Silly Question but......

[steve157]

Can you tune a diesel engine, I have two AD31's and think they should be picking up quicker. Both engines have been serviced and this has been an ongoing problem, they get the boat(28ft Carver) to around 25Knts but it takes an age to get there....At what revs should the turbo's cut in? can you check compression? or is it when you have had a general service with all filters and oil changed thats about it.....Oh also bottoms clean and so are the props....

 

[charles_reed]

Can you tune a diesel engine, Yes

At what revs should the turbo's cut in? Generally about 2000 rpm, but it varies from engine to engine.

can you check compression? Yes, get an engineer with a meter.

Think Motor Boat & Yachting to be a more approriate forum for this

 

[oldharry]

There is not a lot you can do to improve the performance of a diesel engine other than ensure it is set up correctly. Injection timing has to be set to .0001mm, and requires not only good measuring gear but a degree of expertise and skill in using it. Engines will run quite happily with quite seriously retarded timing, but will not develop full power. The only other 'tuning' would involve re-profiling cams and ports.

The turbo will come in at a set speed - I do not have the specs for your engine, but the only check you may be able to do is that the boost pressure is set correctly. Only possible if the manifold has a plug to allow a pressure gauge to be attached. Otherwise take them off and get them checked and set by a turbo specialist, who will ensure the wastegate valve which determines manifold pressure is correctly set.

A cranking speed compression test tells you very little about the engine condition. If you think you may have compression problems get an engineer to do a 'leak down' test, which gives a much clearer indicator whether there is something wrong.

However, if the engines are able to attain their rated RPM at full throttle on load, then there is not much wrong. If top RPM is down then there can be a string of things causing it, ranging from wear, maldajustments, fuel problems, prop size, etc etc... and it needs an engineer to diagnose 'on the spot'.

If both engines are underperforming the same then the problem almost certainly would either be common fuel feed or incorrect propellors. Although the prop may be the right size for the engine the pitch may be too coarse for the diameter and hull speed at lower speeds - a bit like starting the car in too high gear. A larger diameter with a finer pitch may give you better accelaration.

 

[VicS]

[ QUOTE ]
There is not a lot you can do to improve the performance of a diesel engine other than ensure it is set up correctly. Injection timing has to be set to .0001mm, and requires not only good measuring gear but a degree of expertise and skill in using it. Engines will run quite happily with quite seriously retarded timing, but will not develop full power. The only other 'tuning' would involve re-profiling cams and ports

[/ QUOTE ]
You could add valve timing and clearances to that, but I guess they would have to be quite a long way out to seriously affect performance

 

[spannerman]

There are no waste gates on AD31 engines, the 31 is notoriously slow to pick up. The boost on this setup is determined by the amount of fuel injected and therefore exhaust pressure available to spin the turbo.You can increase the boost pressure by adjusting the turbo pressure sensor on the injection pump but you need a manifold pressure gauge to do this. You may get a few more knots but also use a bit more fuel and poss generate some black smoke.

 

[steve157]

Thanks everybody for the info, as these are my first diesels it may be just me being used to the pick up of big old v8 petrols....AD 31's are slow to pick up so its open throttles and go and make a cuppa and wait for something to happen...