The overwhelming performance or HP indicator across
all the various Cylinder Head types and engine sizes
is what the Intake System flows around .87% of Camshaft's max valve lift -to- Cam's max or peak valve lift.
The Intake System Flow CFM from .87% -to- peak or max valve lift
overwhelmingly determines the VE% potential of the Engine .
This is the highest correlation to real-world performance i see in all the Engines i've modeled or have
real-world Track and Dyno data on.
If you look at the Curtain Area Discharge Coefficient it "decreases" as Valve Lift is increased incrementally .
its much higher at Low-Lifts than at High-Lifts, so which Valve Lift's Curtain Area Discharge Coefficient do you choose to go by ?
-VS-
If you look at the Valve Area Discharge Coefficient it "increases" as Valve Lift is increased incrementally .
its much lower at Low-Lifts than at High-Lifts, so which Valve Lift's Valve Area Discharge Coefficient do you choose to go by ?
here's how the 2 above correlate to real-world HP and TQ->
the Valve Area Discharge Coefficient does not correlate as well as the Curtain Area Discharge Coefficient ,
Curtain Area Discharge Coefficient is much more accurate .
ranking them in order of actual real-world correlation would be->
1st = Intake System Flow CFM from .87% -to- peak or max valve lift
2nd = Curtain Area Discharge Coefficient
3rd = Valve Area Discharge Coefficient
This is another way of stating it,
but a more accurate way :
1st = Intake System Flow CFM from .87% -to- peak or max valve lift
2nd = Curtain Area VE% .... as calculated from CFM per SqInch of Curtain Area
3rd = Valve Area VE% .... as calculated from CFM per SqInch of Valve Area
whats going to actually make greater HP potential gains
is getting 1st , 2nd , and 3rd to be the highest between .87% -to- peak Valve Lift .
-----------------------------------------------------------------------------------
just a quick example->
suppose you take a current ProStock Cyl Head
and install a 2.000/1.600 valve combo in it,
with epoxy and effort ... you can make that 2.000" inch Intake Valve have a very high Discharge Coefficient,
higher than what a 2.550 or 2.600 valve would be .
however, a 500cid at 9500-10500 rpm needs a certain amount of CFM to keep up with Engine demands
and to keep parasitic pumping losses down .
lets make it even more simple->
a 2.000" valve flows 300 CFM (95.5 cfm/sq.inch area)
then you install a 2.500" valve , but it only flows 442 CFM ( 90 cfm/sq.inch area)
and the Engine wants 442 CFM bare minimum cfm at 9000 rpm,
the 300 cfm 2.000" valve has a higher DC...but is going to starve that engine and make terrible HP at 9000 RPM
and will not even be able reach 9000 rpm anyway !
---------------------------------------------------------------------------------------------------------
here's real-world Dyno and DragStrip results->
i can't post the following on a public Forum like SpeedTalk because of individuals involved, etc.
a very well known ProStock Guy CNC'd his best 500cid ProStock Port inside a 11deg Dart/Olds heads for us
but recommended 2.450/1.850 combo since it was going on regular Bore centers block ( Legal requirement in NPS )
it had very high DC's !!!!
especially in Mid-Lift range !!!
on the 632cid BBC engine that Cyl Head was down over -100 HP from my Cyl Head with 2.550/1.800 combo on 4.625" Bore
a year later , that same Guy sends us his latest ProStock Port in another pair of 11deg Darts
this time with 2.480/1.850 combo with very high DC's , especially in Mid-Lift
..results still down more than 100 less HP than our Heads 2.550/1.800 combo
because we had made Flow gains in a year since
testing both the 1st and 2nd version of those Dart 11deg Heads on 3 different BBC's ranging from 632cid to 640cid
they were 100 less HP and slower down the Dragstrip.
when i say they had "killer" DC's in Mid-Lift
they flowed not just 4 CFM better
not just 14 CFM better
not just 24 CFM better
not even just 34 CFM better
but they were 40 CFM better than our Heads in Mid-Lift Flow, but my Heads were better at high lift flow
or from .87% to Cam's peak Lift.
the NPS 632 to 638cid with regular Bore center blocks love a 2.500 to 2.550 int valve on a 4.625 bore
even though the DC gets worse , it wants high lift flow numbers
and wants the larger Throat area and Valve out the way for Flow CFM and room for NOS .
basically same with small block Comp Elim A/ND and B/ND with Methanol
it wants nothing but high-lift flow numbers and large valve/ports to make room for Methanol at high RPM
even though the DC's may suffer.
we had Craig's B/ND 23deg RHS castings CNC'd with my 14deg ProTopLine A/ND Port shape,
results was the worst Low-Lift and Mid-Lift Flow numbers i've seen for a 23deg Head with such a large int valve
compared to a Dart Pro-1 with a 2.08 or 2.125 valve.
a Dart Pro-1 2.080 or 2.125 valve out flowed the RHS B/ND with 2.225 int valve till .600' lift
and from .600 to 1.000" lift thr RHS B/ND head was much better ....so much for Low-Lift flow
that B/ND head did set the NHRA Record a few weeks later ...so how bad could it have been ??
and how important is Low-Lift or Mid-Lift Flow numbers or DC's ??? on these type engines.
_________________
Meaux Racing Heads
MaxRace Software
ET_Analyst ( DragStrip Simulation Software )
PipeMax ( Engine Simulation Software )
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Offline maxracesoftware
Post subject: Re: Discharge Coefficient equations
New postPosted: Tue Jun 05, 2012 1:06 am
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Joined: Wed Jul 08, 2009 11:35 pm
Posts: 2335
Location: Louisiana
forgot to mention ,
i just recently re-Ported and installed 2.550 int valves
in the 2nd pair of 11deg Darts that had 2.480 int valves
and Dyno results on DTS Dyno was 80+ HP gains and almost 500 RPM higher for Peak HP RPM point
that particular Engine was dynoed twice on same DTS Dyno
Erland
ganska dumt göra små ventiler (2.45-2.48") till en så stor motor men för avgas hade de större än Meaux, varför det? 
Toyota 4AGE 2.0 20valve rallycrosstopp som vi just gjorde för 50mm spjäll istället 45mm. Effekt finns men bilen bara går inte, han gick nere till fjärde plats nu efter 3 tävlingar, börjar bli bråttom att få inte ens någon medalj till slut.
