3b at high rpm?

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bj70cruzer

10 Year
Joined
Apr 8, 2013
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60
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hey i was wandering if the 3b in my bj70 will beable to cruise at 120km/h on the highway?

it has a 5 speed h55f

will the rpms be to high? if the rpms are high and the motors driven like that for hours will it cause reliability problems?

a mate of mine said 3b's like throwing rods at sustained high rpm?

Thanks!
 
They're a relatively slow revving engine, so you don't wan to be screaming them if you can help it. I would not say that they like to throw rods, that's not been my experience at all.

There are ways of getting your RPM down at 120 kph - you can run the taller of the two common diff gear ratios (3.70) instead of the lower ratio (4.11). You can also move up to taller tires - perhaps a tall skinny tire like a 235 85R16 or a 255 85R16. With either option you are going to have to correct the speedometer reading for either the gearing, the tires, or both.

As for going 120 all the time, it may be a bit much if you're running 4.11s and small, stock sized tires. I used to regularly run about at 105 to 110 kph in my old BJ42 with the 5 speed and 4.11s on 33s. No problem, but it did get slow on hills.

I'd say that you probably don't want to run it much over 2500 - 2600 rpm for a long time, also at those kinds of RPMs they are not that efficient and will use quite a bit more fuel. They like to sit more around 2200 RPM for more efficient operation.

~John
 
120 kph ..... I can't even go that fast in my dreams. :)
 
I havent heard of 3B/13BT's being "crank and rod snappers" Cicak's is the only one I know of thats snapped a rod. Slightly different engine but I hold my 13BT on the governer (4100rpm) no problems, smoother than at lower rpms too.

On the hwy I sit at 2200rpm (peak torque) at 100km/hr, cruises great and fuel economy is decent. 120km/h is something like 2400rpm, does it no worries but fuel economy is terrible, even 110km/hr fuel economy is pretty bad.
 
Rod didn't break it PULLED the piston in 2 when the piston siezed in the block.

Normally I will not go past 3000rpm in my 13B-T even 2500 I change up as it has (HAD boo hoo) so much torque available.

Running down the highway at 4000rpm would not be good the fuel economy would suffer . Even 3000 would be bad for engine and economy , 2600 is what I will try and normally cruise at max.

I agree and running up to 2500rpm returns excellent fuel economy 85.k/liter roughly or more for me even up to 11k/liter

a 3B running down highway at 120k I wanna see that It will get hot.
 
120 kph is rare phenomenon for my 70,only happens on the logest and steepest downhills,but at 100kph i sit at about 2400rpm in fifth and 2800rpm in fourth. im running stock 30*9.5r15 tires with stock 3.7 diff gears with a h55 and a 3B.
 
blueBJ70 said:
120 kph is rare phenomenon for my 70,only happens on the logest and steepest downhills,but at 100kph i sit at about 2400rpm in fifth and 2800rpm in fourth. im running stock 30*9.5r15 tires with stock 3.7 diff gears with a h55 and a 3B.
Click to expand...

Your RPM vs. speed tells me you have 4.11s and not 3.70s.


~John
 
You can hit 120kph with the 3B. I've been doing it recently cruising the Autobahn here in Europe (3B turbo'd, 4:11's, H55 32x11.5x15 BFG AT's). I will say it doesn't like it though. I concur with the rest that 100kph is about max comfortable cruising speed.
 
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