Since You are talking about 700r4's and gears

[348tripower]

We're not getting anywhere fast with this analysis, are we?

Don, give us the full details on this truck. Is it a half ton hotrod or a 2 ton mama? Engine, cam, carb, etc. Everyone's just taking shots in the dark at this rate.

Charlie

1948 F1  S10 subframe.
355 chevy with a 327 350hp hydraulic cam. 600 edelbrock carb. 700r4 trans.  
Gm Hei ignition.  
I don't know what the rear end ratio is, but I do know the speedo is very close to correct and the tach is good.
I will jack this thing up tonite and count revs on the driveshaft and rear wheels.  
Got both hoists tied up right now so I have to do this the hard way!!
I do know that the correct way to check the ratio is by pulling it apart.
Also, pertaining to my first post, I was told this was a 3.00 to 1 rear when I bought it. Soooo  I didn't bother checking it. But according to all of the online info it looks to be 3.50 to1?
Don

[348tripower]

Ok gang. I checked the rear last night. 1.5 turns of the driveshaft to 1 turn of the wheel. This is a open rear so, it shold be 3.00 to 1?.
I don't have any idea why the online calculators don't match my findings, but I am thinking about a 3.73 gear.  We have one in a 40 Ford with a 5.0 and a overdrive trans and it is getting 22 to 24 mph. I don't expect that, it is a injected motor, but anything would help this pig!!!!!!!!!!!
I am open for suggestions.
Don

[Charlie Chops 1940]

Aha.

Don, I have 3.55's in my '40 and find that to be good gears  for that car. It runs about 2200 at 70 in OD. For towing the teardrop or my Mullins it works just fine.

3.73's would be good for towing a car trailer with the engine combo you have. Although not the same, my 7 passenger Trailblazer had 3.73's and pulled a loit stronger on entrance ramps, etc. My current Trailblazer has 3.42's and is noticeably slower in the same conditions. It mileages a lot better though.

Charlie

[348tripower]

Aha.

Don, I have 3.55's in my '40 and find that to be good gears  for that car. It runs about 2200 at 70 in OD. For towing the teardrop or my Mullins it works just fine.

3.73's would be good for towing a car trailer with the engine combo you have. Although not the same, my 7 passenger Trailblazer had 3.73's and pulled a loit stronger on entrance ramps, etc. My current Trailblazer has 3.42's and is noticeably slower in the same conditions. It mileages a lot better though.

Charlie

After checking the ratio of the Ford trans to the 700r4 it seems that a 3.55 would be a better choice.
Don

[slocrow]

Hey Don; Maybe I'm nutz but I think your numbers are incorrect. If one has a 3.00 gear out back then to rotate the wheel once causes the drive shaft rotate 3 times.
4:11 is a little over 4 times that the shaft turns.
Turning the tire once turns the carrier once via the axle. This turns the ring gear once and that turns the drive shaft the rear end number.
If the rear is open then one wheel must be held or on the ground taking the carrier gears out of the picture.
Oh yeah, I've got a 402 BB with a 700r and a 3.50 rear. I turn around 2200 70 (if I remember) and get 13.5 MPG. And it's fun leaving a big carbon print.........Frank

[Leon]

If it is an open rear and one wheel is held, the spider gears will cause a reduction, so 1 1/2 turns of the driveshaft does equal 3 to 1 ratio.  With an open rear to take the spider gears out of the picture both tires must be rotated at the same time, in which case you would now get the 3 turns on the driveshaft.

[UGLY OLDS]

The Ugly Olds has the exact engine / trans combo you have , except I use a 350 / 350 hyd cam...I have 3:42 gears & a 29" tire.. Around town at 25--30 mph , 4th gear is almost useless...If I lock the convertor at those speeds , it lugs the engine speed too far down to drive properly..
 My solution is to keep the convertor unlocked until approx 50 mph in 4th gear..( I use a BIG trans cooler ) ..The "sweet spot" for cruising is about 75ish with the convertor locked...Driving long distances at this speed with the air on I average about 18-19mpg....Knowing then what I know now ,I would have used something around a 3:55 rear gear just to spin the engine "a little" faster around town...My next car has the same basic powertrain but will have 3:80 gears...( I wanna play like Frank.. )

[1FATGMC]

One thing most of you are also leaving out of the equation is tire diameter.  Post that (like above) with the rest of your numbers as it is just as important as the rear gear,

Sum

[348tripower]

One thing most of you are also leaving out of the equation is tire diameter.  Post that (like above) with the rest of your numbers as it is just as important as the rear gear,

Sum

The tire diameter is 29 inches.  

Frank, this was taken from the Drive Train Services web site;
If you have an open or non-locking differential, you must rotate the tire 2 revolutions. This may not tell you exactly what ratio you have, but it will be reasonably close.
Don

[slocrow]

Hummmmm. Guess I was wrong. I still can't figure out what's going on in the carrier with the side & spider gears that halves the number.

As far as how high my tires are, well they're 285-70x15's. I noticed that the charts state one heigth while I actual measure something less when on the car. I think I measured 29 & 1/2" the last time. ....Frank

[348tripower]

Hummmmm. Guess I was wrong. I still can't figure out what's going on in the carrier with the side & spider gears that halves the number.

As far as how high my tires are, well they're 285-70x15's. I noticed that the charts state one heigth while I actual measure something less when on the car. I think I measured 29 & 1/2" the last time. ....Frank

We called our pal in Texas the mechanic and he actually knows he has a 3 to 1 in his truck. It gave the same results

[enjenjo]

Hummmmm. Guess I was wrong. I still can't figure out what's going on in the carrier with the side & spider gears that halves the number

Since you are only turning one wheel, it has to turn twice as fast to keep up with the driveshaft, to allow the other tire to set still.

[phat rat]

425 hp 454HO, 700R4, 3.42 gear, 255/60X15 tire, 2000 at 70 mph, 3700# I've pulled as high as 19.5 mpg wih it

[rooster]

Hummmmm. Guess I was wrong. I still can't figure out what's going on in the carrier with the side & spider gears that halves the number

Since you are only turning one wheel, it has to turn twice as fast to keep up with the driveshaft, to allow the other tire to set still.

My guess is that the failsafe way of doing ratio figuring is to mark the tire with some chalk , and the driveshaft  and then roll the car 1 wheel revelution counting the number of times the driveshaft turns. Be sure not to run over your head though!

[Leon]

I just found on Summit in their clearance section a set of 9" 3.70 gears for $87.50.  I ordered one and will see if it does me some good especially when towing.  I need to get the RPMs up a little.