Originally Posted by Viggen
Okay, so maybe not a lot of the sound but a large majority of it comes from the injection pump. Theres a marked difference in the external noise in a diesel using an inline pump and one using a rotary pump. It also has to do with indirect versus direct injection.
About 8 years ago it was Pendy who explained the difference between direct and indirect injection to me. At that time, Jim and Charlie Haigh were the only guys that I knew of that had any knowledge of both Land Rovers and diesel engines in USA.
At the time, I was building 3.0 GM gasoline engine conversions and didn't care much for diesels, but soon learned the value thanks to those two and Mercedes Jim.
The 200 & 300TDI engines are louder at rpm than say the Mercedes OM617 which has indirect injection. They both clunk a lot at idle, but as the OM617 revs up, it sounds more like a gasoline engine than a diesel and all the the 200s & 300s we've had just keep clunking.
The odd thing is that the Isuzu 4JB1-T is basically a TDI with the "combustion chamber" indented in the pistons and when revved the idle clunking mostly goes away. At very high RPMs, the 4JB1-T is as smooth as the Mercedes OM617.
Have often wondered why this particular Isuzu was so much quieter than the Rover TDI, but just attributed it to the differences in the engines themselves. I guess every diesel is different, especially when compared to the common rail breed.
Also to sort of stay on track with this thread, the indirect injection diesels precombustion seem to generally do a lot better on alternate fuels with a lot less exhaust smoke compared to the 200 & 300 TDIs. Although when the head is off both a 300TDI and an OM617 that each burned lots of veg, they both were surprisingly clean when considering what they were burning and how much of it they consumed.