Exhaust restriction question

Hi,

My car is an 83 Mercedes 300D turbodiesel (3.0L 5-cyl turbo). I needed to replace the flex tube and down pipe coming off of the turbo, which is about

2ft long, and then attaches to the rest of the exhaust by a flange.

To make a long story short, the entire system is 2.25" diameter pipe. When I installed the new downpipe, it was about 1.5 inches too short. To make up for this I bought an 'adapter' from autozone that is about 3" long, and goes from 2 1/8" to 2 1/4" diameter. I slid the 2 1/8 end into the one side of the pipe, so the area where the pipe enlarged would create a tight mating area. I used an OEM exhaust seal ring to ensure the two sides would mateup tightly and not leak exhaust under my car. I tightened the flanges and all is well.

My question is, Would a 2 inch long length of pipe that is 1/8th inch smaller than the rest of the system cause any sort of noticable restriction or backpressure, that I should be worried about it or get the area welded with a larger diameter pipe so that there is no restriction?

As I understand it, a diesel is just a big pump, and the only way to make more power is to burn more fuel. Gas engines have to worry about restrictions because any way to allow more air in and out will allow more fuel (because the ratio needs to be pretty exact, unlike a diesel), and thus more power. Since diesels have such an excess of air, and the fuel isnt changed by the amount of air going in, does it matter as much or at all?

Thanks very much for your help.

JMH

Reply to
JMH
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1) I wouldn't worry too much about such a small difference in diameter. But the length of the adapter probably isn't as important as the reduction.

2) fuel and air are still supposed to be in the right ratio. More fuel is added to compensate for more air. The fact that the air is under more pressure in a diesel doesn't necessarily mean there's more of it. Diesel's use higher compression than gas engines which allows the mixture to ignite w/o a spark. By introducing a restriction after the turbo you could possibly be making it run a little richer.

If it really worries you, find an adapter that goes on the outside of your original pipe instead, or just buy an exhaust flare tool for $10 or $20 and a new adapter and expand it the 1/4 inch to go around the outside instead of fitting in the inside of your other pipe. If it's been running on there for a while I'm not sure if you'd want to try expanding it now that it's been getting hot and cold cycling and probably started to rust a little-- you may have better luck expanding a new one.

How does it run now? Does it seem as good as before?

Reply to
Bob Hetzel

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