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Old 01-16-2016, 10:03 PM
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headers over exhaust manifolds

I have built a 60 over 454 with .210 dome pistons. Voodoo cam with .542/.554 lift, 268/276 duration, 110 deg. Oval port closed chamber heads. Magna flow exhaust. A street rod, not a track car.
My question is, is what is the advantage of shorty headers over cast exhaust manifolds, if any.

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Old 01-16-2016, 11:07 PM
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Shorty headers will over scavenge the combustion chambers. Meaning, it draws some of incoming fuel-air mixture out with the exhaust gases during the valve overlap period.. That reduces the power production (torque) below 4000 RPM. That especially noticeable with smaller displacement engines. Back in the early ''70s, our 355 CI Chevy Jr. Fuel dragster first had shorty headers until we installed boat headers with a 6" diameter collector. We lowered the ET from 8 seconds to 7.57 ET just by changing to boat headers.

A good example is a 100 cc dirt bike with a 1" exhaust pipe and no expansion chamber instead of a 1/2" exhaust pipe and a expansion chamber. The bike will lose 50% of its torque production.
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Old 01-17-2016, 11:27 AM
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Tubular headers are best for high RPM driving and begin to make more power above 3,500 RPM but well designed cast iron exhaust manifolds are best for daily driving.

I have stock ram's horn manifolds with 2.5" exits and lead off pipes on my '62 Chevrolet and they are great for a car that spends 90% of the driving time below 3,500 RPM. Tubular headers would be no improvement. I considered replacing the ram's horn manifolds with tubular headers just because of the annoying spark plug wire routing problem with ram's horn manifolds on a small block Chevrolet engine.
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Old 01-17-2016, 02:23 PM
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I'm running ram horns on my build, but I do plan on going with headers at some point. Most likely a shorty truck type. I have a space issue with the swap I'm doing.

I had them sand blasted (1 is old, 1 is new from Dorman), machined off some of the ugly nubs, sanded them and painted with POR15 header paint.

Manifolds, yeah I may lose some power but the engine will be quieter under the hood and everything I have bolts right up. Using stainless bolts so they won't ever rust.
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Old 01-17-2016, 03:49 PM
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GM made some good cast iron manifolds for BB Chevy engines too. Most pEople place too much importance on tubular headers. They have some advantages when used on a racing engine.
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