What highway RPM do I want for a 360

[N2Jeeps]

Hi guys

Now that my 86' Waggy is home I am trying to figure out what gears to get once the new tires are installed.

Right now she is stock with 235x75 tires and 3.31 gears.

That puts me at 2696 rpm at 70 mph.

Moving to 33" tires and 3.73 gears puts me at 2658 which is almost stock.

I guess my question is... What should my target RPM be for the 360. I know this was a SBC but my Suburban pulled around 2250 rpm at 70 with the OD transmission. If I keep the 3.31s then my RPM would be 2359.

Conventional logic would suggest that lower RPM would equate to better mileage. On the other hand I have know idea what the optimal RPM range is to get the most mpg and still be able to pass.

Thanks again guys

[Michael]

Not sure where you are getting your information mine w/4.10's and 33's or 34's runs 2600 rpms at 68-70

w/33's and 3.73's I would think you would be fine around 2600 rpms

[BRUTUS]

Offroad tech... "70mph" :lol:

Here you go:
http://www.4lo.com/calc/geartable.htm

[N2Jeeps]

I used that same web page but used the RPM calculator.

http://www.4lo.com/4LoCalc.htm

Unless I am wrong... the 727 and the NP228 have 1:1 ratio

So 70mph 3.73 ratio trans 1 xfer 1 Tire diameter 33 = 2658.47


So what did I do wrong?

The chart from the last post said 2469

[BRUTUS]

So what did I do wrong?

The chart from the last post said 2469

The chart on the webpage is for 65mph.

[derf]

*cough* *cough*

http://www.grimmjeeper.com/gears.html

[Serious Johnson]

Hi guys

...Conventional logic would suggest that lower RPM would equate to better mileage...

That's essentially true with a manual transmission, and maybe a close approximation of reality with a modern slushbox. But a 727 with the stock torque converter is horribly innefficient at lower revs. I can't say where the sweet spot might be, but know that when my Wag was more or less stock (2.72s, 30s), it consistently got better mileage at 75 MPH than at 50, which implies huge loss in the lower ranges.

S.J.

[360]

i'm running 32" tyre's with 3.73 ratio's 360/727/amc @100km(61mph)i'm doing 2600rpm-with 33's and 4.1's i'd be looking 2 about 3000rpm@100km(61mph)!!!
ps. question in those charts is a 33" size relate to a 33" tyre or a tyre that measures 33" ie most 33" tyres are from 32.3-32.7 "so this could affect the results slightly....

[shimniok]

FWIW, I am running 3.73's and 33's and am not happy with power, but at least the motor isn't screaming on the hwy. I believe I'm running about 2800 rpm at 75 give or take and about 2600 @ 65. I run MT/R's which are close to a true 33" dia supposedly.

I'm out of Denver so when I say power isn't where I'd like it, I mean I can't climb 6% grades at 9-10k' altitude at a speed I like without being in 2nd and far into the skinny pedal. If you're a flatlander, with all that oxygen available, the same combo might seem a-ok. On flatter stretches like Denver to Ft. Collins, accelerating to 85+ to pass is no problem as long as there isn't a particularly steep hill in the way. :D I got 11+ mpg up and back (doing 65-75)

Michael
PS: for a stock motor, I would expect the peak torque rpm to be somewhere in the 2500-3000 rpm range which is where you'd want your cruise RPM so I have read. (86 lists 1500... :confused:) I'm sure if you can run lower RPM, it saves gas (hence, Overdrive) but in a 3spd auto, it seems like you'd want to gear a bit differently... Curious to hear what others say.

[letank]

on the 74 w the 235 and arrrrgh 2.68 gearing after the QToverdrive conversion... at 65 mph it read about 2250, which is fine on flat land.... going up (5000') where oxygen is rarer... it starts to be a challenge... when you see the hill, starts to pick up speed to keep in the 2500 rpm (70ish) or above, to be in the sweet spot.... So as Michael said... 2500 rpm or above is better

For the high altitude i lean it about 1/4 turn.... It helps a lot... but still a slug on steep incline... of course i have the 2100.

w the 31 on the 85wag w the 3.31, and the 2150... it flies..... No tach on that one....

hope it helps