3B Diesel RPMs/tire size choices....

[Hltoppr]

Let's say, just theoretically for now, that I were to get something with the following:

3B 3.4L Toyota Diesel (non-turbo, 90hp@ 3500rpm)
H55 5 speed transmission (0.84 5th gear ratio)
Stock Transfer Case (1:1 high range)
4.56:1 axle gears


....Running 31" tires would net me about 2923rpm at 70mph, or;

33" tires would net me about 2746rpm at 70mph.

Both tires would be 10.5" wide.

Anyone know what might work better for this motor, with consideration given to mileage and efficiency?


-H-

 

[ntsqd]

Without knowing a derned thing about that particular diesel engine I'm guessing that you want to cruise at under 2500 RPM. Possibly a lot under that number.

 

[Pskhaat]

Yes, well assuming such a vehicle would exist and knowing I've driven a particular BJ60 often, and considering the 4.56s in there, I would venture to say 33" would be the reasonable minimum tire diameter.

IIRC, the 3B has torque peak at just under 2000rpm and HP at ~3500rpm. It is pretty "squared" on the bore:stroke ratio and that contributes to a fairly good power range.

One may want to consider a commodity swap back to 4.10s to get another 11%? I know first hand that 4.10s with 31s and H55f and 3B drive at least to me a little short in the gears.

 

[ChuckB]

Let's say, just theoretically for now, that I were to get something with the following:

3B 3.4L Toyota Diesel (non-turbo, 90hp@ 3500rpm)
H55 5 speed transmission (0.84 5th gear ratio)
Stock Transfer Case (1:1 high range)
4.56:1 axle gears


-H-

Let's say, just theoretically for now, that I am JEALOUS!

Sorry can't help with the tech...

 

[bj70_guy]

My BJ70 has 4.56 and 33s (255/85R16 BFG MTs). It's slightly lower than the stock 235/75R15s + 3.70s.
I've always been happy with the combo. Still able to cruise all day at 120 km/h (as long as it's not uphill...!) and ok low range for wheeling. It'd be perfect with 34s.

4.56s and 31s will be too low, IMHO.
If all you want is mileage and efficiency, you could grab some stock 3.70 pumpkins and run 30s. If you want to wheel it some, 4.56s and 33s is a nice combo.

 

[Hltoppr]

Excellent!

BJ70guy...is your 3B turbo'd? If, say, a Turbo-Glide turbo were put on it...would it still be OK with 33s?

....of course...this is all theoretical...until this weekend....:coffeedrink:

-H-

 

[bj70_guy]

No, it's still NA. But I also have a BJ74 with a 13B-T, it currently has 4.11s and 31s and feels a bit low geared on the highway. I'm going to emu it and run 255/85R16s on it and expect it should be just about right. Quite a few guys up here are running that combo.

What are your hypothetical needs for this hypothetical vehicle?
Daily driver-road tripper, camping/expo machine, wheeler?

 

[Hltoppr]

Daily driver, Expo rig...must fit in 7' garage door....

-H-

 

[bj70_guy]

Are the 4.56s already installed? Turbo'd with 4.11s will turn 33s easily and your speedometer will be right in the ballpark. It wouldn't bother me to run 4.56s and a turbo if they were already in there.

FWIW, my 70 is on Emus with 33s and stands about 6'6" or so.

So 60 or 70? ... hypothetically speaking, of course :elkgrin:

 

[Hltoppr]

4.56s are installed w/ARBs front/rear., OME heavy..70 series...since we're "dreamin."

:sombrero:

Currently running 35s...which are too big IMHO.

-H-

 

[lowenbrau]

I've owned about three dozen Cruisers in the last two decades. Most of them were 3Bs. I am living proof that they don't last. :elkgrin:

There is an enormous difference between a normally aspirated 3B and a turbo-ed one. Normally aspirated are more comfortable to drive at higher revs. 2900 for long periods of time will actually yield better fuel mileage than the same truck with lower revs. I've always found that the same truck with no overdrive will provide better economy than one with a five speed. I have put a lot of miles on rigs with 4:88s and 33s.

All of that changes with a turbo. They have a sweet spot between 2200 and 2500 RPM. If you are seriously contemplating forced induction, don't bother with the gearing swap. If you need improved low range gearing make sure you have the 2.3:1 gearset in your t-case rather than the 2:1 that is common behind the H55f.

I'm now running 37s and 4:11s behind my tweeked 13BT. It would probably be happier with 4:88s but is absolutely drivable as is.

HTH

 

[Hltoppr]

I've followed your build up thread on 'mud...amazing machine! Loved the Alaska expedition too! Those 37s were definitely necessary!

I'm new to the Toyota diesel world...this will be my first oil burner, so that's exactly the type of info. I need!

-H-

 

[hoser]

Gearmaster makes various TC gear combos.

http://www.marks4wd.com/products/gearmaster/lc-extra-low-tc-gears.htm

No experience with them but if anybody out there has these installed, I'd like to know which combo and how much added gear whine noise.

 

[Hltoppr]

I'm not necessarily concerned it'll be to low for the off road stuff...just that it'll be spinning the motor too hard at highway speeds.

-H-

 

[hoser]

I was referring to Option 2:

Option 2
High Range .92:1 = 8% Overdrive
Low Range 2.82:1 = 44% reduction

But looking at the prices, it would be cheaper to just regear the diffs.