Exhausts And Diesel Engines
An exhaust is there for two main reasons. 1) Take the waste combustion gasses away from the engine, and passenger compartment. 2) To reduce the noise produced by the exhaust stroke of the engine.
Not much can be done about point 1. Point 2 however, can create some issues. To silence the exhaust, the gasses need to be slowed down to reduce the energy, and this in turn creates back pressure in the exhaust. This pressure means the engine has to work harder to push the gasses down the pipe, the net result is a loss of power.
There isn't a lot of information about diesel engine exhaust tuning. So I did a few experiments. First the rear box was removed, then the centre box. Here are the results of my testing and the conclusions drawn.
First the rear box was removed. This had no notable impact at all, there was no increase in noise or change in performance.
Next, I made a pipe to replace the centre box. The first thing I noticed was a chandge
in the exhaust tone, and an appreciable whine from the turbo. When it was taken
for a test drive, it sounded like a Fordson Major! Not loud, but unpleasant. The
turbo seemed to spool up much faster giving a bit of an improvement in the mid range
(1000 -
I couldn't live with the noise or power loss, so I tried fitting the rear box in the centre. This removed the tractor sound and turbo whine whilst driving, and returned the top end power. Unfortunately, the rear box was somewhat scabby, with a patch welded on and is a smaller bore than the rest of the system.
From the local boy racer tuning shop I bought a 'Cherry Bomb' silencer. Fitted as the centre box this works a treat! It is a little louder than standard, but not offensive or tractor like, and retains the performance throughout the rev range.
In conclusion, it appears that reducing the back pressure in the exhaust allows too much of the air chaarge to escape during the valve overlap period, thus reducing the volumetric efficiency. In order for the engine to perform correctly, some back pressure is required in the exhaust system. Removal of one, but not both of the silencers appears to give an improvement in performance.
