Gear Set Question

Hello,

I have a Mustang with a 347 putting out 475hp. I plan on road racing this car, no drag racing ever. I am a driver, not a mechanic, so I looking for a second opinion. The shop doing the work on the car wants to put in a 3.73 gearing. I was thinking 3.27 would be better for economy and top end performance. I was hoping someone out there could help me with this.

Thanks!

David

Reply to
SharkMan
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There is no one perfect gear for all road courses. That's why professional race teams carry multiple gear sets to the track. If you're only racing at one track, it's a lot easier. What is the top speed you'll expect to attain? Try and select the gear that places you just past the peak of the torque curve at that speed in 4th (1:1) gear. That will be a good place to start. But expect to make a change or two as the season progresses. Optimally, you'd want a 8 inch rear, with multiple center sections. The center section can be swapped out in less than an hour the first time. All it takes is a couple of hand tools. Even a non-mechanic can do it. The 8.8 is plenty strong enough, but since it has an integral carrier changing gears is time consuming and requires special skills and tools. A 9" rear is stronger, but also requires more power to run it. A well built 8" will last forever on a road course, will be lighter, and will deliver a little more HP to the ground.

Reply to
.boB

Kinda following up on what boB says..... (and I hope you mean a race track when you say "road racing")..... there is no finite answer toyour question.

30 years ago, we would have said the best gear ratio is the one that has you at max RPM in high gear (direct drive at that time) just before you have to apply brake at the end of the longest straight. With the equipment that is available now, and the money willing to be spent, the equation has grown to many, many more steps than what we have been use to.

The ideal situation has us being able to keep our RPM in the area where our peak torque is being developed in acceleration conditions and where peak HP is being developed during sustained high speed conditions. The ideal situation also has us in "direct"... that gear that gives us a 1:1 ratio to avoid gea losses.

The question you have offered is difficult to answer.... add the query regarding 'economy' and all bets are off.

Decide on your priorities and then ask te question again stating what you expect *within reason*. .....

Reply to
Jim Warman

The short answer I think is that you'll want more gear once you get out onto the track. In my 00' GT the 3.27:1's are ok but in lower gears take more time to come back up to torque peak. I have 3.42's in another car with much less power and coming out of the corners I get a better pick up than with the Mustang. Both have the BW T-5 transmission.

...Ron

--

68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert
Reply to
RSCamaro

Hi Bob,

Sorry, I guess more information is neeed. So here it is.

Rear End - 8.8, all 31 spline with Auburn Pro Transmission - the new TKO-600 TCET4617 Ford 1st - 2.87 2nd - 1.89 3rd - 1.28 4th - 1.00 5th - 0.82 rev - 2.56

The road racing I am taking about is not just track based, but also open road racing like the Nevada Silver Stakes Race. My car is speed classed to 160 mph. It can go faster once I do more aerodynamic work.

Thanks for the advice on the center section, I will look into that. It is my desire not to be helpless with a wrench in my hand.

Thanks for the information.

Respectfully,

David

1983 GT Hatchback
Reply to
SharkMan

Hello Jim,

Please see my response to boB. I think most of your questions are answered there. By economy, I am saying that with tight gas allocation, I need gearing that will be able to make the tank last the length of the race.

I am not a street racer. I will be running only in SCCA sanctioned events. I mis-typed in my previous response, it is the Nevada Silver State Classic. These are the types of races I will be running. The distances vary between 90 to 125 miles. So I am looknig for the gearing that will make the 22 gal fuel cell last to the finish line. The last thing I want to do is not finish by running out of gas. I am not sure what the fuel consumption will be just yet. The dry empty weight of the car is around 2400 pounds. I also will have a race-built

331 available shortly meaning Race gas only. The 347 is all SFI approved, but the engine will run on 92 octane gasas an emergency back-up car. I.E. when my daily driver is in the shop.

I hope this makes a litle more sense now.

Thanks for your advice,

David

Reply to
SharkMan

OK... I was thinking strictly in terms of close course racing. The 3.73s would be a pretty drastic change and may reduce your top speed. There are several free gear ratio calculators on the internet that will let you compute theoretical top speeds for different ratios. These may help make a decision for you.

If you follow boBs advice and go with a banjo style housing (and your racing budget will allow it), changing ratios for sifferent tracks/events can go pretty quick if you only need to swap out the pumpkin.

Reply to
Jim Warman

lmfao jim your my pumpkin

h u

r c

a

s t

Reply to
mustrang888_8

You ilterate moron, keep your stupidity to yourself. Go play with your

16 cats and stop trying to act like you know anything!
Reply to
SharkMan

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