Projects What gear ratio in AV8 rear axle?

Hi !

I have a question for you... i got a AV8 Ford '30 with ha 46 flathead V8 with a 4" mercury crankshaft but except that its a standard engine .
Also 39' Ford standard gearbox.

Now im looking for a new gear ratio in my rear axel and wondering what would be best?


A pinion 3:54 or a 3:27?

I dont race with my car only crusing on the highway and drive to hot rod meetings.

// André !

 

It seems everybody wants the 3.54s. They are fetching good money nowadays, are 3.78s too steep? That is what I have but car nor running yet

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Thanks for the quick answer wheeldog57. Yeah the 3:78 is way to steep for me! And also the gas price in sweden are in the sky so a car that needs 2 liter á 10 kilometer needs another ratio . Have a friend with a blown 51 flathead and he uses the 3:27 but of course he has twice the HP compared to me.


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André,
My first thought is that the 3.27 gear is a good gear, a standard bore flatty with the long arm of the Mercury should develop pretty good low end torque. But then I remembered that there are lots of mountains and few flats where you live. If you have tall tires and all those hills to climb you are going to be better off with the 3.54 gear.

My choice the 3.54:1 ring and pinion.

 

Thanks porknbeaner !!!


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We had a 3 speed and 3.54 gears in our 32 hi boy with 750 x16 rears ,it had no issues on the hills here in NZ. Smiling as we passed a stock 57 chev on a 4 lane hill.
I don't think I would go to taller gears as we have a big cam and the low end torque was down a little . We were lucky and found an original 39 merc axle to rob. New gears are a little spendy.

 

3.54 or less is much better,not more for street with any type of flathead motor/rember flatheads of anytype don't normuly turn RPM like a OHV motor. So around 3.0 is best. High numbers are nice for drag racing only.

 

So dana barlow you mean 3:54 or 3:27 is the one to go with? Not the 3:78?



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Thats right, 3;27 better for street driving then 3;78, all though both work,3;27 will keep RPM down some an give better MPG. It's also a bit stronger cuz the teeth are a tiny bit bigger. None of that matters for drag racing,but for street is golden.

 

3.78 with tall tires should remain in the choice list. Very good combo. Consider also spending more, getting Mitchell OD, and going with 4.11

 

Lot's of opinions here.
My method is to see what is the lowest speed you accelerate from in high gear. Note the engine RPM at that speed. Then, see what speed you would be going at that RPM with your proposed ratio.
Without changing anything else, the speed changes are as follows:

3.54 will be 1.07 x 3.78 speed
3.27 will be 1.16 X 3.78 speed

So if you can accelerate from 25 mph with a 3.78 gear, you will have to be going at least 29 mph to accelerate with a 3.27 without down shifting. A 3.54 gear would require you to be going 26 3/4 mph.
Sorry about the mph but I'm old school.

Of course, you could get a Quickchange and dial it in for whatever the occasion.

 

Had to resurrect this


What gears is everyone running with their AV8s

 

i have 2 cars w/flthd's , Oakland rdst pu, 53 merk mostly stock 26t linc gears,4.44 rear w/columbia od , 7;00x16 best of both worlds. other 27 T cp most stock 51 ford eng, 48 stock trans, 4.11 w/columbia od.7;50x16, overdrive is the way to go....