alistairolsen
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| posted on 4/5/09 at 05:06 PM |
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Boost control on big turbo diesels
The engine in question is a marine ford sabre 225. Id imagine any large bus/truck engine would be similar.
Dad called to pcik my brains on boost control and while i know how normal automotive petrols control their boost levels, I was stumped on this one.
Engine runs up to revs with the boat lightly loaded, making mid 20s psi boost pressure.
If the boats loaded up with divers etc, engine runs round to 40psi and wont come up to full revs.
Its one of a pair, the other behaves fine,this one did before a rebuild last year.
Apparently there is no sign of an actuator or lever for an internal wastegate, nor any pipework or external wastegate...
Do big diesels somehow control boost by adjusting the fuelling? Or are we missing something?
Cheers
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Volvorsport
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| posted on 4/5/09 at 06:04 PM |
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older diesels dont run wastegates .
the newer ones do since they are more efficient to produce low down power, and need wastegating to stop them overbooosting at high load , something a
big holset might not need .
IIRC diesels can cope with a variety of air fuel ratios quite happily , the more fuel you add , the more power you make .
its overspeeding the engine that would damage a diesel .
i think basically youll need to look at the fuelling side to see whats up .
www.dbsmotorsport.co.uk
getting dirty under a bus
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alistairolsen
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| posted on 5/5/09 at 10:25 AM |
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Cheers!
I just cant get my head around it, if you fit a turbo that will make 225bhp at 2200rpm, and the boost tails off as you approach 2400 rpm, then why
does it not try and make enourmous boost pressure at 1800rpm?
Like if i removed the wastegate operation from a RICA T5, itwould still make the same boost at the rev limiter as the turbo cant flow more air up
there, and it would still begin to make boost at the same point, its just the boost in the midrange would break everything...
But then in thatscenario, boost is limited to torque because you are forced to maintain the afr. In a diesel, you might get away with 40psi in the
midrange, you just inject less fuel andhence dont break things with torque?
[Edited on 5/5/09 by alistairolsen]
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