Gotta side with warp2diesel on this one, on just about every one of his comments. Pittsburgh Power has done a lot of research on backpressure in modern diesels. Increased backpressure causes a slowing of exhaust gasses such that it increases EGT's at the turbo. Not good The idea with diesels is to get that exhaust out as quickly as you can to gain maximum performance and fuel economy. Many owners of larger diesels in semis, including me, have "opened" up the exhaust and have experienced faster turbo spool ups, lower EGT's, better performance, and decidedly better fuel economy. For instance, my Cummins 435ST in my big truck now will pull loads up the hill right along with higher horsepower engines with stock exhaust systems. My Cummins is rated at 435 HP / 1650 lb torque, but will walk up a hill right along with 450's and 475's, with all of us pulling roughly the same payload weights. Meanwhile, while experiencing 100-200F lower EGT's than before opening up the exhaust. Also, my overall fuel economy on the semi has gone up roughly 13%. I do have to watch out where I engage the Jake brake though... it is not a good idea to be along side my stacks when the jake comes on. Straight piped Harley's have nothing on me.
This led me to cut off the cat on my CRD, put a 2.5" pipe in place of it, go with a 2.5" dynomax flow thru and 2.5" tailpipe. Results are better than stock and only cost a total of $180 in parts. I do not have to experience such things as emissions inspections in Iowa. For those that do have to deal with this, just gut out the cat to get the same effect.
Even if one decides to shell out the cash for performance upgrades like ECM tunes and Turbos, opening up the exhaust would be needed to really get the full benefit of any other upgrades. And it offers just about the best bang for the buck as far as modifications go and is a good place to start.
warp2diesel wrote:
In the early years mostly on gasoline engines, back pressure was taken advantage of to reduce the stress on the connecting rod cap bolts during the exhaust stroke. To allow the engine to run better, carburetor jets were sized to compensate for the flow through the engine. Change the exhaust, the carburetor had to be modified from stock to allow the engine to run properly.
Early naturally aspirated Diesels used the same trick to help reduce the stress on the connecting rod cap bolts during the exhaust stroke.
Add a turbocharger, you have the internal back pressure that drives the turbocharger. As far as the connecting rod cap bolts are concerned, they don't get yanked on when the piston goes up on the exhaust stroke. In fact some engineers have gone through the stress calculations and found that if you could remove the connecting rod cap bolts with the engine running, there would be enough pressure on the upper journal to allow the engine to keep running.
Conclusion: With a turbocharger, you don't need exhaust system back pressure to hold the engine together, the turbo provides enough. Get rid of the back pressure which is
USELESS with a turbo diesel, your turbo boost will clime faster and you will move more air through the engine and lower the EGT. Many of us have found out that opening the exhaust up to 2 1/2" CAT back provides optimum performance. Whe I ran a gauge between the turbo and cat, I would get as much as 5PSI when towing. After I opened up the Exhaust to 2 1/2" the back pressure dropped to
0.0PSI.
Conclusion: Opening up the exhaust and getting rid of the BEAN COUNTER ENGINEERING stock muffler is the
CHEAPEST way to get quicker boost with out shelling out for a more aggressive turbo.
True, someone can always come up with a turbo (turbo manufactures love to sell them) that will give more boost and remap the ECM (tuners love to give you that magic fairy dust flash), but when you can do something in between the crappy doggy stock muffler and hanging on a turbo kit that will also provide thrust out the tail pipe like a jet engine, opening up the exhaust has more bang for the fewest bucks performance upgrade.
Besides, if you go with the turbo kit that also provide Jet Engine thrust, you better have an engineered exhaust system bigger than 2 1/2" and have the discharge of the exhaust in the middle so it does not effect handling, you don't want to swerve into oncoming traffic.
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