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Offline Pintocrazed

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GEAR SWAP
« on: January 27, 2015, 10:24:03 AM »
HEY HEY GOT A 73 RUNABOUT 2.0 THATS GONNA BE BORED .30 OVER  WITH CAM HEADER AND BIG VALVE HEAD.AUTO TRANS MIGHT SWAP TO 5SPEED. HAVE FACTORY 3.40 GEARS BUT FOUND 4.30 GEARS FOR THE 6.75 DIFFERENTIAL.A NYBODY EVER USED THESE GEARS?

Offline pinto_one

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Re: GEAR SWAP
« Reply #1 on: January 27, 2015, 10:37:36 AM »
I have and also got a new set of zooms 4.11 geasr still in the box, but its going to scream on the highway with the auto, but the T-5 over drive will help a whole bunch, auto on a 2.0 was a real dog unless you had turbo , also you can use a wider taller tire for traction and slowing the engine down some what ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline Pintocrazed

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Re: GEAR SWAP
« Reply #2 on: January 27, 2015, 10:44:25 AM »
YOUR 4.11'S ARE FOR WHICH REAREND

Offline pinto_one

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Re: GEAR SWAP
« Reply #3 on: January 27, 2015, 12:02:35 PM »
its for the 6.750 , or 6 3/4 , or one that has the tin rear cover , not the 8 inch,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline Wittsend

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Re: GEAR SWAP
« Reply #4 on: January 27, 2015, 12:30:00 PM »
I'd use one of the may on line calculators and see the RPM numbers you are going to have.  And remember changing tire diameter does the exact same thing as changing rear gears. So, both those need to be factored.  Anyway, once you get an RPM number for highway speeds (65 MPH) use whatever gear in your present setup that comes closest to that RPM at that speed. I'll guess about 3rd gear (manual) 2nd (auto). Drive it for 10 miles in that 4,000 or so RPM range and ask yourself if you REALLY want that all the time.

Years ago I was given a Datsun 510 that has 3.90 gears. Coupled with 215-50-13" tires (remember, as I said they affect ratio too) the car was 4,000+ RPM on the highway. In normal driving I was shifting into 3rd gear before I even crossed an intersection.  There was no presence of acceleration, just an all too quickly winding out engine.  Thankfully early Z-cars had 3.36 gears and they made the car so much more drivable.

In my Turbo Pinto application my 8" rear had 3.00 gear. Coupled with a T-5 and 175-70-13" tires the car seemed to never have the right RPM for any posted speed regardless of the gear selected.  Going to 3.40 helped significantly. The car is now drivable.

Tires size aside for the street 3.25-3.55 seems to be an appropriate range.  I'd stick with the 3.40 and see what it is like. With the 6-3/4" rear you not only have the cost of the gears, but properly setting them up as well.

Offline Pintocrazed

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Re: GEAR SWAP
« Reply #5 on: January 27, 2015, 01:50:40 PM »
IM GONNA RUN 245/65/14 TIRES

Offline amc49

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Re: GEAR SWAP
« Reply #6 on: January 27, 2015, 06:40:45 PM »
Practically any cam you put in motor will be too much for good ATX performance, you WILL be looking for a manual trans. Any more than around 220 degrees intake timing at .050" lift and the ATX will spit its' guts out with a stock converter. That severely limits performance cams in these motors.

Just having an ATX requires about .4 to .5 more rear gear number to stay the same as MTX as far as umph off the line and good all around driving behavior.

Setting up the gears correctly is mandatory, many cannot do that worth spit but they sure will charge you for it. It takes a better than normal mech to do that correctly, one that knows about bearing preload and how to get it properly. No way do they simply bolt together.