Ultimate goal is to build an AV8 with a stock 8BA ( I currently have the motor) and a 39-48 3 speed trans. I would like to keep the torque tube and banjo rear end if possible. What kind of cruising highway speed can I realistically expect? I only plan to drive to car shows and club meets throughout southern California. If I can't do 65 mph consistently with this setup I will have to rethink my plans. 65 mph will get me the slow lane on the freeway which will suffice. I would prefer not have to go to an open drive line and T5 if possible, but if that's what it takes, I'll go that route. Thanks, Tony
36-3window, I currently only have the motor at this time. I just wanted to try to get all my ducks in a row (as opposed to previous projects I've done) before I get too far into the build. I thought with a goal of general street cruising and occasional highway travel I better find out if my plans were feasible before I spend any more money. Tony
Simple to figure RPM at 60; (tire height x 3.1416) divide by 12 to convert to feet: 5280 divided by # of feet and multiply by rearend ratio = RPM @60 28" x 3.1416 = 87.96; 87.96 / 12 = 7.33'; 5280' / 7.33' = 720.32; 720.32 x 3:54 = 2549.9 RPM @60mph; 720.32 x 3:78 =2722.8 RPM This is the RPMs on the flathead powered Model A I'm building with a 39 trans and a 3:54 rearend, I have used this formula on several other cars. With a standard 3:78 rearend the RPMs are slightly higher but should be able to run at highway speeds with no problems.
There are a bunch of these calculators on the web. This one is from Summit and all you do is plug in the figures you have / need to search for desired results. Gary http://www.summitracing.com/expertadviceandnews/calcsandtools/gear-ratio-calculator
Thanks for the info guys. Just wanted to make sure that the stock 8BA and a 39-48 trans would allow me to travel on the freeways. From you experience it looks like I'm good to go, now to find a transmission. Tony
don't forget, ya gotta be able to stop real good on So Cal freeways with all of the traffic. switching to 12v would help brake lights to be seen, etc
Gotcha Jalopy Joker, I'll be going with 12v as well as juice brakes. By the way I've found a 1941 pick-up transmission that I will be checking out for condition. I was thinking about this trans because of it's a floor mounted shifter as well as being in the 1939-48 range. From what I understand I should be able to mount this trans behind my 8BA through a 1948 truck bell housing. Does this sound correct or are there fine points I'm missing. TIA Tony
That trans is a good choice, will bolt up with the truck bell housing. Make sure you get the starter plate with the bell housing, they are differences in them.
Tony, When someone says AV8 to me I immediately get an image of a lowered fenderless roadster in my mind. It could just as well be a full fendered, stock height 4 door sedan. What does it mean to you? The engine should pull either one to 65 MPH with the correct rear end but the stock height full fendered 4 door would be a bit of a handful at that speed with its large front and side profile. Do you have the body yet? Maybe if you are looking you should tell us so we can keep our eyes open in Southern California. Charlie Stephens
I don't know how much of a budget you have but other possibilities would be a Columbia rear end or a Quick Change where you could change gears easier.
A well tuned 8ba with 3.54 gears will cruise all day at 70 mph with a stock transmission but don't forget, it is possible to install a T5 and keep the torque tube with no machine work. It keeps the transmission UNMODIFIED. The conversion has been posted several times on the HAMB and Fordbarn.