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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: WO23Coronet]
#1727921
01/13/15 10:00 PM
01/13/15 10:00 PM
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Joined: Jun 2006
Posts: 5,163
CT
GTX MATT
master
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master
Joined: Jun 2006
Posts: 5,163
CT
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Head flow is king, period. If you've got a good set of heads you will make power.
Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: GTX MATT]
#1727922
01/13/15 10:05 PM
01/13/15 10:05 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Quote:
Head flow is king, period. If you've got a good set of heads you will make power.
It's not that simple...
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: Street Monkies]
#1727925
01/13/15 10:23 PM
01/13/15 10:23 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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If I have a head that peaks flow at (we will say) .700 lift.. I want a cam thats in the .800+ lift.. you have a lot more time at the max(you would see the max twice and all the time over it).. duration is rpm for our wedge stuff... not really true with the new style head that has a great velocity ... but I'm still playing with old junk.. my last set was W-9 
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: BradH]
#1727926
01/13/15 10:31 PM
01/13/15 10:31 PM
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Joined: Feb 2004
Posts: 4,501
Gainesville,FL
goldmember
master
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master
Joined: Feb 2004
Posts: 4,501
Gainesville,FL
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Quote:
Quote:
... Where you run into limitations is a proportionally huge port (like a Cleveland Boss 302) on a small displacement motor, it's hard to avoid a peaky (light switch) type torque and power curve with that type scenario. you effectively kill as much duration as you can to try to give it some "passable" bottom end....and (like ford) you gear the wee out of it (4.33 gears, etc).
That's along the lines of what I was going to add to my original post about how even a "good" head still needs to have enough cubes & compression under it to make the combination effective.
It's another example of a poor parts combination that looks cool on paper, but doesn't pan out in the real world.
Nothing worse than a great flowing head(300cfm?) that makes 425hp because it's got a tiny cam and other restrictions. My crude rule is if you don't make 2hp per CFM(in a street engine) something is off. Maybe I'm off but that's my street engine yardstick.
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: Cogito]
#1727927
01/13/15 10:34 PM
01/13/15 10:34 PM
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Joined: Dec 2012
Posts: 41
PA
R5P7 Bantam
member
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member
Joined: Dec 2012
Posts: 41
PA
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Quote:
Quote:
What controls velocity?
Piston speed and port/runner shape. In essence, the geometric profile (tube) in which the air travels to the base of the valve head. This geometric shape starts at the top of the intake manifold (carb plate) and some may include the shape of the venturi's w/in the carb/throttle body.
This is the response I see most often on the internet.
How about valve events and ramp rates?
Valve timing events are critical. We can get really in depth with this if you like......but for now we'll just keep it basic. As the piston lowers in the cylinder, it "pulls" on the intake port as the valve is opening (the scavenging effect). Just before the piston reaches BDC, the intake valve should close (tightly) thus getting the max cylinder volume of charge (air and fuel). It is very possible to actually achieve more than one atmosphere during this operation w/o forced induction. Then the piston goes up and down, and on the following up stroke it "pushes" the fired charge out the exhaust port.....But, this is where it gets good!!!! The velocity in which it travels out the exhaust while the intake begins to open (split overlap) can actually create a negative charge on the intake chamber thus pulling in the new fuel charge at a greater velocity that standard flow (ie, form of forced inducing). This fills the cylinder as the piston drops and......we're at the beginning. But, possibly more than one atmosphere of volume inn the cylinder = VE approaching and exceeding 100%.
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: R5P7 Bantam]
#1727928
01/13/15 10:45 PM
01/13/15 10:45 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Valve timing events are critical. We can get really in depth with this if you like......but for now we'll just keep it basic. As the piston lowers in the cylinder, it "pulls" on the intake port as the valve is opening (the scavenging effect). Just before the piston reaches BDC, the intake valve should close (tightly) thus getting the max cylinder volume of charge (air and fuel). It is very possible to actually achieve more than one atmosphere during this operation w/o forced induction. Then the piston goes up and down, and on the following up stroke it "pushes" the fired charge out the exhaust port.....But, this is where it gets good!!!! The velocity in which it travels out the exhaust while the intake begins to open (split overlap) can actually create a negative charge on the intake chamber thus pulling in the new fuel charge at a greater velocity that standard flow (ie, form of forced inducing). This fills the cylinder as the piston drops and......we're at the beginning. But, possibly more than one atmosphere of volume inn the cylinder = VE approaching and exceeding 100%.
This is where a GOOD set of headers comes into play
with equal length primaries so it pulls on the
intake charge at the right time.. unlike the off the
shelf headers that fit in the car and thats about it
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: BradH]
#1727930
01/13/15 11:04 PM
01/13/15 11:04 PM
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Joined: Jun 2006
Posts: 5,163
CT
GTX MATT
master
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master
Joined: Jun 2006
Posts: 5,163
CT
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Quote:
Quote:
Head flow is king, period. If you've got a good set of heads you will make power.
It's not that simple...
Sure its not, or else we wouldn't have aftermarket cams, intake, headers, carbs, etc. But its pretty easy to make power with the right set of heads. The power limit lies in the heads.
Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: R5P7 Bantam]
#1727932
01/13/15 11:20 PM
01/13/15 11:20 PM
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Joined: Feb 2005
Posts: 4,316
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,316
Prospect, PA
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Quote:
We can get really in depth with this if you like......but for now we'll just keep it basic.......
Just before the piston reaches BDC, the intake valve should close (tightly) thus getting the max cylinder volume of charge.....
Really?
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: Street Monkies]
#1727933
01/13/15 11:25 PM
01/13/15 11:25 PM
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Joined: Dec 2012
Posts: 41
PA
R5P7 Bantam
member
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member
Joined: Dec 2012
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Quote:
Good info. Volumetric efficiency is very important to make power. Usually your street rod motors are only in the 80s and maybe 90s if they got it hyped up. A good all out race engine can start in the upper 90s and go in the 110-115 range. Usually takes a pretty big cam 260+ @ .050 a lot of cr 12:1+, good flowing heads 280+ ect to achieve anything over 100. Who also has good info on this is Rehere Morrison Championship Engine Assembly.
Very true, but we're mixing the pews in the church.
High compression ratios's are not necessarily required for high VE. Also, large duration profiles are not the answer either.
Here's an example:
350 cu in engine Cam in the 260 - 270 deg @ 0.050"
Decent flowing head 10:1 static comp
VE at 6000 rpm < VE at 8000 rpm.
Why?
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: WO23Coronet]
#1727937
01/14/15 05:34 AM
01/14/15 05:34 AM
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Joined: Jul 2009
Posts: 413
Norway (old world)
Oyvind Mopar
mopar
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mopar
Joined: Jul 2009
Posts: 413
Norway (old world)
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Quote:
Oyvind's combo will make power for sure, just thinking he might've gone to small on the cam as 500+" will eat a lot of duration
Yes, I know. I do have some cams on the shelf, and this was the first try. Have not started the engine yet, but if too little cam I have another roller one symmetric at 242 degrees @050 with more lift. But as this is a street engine with manual and OD I would like to try the small first. In this combo I am not looking for high rpm horsepower, but driveability and spare power. I guess I will have a big detonation problem if running on gas. And with the small overlap I guess the headers do not help much either.....
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Re: Big Ports, Big Flow #s, And Low Duration Camshafts
[Re: Oyvind Mopar]
#1727938
01/14/15 11:04 AM
01/14/15 11:04 AM
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Joined: Jan 2003
Posts: 10,010
Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,010
Frostbitefalls MN (Rocky&Bullw...
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"Very true, but we're mixing the pews in the church.
High compression ratios's are not necessarily required for high VE"
High CRs enhance cylinder fill because the overlap cylinder fill becomes more efficient. With less volume to pull on, the exhaust pulse vacuum can pull more fresh charge earlier increasing overall effectiveness. With the overlap period creating up to five times the draw of the piston at max velocity any change to the package is significant. Look at the latest Hemis, 10.4 or higher compression, big intake ports, very long tuned intake runners, short cam. It all has to be right, but then the power is amazing.
As to how much exhaust tuning helps, I think most know it is huge. Look what happens to hp when a motor is run with Zoomies. If there is no tuned length etc, power goes way down.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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