41% discrepancy between exhaust ports and manifold - Defender Source
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  #1  
Old February 13th, 2012, 11:52 PM
cdb
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Clark Bowen
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41% discrepancy between exhaust ports and manifold

I measured the surface area of the exhaust ports and they are 665mm square per port = or 2,660mm square from one bank of the motor.
However, where the manifold meets the NRP downpipe the surface are is reduced to 1,578mm.
Isn't that a 41% reduction in air flow?
Is there some aspect of fluid dynamics that I'm missing here or does this seems like a substantial restriction.
If headers changed this, it would seem like there should be a substantial performance gain from them?
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  #2  
Old February 13th, 2012, 11:58 PM
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4 stroke. The cylinders are exhausting around 1/3 of the time.
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Old February 14th, 2012, 12:15 AM
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Clark Bowen
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Duh.
Of course.
Thanks
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  #4  
Old February 14th, 2012, 08:25 AM
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Funny, they could have shortened the book down to one page!

Quote:
Originally Posted by JSBriggs View Post
If I remember correctly, 'Tuning the Rover V8' had recommendations for various set ups. One being to use the Buick 300 crank and heads. You could go crazy and port match the heads an manifold, get headers etc. But really, SBC is the biggest bang for the buck.

-Jeff
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Old February 14th, 2012, 08:59 AM
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Quote:
Originally Posted by cdb View Post
I measured the surface area of the exhaust ports and they are 665mm square per port = or 2,660mm square from one bank of the motor.
However, where the manifold meets the NRP downpipe the surface are is reduced to 1,578mm.
Isn't that a 41% reduction in air flow?
Is there some aspect of fluid dynamics that I'm missing here or does this seems like a substantial restriction.
If headers changed this, it would seem like there should be a substantial performance gain from them?
Exhaust gas temperatures will drop several hundred degrees C by the time it reaches the end of the exhaust manifold. As gas cools it occupies about 1/273 less volume for each 1 degree C in temperature.
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Old February 15th, 2012, 12:03 AM
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Clark Bowen
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Quote:
Originally Posted by down_shift View Post
Exhaust gas temperatures will drop several hundred degrees C by the time it reaches the end of the exhaust manifold. As gas cools it occupies about 1/273 less volume for each 1 degree C in temperature.
So if I ceramic coat the exhaust manifolds then there will be more volume as it flows into the downpipe than if I left them stock?
If it drops 273 degrees C, for illustration purposes, does that mean there is nothing at the downpipe? Of course not, but I don't understand how it works out in the real world. I'm curious. Thanks

------ Follow up post added February 14th, 2012 09:04 PM ------

Jeff....

What is "SBC"?
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Old February 15th, 2012, 06:47 AM
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Short blonde chick
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  #8  
Old February 15th, 2012, 12:53 PM
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Clark Bowen
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Short blonde chick
Had one of those for the past 27 years. Highly recommended.
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  #9  
Old February 15th, 2012, 01:49 PM
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Quote:
Originally Posted by cdb View Post
What is "SBC"?
Small Block Chevy, I'm guessing.
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  #10  
Old February 16th, 2012, 08:20 PM
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Clark Bowen
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Probably better. The Chevy would be cheaper in the long run than the other type of SBC.
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