I have recived many requests for a detailed explanation of some of my modifications for the 617 engine.

In actuality, I make rather extensive modifications to these engines which is not only overkill in many respects, but difficult and costly to replicate. However, I will mention just a few of the many changes I make to the venerable 617 Turbo Diesel.

Aside from a fully ported and polished intake tract/cylinder head, I use the larger Buick V6 'Grand National' Exhaust Turbine to improve spin-up at lower exhaust gas velocities. This requires extensive modification of the turbocharger housing, but makes a tremendous difference in low rpm throttle response.

All the injektors are fired on a test stand and the springs are shimmed to bring all injektors to within 10 psi of each other. This isn't as costly as it is time consuming, but can yield tremendous benefits in terms of smoothness and overall performance.

I have even experimented with installing the larger intake valves in the exhaust position for increased exhaust flow, but this is again a very expensive and time consuming operation.

Despite all these tricks, probably the greatest performance potential exists in proper camshaft & injektor pump timing.

I have been asked repeatedly for information on how I time the 617 engine. This post is in response to those requests.

Consider first the two different camshafts available for the 617 engine. The early versions (617.950) used a camshaft marked '00' that had the following timing figures at 2mm valve lift:

Intake Opens 13.5° ATDC Exhaust Opens 19° BBDC

Intake Closes 15.5° ABDC Exhaust Closes 17° BTDC

I prefer the lengthened valve timing of the later (617.951/952) camshaft marked '05' and use it in all 617 engines I work with. The valve events at 2mm valve lift are as follows:

Intake Opens 9° ATDC Exhaust Opens 27° BBDC

Intake Closes 15° ABDC Exhaust Closes 16° BTDC

Mercedes gives these specifications when a new timing chain is used and offeres the following valve timing figures for engines with 20,000 km or more:

Intake Opens 11° ATDC Exhaust Opens 29° BBDC

Intake Closes 17° ABDC Exhaust Closes 14° BTDC

Based on these figures, it is clear that Mercedes wants about 2° of initial advance on the camshaft to account for the eventual stretch/wear of the timing chain.

On my engines (and those of customers) I advance the camshaft timing a full 4° to the following specifications:

Intake Opens 7° ATDC Exhaust Opens 25° BBDC

Intake Closes 13° ABDC Exhaust Closes 12° BTDC

If you consider the theory that the timing will retard approximately 2° after 20,000 km of operation, 4° of advance would cause the engine to 'wear into' the original specification instead of wearing out of specification.

Mercedes offers offset camshaft wooddruff keys ranging from 2° all the way to 10° of correction. I will post the part numbers later this weekend for reference, although they are easy to find at around $7.00 (USD) each.

The important thing to keep in mind when advancing the camshaft timing is to advance injektor pump timing the same amount in camshaft degrees.

Advancing the pump timing 4° from its recommended setting of 24° BTDC would result in a static setting of 28° BTDC overall.

However, after about 20,000 km of operation and a loss of approximately 2° of timing overall, the pump timing would retard to around 26° BTDC.

Keep in mind that Mercedes allows + or - 1° on injektion pump timing making 26° approximately 1° advanced above specification.

The slight amount of advance definitely improves low rpm throttle response and overall smoothness of engine operation, although it does increase the noise of the combustion process slightly at idle.

You would be amazed to see and hear how these engines run when the time is taken to ensure everything is set to an exacting specification.

I hope this information is helpful...Bert