Low Gear 727 with 3.23s

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Big_Schitt

Big_Schitt

'71 440 Demon
Joined
Jan 18, 2016
Messages
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Location
Celina, Texas
Presuming I could find a low gear set for my 727: 2.74/1.54/1.00 (Looks like I may have found them). Then I would change out ring and pinion from 3.73s to 3.23s. If my rough estimates are correct this would give me a slightly better launch than my old 3.55s did with the stock gears (though not as good as the current 3.73s) and I would lower rpm at 75mph by ~500.

If I am right? I am trying to figure out why so many people pay a lot more to go to an OD four speed and I don't see people doing this all over the place. I get the feeling I am missing something and this is a bad idea for some reason.

My '71 Demon is a street car and I am thinking about joining the Power Tour this year, but I really want to get the highway RPM down if I am going to drive ~1,500 miles over a few days.

Notes:
Rear End: 741
Rear Tires: 295/50/15
Engine: '77 440
 
You are correct! When I had my automatic, I used a 999 gearset (904 unit) with 2.94s and still ran 12.60s. I love poor mans overdrive. I run a 4 speed now with a 3.09 first and 1:1 4th, still with the 2.94s on the road course. Silky smooth with an alum driveshaft and stock driveline angle. Of course more gears and deeper gears would be better, but the mild rear gears are great.
 
because I like hard launches doing donuts ,and carving up the asfault no more hyway cruzing for me , but I did keep the 3:23s 360 rhs heads , m1 727 , 3:91 750 cfm mechanical with 295 x 29" x9.5 . Looking for a duster roller within 4 hours of Madison wisc. TSI WILL BUILD YOUA GR8 TRANNY
 
I have read that a low gear set for a 727 was never produced by the factory....good luck
 
You know you can swap chunks in an hour and a half,(possibly less) in your driveway, right? And another 90 minutes to put it back. For a grand total cost of Zero Dollars, unless you tear the gasket, or accidentally spill the drainpan.
 
AJ/FormS said:
You know you can swap chunks in an hour and a half,(possibly less) in your driveway, right? And another 90 minutes to put it back. For a grand total cost of Zero Dollars, unless you tear the gasket, or accidentally spill the drainpan.
Click to expand...

This is my plan for my final 340 configuration. I have a 742 chunk with 3.23s and a 741 chunk with 3.91s. Both of them are clutch type sure-grips.
I plan on using a ThermoQuad to take advantage of the small primaries for the 3.23s and the humongous secondaries for the 3.91s.
 
AJ/FormS said:
You know you can swap chunks in an hour and a half,(possibly less) in your driveway, right? And another 90 minutes to put it back. For a grand total cost of Zero Dollars, unless you tear the gasket, or accidentally spill the drainpan.
Click to expand...

Please forgive the the novice here. When I took on this project nine years ago, I had not worked on a car myself outside of oil changes and plugs type work.

Do you mean just get a new pumpkin with 3.23s, use that for power tour, then get back home and put the pumpkin with 3.73s back on?

If so this is something I am considering, but the 727 has a small leak and has not been rebuilt since I bought it; therefore, seems like a good excuse to just go through the thing. Also I would prefer a long term solution where I don't have to change the pumpkin every-time I want to go out of town. Especially since I have twin 3 yr olds at home and when I have an opportunity to take a long drive I would like to jump on it and not lose precious free time changing gears before and after I go.
 
DFX 340 Duster said:
This is my plan for my final 340 configuration. I have a 742 chunk with 3.23s and a 741 chunk with 3.91s. Both of them are clutch type sure-grips.
I plan on using a ThermoQuad to take advantage of the small primaries for the 3.23s and the humongous secondaries for the 3.91s.
Click to expand...

Is everything else interchangeable on the 742 and 741? I didn't think I could switch them like that...
 
The complete chunks are interchangeable. Gears do not swap between the three popular pumpkins. The S.G.s, and or cases, do.
The custom gear set seems to me to be an expensive solution to this age-old problem.

Here are some numbers;
using the standard tranny ratios,and
using the 3.55s, the final drive ratios are; 8.70-5.15-3.55
and with 3.73s,...................................9.14-5.41-3.73
But with 3.23s and the wide-ratio set ......8.85-4.97-3.;

The 3.23s will knock your cruise rpm down; 3.23/3.73 =.87; or to about 87 % of it's current rpm
 
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