Transmission gears ratio w/ flathead??

OK GUYS......RUNNING A 8BA FLATTIE....T5 CHEVY S10 TRANS WITH THE GEAR RATIOS IN THE PICS...8BA IS GONNA BE AROUND 200-210 HORSEPOWER....ANY IDEAS OF A GOOD REAREND DIFF GEAR RATIO????OHHHH AND I'M GONNA HAVE TALL SKINNY TIRES IN BACK ...LIKE FIRESTONES WHITEWALLS 750-16'S

 

I picked up the S-10 rear with my S-10 T-5. That way you've got a decent OD and the ratios should be matched up pretty well. Unless you're sidestepping the clutch all the time, I've been told that combo should hold up OK. Plus, with the S-10 rear, your backing plate to backing plate width (on mine anyway) is only 53" so you can keep your narrow tires sucked in tight if that's what you're looking for. Just my .02. Lotsa guys here have lots more technical expertise and may be able to give you some other ideas...

 

Just worried about what gear ratio to run in the back???

 

and help here....know one builds there own cars??? lol

 

Chill.... someone will be along to help you soon.

 

3.78 is perfect for me, I used 700 x 16 with widened wheels (6") very happy engine at 55 MPH, I usually run below that. Had to get the correct speedo drive "turtle" (17 tooth) so speedo will work right for tire height/ratio with torque tube, advice from fordbarn. For S10 may have to get a correcting gearbox to get that right.
I forget what the tach says, maybe if it gets warm today I can go for a ride & check the speed/RPM in direct, from there you should be able to calculate what overdrive will get you.
Maybe a S10 5 speed will have a low gear, I put late car gears in my '37 case & first gear too high for putting around crowds & parade, too much clutchin going on sometimes.

 

This might help--what do you want to get to?? Low rpm on hiway at 70 mph?? Here is the formula---MPH (what you want for road speed) X rear end ratio X 336 divided by tire height---dont forget to adjust rear end ratio by the .76 of your tranny's final. This worked for me.

 

I'd bet a 4.11:1 would be just fine.

 

can you provide the gear ratios of the transmission and the vehicle that it will be going into? What type of use are you planning for the car, strip, street, daily driver, highway????

There is a lot more to picking a rear end ratio than just the rear tire size. Those who "build their own cars" know things like this...

 

a 3.55 gear ratio would work well. burn as much tire as you want & tach around 2300 rpm at 75 miles per hr with the 30" tall tire.

 

With your 3:76 1st gear and 30" tires, I would go for something around 3:75-4:00:1. Any lower and your 1st gear will be useless. I am running a Mustang T-5 with a 3:35 1st, 4:11 rear gears, 7.50 31" "stones" in a '32 highboy and find the gearing perfect for my kind of driving. Do some math and figure out what will work best for you.

MPH = tire radius / 168 X RPM / gear ratio.

OR

gear ratio = tire radius X RPM / 168 / MPH.

OR

RPM = 168 X gear ratio X MPH / tire radius.

 

With the 4.03 first gear in that trans you won't have any trouble getting off the line so you can go to a higher rear. You didn't say what car it is going in. A heavy 53 sedan or a light T bucket. It will make a difference.

I was lucky and my free S-10 T-5 came with the taller 3.50 first gear. I use it in front of an 8" Ford rear that was already in my 34 Ford PU. I don't know it's ratio. Not much help but I know it's got to be in the low 3s. In OD on long hills it feels like it's lugging some. It's never a problem bad enough for me to down shift into 4th gear. I'm glad mine doesn't have the 4.03 low gear. Like your flathead my Studebaker makes good low end torque and doesn't wind too high.

If you go too low on the rear gear with that low gear, you won't be across the street before you need to shift especially with a light car.

I was going to try to find a 3.55 rear for my 8" but it's not worth the cost or the effort to me. It might be a little better on long hills but I like the present gearing around town.

Unless you have a heavy load to get rolling I'd stay in the low 3s for a rear cog. Anything in the upper 3s will make that first gear useless. IMHO

 

You've got pretty wide ratios there. I think about 3.50 or 3.55 for a rear gear would work. First gear will be plenty low (about 14:1) and high gear will work out to 2.60-something. I don't think I'd want to go lower than that in first, or much higher than that in fifth.

 

I ran a flatty much like the one you talk about with the same trans. I had 2.35 radials, and a 3.89. It was in a light car, (2200 lbs), but the gears were perfect. On straight level ground, I could start out in second, but in traffic, uphill, or on rough road, I started out in first.

 

the transmission ratios are listed in the attached pic of the trans

 

its going in my 32 roadster i'm building

 

I wouldn't go any more than a 3.55, those are the gears I had in my shoebox when I first put my t-5 in her. I ran the 3.55 gears with a 28" tall tire and first gear was just about useless, and it was about 800 lbs heavier. You could easily get away with going a little lower, say closer to a 3.00, but depending on what rear end you're going to use you may be limited as to what ratios are available.

 

hmmmm some people here say....4.00...some say nothing more then 3.55

this is why it is confusing...............lol

 

I really want to use my 1st gear....and stay about 2300 -2400 rpm for 75mph

 

Just ran some numbers...

75mph, 30" tire, 2350 rpm requires a total gear ratio of 2.80

Now not sure what your fifth gear overdrive ratio is, it could be either 0.73 or 0.79 ?

That would make your required diff ratio either 3.83 (with the 0.73) or 3.54 (with the 0.79) to get those revs at that speed with a thirty inch tire.

If you go to the taller 3.54 diff, with a first gear of 3.76, that gives an overall reduction of 13.3 in first, which is going to pull plenty hard in first gear. So there is no problem in gearing it up pretty tall for the freeway.

 

OK, we didn't use charts and formulas on Flower's flathead truck. It weighs in at 2200lbs and has a T-5. The rear tires are 31" tall. We built the car originally with an 8" Ford rear and a standard three speed from the same 1951 Ford that the engine came from. The rear end had a 3.00:1 gearset so we left it alone. The car drove well with the three speed except it seemed a bit "short legged" on the freeway (no tachometer in the car). When she installed the T-5 we elected to see how it worked with the existing 3.0 gears...it works great. The car cruises easily at 65-70 mph, will run all day long at that speed...even in 100 degree weather the 8BA is still happy. Last time we were on a road trip the car buzzed up a few good grades in 5th gear, no problem.

I think each set of circumstances are going to be different...this is just our seat-o-the-pants observation.

 

ok.....ummmm just to get it straight..

car: 1932 ford roadster

rear tires : 750 - 16

transmission gears : 1st/4.03 2nd/2.37 3rd/1.49 4th/1.00 5th/0.86

engine: 8BA Flattie w/ about 200 horse

want to be able to run first gear...and be on the highway crusing at about 75mph / 2200-2300 rpm

 

my flathead has 220 hp with the t5 overdrive gear set at .73 the rear end gear is 4.10 and 750-16 rear tires this is the setup that was recomended to me by modern driveline.

 

hows your 1st gear work??? nice flathead btw

 

Use a 3.00 rear gear..you will be fine..

 

would a 3.25 bog a mildly warmed up flathead?

 

wtf.....everyone says use something different....this is crazy

 

get rid of the t-5. put a 3 speed in it and run 3.54. very simple....

 

wow..sounds good! then I can do 75mph at 8000rpm.....I love throwing rods in my flathead

 

At 75 Mph, 30 inch tire, 3.0 diff, with 0.86 overdrive, works out to 2,167 rpm.
At 75 Mph, 30 inch tire, 3.2 diff, with 0.86 overdrive, works out to 2,312 rpm.