Diesel turbos - do they have dump valves?

Alibaba99 · 13 Nov 2009 at 18:47

Bug One said:
Really. I'd always assumed they were quite low boost.

I have a real lack of knowledge when it comes to diesel engines. Probably for the best. Will prevent me tinkering with it.

The BMW 123d runs 2.85bar of boost.

gurusan · 13 Nov 2009 at 18:47

That is higher though, most petrol turbocharged engines don't run much over 1/2 a bar stock.

[TW]Fox · 13 Nov 2009 at 18:48

Alibaba99 said:
The BMW 123d runs 2.85bar of boost.

In total or per turbo?

Alibaba99 · 13 Nov 2009 at 18:57

That will be the manifold pressure. Don't know if it's gauge or absolute, though 1.85bar gauge is still way higher than standard petrol turbos,

Clarkey · 13 Nov 2009 at 18:58

[TW]Fox;15310935 said:
In total or per turbo?

No such thing as boost 'per turbo' :confused:

2.85bar does sound stupendously high though, 1.85 sounds a bit more like it.

s0ck · 13 Nov 2009 at 19:20

It will be the vanes on the turbo. Decat a new diesel and it makes a massive whoosh sound, very similar to a proper petrol BOV (but out the exhaust). Hearing this noise on an otherwise standard car... impending hardware failure?

86JR · 13 Nov 2009 at 19:32

Mines so loud my mate could hear it over his supersprint exhaust in the saltash tunnel and he was infront of me....which is very embarresing!

Matt82 · 13 Nov 2009 at 19:59

NickK said:
However that would leave the engine running oxygen rich which probably isn't good for it either.

Are diesel turbos running at a lower boost? If so you may not hear it compared to a higher petrol boost.

they do run extremely lean off throttle, the injectors will be shut in some circumstances, just another thing that makes them tres efficient

gurusan · 13 Nov 2009 at 21:08

In petrol engine terms, they run extremely lean during full throttle as well.

Not to mention stoich on diesel fuel is slightly different of course.

Jonnycoupe · 13 Nov 2009 at 21:13

[TW]Fox;15310935 said:
In total or per turbo?

In the manifold.

Dave L · 14 Nov 2009 at 09:51

Alibaba99 said:
The BMW 123d runs 2.85bar of boost.

Sounds very high to me! Got an online reference to substantiate that pressure?

gurusan · 14 Nov 2009 at 13:21

2 liter 200hp there is no way it's running 2.85 or 1.85. Probably more like .6-.8 bar

Jonnycoupe · 14 Nov 2009 at 13:24

It its a 2 litre than only revs to what - 4500rpm though.

I imagine 2.85 absolute could be a possible value.

gurusan · 14 Nov 2009 at 13:29

It's also got twin turbos. There's got to be some published spec somewhere

Leeum · 14 Nov 2009 at 13:37

Possibly a boost leak or a split hose somewhere? My mate's Ibiza FR PD130 made a 'wooshing' noise sound when booting it and coming off the throttle/ changing gear. That was diagnosed as a boost leak.

Fuzz · 14 Nov 2009 at 14:03

Felix Da Housecat said:
It will have some sort of dump valve as the presure has to go somewhere when you come off the gas.

LOL
There is no pressure build up.
All you do when coming off the gas is lessen the amount of fuel going in.

Dave L · 14 Nov 2009 at 19:31

Jonnycoupe said:
It its a 2 litre than only revs to what - 4500rpm though.

I imagine 2.85 absolute could be a possible value.

40psi boost pressure in a road going engine that has to be durable etc??

I don't think so.

Unless I'm proven wrong by some written [credible] evidence, I'll eat my shorts!

gurusan · 14 Nov 2009 at 19:49

Dave L said:
40psi boost pressure in a road going engine that has to be durable etc??

I don't think so.

Unless I'm proven wrong by some written [credible] evidence, I'll eat my shorts!

perfectly possible in a diesel engine, with that power output I think it's very unlikely though. Also he said 2.85 absolute pressure.

Clarkey · 14 Nov 2009 at 19:58

He said absolute pressure, so 1.85bar gauge pressure, about 27psi. It's high, but diesels are mega strong.

Jonnycoupe · 14 Nov 2009 at 20:14

Dave L said:
40psi boost pressure in a road going engine that has to be durable etc??

I don't think so.

Unless I'm proven wrong by some written [credible] evidence, I'll eat my shorts!

You do know what absolute pressure is don't you?

Heres a clue, its boost pressure + atmospheric. Ie the actual pressure. Boost pressure is just the pressure differential a gauge would see.

I have no idea what it would be, was trying to put some crediblilty to any claim of a pressure with .85 as a decimel. 1.85 would be too low in my book though. Thats similar to a Rover T16 and makes 200bhp but petrol and almost 50% more revs available.