2 1/2 or 3 inch Exhaust HDJ81

[ScottJacob]

Hey folks. I have a quick question. I'm looking into replacing the exhaust on my HDJ81 and I'm wondering what the pro and cons are of either going for 2 1/2 inch or 3 inch piping. So far, I've been told that bigger pipe lets the motor breath better but it will cost me $200-500 more. I'm not sure if this makes any difference, but I am running waste veg oil from the secondary fuel system I have installed. Also, does any one know what size pipe these things came with from the factory in Japan? Was it 2 1/2 inch pipe?

Any insights into this would be much appreciated. Thanks!

 

[htownlc]

Hey folks. I have a quick question. I'm looking into replacing the exhaust on my HDJ81 and I'm wondering what the pro and cons are of either going for 2 1/2 inch or 3 inch piping. So far, I've been told that bigger pipe lets the motor breath better but it will cost me $200-500 more. I'm not sure if this makes any difference, but I am running waste veg oil from the secondary fuel system I have installed. Also, does any one know what size pipe these things came with from the factory in Japan? Was it 2 1/2 inch pipe?

Any insights into this would be much appreciated. Thanks!

Here’s what Beaudesert Exhaust says about it, further down that page. I’m not an expert, but like the 3” muffler-less system from them.

 

[ScottJacob]

Thank you, this was helpful.

 

[htownlc]

Thank you, this was helpful.

Here was my experience with them.

 

[mudgudgeon]

If you have any intention of increasing power, definitely go 3"

The factory exhaust is 2¼, and is crushed almost flat at the rear crossmember at the diff.

I would find a so that can make a system that runs on the inner side of the frame from turbo, all the way to the back. Its a much straighter path and reduces the number of big bends in the pipe dramatically

Personally, I don't like the sound with no muffler. A couple of full flow mufflers will keep it quiet with no loss of power

Have a search on the diesel tech section

 

[AussieHJCruza]

3" straight pipe for me personally, but if you don't like it loud, chuck a decent full flow muffler or 2 into the system.

 

[cody c]

I have a bit of a different beast, early 90’s 6BT with a 3” exhaust...

I was pulling a trailer years ago with an exhaust that ended just before the rear axle, the extra load and extra heat started to melt one of the airbags so I had the pipe run out to the bumper (3”). The extra length of pipe made a notable difference to engine performance, it builds boost just a pinch later.

I definitely want to go to 4” on it, it should perform closer to having a 2’-3’ long piece of 3” and be a bit more responsive with spool up.

Based on my experience, I would definitely recommend 3” pipe for the H series motor

 

[ZCissner]

B6111027-CD10-44CE-8ED4-59B8CB374FF2.jpeg

• ZCissner
• Jun 4, 2020

E6E2DF69-9F76-4F50-8032-E35235881B55.jpeg

• ZCissner
• Jun 4, 2020

3 inch, and it will fit inside of the frame

 

[mudgudgeon]

I have a bit of a different beast, early 90’s 6BT with a 3” exhaust...

I was pulling a trailer years ago with an exhaust that ended just before the rear axle, the extra load and extra heat started to melt one of the airbags so I had the pipe run out to the bumper (3”). The extra length of pipe made a notable difference to engine performance, it builds boost just a pinch later.

I definitely want to go to 4” on it, it should perform closer to having a 2’-3’ long piece of 3” and be a bit more responsive with spool up.

Based on my experience, I would definitely recommend 3” pipe for the H series motor

On both my HDJ81 and HZJ105 I used 4"pipe from turbo to T-case.
Initially tab the HDJ81 with no mufflers, but with the 4" pipe it was too noisy, so added mufflers.

Some pics here

Rolling the dice - slow moving turbo HZJ105 project

forum.ih8mud.com