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In Warren's good ole turbo guide, he says that aggressive headwork decreases power in the lower-end of the powerband (for the Supra, anway) but increase it in the upper-half.

This doesn't really make sense to me though, because if you can have more airflow, then wouldn't the amount of air the engine can consume increase, increasing power with it?

Hmm, can someone answer this for me?
 

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http://www.t04r.com/tech.html

http://www.dpr-racing.com/content/tech/artofthecylinder.html

http://www.se-r.net/about/200sx/scc/feb98/february.html

"In cylinder head porting, the intake and exhaust ports of the head are carefully reshaped by hand. They are enlarged and streamlined to reduce pumping loss inducing restrictions to as low a level as possible. Porting involves extensive hand finishing to remove tooling cuts, sand casting pits, and lumps and bumps made by the mass-production tooling of the factory. Keep in mind, except in rare cases like the Integra Type R, heads are not ported by the factory, as it is much too labor intensive and expensive.

Porting, as with most high performance modifications, has its limitations. It is possible to make your ports too big. An amateur cylinder head tuner will simply hog the ports out, making them as big as the Holland tunnel. Big ports can flow big numbers, but big flow numbers alone will not make big horsepower. Larger ports have a lower velocity given the same flow demand. An air column of a given mass at a lower velocity has less inertia, negating any ram effect.

The ram effect is critical for obtaining complete cylinder filling at low rpm. Incomplete cylinder filling at low rpm causes an engine to have poor low-rpm power. A symptom of excessive porting is a soggy bottom end that only makes horsepower in a narrow, few-hundred-rpm range at high-rpm.

Ports that are way too big will make significantly less bottom end grunt, and perhaps even less power than a stock head at high rpm. In carbureted or throttle body injected motors, oversize ports with low velocity can cause poor fuel atomization with its attendant bogs and stumbles. Typically, an engine with overly big ports, a high performance camshaft and a carburetor will barely run at low rpms. Going too big in the ports can also mechanically weaken your head to the point where it flexes, blowing head gaskets frequently or even causing cracks. The main trick to effective head porting is making the "straw" wide enough to feed your thirst but not so large that you can't suck hard enough to bring the milkshake to your mouth.

Truly effective porting is artwork. There are no hard and fast engineering rules that can be applied to all cylinder heads. A good cylinder head artist tries to shape the port to get the maximum flow with a minimal amount of enlargement, and keeping the velocity high a priority. Most good cylinder head tuners have their own closely guarded shaping secrets for finding the magical diametric combination of high velocity and high flow. In NASCAR, CART and Formula One competition, port shape is one of a team's most highly guarded secrets."
 

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Re: Re: Headwork on a Supra...

MADMKIV said:
http://www.t04r.com/tech.html

http://www.dpr-racing.com/content/tech/artofthecylinder.html

http://www.se-r.net/about/200sx/scc/feb98/february.html

"In cylinder head porting, the intake and exhaust ports of the head are carefully reshaped by hand. They are enlarged and streamlined to reduce pumping loss inducing restrictions to as low a level as possible. Porting involves extensive hand finishing to remove tooling cuts, sand casting pits, and lumps and bumps made by the mass-production tooling of the factory. Keep in mind, except in rare cases like the Integra Type R, heads are not ported by the factory, as it is much too labor intensive and expensive.

Porting, as with most high performance modifications, has its limitations. It is possible to make your ports too big. An amateur cylinder head tuner will simply hog the ports out, making them as big as the Holland tunnel. Big ports can flow big numbers, but big flow numbers alone will not make big horsepower. Larger ports have a lower velocity given the same flow demand. An air column of a given mass at a lower velocity has less inertia, negating any ram effect.

The ram effect is critical for obtaining complete cylinder filling at low rpm. Incomplete cylinder filling at low rpm causes an engine to have poor low-rpm power. A symptom of excessive porting is a soggy bottom end that only makes horsepower in a narrow, few-hundred-rpm range at high-rpm.

Ports that are way too big will make significantly less bottom end grunt, and perhaps even less power than a stock head at high rpm. In carbureted or throttle body injected motors, oversize ports with low velocity can cause poor fuel atomization with its attendant bogs and stumbles. Typically, an engine with overly big ports, a high performance camshaft and a carburetor will barely run at low rpms. Going too big in the ports can also mechanically weaken your head to the point where it flexes, blowing head gaskets frequently or even causing cracks. The main trick to effective head porting is making the "straw" wide enough to feed your thirst but not so large that you can't suck hard enough to bring the milkshake to your mouth.

Truly effective porting is artwork. There are no hard and fast engineering rules that can be applied to all cylinder heads. A good cylinder head artist tries to shape the port to get the maximum flow with a minimal amount of enlargement, and keeping the velocity high a priority. Most good cylinder head tuners have their own closely guarded shaping secrets for finding the magical diametric combination of high velocity and high flow. In NASCAR, CART and Formula One competition, port shape is one of a team's most highly guarded secrets."
 
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