727 Lower Gear Set for street/highway use

[BT67Dart]

I have a 67 Dart, 727 Trans, 340 engine for power (not yet built), will likely use aluminum heads, decent cam (solid flat tappet or solid roller), slightly less than 10:1 compression to run pump gas.
I've been researching gear ratios and automatic transmission options for street/highway use. I know this is the same problem many have discussed, but I am still trying to get the best of both worlds without installing a transmission or overdrive unit that does not fit the car (major rework to frame/floorpan). Meaning, fun to drive on the steet, but decent RPM's on the highway, not interested in the droning noise of high revs going down the highway. So, one option I thought was of interest was the A998/A999 trans, lock-up would be nice, but those are difficult to find, unclear on part availability as well. So, what about the option of using a low gear set (2.74, 1.54, 1)in the 727 trans. Seems like you can get the benefit of a lower starting gear, more torque at the rear wheels initially, yet still have a final gear ration that is somewhat decent on the highway. Here's a comparison between two 727 gearsets, attached image.

It compares the gearsets wiht a 2.94 rear gear, 28 inch tire. Its just a rough comparison, no doubt the inputs might be off here and there.

I could also go with a 904 that already had this setup, if it was reasonably built.

Anyone have actual experience with this setup (pros, cons)?

 

[TT5.9mag]

All of the torqueflights are 1:1 in third. Your highway cruising rpm will not change with the lower first gear set. Listen carefully, if you want the benefit of deep starting gears AND highway cruising, put some kind of overdrive transmission in it. Period. The amount of work it takes to install one is not terribly difficult and it’s always worth it.

 

[BT67Dart]

All of the torqueflights are 1:1 in third. Your highway cruising rpm will not change with the lower first gear set. Listen carefully, if you want the benefit of deep starting gears AND highway cruising, put some kind of overdrive transmission in it. Period. The amount of work it takes to install one is not terribly difficult and it’s always worth it.

You are right about the cruising speed RPM, I should have worded that in a better manner. What I was getting at is that you can run a higher rear gear (say 2.94 vs. 3.23), getting lower cruising speed RPM, and still have a decent low end gear set/torque to start.

All of the OD options I have read about require significant frame changes, can't see doing that personally. The GV overdrive gearset is expensive and photos of the installation shows a fair amount of floorpan changes.

I hear what you are saying, just trying to minimize the fabrication and cost impacts. Maybe it's just not possible without going that path, at which point I might simply forego highway driving and leave it as a street car

 

[TT5.9mag]

You are right about the cruising speed RPM, I should have worded that in a better manner. What I was getting at is that you can run a higher rear gear (say 2.94 vs. 3.23), getting lower cruising speed RPM, and still have a decent low end gear set/torque to start.

All of the OD options I have read about require significant frame changes, can't see doing that personally. The GV overdrive gearset is expensive and photos of the installation shows a fair amount of floorpan changes.

I hear what you are saying, just trying to minimize the fabrication and cost impacts. Maybe it's just not possible without going that path, at which point I might simply forego highway driving and leave it as a street car

You can have an excellent, quick driver with 3:23 gears and a 3 speed with 1:1 3rd. You just might have to change your expectations of highway cruise speed. Around here, there are freeways everywhere and 75 mph is a minimum drive speed. My D100 has a 46re with 3:55 gears. It’s about (in my opinion) the perfect combination for a driver. I drive 75-80 down the freeway at 2400 and still have plenty of starter gear for stoplight fun. If you’re concerned about chassis modifications, look in to the extreme automatics 2004r for a small block mopar. Very little massaging has to be done and that can be a great trans. Lots of $$ though. Personally I think a 42rh should be used by more guys in the mopar hobby. Everyone would drive their garbage much more.

 

[Mopar Sam]

Personally I think a 42rh should be used by more guys in the mopar hobby. Everyone would drive their garbage much more.

I would be tempted, if, there was an affordable reverse pattern vb for them. I would prefer one with a toggle for 4th. That way it would work with my dash shifter. That, and I'd have to trade my 727 8" converter for a 904 8".

I did run one behind a very mild 360 in a Dakota, but could not stand the forward vb.

 

[65 Dartman]

When I acquired my 65 Dart wagon,, I made a list of what I would like to have and one was OD behind a V8. I sourced a 42RH, had it rebuilt and beefed up where it could be. After mocking the engine/trans in the chassis, did the modifications to the upper crossmember, tunnel and rear transmission support. I think I can use the 3.23 rear gears but if needed I have a set if 3.55s I can swap. I hope to get this thing on the road next year

 

[BT67Dart]

I looked at the 200r4 as well, lots of info on that setup, but still more money and rework than I want. Later model overdrive trans are similar in terms of rework. Thanks for your insights, much appreciated.

 

[GY3 WEDGE]

I have a 67 Dart, 727 Trans, 340 engine for power (not yet built), will likely use aluminum heads, decent cam (solid flat tappet or solid roller), slightly less than 10:1 compression to run pump gas.
I've been researching gear ratios and automatic transmission options for street/highway use. I know this is the same problem many have discussed, but I am still trying to get the best of both worlds without installing a transmission or overdrive unit that does not fit the car (major rework to frame/floorpan). Meaning, fun to drive on the steet, but decent RPM's on the highway, not interested in the droning noise of high revs going down the highway. So, one option I thought was of interest was the A998/A999 trans, lock-up would be nice, but those are difficult to find, unclear on part availability as well. So, what about the option of using a low gear set (2.74, 1.54, 1)in the 727 trans. Seems like you can get the benefit of a lower starting gear, more torque at the rear wheels initially, yet still have a final gear ration that is somewhat decent on the highway. Here's a comparison between two 727 gearsets, attached image.

It compares the gearsets wiht a 2.94 rear gear, 28 inch tire. Its just a rough comparison, no doubt the inputs might be off here and there.

I could also go with a 904 that already had this setup, if it was reasonably built.

Anyone have actual experience with this setup (pros, cons)?

View attachment 1716484494

 

[273]

For a street car power generally starts kicking in at 3,000 rpm's (hp is 57% of torque) the lower the mph you can get there easier it is to get into the powerband at reasonable road speeds, a set of 3.23 only gonna add about 250 rpm to cruising speed and with 2.74 1st would be a good compromise. (3,000 rpm @ 28.25 mph) deeper gears gives a diminishing return of lower the mph the powerband starts at.

 

[BT67Dart]

For a street car power generally starts kicking in at 3,000 rpm's (hp is 57% of torque) the lower the mph you can get there easier it is to get into the powerband at reasonable road speeds, a set of 3.23 only gonna add about 250 rpm to cruising speed and with 2.74 1st would be a good compromise. (3,000 rpm @ 28.25 mph) deeper gears gives a diminishing return of lower the mph the powerband starts at.

I see what you are saying, with a 1st gear 2.74 around 3000 rpm (where the power starts), you will be around 30 MPH, fun streeter. 3.23 has been a popular gear for a street car.....might be a better shot for my application than say a 3.55. Rear end currently has 3.91 gears in it....too low for what I want.

 

[forphorty]

I see what you are saying, with a 1st gear 2.74 around 3000 rpm (where the power starts), you will be around 30 MPH, fun streeter. 3.23 has been a popular gear for a street car.....might be a better shot for my application than say a 3.55. Rear end currently has 3.91 gears in it....too low for what I want.

My PTC 9.5 flashes to 3500 and gets me in the powerband instantly. No waiting around until 30 mph. Drives fine with 3.23s. The low gear sets for 904 are fairly cheap and available . Low gear sets for 727 are pricey. My opinion: Since you haven't built the engine yet, spend the money on a 4.00 stroke crank. The added displacement (414?) will make more difference than the low gear set and most likely be cheaper. Then run 3.23s.

 

[BT67Dart]

Thought about that, stroker kits are not cheap either, close to $2K for a rotating assembly. Just the crank would be less, will have to check that and compare it to the cost of a lower gear set. Nothing is cheap for parts these days

 

[ir3333]

You will love the transmission utilizing the first and second lo gears. With 2.94 rear gears your first gear will be the same as having 3.30 gears and a regular 727. But 28" tires will destroy the lo rpm torque you are seeking.
Target a minimum of 9:1 final drive in first gear for good lo rpm performance.

 

[71Demon540]

If I’m not mistaken, putting any kind of overdrive transmission or gear vendors unit on your 727 will require some modification to the floor to fit. From what I have gathered and heard of, the GV unit is relatively easy to make fit. Just need an air hammer to make a few dents in the floor. I built one for a guy couple years ago and he said it dropped his RPM significantly on the highway at 75mph. I can’t remember exact RPM drop but he drives the car from Butler, PA to Carlisle, PA which is about 3-3.5 hour trip in his car. So if you would ask him, he would say the GV is worth the investment.

 

[BT67Dart]

If I’m not mistaken, putting any kind of overdrive transmission or gear vendors unit on your 727 will require some modification to the floor to fit. From what I have gathered and heard of, the GV unit is relatively easy to make fit. Just need an air hammer to make a few dents in the floor. I built one for a guy couple years ago and he said it dropped his RPM significantly on the highway at 75mph. I can’t remember exact RPM drop but he drives the car from Butler, PA to Carlisle, PA which is about 3-3.5 hour trip in his car. So if you would ask him, he would say the GV is worth the investment.

One of the gv installs I read thru cut up the floorpan to get it in. Others have lifted the engine up a bit, dropped the trans down a bit to get the floorpan clearance.....still not a cheap option though

 

[71Demon540]

One of the gv installs I read thru cut up the floorpan to get it in. Others have lifted the engine up a bit, dropped the trans down a bit to get the floorpan clearance.....still not a cheap option though

Definitely not cheap by any means. None of this is cheap unfortunately