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+--- Thread: Destroking a diesel (/showthread.php?tid=6086)
Destroking a diesel - Matej - 12-25-2014
Hello gentlemen,
Has anyone on here successfully destroked their motor? As far as I can tell from looking at pictures of crankshafts, it seems that the Mercedes diesels share the same crank design as their petrol counterparts. The only difference is the stroke, which is usually lower in the gasoline engine. For example, it looks as if an M103/104 crank (80.2mm stroke) would be a direct fit into an OM603/606 (84mm stroke). Can anyone confirm this?
I understand why many may be against this and I know the downsides of destroking a motor, however, for a primarily performance-oriented application, I believe the upsides would make it more than worth it.
Destroking would allow one to safely run even more ridiculous amounts of boost than the motor can already handle right out of the box, but the main advantage would be the rpm gain. Unfortunately I do not recall where, but I have read a couple of articles in the past stating that the best thing one can do when building a diesel motor for racing is to broaden the rpm range.
The main obstacle I am concerned about is the injection pump. What adjustments or mods, if any, would need to be performed in order to take advantage of the quicker-revving higher-rpm motor?
Any information is appreciated.
Thank you.
RE: Destroking a diesel - Mark_M - 12-25-2014
Have you looked at the dimensions of the petrol crank, as in big end, main bearing and mass? No knowledge of merc cranks but in general diesel cranks are very much heavier than petrol cranks. The rods are much heavier as well.
Do the static compression calculations as well. You won't be able to shorten the stroke by much before you won't be able to ignite the fuel, especially getting it to start.
RE: Destroking a diesel - Edian727 - 12-25-2014
Do the static compression calculations as well. You won't be able to shorten the stroke by much before you won't be able to ignite the fuel, especially getting it to start.
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Unless you use a longer rod. i wouldnt know if theres is a rod that'll work in this situation. but this may end up being a plus if it lower's your comp. ratio a little. from what i've read 18:1 is about as low as you want to go.
RE: Destroking a diesel - raysorenson - 12-25-2014
The OM60x motors already sport an extremely relaxed 1.76 stroke/rod length ratio and they already love to rev like gas-burners. I don't see any upside to destroking this setup other than lowering mean piston speed, which isn't a problem in the first place.
RE: Destroking a diesel - Matej - 12-25-2014
(12-25-2014, 11:21 AM)Edian727 but this may end up being a plus if it lower's your comp. ratio a little.This was the idea. Compensating for the lower compression with more boost, and enjoying the broader powerband.
RE: Destroking a diesel - Volker407 - 12-26-2014
(12-25-2014, 12:41 AM)Matej Hello gentlemen,
Has anyone on here successfully destroked their motor? As far as I can tell from looking at pictures of crankshafts, it seems that the Mercedes diesels share the same crank design as their petrol counterparts. The only difference is the stroke, which is usually lower in the gasoline engine. For example, it looks as if an M103/104 crank (80.2mm stroke) would be a direct fit into an OM603/606 (84mm stroke). Can anyone confirm this?
The petrol crankshafts will physically fit in a diesel engine block but they are too weak for the torque load.
Plus I would never reduce displacement
Reducing the compression ratio to run more boost is a good idea, but should be done with a thicker head gasket(my preference) or different rods.
In case of an engine repair the "Mercedes Parts Catalog" says all crankshafts from M103, M104 and OM603 are replaced with a OM606 crankshaft!
And to be a little nit-picky the gasoline crankshaft stroke is 80,25mm.
Gruß
Volker