I would honestly have to say that the porting & polishing probably is overkill in this application. However, since I have done it for years on competition engines, I just went ahead and did the same thing to this engine.

Keep in mind that seldom will a single modification give you a measureable benefit. It often takes a number of small modifications, carefully chosen to work togther, to realize the full benefit in terms of performance.

On an engine with 250,000 miles, I would suggest timing chain and rail replacement along with a new tensioner before making performance modifications.

While you are at it, make sure injektor and camshaft timing are set correctly.

Correct boost pressure (within specification) will do a lot for your performance. Keep in mind that 99% of these engines on the road have badly worn turbochargers.

I have seen some worn so badly the intake turbine actually sawed a hole in the housing. This sprayed aluminum flakes into the engine which casued other damage.

Adam:

The low idle speed cold shouldn't be an issue with only 2° of advance. The opposite should be true when you employ an advanced delivery setting over one that is retarded. The question is, just where is your total injektor pump timing???

Considering the specification non the 617.950 engine is 24° BTDC and these engines will accept settings as high as 28° with no problem, I have seen amny people advance the timing as high as 30° and wonder why the engine isn't running correctly.

I set initial injektion timing with the 'drip' method, as outlined in the 617.950 Shop Manual, but I ALWAYS verify it with a timing light and impulse adapter to be absolutely sure.

I believe what you might be recognizing as a low 'cold' idle speed is the fluid friction of the oil and the resulting resistance to being pumped through the engine.

As far as head gasket life is concerned, I don't see any risk at normal operating temperatures. I use a 70°C thermostat in all my Diesels, which I feel is optimum under most all conditions.

The biggest risk to the head gasket comes from the use of too much boost pressure and the old style (617.950) 'straight-shank' head bolts. These are the ones with the allen heads, not the 'torque-to-yield' bolts with the 12mm 12-point head.


JDMills:

As previously stated, chains, rails, tensioner and timing would be a good start on your engine. Ensuring you have a properly functioning turbo and adequate boost pressure would be the next step. Finally, adjusting the ADLA slightly could very well give you the flatter torque curve you are looking for.

I hope this information is helpful...Bert