So, 3.27's or 3.55's?

Advice will be appreciated.


NASA Mid-Atlantic (VA)

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Ah-ha! That other green Mustang! I met you at the October event... I was down for the Seat Time on Friday and the NASA weekend in the dark green LX, AI#61. You seemed to have you share of problems that weekend, but it looks like you got it sorted out for the next one. Congrats.


The gear choice really depends on what you plan on doing with the tranny. The standard OD in a T5 (.63) is a losing proposition.


I have 3.55's and a .83 5th gear (T5), and at Summit I can hit the rev limiter (6250) in 4th with plenty of track to go. I'm in 5th for quite some time. If you don't plan on getting a short 5th, you better stick with the 3.27's... but even with 3.27's it will be borderline. You might find yourself approaching redline and cruising for the last part of the straight, which will have a major impact on laptimes and make you a sitting duck for getting passed into turn 1.

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Don't bother changing the rear IMHO. It will just give you more top end (more speed before you hit 5th) in exchange for less grunt off the corner.


Leave the 3.73 in, and get a .80 (or .82 or .83, depending on the trans) 5th gear in there. You'll be very happy you did!



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Ask for Steve. He'll take care of you. If he says he doesn't have one, just reply with "Oh, so that's why your car is so slow...", and he'll find one.

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I also find myself shifting between T1 and T3. Coming out of T1 in 3rd I have to go to 4th for the short straight before T3, then have to decide whether to go back to 3rd for T3 and shift into 4th going up the hill and through the chute before going back to 3rd for T5, or stay in 4th for T3 and up the hill.



3.55 should allow me to stay in 3rd through T3 then 4th up the hill and through the chute, then 3rd all the way throughT9.


Where 3.27 would probably make me go down to 2nd for T1, then 3rd for T3 through T10.


??? Thoughts?

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All depends on how fast you want to go. With 3.55's I still have to shift into 4th between T2 and T3, and back down to 3rd for T3. I'm not sure that 3.27's would even get me out of the shift, although the lack of grunt off of T2 would certainly lower straight speed. T1 is a fairly low speed turn, T2 is fast, and the T2-T3 straight is pretty long-- I think it is unreasonable to expect to do it all in one gear.


I think that 3.55 is the best gear for you. You'll pick up 6mph in 4th, which may not be quite enough, but it's a lot closer. The only thing that 3.27 will buy you is some more top end in 4th, I think it will hurt you everywhere else. Put the right gear in now, in preperation for the 5th gear that you'll do later


What kind of lap times are you running? Remember that as you get faster you will achieve higher speeds everywhere on the track, and that means you will need to upshift where you didn't before, and some downshifts may be unneccesary.

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D&D did have the gearset. Said they have a few although Tremec is no longer making them. $189 plus shipping.


Now....alll I have to do is put it in


Again, thanks.

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