Which Speedometer Gear... 2.73's!! - TCCoA Forums
 
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post #1 of 8 (permalink) Old 02-10-2005, 12:50 PM Thread Starter
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Talking Which Speedometer Gear... 2.73's!!

Yes, I'm going to install 2.73's in my Cougar. Yes, I know it will be slow. Yes, I'm going for fuel economy.

Anyway: 95 4R70W needs what speedometer gear to get the speedometer close to being accurate?!?!

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post #2 of 8 (permalink) Old 02-10-2005, 01:18 PM
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http://www.sccoa.com/faq/speedgr.html

Shows a 14.5 tooth gear when I plug in the number. The closest you'll get is 15.

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post #3 of 8 (permalink) Old 02-10-2005, 01:35 PM Thread Starter
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I had already found that page and came up with a 16.3 tooth (235/60/16 (27") tire).

I just wasn't 100% sure the 4R70W had the 8 tooth or the 7 tooth drive gear.

Thanks.

Now, have a part number.

97 Lincoln Mark VIII LSC (Chip'd, 3.73 T/L... so far... )
97 Ford Aspire (Slow, but getting 36 mpg (f'n Ethenol!! )
84 F250 Dually w/6.9L Diesel (7.3L IDI pending)
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69 F100 LWB w/460 Engine
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post #4 of 8 (permalink) Old 02-10-2005, 02:55 PM
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Well, with the taller tires, now you need a 14.3 tooth gear. Closest that Ford offers is a 16 tooth for an auto. trans. D0AZ 17271 B. On a manual trans. application, you could change the drive gear on the output shaft. But on the 4R70W, that gear is a machined part of the shaft.


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post #5 of 8 (permalink) Old 02-10-2005, 04:43 PM
 
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*HIJACK* Need a set of 2.73s? *End HIJACK*
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post #6 of 8 (permalink) Old 02-10-2005, 06:41 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L
Yes, I'm going to install 2.73's in my Cougar. Yes, I know it will be slow. Yes, I'm going for fuel economy.
Keep in mind that a lower numeric ratio will not always improve fuel economy. You may end up giving it more throttle to get the car going. Or end up with revs at highway speed being too low in OD, that the engine is lugging and working harder than if it was running a few hundred rpm higher. Food for thought anyway.

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post #7 of 8 (permalink) Old 02-10-2005, 06:55 PM
 
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Also keep in mind that with the wide ratio trans and 2.73:1, first gear is still noticably steeper than an AOD's 1st gear with 3.27:1 gears.

If you do mainly highway driving, it may work out ok.

Jeramie
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post #8 of 8 (permalink) Old 02-10-2005, 08:10 PM Thread Starter
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Quote:
Originally Posted by fast Ed N
Keep in mind that a lower numeric ratio will not always improve fuel economy. You may end up giving it more throttle to get the car going. Or end up with revs at highway speed being too low in OD, that the engine is lugging and working harder than if it was running a few hundred rpm higher. Food for thought anyway.

cheers
Ed N.
I agree 100%. But most (95%) of my driving is at 78 mph and I'm getting around 24/25 mpg now. If I slow it down to 65 mph I have gotten a best of about 28 mpg. So my logic is keep the speed, but lower the rpm's slightly. If my driving was normally at 65 mph then yes I agree that the engine would be lugging and I would loose gas mileage.

All I can do is give it a try. I'm still shooting for 35 - 40 mpg, but it will be VERY difficult. (If I can break 30 on a regular basis I'll be happy). But I think with a "MPG" tune and the 2.73's, 30's are definitely possible.

My “goal” is 35 – 40 mpg highway and 15.9999 or faster in the 1/4 mile.

97 Lincoln Mark VIII LSC (Chip'd, 3.73 T/L... so far... )
97 Ford Aspire (Slow, but getting 36 mpg (f'n Ethenol!! )
84 F250 Dually w/6.9L Diesel (7.3L IDI pending)
73 Mercury Cougar Convertible w/351C 4V (Partially Restored)
69 F100 LWB w/460 Engine
76 Glastron Carlson 23' Jet Boat w/460 CJ Engine
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