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Old 04-05-2009, 09:33 PM   #1
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sabre 225 problem

What do you think of this.. its on a car forum i visit. Perkind sabre M225Ti???

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?

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Old 04-05-2009, 10:05 PM   #2
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Just thinking and if it is an M225ti then they are actuated? He put they can not see an actuator.
sounds like the engine is being overloaded?? not reaching full RPM and boost gaining?
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Old 05-05-2009, 12:19 AM   #3
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Not all marine diesels have wastegate's, especially the older and non Jap stuff.

If you load one of these non wastegated engines up there's every chance the boost will run sky high.

I wonder if this boat got a new prop at the same time of the engine rebuild (on one motor)

If it's making 40 psi of boost, it's certainly trying hard. So there's plenty of oxygen getting in, and to produce all that oxygen (read boost) there must be plenty of exhaust gas, which means there must be plenty of fuel.

Over-propped me thinks. (or wrong impellor if it's a jet)
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Old 05-05-2009, 12:51 PM   #4
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older diesels use the exhaust housing size to regulate psi

the larger the housing, the more gas can slip through unused. Sounds like you have that type of system. Was the housing changed during the rebuild?

This may sound like a silly question but are you reading the psi from the exhaust side by mistake, cos that would point to a backup in the exhaust. it could be blocked or the engine is finding it difficult to suck in air.
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Old 08-05-2009, 11:42 AM   #5
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buy a cheap durite multi meter with temp probe and measure exhaust temp and you can be sure if engine is working at full load.
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