gear ratios

[Hammer396]

I'm putting a ford 8" in my model A , it's out of a 73 comet, ratio is 2.79:1, I'm running a 350, turbo 350, with 28" tall tires,
now the question is , will this be a good ratio for this car? should I put a little lower gear in it? 3.08:1, or 3.23:1? what are you guys running out there?
I do want a good highway speed, but do not want it to doggie in town.

[Davey_Joe]

hammer,... the common one the fellas like to use are 300;1... used with 235/15 tires, this gives ya the better cruise... 2;79s are gittin' a tad ta the doggie side o' things..... lower stuff will give ya more jump,... less milage.... hypothetically......... ya know,... like 4;11s,... 4;56....

[dale48mrc]

I had the mathmatical formula to give final drive ratio based on gear ratio and tire diameter but,I'll be damned if I can find it.Maybe someone elsle on the forum will have it,or maybe I'll just get outta here and do a search!

[dale48mrc]

Found them online!http://books.google.ca/books?id=NNWf3oWPEkoC&pg=PA98&lpg=PA98&dq=Mathmatical+formulas+for+determining+final+driv e+ratios+&source=web&ots=by8XalmXaw&sig=ekVqnMQd8A2CICQzSuhTxj8RNCI&hl=en

[Hammer396]

I guess if I go with lower gears, the larger (taller) tires will compensate... I'll try to get a final ratio of around 3.00:1 using the formula. thanks for the Info guys....

[49stovebolt]

Ian, I have a 8 inch open 3.00 Maverick rear end in my 49 Chevy. Unfortunately, I have it in the car for mock up.

I will be in the same boat as you but I am looking for a 3.50 or 3.80 ratio with a posi. I am planning on running a 4l60 or 700r with 28 inch tall tires.

You should be able to find the 3.00 gears there are quite a few around. If you are looking for a posi they are harder to come by. I saw a few at the Portland swap meet. About $500-$600 with the posi.



Todd

[PG409]

My 351W/C6 powered 54 Ford just got 21 mpg and 1/2 was running
in the city. Have a 2.79 Comet rear and it seems to have lots of
grunt. No complaints here. Great cruising at 60 mph at around 2100 rpm.

[Hammer396]

I'll try the 2.79:1 gears for now, I have a feeling I'll be changing them though.......I think the bigger tires will make too much of a difference....but as long as I can get if on the road this summer I'll be smiling no mater what gearing I have..

[Gramps]

I have 3.73 gears with 15" tires on my A

[Hammer396]

hey gramps....what tranny do you have? an overdrive? just wondering what your revs are at 60mph?

[Gramps]

I got a 200-4R tranny. RPMs at 60 are 2000 and with the stall converter switched on it drops it to 1800. This is a OD tranny and so far it has worked well for me.

[dustyrustee]

I'm putting a ford 8" in my model A , it's out of a 73 comet, ratio is 2.79:1, I'm running a 350, turbo 350, with 28" tall tires,
now the question is , will this be a good ratio for this car? should I put a little lower gear in it? 3.08:1, or 3.23:1? what are you guys running out there?
I do want a good highway speed, but do not want it to doggie in town.


this link may help you out....

http://www.users.interport.net/s/r/srweiss/

good formulas....plug in the numbers....

Ian

[JRR]

Hey Hammer ,have a look at this site ,it should help you .
http://www.project33.com/tiresize.cfm#trans_rpm
I used this when building 32 pickup
John.;)

[Hammer396]

Thanks guys , awesome info....

[dustyrustee]

Hey Hammer ,have a look at this site ,it should help you .
http://www.project33.com/tiresize.cfm#trans_rpm
I used this when building 32 pickup
John.;)

john....thanks for the link.....very handy calculators!!

[Henry J]

Hmm I use a 325 gear and a 29 inch tire in my Henry J it runs about 2400 at 70 mph and can still put down a 13.42 at the strip

[John in Oz]

Hammer for what it's worth I had 2.75's with 31" tall tires on an A and a 307 Chev with Powerglide, it ran quite good, turned a 14.16 at Willowbank drag strip, the engine was just a very mild but matched up thing, when I say matched up it had been balanced and all the ports matched each other, just right as in no steps, so it was just a mild thing. I never did a mileage test on the car.

You have to remember an A is a fairly light weight car so unless you are going drag racing I'm thinking those gears you have in there now should be alright for every day use.

My 33 also has 2.75 gears and it's able to turn the tires when ever I wand to. I have even spun the rims inside the tyres about 1/8 to a 1/4 of a turn after a night of a few hard runs. But then again that has a 402 with some extra work done to it and a Powerglide again and 275/60/15 tires on the rear, but it would not be right to use this car as a comparison because of the engine. With this car I feel the diff gears could be changed to around 3.25 because now we live in the city and it runs somewhere around 1800 revs on the highway.

With the A roadster pickup the only reason I ran 31" tall tires at the time was to fill out the wheel arches and when the car was finished they really did look too tall (and you will use twice as much tire shine :D, no just kidding you there), I would have gone to a smaller tire when I wore them out but I sold the car before I had to fit new ties and built a new car.

Just give it a go with what you have and with the price of gas today you might be happy you have a slightly taller diff in the long run. As I say with the weight of the car in reality unless you are racing the diff gears wont worry you with what you have and they will be good for highway fuel on long distance hauls.

Cheer, John

[Hammer396]

thanks John, I think i'll try the 2.75's, I'm running around 350 to 400 hp so it should have enough hp to turn the tires. besides, it doesn't take long to change gears if I don't like them...

[Windsor-408]

I had a 88 Mustang with 3.08 gears from the factory. I swapped them for 3.73 gears and with the five speed overdrive it was still up at 2400 rpm's at 100 KMS. I had to swap in taller tires on the back to get the revs down a bit, but it lunched real hard.Is your diff an 8 in or 8.8? I still have the 3.08 ring and pinion for the 8.8 I can let it go cheap. Cheers.Wes:cool:

[Hammer396]

My dif is a 8", but I have a few friends with mustangs, I'll keep your gears in mind when I talk to them next..

[larry]

I'm putting a ford 8" in my model A , it's out of a 73 comet, ratio is 2.79:1, I'm running a 350, turbo 350, with 28" tall tires,
now the question is , will this be a good ratio for this car? should I put a little lower gear in it? 3.08:1, or 3.23:1? what are you guys running out there?
I do want a good highway speed, but do not want it to doggie in town.

I've been playing with 8" & 9" rear ends for years, and the best gear for street rods is either a 3:25 or 3:50, a 3:25 will give you @ 2,300 rpm @ 60 mph. Hope this helps...Larry.

[Olrodder]

I have a glass Model A with a very mild 302 Ford and C-4, with an 8" with 2.79 gears, and it's not a bad driver at all. It has legs on the freeway, and because it's light it runs around town with fair pep. Being a mild motor it's no tire smoker, just a fun ride, but it's still fairly quick.
In my fenderless 27 I run a warmer 350 TH400 with a 9" and 3.00 gears. At 2060 pounds this combination works well, even when I tow my tear drop trailer. With the cruise set this combination has given me over 20 mpg on longer runs.
Keep in mind that the taller gears (lower numerically) will keep the tires spinning a lot easier than low gears (higher numerically) once they are broken lose. The lower gears keep the actual wheel speed down per rev allowing better bite and traction control. The taller gears allow wilder wheel speeds..... that's why drag cars rarely do burn outs in 1st gear.
I'm building another roadster right now, and have settled on an 8" with 3.00 gears, but it has a way tall tire (285-70-15) so I have 3.50's just in case.
Hope this helps in some way....
Clarke

[dustyrustee]

you may find this link with formulas quite useful...should help you figure things out pretty good...........cheers. Ian

http://users.erols.com/srweiss/#jcalc

[John in Oz]

Hammer I ran 2.75 gears in an A roadster pickup and it was a shade tall but wasn't really a problem, with a powerglide 307 Chev and the 8" it still turn 14.16 at the strip on a fun day, I had 31" tall tyres and I feel that 28" would have been a lot better for looks as well as gearing but at the time all I could get was 31" tyres.

With the 33 I run a 9" with 2.75 gears and powerglide but 275/60/15 tyres, the BBC has a ton of torque so gearing really is not an issue. The main reason for running the tall gears at the time of building these cars was for long distance highway driving so I would get better MPG and it helps for a bit of top end on the highway as well. I think if I was just doing around town driving though I would be considering going to 3.25 gears in my 33

If I was in your position I would be trying them and just see how it is because they are not to far off and do you need to spend the bucks at the moment.

All the best with it, John