Trying to figure final Gearing HELP NEEDED.

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Anonymous

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OK so I want opinions on this...

I am trying to figure my final gearing and need some help.

I am considering using a cam like this:
Adv 268/274, 208/218@ 0.50, .460 lift 110° lobe centers.

Now running a stock 2.3L T5@
3.97/2.34/1.46/1.00/0.79/3.70R

what would be the best choice for gearing if I wanted decent off the line and great highway performance.....
currently I am @2.79:1

How can I fugre the math on this? Running these tires?
Wheel 15X7/14X6 with – 205/60R-15 or 215/14 for the smaller wheel.

I have heard of dropping the 5th gear to 0.68? and using either 3.00:1 or 3.20:1 in the rear.
 
i've got 3.20s and 24.16" diameter tires(215/60/14) and with a .70 overdrive on the SROD i figured it to be about 2000rpm going 65mph with a theoretical topspeed @ 4000rpm of 128.4 mph, good luck getting there, heh

when i finish installing the srod ill get you some more numbers, but by the time i do that, you'll probably have all this figured out
 
205/60-15 tires roll at about 842 revs/mile. For argument's sake, lets say you want to cruise at 2400 RPM at 65 MPH. Thet would be:

842 x (65/60) = 912 tire RPM

and: 2400 / 0.79 = 3038 driveshaft RPM

final drive ratio = 3038/912 = 3.33

a 3.20 would give you 2300 RPM @ 65
a 3.00 would give you 2160 RPM @ 65
your present 2.79 gives 2010 @ 65

You may want to look at speed in 1st gear, it has a lot to do with dricvability. Too tall or too deep can really make the car no fun to drive

28 MPH with a 3.20
30 MPH with a 3.00
32 MPH with a 2.79

Not a lot of difference there. I'd tend to go with more is better, especially in an underpowered car (no offense intended.) You may discover that with the 3.20 and the 3.97 1st you'll have enough torque to warrant a Trac-Lok to keep from lighting the right rear up. :D
 
heh, just use the 2.77 reverse gear, it's something like 4.30, before i broke it i would do mad smokey burnouts with it
 
That's great I can finally start to figure the math out....

I see what you are talking about... I like the 2000 RPM's at 65mph. that would create a real screamer, but the 32mph 1st gear is a little high... seems like the 3.00:1 for this tranny is the best combination....

I would never go lower than 3.20....
 
The following are my opinions based on the formulas and other stuff i've used over the last 20 years of car analysis. My view only.

In Aussie the 1982 3.3 liter I6 in a 2900 pound Falcon had a 5-speed manual with the 3.23:1 ratio. Ratios were 3.22/1.96/1.26/1.00/0.79. It was the best gearing around, very close, and a gear for each situation. Later, they lowered the first to 3.47:1 to cope with towing trailers..but that shouldn'r concearn you here! The Falcon could do 100 mph at 5500 rpm in third, and a top wack of 112 mph in a brick like sedan! Your Mustang has about 10% less frontal area (22 sq ft verses 24.4 sq ft) than a 74 inch wide Oz Falcon, and the drag factors are similar at about 0.48 cd.

My suggestion would be the 3.20:1 diff. The other guys are dead right about the loaded wheel diameter. I got about 24.15 inches with a 205/60 H15.

Speeds in gears are :-3.97/2.34/1.46/1.00/0.79/3.70R

Ist 5.66 mph per 1000 rpm, or 31 mph @ 5500 rpm readline
2nd 9.60 mph per 1000 rpm, or 53 mph @ 5500 rpm
3rd 15.38 mph per 1000 rpm, or 85 mph @ 5500 rpm
4th 22.46 mph per 1000 rpm, or 106mph @ 4700rpm potential. (118 hp)
5th 28.42 mph per 1000 rpm, or 112 mph at 3940 rpm potential. You'd only need about 140 hp, or 109 hp at the rear wheels at 4000 rpm.

At 55 mph in top, 1935 rpm in 5th. A down change to 4th would result in the car coming on the cam really well at 2450 rpm. A snap shift to 3rd would hit 3600 rpm, and the engine would really fly! The cam you have would kick butt at 2800 rpm through to 4000 rpm. The best red line, or max change-up point, would be better as 5000 rpm. But even with cast rods and marginal rod bolts, 5500rpm should be safe.

If your maximum power will come in at over 4000 rpm, at say 4800 rpm, then you may wish to lower it from the 3.20:1 ratio to a 3.73:1. It really depends on how much torque you've got down low. But then you'd really be looking for a close ratio gearbox. And the super-low intermediates in the 'box as it is would be a pain buzzing through.

I'd forget the 0.68 as an option. The 5th gear should be usable. On a slick, low drag car you use it, you should be able to use the 0.79 ratio often. The 5-speed will make the car. Don't be afraid to use the 3.20:1!
 
XECUTE":3nywvabj said:
The following are my opinions based on the formulas and other stuff i've used over the last 20 years of car analysis. My view only.

In Aussie the 1982 3.3 liter I6 in a 2900 pound Falcon had a 5-speed manual with the 3.23:1 ratio. Ratios were 3.22/1.96/1.26/1.00/0.79. It was the best gearing around, very close, and a gear for each situation. Later, they lowered the first to 3.47:1 to cope with towing trailers..but that shouldn'r concearn you here! The Falcon could do 100 mph at 5500 rpm in third, and a top wack of 112 mph in a brick like sedan! Your Mustang has about 10% less frontal area (22 sq ft verses 24.4 sq ft) than a 74 inch wide Oz Falcon, and the drag factors are similar at about 0.48 cd.

My suggestion would be the 3.20:1 diff. The other guys are dead right about the loaded wheel diameter. I got about 24.15 inches with a 205/60 H15.

Speeds in gears are :-3.97/2.34/1.46/1.00/0.79/3.70R

Ist 5.66 mph per 1000 rpm, or 31 mph @ 5500 rpm readline
2nd 9.60 mph per 1000 rpm, or 53 mph @ 5500 rpm
3rd 15.38 mph per 1000 rpm, or 85 mph @ 5500 rpm
4th 22.46 mph per 1000 rpm, or 106mph @ 4700rpm potential. (118 hp)
5th 28.42 mph per 1000 rpm, or 112 mph at 3940 rpm potential. You'd only need about 140 hp, or 109 hp at the rear wheels at 4000 rpm.

At 55 mph in top, 1935 rpm in 5th. A down change to 4th would result in the car coming on the cam really well at 2450 rpm. A snap shift to 3rd would hit 3600 rpm, and the engine would really fly! The cam you have would kick butt at 2800 rpm through to 4000 rpm. The best red line, or max change-up point, would be better as 5000 rpm. But even with cast rods and marginal rod bolts, 5500rpm should be safe.

If your maximum power will come in at over 4000 rpm, at say 4800 rpm, then you may wish to lower it from the 3.20:1 ratio to a 3.73:1. It really depends on how much torque you've got down low. But then you'd really be looking for a close ratio gearbox. And the super-low intermediates in the 'box as it is would be a pain buzzing through.

I'd forget the 0.68 as an option. The 5th gear should be usable. On a slick, low drag car you use it, you should be able to use the 0.79 ratio often. The 5-speed will make the car. Don't be afraid to use the 3.20:1!
Click to expand...

As usual, many more things to worry about. Brought to you by xecute. :LOL:
 
That's why people want me head separated from my body. Saves a lot of worries.

Fat chance of that KC!


:LOL:
 
8)

I was going to recommend a 3.45:1 or a 3.55:1 rear.

My 79 carb turbo 2.3L has a 4 speed and 3.45:1 rear. 4th gear is .97:1 and it topped out about 120mph.

With your 5th gear you should be able to cruise just fine.
 
XECUTE

I cannot thank you enough.... that was the post I have needed, you make a lot of nice points about my specific setup. I am going 3.20:1 maybe even 3.25:1 if I can work out a trade on this limited slip....

got the tranny today... very pretty. Was recently rebuilt, has bout 21,000 miles on it, steel bearing retainer and all. I am having great luck these days on finds....

I know I am going to be very happy with this new setup.

OH YEAH, I pulled the block today, it's on the truck and off tomorrow to be rebuilt.

Stang looks weird with no engine...

Thanks again

Jim
 
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