RPM's: What's Yours? (1 Viewer)

[rangerJ401973]

Hello All,

Since I have rebuilt my J40. I put a tach on it. To my surprise I'm running 4000+rpm's at freeway speed....Is this possible, or is my new tach a piece of garbage.

Here's what I run, SBC 350 with a stock 4 speed w/4speed t/c. The rearend is stock and I'm running 32" BFG a/t's. Needless to say, my gas mileage stinks(6 mpg). I probably could use a carb rebuild, that's next on my list.

Just wondering what rpm range everyone else is running, or, if mine is unique and I'm going to blow everything up. I'd like to keep my rearend as is. Don't want to really change the gearing, SO, AM I STUCK WITH IT??

Thanks, Tim

 

[camcruiser13]

well that sounds high to me but its no biggie for your 350

i run 3000-3500 on the freeway

still sounds like shes gonna blow but no worries

 

[CruisinGA]

Your most basic options are taller tires, or lower (numerical) gearing.

You could likely easily trade your 4.11 diffs for some 3.70's out of a 79-83 FJ40, or FJ60.

5 speed tranny is also another solution, lots more time/money.

 

[Mark W]

It would help a little bit to know what you mean by "freeway speed". 55? 85?


Maek...

 

[camcruiser13]

It would help a little bit to know what you mean by "freeway speed". 55? 85?


Mark...

tru

im going only 60-65 when im at those previously stated rpms. you must be doing 70-85 easy

 

[rangerJ401973]

tru

im going only 60-65 when im at those previously stated rpms. you must be doing 70-85 easy

Speedo doesn't work, you are all right though. I could be going anywhere from 55mph to 80mph. Just try to "go with the flow" of traffic. Only good things is, the motor sounds like it is not "working" too hard, pressure and temp are always good too. Just thinking, that down the road, I will need a motor rebuild sooner if there's something wrong. Sounds like changing out the rear is the best option after all. Will this really hurt my offroad capabilities if I do this??

Any input is great!

Thanks, Tim

 

[Jerry D.]

The way I figure it, 4:11 gears, 32" tires, 1:1 trans, 1:1 xfer at 4000 RPM = 92.69 MPH. At 3000 RPM it would be 69.52 MPH.

I would check the tach...

Jerry D.

 

['74 UA FJ]

Your tachometer is probably on the 6 cylinder setting.

 

[rangerJ401973]

Your tachometer is probably on the 6 cylinder setting.

THANK GOD!!!!! I looked at the instructions for the tach(if all else fails) I didn't even know there was a 6 cylinder setting. My cruiser moves, but not 90mph!! so I must the tach set wrong.

Phew, now I'll change the setting and see what I've got. If I'm around 3000 rpm at 70mph, I can live with that(motor can too).

Thank you for all of your input, you just saved me a fortune in upgrades I did not want to do.

Tim

 

[REZARF]

Seriously though at 6pmg, you should do a little more checking. That is tragic mileage. I am getting nearly 17 with the old 2f and a lot of tuning and 35's.

I would have a good look at everything. I would think the v8 would be better on gas than that?

Rezarf <><

 

[camcruiser13]

and i think you would know if you were going 90 in a cruiser

 

['74 UA FJ]

Seriously though at 6pmg, you should do a little more checking. That is tragic mileage. I am getting nearly 17 with the old 2f and a lot of tuning and 35's.

I would have a good look at everything. I would think the v8 would be better on gas than that?

Rezarf <><

I get 9-10mpg with my 350, fwiw.

 

[camcruiser13]

I get 9-10mpg with my 350, fwiw.

OUCH





















me too

 

['74 UA FJ]

OUCH

me too

It's not bad when you put it in perspective.

I got like 12-14 with my F motor.
I more than doubled (maybe even tripled) horsepower and torque outputs with the swap and milage only dropped about 3 mpg.

I feel confident that I could get 12 mpg with my 350 if I kept my foot out of it...but that is hard to accomplish .

 

[slickrock]

Just to throw it out there. Running with 35" tires (true 34.75") 1973 Fj40 with F engine and stock drive train, between 2600 and 2650 by GPS says I am going 65 MPHs. My scales are by 100s so it is hard to tell 50 RPMs give or take. I do not usually go faster than that since it is the speed limit and fast enough in my cruiser.

 

[camcruiser13]

It's not bad when you put it in perspective.

.

not bad when my car gets around 35mpg


good thing i drive sparingly around town in the cruza

 

[madoc1]

in perspective-at 60 mph on the original speedo i am at 2800-2900 (hard to see on asmall tach). 350 +all original. 17.87 mpg. just a question- does it take forever to fill your? seems like it just dribbles in there until it over flows. jim

 

[rangerJ401973]

Seriously though at 6pmg, you should do a little more checking. That is tragic mileage. I am getting nearly 17 with the old 2f and a lot of tuning and 35's.

I would have a good look at everything. I would think the v8 would be better on gas than that?

Rezarf <><

Well, I got home and sure enough, it was set on "6 cylinder" I now run at about 3000 rpm's at around 50-55 mph. As far as gas mileage goes, yeah, it's hard not to "get on it" when you have a 350/dual exhaust and you've been working on it for over two years. I could probably get around 10 mpg with a carb rebuild/lead foot rebuild.

Oh well, it's not a DD, but it's a bummer to go wheelin' when you only have a 12 gallon tank(now carry two 5 gallon cans too)

Thanks for helping me solve the mystery, and yes, I was going 90mph, I'd know.

Thanks, Tim