Cummins 4BT & Diesel Conversions Forums banner

Is black smoke due to restrictive exhaust manifold?

5819 Views 48 Replies 7 Participants Last post by  Tickford
First post on here, and I dont like jumping in just for info. So here is a bit of background.
I was working in Bougainville as a Stock Inspector back in the 70,s when I found this Forward Control Land Rover down the bottom end near Buin.
My wife and I rescued it for a slab of SP beer and towed it back to Kieta on an A frame behind my old diesel wagon.

We got the 6 cyl going and used it for work then when I finished my contract in 1980 we took it to NZ. NZ did not work out so we moved to the Sunshine Coast in Qld
Australia. There I fitted a Perkins 6-247 and used it towing a skidsteer on a semi trailer.
In the 90,s I gave it a refit with a 4BD1 and an LT95 gearbox. I also fitted Salisbury axles front and back with Maxidrive difflocks. and a camper back.

Tried for pics but I cant on first post. So more later.
  • Like
Reactions: 1
41 - 49 of 49 Posts
Must be having a good day. Found it. Its the mounting stud holding the filler. Leaking past the thread tapped right through. Well I guess some Loktite should fix it馃檪
131478
See less See more
  • Like
Reactions: 1
I am finding more and more references to drive pressure but not much info on how to measure it. As seen in the photos my custom manifold is made of stainless T,s with the turbo at the back of the engine. Then the exhaust from the turbo is a mandrel bent U then a 90 then straight 3 inch all the way back. No muffler.
Should I be concerned about drive pressure? If so how do I measure it?
I am finding more and more references to drive pressure but not much info on how to measure it. As seen in the photos my custom manifold is made of stainless T,s with the turbo at the back of the engine. Then the exhaust from the turbo is a mandrel bent U then a 90 then straight 3 inch all the way back. No muffler.
Should I be concerned about drive pressure? If so how do I measure it?
To measure drive pressure you need a metal line off the exhaust manifold getting far enough away to lose conducted heat. Then you need something in the line to damp out the pressure pulses. A small restriction can work.
A boost gauge can work well as long as it's got enough range.

You'll want a gauge that can measure double your expected boost. It should also be possible to run an electrical gauge (oil pressure gauge etc) to avoid running exhaust lines into the cabin.
  • Like
Reactions: 1
Thanks.
Would an oil pressure gauge with the thin copper tube from the manifold to gauge work?
Then I am not sure what I am looking for. Some posts I found have higher drive pressure than boost and some lower. What is normal and what might I see if my manifold / exhaust is restrictive?
Thanks.
Would an oil pressure gauge with the thin copper tube from the manifold to gauge work?
Then I am not sure what I am looking for. Some posts I found have higher drive pressure than boost and some lower. What is normal and what might I see if my manifold / exhaust is restrictive?
Yes and that's what I've done in the past. I coiled the line to absorb vibration better.

Turbos feed off heat and it's completely dynamic. When your exhaust and turbo is cold you'll see the highest drive pressure, as they warm up they get more efficient and drive pressure drops for the same boost.
My 4BD1T last time I measured it (about 10 years ago and I've had a lot of changes since).
Accelerating cold, up to 40psi drive for 20psi boost.
Sustained load at 2000rpm with EGT above 650C, 18psi drive for 20psi boost.
Flat road cruising 2000rpm, EGT 420C, 12-13psi drive for 8psi boost.

As rpms climb and wastegates open the drive pressure climbs to maintain boost. This is completely normal and why bigger turbines deliver more top-end power.
  • Like
Reactions: 3
FOUND IT1111111
Pulled off the dump pipe to see if it smoked without it, looked down and there was the bloody exhaust brake shut.
I had looked at it previously, checked it with the engine going and it moved OK and did not seem to make much difference at a fast idle so ignored it. But here it is shut. I must have put the pipes on the wrong way around. They are both the same colour, black, so too easy. Swapped them around , no smoke and low EGT..
I will blame the onset of oldtimers disease. I was 74 a couple of months ago so that will do
So thats a lesson, a blocked or restricted exhaust can cause those symptoms.
I will take it for a burn up and down the drive next, see how it behaves before a road test.

turbo install.03 by https://www.flickr.com/photos/141809
Well I am 77 now and the truck is still going, however I read somewhere I should have re torqued the head. This I did not do. Should I do it now and if so what is the process?
Thanks.
Keith
Well I am 77 now and the truck is still going, however I read somewhere I should have re torqued the head. This I did not do. Should I do it now and if so what is the process?
Thanks.
Keith
How many km since your install? Is everything still behaving?
only about 4000 k,s but yes its going well so far.
Keith
41 - 49 of 49 Posts
Top