Which Gear Ratio To Go With? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
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post #1 of 10 (permalink) Old 11-03-2013, 02:49 PM Thread Starter
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Which Gear Ratio To Go With?

Hi folks,

Haven't posted anything here since around 2012. Ground up restorations take longer then I had anticipated. And with the changes I've decided to incorporate, a lot more money. But I expected this. TCI front and rear suspension kits etc. Here's a pic of the car prior to disassembly.



I have a 1965 Falcon Ranchero undergoing a full restoration. Body's still in the shop but I have the 1965 289 built along with the 1985 Mustang 5.0 HO World Class Tremec T5 I'm running behind it. It's also been very well built. They're bolted together and ready for a fit check as soon as I get the body back.

Pic of engine and trans. The valve covers are temporary.



I'm ready to build the 8" rear end. Wish I had a 9" but the budget is already blown out of the sky on this one. I'm trying to figure out what gear ratio I want in the rear end. I'm going for a nice "hole shot" along with a decent fuel mileage at hiway speeds. I would like to be turning around 2,500 RPM in the 5th gear overdrive at 70 MPH. I won't be drag racing this car but I will occasionally have some fun with it. Okay, maybe a little more then occasionally. I found an online calculator that comes up with a 3.08:1 ratio. It'll be a posi rear end.

I'd like to get some opinions on this rather then just trusting this calculator. I know you'll have more questions, wheel height etc. etc. that I will be more then happy to answer. I restore antique radios and belong to 3 related forums. I know forums are the best place to get good info and lots of ideas.

So if anyone would like to share some of your ideas concerning this 8" posi differential ratio I'd sure like to hear them.

Thanks,
Hacko
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post #2 of 10 (permalink) Old 11-03-2013, 03:26 PM
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post #3 of 10 (permalink) Old 11-03-2013, 03:42 PM
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Re: Which Gear Ratio To Go With?

Hey Hacko, Welcome Back. Not sure about the ratio but from things I have read seems like a 3:50 ratio comes up .
Also noticed a slider back glass . Would you share that info ? Please ?

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post #4 of 10 (permalink) Old 11-03-2013, 04:21 PM
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Re: Which Gear Ratio To Go With?

3:50 is a nice highway/acceleration combo.

I have 3:50's on my Galaxie (14" tires), and would not go any deeper.
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post #5 of 10 (permalink) Old 11-03-2013, 04:43 PM
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Re: Which Gear Ratio To Go With?

3.00-3.25 is the best!
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post #6 of 10 (permalink) Old 11-03-2013, 05:17 PM
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Re: Which Gear Ratio To Go With?

Quote:
Originally Posted by Hacko View Post
Hi folks,

Haven't posted anything here since around 2012. Ground up restorations take longer then I had anticipated. And with the changes I've decided to incorporate, a lot more money. But I expected this. TCI front and rear suspension kits etc. Here's a pic of the car prior to disassembly.



I have a 1965 Falcon Ranchero undergoing a full restoration. Body's still in the shop but I have the 1965 289 built along with the 1985 Mustang 5.0 HO World Class Tremec T5 I'm running behind it. It's also been very well built. They're bolted together and ready for a fit check as soon as I get the body back.

Pic of engine and trans. The valve covers are temporary.



I'm ready to build the 8" rear end. Wish I had a 9" but the budget is already blown out of the sky on this one. I'm trying to figure out what gear ratio I want in the rear end. I'm going for a nice "hole shot" along with a decent fuel mileage at hiway speeds. I would like to be turning around 2,500 RPM in the 5th gear overdrive at 70 MPH. I won't be drag racing this car but I will occasionally have some fun with it. Okay, maybe a little more then occasionally. I found an online calculator that comes up with a 3.08:1 ratio. It'll be a posi rear end.

I'd like to get some opinions on this rather then just trusting this calculator. I know you'll have more questions, wheel height etc. etc. that I will be more then happy to answer. I restore antique radios and belong to 3 related forums. I know forums are the best place to get good info and lots of ideas.

So if anyone would like to share some of your ideas concerning this 8" posi differential ratio I'd sure like to hear them.

Thanks,
Hacko
Using the ford online calculator 4:11 would get you 2,524 RPM's at 70 mph in 5th gear. This is with a overdrive(5th gear) ratio of 0.68 and 26 inch tall tires

4:11's = nice hole shots too.

Lou
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post #7 of 10 (permalink) Old 11-03-2013, 05:46 PM
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Re: Which Gear Ratio To Go With?

I have 3.25:1 in my Falconaround, your calculations are off. I run 195-70/14's in the rear and a .068 5th in my T5. I'm doing about 2700 in 5th at 70 mph.

Those 4:11's would put him over 3K in 5th at 70.
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post #8 of 10 (permalink) Old 11-03-2013, 05:57 PM
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Re: Which Gear Ratio To Go With?

Quote:
Originally Posted by FEandGoingBroke View Post
I have 3.25:1 in my Falconaround, your calculations are off. I run 195-70/14's in the rear and a .068 5th in my T5. I'm doing about 2700 in 5th at 70 mph.

Those 4:11's would put him over 3K in 5th at 70.
Not my calculations. Used the ford muscle online calculator .

70 mph. Rear ratio 2.79 (4.11 x overdrive ratio 0.68 = 2.79 gear ratio) and 26 inch tall tires the calculator says 2,524 rpm,s

With a smaller tire like a 195/70/14 which looks like it is close to 25 inch tall the calculator says 2,625 RPMs at 70.

Maybe the calculator is wrong?

FORDMUSCLE.com webmagazine - Gear Ratio / Engine RPM Calculator

The summit racing calculator comes up with 2,523.88 RPMs at 70 mph with 4.11's, 0.68 overdrive and 26" tires.
http://www.summitracing.com/expertad...tio-calculator

Lou

Last edited by Arabian454; 11-03-2013 at 06:02 PM. Reason: Added summit info
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post #9 of 10 (permalink) Old 11-03-2013, 10:13 PM Thread Starter
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Smile Re: Which Gear Ratio To Go With?

Responding to the question of the slider rear window... It was the first thing to go. Obviously aftermarket and a pretty bad installation. Tried to sell it and finally it ended up in the trash. It needed a lot of work. I'll have upwards of $20,000 into this car when done and sliders are just too vulnerable for me. Even though the alarm system will blow up the car within 60 seconds if the proper security code isn't input correctly.

Well there's a lot of ideas for the gear ratio. I'll be running 15" wheels with a slightly lower profile tire. Can't find my number of the overall height of the tire and wheel assembled but I'll have that tomorrow. The number that pops into my head is 25.11" but I'm not sure of that tonight.

The 4.11's aren't going to work for me. A guy in town has a set of 4.11's in his '65 and that car is a drag car. Here's the specs on my T5 trans. The torque may be correct for the stock trans but I know mine is built to handle around 400 ft. lbs. at least.

Tag Number Year & Engine Torque? 1st 2nd 3rd 4th 5th
1352-126 85-5.0 265 3.35 1.93 1.29 1.1 0.68

I can say that the original 1985 Mustang with the 5.0 HO engine and the Tremec T5 above was running a 3.08:1 ratio. My daughter had one and I had the opportunity to drive it. One fast car from the line until my son in law asked me to slow down at 105 MPH in 4th gear.

I'll get that tire diameter tomorrow. But it appears from all these replies that something between 2.79:1 to 3.25:1 is going to be the choice. Maybe the 3.25's with the 15" tires.

Hacko

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post #10 of 10 (permalink) Old 11-07-2013, 11:27 AM Thread Starter
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Re: Which Gear Ratio To Go With?

I have my tire diameter. Two of them. One tire is 8.5" wide and the other 8.8" wide. These are 15" tires.

8.5" tire and wheel is 26.10" in height.
8.8" tire and wheel is 25.60" in height.

I used the calculator from the link below to determine my RPM at 70mph.

Differential Gear Ratio Calculator | West Coast Differentials

If you want, you can run the numbers and tell me what you think. 5th gear with 3.08's at 70mph, 25.6" tire = 2,264rpm.

3.25's in 5th gear at 70mph, 25.6" tire = 2,389rpm.

If this calculator is any good and I can fit an 8.8" wide tire on the car, the 3.25's look like a pretty good choice.

Thoughts?

Hacko

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