warp2diesel wrote:
With a turbo outlet that is 2 1/2" going with 3" will do little to help.
I ran for months with a boost gauge in my down pipe right behind the turbo.
With the stock muffler and 2 1/8" choke point in the rear CAT flange, I would get up to 5 PSI of back pressure. I got rid of the choke point and stock muffler going 2 1/2" all the way back with the CAT in tact. My back pressure went to 0.0PSI and never budged. I run an Inmotion Stage II tune and the 2 1/2" does the job.
This isn’t completely true. True the turbo outlet is 2.5”, however it’s a very short distance and length has a lot to do with the flow through an orifice as well as diameter. You’ve proven that there is back pressure difference when you get rid of the bottlenecks in the cat and muffler.
One thing you haven’t measured or considered are EGT’s. In the diesel pickup world I’ve seen time and time again when going larger diameter than the turbo outlet and getting rid of the cat and muffler that EGTs were reduced by 50°-100°.
Hoosier you are very correct in that a lot of the big truck guys want huge systems and tons of smoke and those guys are posers. It is funny how the guys who actually make power want as little smoke as possible and don’t have much if any interest in huge diameter systems or stacks. However the posers that just want to look fast want as much smoke as possible and huge systems. Those guys remind me of the kids with the fart pipes on the little imports.
hucorey wrote:
it is illegal here too to remove the cat, but for some reason a lot of people do it. I guess they are willing to get caught
This is true, however, in most states anyway, there isn't any penalty for an owner to remove it other than if you have to go through emissions you may have to reinstall it for the emissions testing. However if a shop removes a cat there could be huge finds in the neighborhood of $10,000 per instance.
Irollgen4s a turbo is considered a muffler so no worries about getting rid of the muffler.
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