3bt Ii Vs 13bt

[crushers]

so an impromtu test was carried out between a 1989 BJ74 automatic with 4.11 gears and 31s vs a 1989 Turbo'd BJ70 5 spd with 4.11 gears and 35" boots.
the BJ74 auto was quicker off the line and a dead match at speed and on hills. the BJ74 was then fitted with a Belton lift and 35" boots installed. and the same test was performed again. this time the BJ74 still beat the BJ70 off the line and with the long legs of first gear in the auto it took a bit for the BJ70 to catch up but before shifting to 3rd the 70 had caught back up and then pasted the BJ74 smoothly both on the flat and on the hills.
this was surprising since i always figured the auto to be slow off the line but that is not the case. i was pleasently surprised that the 3BT II did perform as well as it did since it is IDI and the 13BT is DI...
just for chat sake...
cheers

 

[HZJ60 Guy]

That's great Wayne. I love these kinds of posts. You cant get this info anywhere.

Auto's are faster shifting senarios that are manuals. I hope to get me a BJ74 auto here sometime soon.


TB

 

[Greg_B]

Cool. thanks for the tests.

Now to play a little devils advocate:

What do you think the percentage is that you have gained from stock form with the mods on the 3BII if stock form/power is 100%.

Now, make those same pecentage changes starting with a stock trim 13BT via any combination of: boost adjustment, fuel adjustment, intercooler, propane...etc

Now you have two vehicles that have had X% changes done over above the stock datum of 100%...to compare to each other.

Interesting about the auto. I wonder what effect an extreme wholesale automatic replacement would make?

btw to anyone new reading this, I have driven the truck with the 3BII that Crushers is talking about, and it does pull nice!

gb

 

[Diesel Dude]

The 3B also has a different compression raito it is 20:1 and the 13BT is like 17.9:1 I would think that would make a difference.
Cheers

 

[crushers]

true, there is a compression ratio difference. the comparrison was done for the sake of arguing whether there is much difference between the 13BT and the 3BT II.
the boost could be raised in the 13BT to 13 lbs which will make a noticable difference and at that time the fuel could be turned up. the 3BT II has no black smoke coming out so it could have the fuel cranked up a bit as well...
cheers

 

[Greg_B]

At the end of the day it's all good Wayne! I am glad you took the time to do the comparison...

Lower the compression, and pile in some boost on a 13BT and I bet you end up close to the same psi in the cylinders as healthy IDI 3B...which is likely how the Toyota Engineers figured it...

gb

 

[wesintl]

Great comparison... I love arguing diesels. We all win

almost forgot, this thread is worthless without pics

 

[dieseldog]

There's a huge difference in effective ratios also due to different tire sizes. It doesn't surprise me that the 74 with 31's would be quicker off the line than the 70 with 35's. Modern slushboxes shift more optimally in many cases than a cool hand on a stick shift. In any case, I think the true tale of the start was from tire size. It doesn't surprise me at all that the 70 would catch up and hold on later though. Once on boost and at speed, the higher effective gearing due to the bigger tires would make an all out flatland run go to the 70.

 

[tlcruiserman]

Great comparison... I love arguing diesels. We all win

almost forgot, this thread is worthless without pics

More photos to Come later....

 

[Chang-kuao-lo]

how does one increase boost pressure to 13psi? (on a 1-3BT, that is.)

 

[brownbear]

More photos to Come later....

thats a tight fit getting thru the door on that garage. nice pics!!!