Probably a "dumb" question...
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Lead Driver
Joined: Jul 2009
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From: Sheffield, AL
Probably a "dumb" question...
1986 F150 4.9L stock exhaust [driven conservatively for gas mileage].
If replacing the stock exhaust from manifold back [the headpipe does not use a doughnut, but rather the flared end technique], can the pipe diameter be upsized any? I realize the log manifold will still be the restriction, but perhaps overall back pressure can be minimized.
I plan to replace the two original catalytic converters with one 3-way converter.
Thanks for your input!
If replacing the stock exhaust from manifold back [the headpipe does not use a doughnut, but rather the flared end technique], can the pipe diameter be upsized any? I realize the log manifold will still be the restriction, but perhaps overall back pressure can be minimized.
I plan to replace the two original catalytic converters with one 3-way converter.
Thanks for your input!
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
Don't upsize the exhaust tube you will lose low rpm power and fuel milage. This motor doesn't make much horsepower which means it doesn't move much air so it really doesn't need anything bigger than a 2.5" single exhaust with the typical compression bends you see in the the factory pipes or if you had something bent up at a muffler shop. Replacing the stock cats with anything from the aftermarket will increase airflow enough to notice and provide a small boost in power.
Postmaster
Joined: Oct 2009
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Chances are the stock pipe is already the right size, maybe even slightly oversize. Larger pipe does not necessarily mean less backpressure. Large pipe increases the total mass of the exhaust system. More mass, means more energy to move it. How well the exhaust flows is a function of velocity. You want the exhaust to have a good velocity without backpressure under the conditions it operates most of the time. Larger pipe is good for high-RPM racing applications, but terrible at 2,000 rpm cruising.
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Jan 13, 2005 12:13 AM
