Backpressure & Exhaust Systems
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09-26-2011, 05:16 PM
Join Date: Mar 2009
Location: Northwest Ohio
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Backpressure & Exhaust Systems
Did some interesting experiments the other day and thought some of you might like to hear about them.
I have a bunch of gauges mounted, including an exhaust backpressure gauge (yeah, my name is Jim & I'm a gaugeohaulic).
I needed to do some muffler tests so I came up with a repeatable backpressure test that involved sharp acceleration from 20 to 50 mph and a rev up to 5300 rpm. I measured backpressure (probe in the exhaust manifold) on the system currently installed (Dynomax 3-inch single) and it yielded a maximum of 5 psi.
I was going to test that system with a new muffler installed (the new Dynomax VT "No-Drone" muffler), but I thought I may as well test it with no system installed. Nothing from where the two pipes meet back. Maximum backpressure: 5psi @ 5300 rpm. Hmm?
I installed the VT muffler... 5 psi maximum backpressure (maybe a half a needle-width higher than the previous two) @ 5300 rpm. Maybe 0.5 up to 1 psi higher but it's hard to read at that low level. Oh, and no drone ( : < )!
The conclusion to me is that the cats are the major restriction in the system. I am tempted to reinstall the stock 2.5 inch system and see how it stacks up in this game. If I do, I'll post it.
In all cases, here is how the restriction stacks up on my setup based on rpm from 3000 on in 1000 rpm increments:
3000- 1-2 psi
4000- 3 psi
5000- 4-4.5+ psi
5300- 5 psi
Your system could be different from the cats back but since my truck has low miles (just 35K now), it's a pretty safe assumption that any Ford truck with the same cats would share this amount of backpressure. It will probably go downhill from here as the cats begin to decline with age and miles.
I have a bunch of gauges mounted, including an exhaust backpressure gauge (yeah, my name is Jim & I'm a gaugeohaulic).
I needed to do some muffler tests so I came up with a repeatable backpressure test that involved sharp acceleration from 20 to 50 mph and a rev up to 5300 rpm. I measured backpressure (probe in the exhaust manifold) on the system currently installed (Dynomax 3-inch single) and it yielded a maximum of 5 psi.
I was going to test that system with a new muffler installed (the new Dynomax VT "No-Drone" muffler), but I thought I may as well test it with no system installed. Nothing from where the two pipes meet back. Maximum backpressure: 5psi @ 5300 rpm. Hmm?
I installed the VT muffler... 5 psi maximum backpressure (maybe a half a needle-width higher than the previous two) @ 5300 rpm. Maybe 0.5 up to 1 psi higher but it's hard to read at that low level. Oh, and no drone ( : < )!
The conclusion to me is that the cats are the major restriction in the system. I am tempted to reinstall the stock 2.5 inch system and see how it stacks up in this game. If I do, I'll post it.
In all cases, here is how the restriction stacks up on my setup based on rpm from 3000 on in 1000 rpm increments:
3000- 1-2 psi
4000- 3 psi
5000- 4-4.5+ psi
5300- 5 psi
Your system could be different from the cats back but since my truck has low miles (just 35K now), it's a pretty safe assumption that any Ford truck with the same cats would share this amount of backpressure. It will probably go downhill from here as the cats begin to decline with age and miles.