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Re: SVO: Header VS. Ported manifold?



On Mon, 8 Dec 1997, joseph edward morgan wrote:

> Unless the headers were exactly the same size as the exhaust port (and
> they aren't), with a real collector (which they don't have) and well
> insulated, they aren't gonna "...provide awsome (1800rpm) spool up...".

Actually there are two main stragies whjen making a manifold..One is a
constant pressure design, like the stock manifold..That arrangment
basically has all the ports feeding a plenum, where the pressure is
attemped to be dampened or whatever into a fairly solid exhaust stream. 
Obviously it is not the case, but that is what it strives for...  The
other way, which is the expensive way, is the tuned lentgh deal, where the
runners are all the same lenght and diameter, meeting at the
outlet(collector).  The object is to design the diamter and length so that
the pipe flows enuff volume, but also at a velocity that will make it so
that just as the pulse hits the turbo, bounces back to the port, and
combines with the next pulse coming from the port, intensifying the pulse
that spins the turbine.....it may not be exactly that way, but I am
exhausted and its been a few years since I looked at it..But the
difference is in every other system, or actully at any other RPM/load
combination even on the header, the pulses get out of phase and cancel
eachother out, and weaken itself...

So bottom line is if the header is tuned to operate at ~2000 rppm it will
provide a gain there...how much I have no clue.  I read a few books that
said the kinetic energy in the exhuast is a small part of what drives the
turbine, and the ki0netic enrgy is what is affected here.

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Scott
-71 Pinto, stock 2.3 turbo, 13.67@98, radials
	8.1@85 1/th mile on slicks
	Big intercooler ON!
	T4 Compressor soon to be on!

-85 Merkur, let the modding begin! 
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