Compression Spec on 13BT

[A2B in a TLC]

Anyone know what the cylinder compression spec is for the JDM BJ74 Turbo Diesels?

Thanks,

Bruce in Tsawwassen

 

[wesintl]

The manual states 3BT 427psi. Min of 284psi with a difference of 28psi between cylinders.

 

[HZJ60 Guy]

The manual states 3BT 427psi. Min of 284psi with a difference of 28psi between cylinders.

Wow, my 1HZ tested above 600 in each cylinder. I guess the factory turbo units have a lower psi.



TB

 

[crushers]

each engine has it's own compression...

 

[lowenbrau]

IDI engines seem to be higher. I believe I was told they need the big pressure to start but maybe I just made that up.

I know that is why some gurus think it is inappropriate to t-charge an IDI Toyota diesel without lowering the compression.

 

[Greg_B]

The manual states 3BT 427psi. Min of 284psi with a difference of 28psi between cylinders.

Good subject:

In the wonderful world of the Toyota FSM is states in a few books no difference of 2.8 psi between cylinders, then on another page in the same book shows 28.0 psi. On the page that says no more then 2.8 psi difference page in the 2H/12HT manual is says 398 psi or more, with a minimum of 284 psi for the high compression piston IDI 2H, and then on the next page for the low compression piston DI 12HT is says minimum, 427 psi or more, with a minimum of 284.

In the 3B/13BT manual it references the same pressure for both engines, per wesintl's quote.

I don't know if there were any service bulletins to the Toyota dealers, however I have wonder how you can take an engine with the same displacement. one have high compression pistons, and one have low compression pistons, and then reference the same compression stats.

Perhaps the 2H/12HT has the correct numbers, but in the wrong location, and the 3B/13BT simply used the same numbers for both.

The turbo forcing the air in would increase the pressure in the cylinders, so the factory installed lower compression pistons...which would lead to the reason some "guru's" think it appropriate to lower the compression on the IDI engines when adding a turbo.

gb

 

[A2B in a TLC]

Good stuff, Greg. I spoke with Sheldon yesterday re the parts supply for the JDM BJ74. He was a big help as well.

Thanks,

Bruce in Tsawwassen

 

[lowenbrau]

That's interesting. I rely too much on my RF addled memory. I was sure the DI diesels were meant to have lower compression.

Just for the sake of conversation. P Straub's immaculatly maintained (before he got it) BJ70 had over 500 PSI compression at 525,000 kms. I have never seen a rig under 250,000kms get close to that. These things take a long, long time to break in.

 

[Greg_B]

Hi Bruce.

Yes, you are correct. DI motors ifaik are meant to have lower compression, as the forced air makes it up.

That is what makes the 3B/13BT FSM strange when using the same stats, and even stranger in the 2H/12HT manual as it states higher for the DI and lower for the IDI engine.

I "think" my addled memory recalls 500 psi for Sheldons 3B before we pulled it for the 13BT swap.

gb

 

[wesintl]

I've always wondered about that IDI vs. DI... What kind of high end psi do you see in the 3bt's Greg?

 

[hj60]

IDI will generally have higher compression, because the entire volume of the cylinder has to fit in the pre-cups. This is part of the reason they are so much more tolerant of lower quality fuels and SVO/WVO.
With enough compression, you can ignite just about anything that will react with O2.
I suspect this is also why Toyota stuck with IDI for so long while most others had DI and TDI offerings.

 

[Greg_B]

I've always wondered about that IDI vs. DI... What kind of high end psi do you see in the 3bt's Greg?

3B-T's or 13BT's?

Never checked any 3B-T's. A few others on the board will have much more experience then I in this area. Ive' seen 3B's from 420 across the board, to 500 across the board.

Our real world experience with the 12HT's anbd 13BT's has been typically 380 to 400. Speaking to other people local who have tested and worked on these engines they are finding the axact same thing. Some variance to 370.

1HZ's are quite a bit higher...reaching 600psi.

gb

 

[wesintl]

Our real world experience with the 12HT's anbd 13BT's has been typically 380 to 400.

I was wondering about the 3BT and DI vs the 3B with IDI. I guess they are in the same proximity. I found that interesting in the FSM.

Thanks