400 Exhaust Pipe Diameter
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Joined: Mar 2008
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Originally Posted by Colo79Ford
I run 2.25" dual exhaust on my 79 f-250 4x4 with a 400. I tried bigger exhaust, it slowed it down, tried open exhaust, it slowed it down, went back to my ugly 2.25" setup and runs like im used to. Im planning on some time over the summer putting factory manifolds back on it (ran better with manifolds than headers) and then doing 2.25" down pipes off the manifolds into a single 3" exhaust. The truck is the one in the link in my signature.
I had a 77 F150 351M truck drop 4 MPG when it was switched from headers back to manifolds and stock exhaust. Some of that may have been carb related.
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Joined: Jan 2004
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From: Colorado
Tried 2.5 and 3" exhaust. MPG is at 13 MPG with the headers and was also 13 MPG with stock manifolds. MPG dropped to 10 MPG and power dropped significantly with the bigger exhaust, but thats just my truck, every one is different. Having the exhaust back pressure that works best with the engine is whats important. Too little back pressure looses power just the same as having an exhaust system that is too restricted.
All loses were seen the most in torque with my truck when switching to bigger exhausts. Bigger exhaust may help with high RPM situations, but how regularly will a 351M or 400 even reach high RPM (4500 - 5000+) in a street situation.
All loses were seen the most in torque with my truck when switching to bigger exhausts. Bigger exhaust may help with high RPM situations, but how regularly will a 351M or 400 even reach high RPM (4500 - 5000+) in a street situation.
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