[Dieselwrencher]

Originally Posted by CG

I know zero about diesel engines so Im curious, why do most of the diesels I see run such large exhaust diameters?

I know on your basic small block Chevy the really large diesel size exhaust pipe diameters is detrimental.

Not wanting to hijack your thread, but who better to ask something Ive always wondered =)

Not hijacking at all. Diesels have a higher compression ratio plus most have a turbocharger, which also adds heat. Both combined lead to very high exhaust gas temperatures and they need the larger exhaust to help expel the heat. 5" and 6" on most light duty pick ups is over kill. I have seen 5" exhaust on light duty trucks that tow heavy run cooler coolant temps at weight than with 54" so I can't say that it isn't necessary. It just depends on hat's all done to the truck.

Most medium duty trucks that have similar engines to the light duty diesel pick ups do have 3" or 3.5" exhaust down pipes and then step up to 4" or 5" at the muffler and tail pipe. You typically see 900* on an exhaust gas temp gauge pre turbo on a grade hauling. General rule is to not go over 1250* for more than 15 seconds. Bad things tend to happen and you will have costly repairs soon.