rearend gears

[TedIII]

How much compromise is running a 389 instead of a 411. I have always hear of most people running the 411. And since I have never ran either but I do have a 9" ford with a 389 locker in it, I would like to known how much am I giving up, as far as time and streetable.

[lt1s10]

Originally posted by TedIII
How much compromise is running a 389 instead of a 411. I have always hear of most people running the 411. And since I have never ran either but I do have a 9" ford with a 389 locker in it, I would like to known how much am I giving up, as far as time and streetable.

it dont work that way. you could put the 4:11 in and slow down. need more info.

[TedIII]

Originally posted by lt1s10
it dont work that way. you could put the 4:11 in and slow down. need more info.

what information do you need?

[lt1s10]

Originally posted by TedIII
what information do you need?

every thing , tires, motor, carb, heads, exhaust, trans, wt. driver, the way you adj. you valves makes a dif. i dont think there is a rule of thumb on that. the starting point is to figure how many rpm's you wonted to turn in the 1/4 mile and and get the tire size and gear ratio so when you go through the lights at the end of the 1/4 youll be turning the rpm you fell like you should to be getting max. power out of you motor.. if you think you set up works best at 5500 rpm then thats what you wont to turn when you go through the trap. use your cam as a start.

[Don Shillady]

I have recently been through this calculation for a roadster with a mild SBC 350. You need to know what your rear tire size is, the gear ratios of the various gears in your transmission, whether you have a 1.0 high gear or OD and the ratio of the OD gear. In addition you need to know at what rpm your engine torque will be able to pull the car in OD to avoid constant downshifting from top gear. I found the following site to be very helpful once you have that data:

http://home.tampabay.rr.com/1bking/c...calculator.htm

I figured I would like to be in OD as low as 55 mph for mileage purposes and that the 700R4 I am using has a very low ratio for first gear so I need to cover fairly high rpm like 4500 if I wind it up in low gear. Fortunately the SBC 350 with my Crane street cam can easily run between 1500-4500 rpm. Then the last thing to consider is the stall rpm of your converter. It is no good to have an OD gear set up for 1800 rpm if you are using a high stall converter set to catch hold at 2500 rpm, if you see what I mean.
Play around with the calculator above and see what that tells you. I ended up choosing a 3.55 rear gear for a 2500 lb. roadster with the hope of good acceleration due to the very low ratio of the700R4 and hopefully (?) 20+ mpg with the 0.7 OD gear. As told above you also need to know the carb size because that will strongly effect your top rpm, assuming the distributor still works above 5500. In my case I just set up for the street, but the calculator above should work anyway to tell you what gear is matched for whatever rpm range you want.

Don Shillady
Retired Scientist/teen rodder

[TedIII]

Originally posted by lt1s10
every thing , tires, motor, carb, heads, exhaust, trans, wt. driver, the way you adj. you valves makes a dif. i dont think there is a rule of thumb on that. the starting point is to figure how many rpm's you wonted to turn in the 1/4 mile and and get the tire size and gear ratio so when you go through the lights at the end of the 1/4 youll be turning the rpm you fell like you should to be getting max. power out of you motor.. if you think you set up works best at 5500 rpm then thats what you wont to turn when you go through the trap. use your cam as a start.

tire are quick time 10.5x28x15" Motor is a 460 with blue thunder heads with chevy exhaust ports. The carb is 1050 Holly ultra, the weight of car minus me is 3100lbs. Engine has 13.1 compression is built to produce 650 horses Havn't been dyno yet but it will be. Trans is a reverse shifting C-6 work with a 4500 stall, expect to run up around 7000 rpms. Headers havn't been built yet. Car has mustang II front suspension on it. The cam is a 1550 flat tappet with #145 seat pressure and 410 open

I had car for a few years and work on it here and there. Took about fifteen off to raise kids, and now I get to go hide in the garage with my 50 cents.

[lt1s10]

Originally posted by TedIII
tire are quick time 10.5x28x15" Motor is a 460 with blue thunder heads with chevy exhaust ports. The carb is 1050 Holly ultra, the weight of car minus me is 3100lbs. Engine has 13.1 compression is built to produce 650 horses Havn't been dyno yet but it will be. Trans is a reverse shifting C-6 work with a 4500 stall, expect to run up around 7000 rpms. Headers havn't been built yet. Car has mustang II front suspension on it.

I had car for a few years and work on it here and there. Took about fifteen off to raise kids, and now I get to go hide in the garage with my 50 cents.

no body cant tell you that. come up with what rpm you wont to turn your motor, with the gear youve got now, put a set of rear tires on that will get you to the rpms you wont in the 1/4 and go try it. thats the only way to know. use the
http://home.tampabay.rr.com/1bking/c...calculator.htm
to get the right tires and go see. then youll have something to work with.

[Don Shillady]

Well with a 4500 rpm stall and 650 H.P. you are certainly aiming for racing, so I hope that some other folks on this Forum answer you. I only know that traction and chassis hookup are very important besides the engine and gears.

Don Shillady
Retired Scientist/teen rodder

[TedIII]

Originally posted by Don Shillady
Well with a 4500 rpm stall and 650 H.P. you are certainly aiming for racing, so I hope that some other folks on this Forum answer you. I only know that traction and chassis hookup are very important besides the engine and gears.

Don Shillady
Retired Scientist/teen rodder

Going to have some fun either way.
Thanks
Don Shillady

[Dave Severson]

My calculators shows the difference to be:

4500 RPM, 30" Dia. Tire, 3.89:1 gear =103.28 mph

4500 RPM, 30" Dia. Tire, 4.11:1 gear = 97.75 mph

Hope that helps ya out.

[TedIII]

Originally posted by Dave Severson
My calculators shows the difference to be:

4500 RPM, 30" Dia. Tire, 3.89:1 gear =103.28 mph

4500 RPM, 30" Dia. Tire, 4.11:1 gear = 97.75 mph

Hope that helps ya out.

It helps, will be able to use all information, so doing some of the building allow for bigger tires