Why Do Turbo Diesels Whistle?

[Bennis]

This is something I just cannot get my head around.

Before my current skyline, I had a GQ Patrol.

It had a 4.2 liter turbo diesel, straight through 3" exhaust. It whistled like crazy from the exhaust and sounded really awesome.

Why is it that only turbo diesels seem to emitt a turbine whistling sound where as petrol motors do not? (Our whistles are usually intake sound or the sound of a surge ported compressor cover eg gt3076r or t51r)

Is it to do with the fact that diesel motors use considerably smaller turbochargers than their petrol equivalents of the same engine capacity?

My patrol had a gt2860rs on the TD42, I would bet if you put the same turbo on the TB42 (the 4.2 petrol equivalent) with a straight through 3" exhaust there would be no whistle.

Someone school me on this as its driving me nuts. The internet isnt much help, mostly I get results linking me to redneck american diesel forums and they are painful to read.

[Bennis]

3" straight pipe.

Older video of 2.5" press bent + muffler

Heres my old patrol for anyone who isnt too sure what im on about but ide say you all are anyway.

TD42 & GT2860RS...

You dont here any skylines with disco potatos whistling like that, muffler or no muffler!

Edited October 11, 2013 by Bennis

[AngryRB]

Ive turnt my head many times hearing those patrols whistling at the shops, lol..

Im interested to know too

[shaunus]

No idea but my D40 Nav doesn't do it. Has epic of amounts of intake noise/flutter but no whistle probably due to cat and DPF. I also see a lot of Toyota diesels that make like a BOV sound when changing gears....that has me stumped also haha.

[Bennis]

Diesels can produce a "dose" out the exhaust as opposed to the intake where petrols do.

In the first video I linked of my old patrol you can feintly here it but its not as loud as some.

Its due to the design of the dump pipe. A tight angled restrictive dump pipe on a turbo diesel will create a dose sound. Dont ask me why, but only a diesel will do it.

Example

http://www.youtube.com/watch?v=VYT9ezp3lMk (this is a good example of the dosing sound, as well as the spooling whistle that I originally asked for an explanation on)

Most commonly associated with the turbo kit that Denco Diesel makes for the patrol. The dump pipe is a dead 90degree bend. Changing it eliminates the sound, hence how the cause of the noise was deduced.

Alot of larger trucks make the sound too, like the standard Cummins N14 motors. (starts about 45 secs. Pure turbo diesel porn lol)

http://www.youtube.com/watch?v=4q0dr3Fzc2A

Its not the sound I am referring too however, I am basically asking why the whistle is audible via the exhaust. By whistle I mean spooling up.

Edited October 16, 2013 by Bennis

[AngryRB]

The diesel turbo's mentioned are at maximum torque at 2000rpm or less and have either open pipes or large exhausts, im guessing that combo must spin the smaller turbines up really fast in comparison to our petrol engines.

[ZRBE]

Hmm I'm interested to see how it sounds.. But this SAU app has no noise when I view the YouTube videos.. Bummer

[eightsixboy]

Maybe there just happy?

[89CAL]

Less RPM, Less engine noise, no CAT Converter. I dunno but I'd say these are the main contributors.

Diesels make power and spool turbos at much lower RPM's than Petrols (obviously not a rediculous big turbo on a small diesel, you get the idea)

I think this has to do with it. But not 100% sure its the reason

[StevenCJR31]

Modern diesels do have cat converters

Edited October 18, 2013 by StevenCJR31

[Super Drager]

GF's Audi A3 TDI doses low rpm/high load too.