[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: SVO - svo Digest - V01 #57



Hi all List Members
I am new to the list, but have been following this cam debate,  as a
lurker(sp) for some time now.  As a Product Engineer for Toyota, I have
learned, that if I can not prove my thoughts on paper,   DON'T bring it up
in the board meeting.  The laws of physics can NOT be f*cked with.  END OF
STORY.....
Shall we go back to camshaft basics?
I think we shall.
The first items is, were does the head flow the best....  A good porter
will  work on the average range of .350 - .450 lift for the street driven
engine.   MY question is!! Have you flow tested a stock head  and have you
flow tested a ported head??    I ask because there is NO reason to raise
the duration & lift of a cam beyond the flow limits of the
head..................................................WAISTED ENERGY is the
pittfall of the internal combustion engine....And if  we magnify it by the
excess stress of valve spring opening pressure (spring pressure raising as
lift goes up)  AND the cool intake air going out the exhaust caused by
overlap, slowing the rate of spool(for turbo engines) the gain of an
agressive  cam is, at best, minimal. ANY cam with a duration of more than
215 degree @ 50 is considered agressive.   we find that if the cam specs
are based upon the flow rate of the head, MORE power is
gained.............. It is like finding the sweet spot  of the turbo, ALL
mechanical objects have a set area in which they perform best. Build a cam
closer to your  heads flow rate and maximum HP will be achived...  I will
use the "Tiny Avenger" for instance.  In the second article, they posted
that the stock (50mm) throttle body flowed 254 CFM and that the upper &
lower intake flowed 200 CFM.  Did they need to put on the 65mm throttle
body??? NO, the 50mm the throttle body flowed 54CFM more than the upper &
lower intake.  That 65mm throttle body could flow 500CM and the combustion
chamber  would only see 200CFM......... WHAT IS THE POINT.

I have spent seven years working with the 2.3T heads and the best head I
have now flows 185CFM at.400 and 192CFM at .500 and 1 & 4 flow 194 at .600
and 2 & 3 flow 197 at .600     Do the math (sorry)

In closing: In naturaly asperated engines, long duration allows air to flow
in the cylinder after BDC because of the differnce betwenn piston speed and
the speed of atomospheric pressure.  In a turbocharged engine the cylinder
volume and pressure follows compressor volume & pressure.  Where as the
volume & pressure of the cylinder at BDC is equal to the potential volume &
pressure of the turbo . If you match the max flow rate of the head to the
turbo, maximum performance is found.. 
Think of like this  "There is no replacement for displacement"  Close the
intake valve later, and you have pushed a 15 PSI column of air OUT of the
combustion chamber.( supposing you are running 15PSI;  the degree of
rotation before valve closure after BDC determines the volume of air pushed
out of the cylinder)

RS