January 27, 2013

A Diesel has to Blow as much as it Sucks.

GM 6.5L Detroit Diesel (L65)
credit: http://www.gearheadengines.com
There's a lot of Voodoo on the internet regarding how to make your Diesel have more torque, more horsepower, more black smoke, more everything... but I take it all with a grain of salt, because it's just internet chatter, right?

Well, one of the things I'd heard was Diesel engines need big exhaust, straight pipes are best, but at least something with low restrictions, the less back-pressure the better.  Diesel engines also need to suck in a lot of air.  Until today, I hadn't been able to really see how that applied to my 6.5L Detroit Diesel "L65" and the Turbo in my Suburban... so today I had a little epiphany.

Taking you back in time; my Suburban's exhaust system (when I bought it) was patched, and barely keeping together.  In the first few thousand kilometres the gasket between the downpipe (after the Turbo) and soot-trap/exhaust pipe/muffler was totally blown away - literally.  Also, there was a major exhaust leak through a hole in the exhaust manifold.  Well, my mechanic found the blown gasket and repaired it, allowing the exhaust to go all the way through the soot trap and muffler and go out the tail pipe as it was meant to.  I patched the exhaust manifold afterword, since a hole in the manifold would sap the turbo of any pressure, and rob the engine of any boost.  After both of these repairs, I didn't hear the turbo spin up or down anymore... I hadn't heard the turbo whine since before the downpipe gasket was replaced, actually.  But why?  Back to the internets.  Up popped the same complaint from several other people running stock exhaust.  I have an aftermarket K&N filter installed, and I even tested without any air intake filter installed - so I'm very sure the engine was getting enough air IN - but with the stock exhaust, and the exhaust "leak" (the gasket) fixed, I was no longer running the equivalent of straight pipes - I was choking and restricting the exhaust on the way out.  I'm told (from the internets) that changing the exhaust to something high-flow, or straight pipes, will bring back the turbo whine.

The saying that a Diesel engine needs to be able to blow out as much as it sucks in doesn't just make sense, it's true, and I think I've proved it.

Something you may not know; the 1999 L65 Suburban didn't have a catalytic converter, it only came with a soot trap.  My Suburban doesn't have any vacuum operated EGR valves either, which means one less vacuum operated system to go wrong.

I think a Diamond Eye exhaust system is going to be on next year's Christmas list...

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