for those of you with 460s, what is your 70 mph RPMs?
stock, modified, auto, manual, different size tires
what 'ya got? are you happy with it?

I'm in the planning stages for a 78 Bronco 460 with a manual tranny. most likely will keep the D44 & 9"
I need some ideas to select gears, will probably have 33 tires.

it will be mostly street driven and medium trail capable, no plans for any hard core off road stuff.

Thanks

 

What trans you gonna run? Gearing will be different for a stock 4spd vs something with OD. Have you ran any gearing calculators to see what different ratios will get you for rpm@ speed?

 

I've got two of em, C6 and NP435, both 460's. These are both extremely nice/clean survivors and are not offroaded at all. I swapped the stock 3.50's for OEM (in 78 only for Bronco's I believe) 3.00 gears. Couldn't be happier, but again street driven only. I do have low range in the 205's if needed.

 

According to a calculator, ( I don't have a tach) my 460 with C6 auto, 3:73 gears and 33 inch tires on rear is turning 2700 rpm at 70 mph. My engine runs smooth and truck will do 70 mph all day so long as I can find a gas station every hundred miles or so...

 

Friend of mine and I traveled over 100 miles to Floyd, Va. in the later '70s to go get his just purchased 1970 Torino 429 SCJ, it had about 27" tall but fat rear tires on 8" wheels stuffed under them fenders, was a 4 speed, about 8 leaves in each rear spring, no back seat, 4.10 gears, It spun up just over 3,000 @ 60 as I recall, and judging by the ride it would tote a load and not sag in the rear, like built for "sneaking a load". It had a bar behind the seats with a big black blanket hung over it like to keep the load out of the sun. I'd say it likely turned 3,500 rpm at 70 mph.

 

definitely want overdrive, plans are for a ZF5-42.
if I can locate a tail housing & output shaft to convert a 2wd to a 4wd
with the creeper 1st I'll drive it like a 4 sp.

interesting numbers so far, I was thinking 1900 to 2200 RPMs at 70 should be OK.
I'm good with the calculators, except when doing a budget

 

Earlier you said 33" tires. A 33" tire will roll out 103.67 inches or 8.6394 feet in one revolution, which means it must rotate 713.01 times in one minute to cover 6,160 feet or 1.1666666 miles in that one minute to travel @ 70 miles per hour ... 70 miles is 369,600 feet.
If trying for 1900 engine rpm, 1900 / 713.01 = 2.6647:1 overall gear ratio in high gear.
If trying for 2200 engine rpm, 2200 / 713.01 = 3.0855:1 overall gear ratio in high gear.
"Overall gear ratio" is transmission ratio x rear axle ratio. If you know what rear axle you are using, you can divide that into the overall to to find the trans ratio you need ... or ... if you know your highest transmission gear ratio like OD, divide that into the overall to find what you need in the axle. Example ... say you have 3.50 axle gears ... and you want 2200 at 70 mph ... 3.0855 / 3.50 = 0.8815:1 = Overdrive needed at the trans.
You could insert a separate overdrive unit .... like a "Gear Vendors" I think they call it.

With a C-6 auto, you'll see slightly higher rpms due to torque converter slippage.

With shorter tires or deflated tires you'll see higher rpms too, but then your speedometer will be reading fast too, so it will look normal unless running Garmin, etc.

U-joint slippage can ruin your best efforts too.

I used to occupy time on rides with my family with puzzles like this when a kid in the '60s, in my head, no paper, pen, or calculator. I would of course, truncate results before compartmentalizing them in my head.

 

I really like this calculator for messing with this sort of thing. https://www.blocklayer.com/rpm-gear You can put in the ratios of the transmission, tire sizes, ratio for rear end, then change things and see how it changes RPM vs speed.

 

I'd like to re-phrase/modify the question.
I'm interested at which RPMs the 460 would be running the most effortlessly, or shall we say the most efficiently cruising at 70 with no load.
I'm more concerned with gearing it to hit the sweet spot between too much wasted power at 3000, and bogging it down way below 2000-1700?

using a BFG AT T/AK02, spec'd at 640 revs/mile, 0.79 5th gear :
3.50 gears are 2065 RPMs @ 70
3.73 is 2200
4.11 is 2425

with the 4.11s I would consider taller tires

 

460 CID - NP 435 - divorced 205 - 4:88 gears - 8R19.5 tires (34").
62 MPH = 3,500 RPM.

SCREAMIN 4x4 Dumptruck!


WC

 

You'd need to know the TQ curve of the engine and choose gearing to put you around the RPM where TQ starts really picking up, or where it's into the curve already. But you need to be careful with OD trannys, they don't usually like a lot of power in OD. You'd be better off gearing to be in the TQ curve in 4th gear and have OD as just a low RPM, cruising to moderate throttle, gear. If you could gear it to put 4th @ around 2200-2400rpm at speed, that'd put you at about 1700in OD and you'd be in the power when you downshift.