Port CCs
#2267238
03/11/17 06:10 AM
03/11/17 06:10 AM
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Joined: Mar 2017
Posts: 43 California USA
LowDeck451
OP
member
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OP
member
Joined: Mar 2017
Posts: 43
California USA
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Hey all, new to this site, like it a lot! Been wondering, when talking about port size in CCs, I assume they are measured with a valve installed, if so, the shape of the valve would change the volume, as in, a nail head style compared to a tulip style, stem size etc. I realize it wouldn't be a big difference but, just figured there would be a way of measuring volume without a variable like this. Thanks!
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Re: Port CCs
[Re: LowDeck451]
#2267505
03/11/17 04:59 PM
03/11/17 04:59 PM
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Joined: Jan 2003
Posts: 14,539 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,539
So. Burlington, Vt.
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The main thing to keep in mind when trying to compare runner volumes is to make sure you're comparing heads of similar port configuration. Raised ports with long valves and extended runners will have more volume than low port heads with std length valves........ Although they wouldn't necessarily have a larger min csa to go along with the extra volume.
The best bet is to compare runner volumes of the same type head to each other. That will give you a better idea how much extra csa the larger port might have.
As an example, an ootb stealth head is 210cc, while the CNC ported version is just over 250cc.
A std port Victor is 280cc, while an EZ-1 is 275cc...... Yet the MW sized EZ-1 actually has the "bigger" intake port.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Port CCs
[Re: LowDeck451]
#2267991
03/12/17 01:36 PM
03/12/17 01:36 PM
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Joined: Nov 2015
Posts: 898 Missouri
jwb123
super stock
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super stock
Joined: Nov 2015
Posts: 898
Missouri
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I use computer engine programs to determine what runner length and port volumes are the best for what ever combination I am trying to put together, the calculations the programs make are way over my math ability, but they give the average guy the ability to make decisions formerly only engineers could calculate and make. After I have a cylinder head for the combination and I flow it on the bench, in porting I try to make the head flow the most cfm with the smallest increase in runner volume, that tells me if I am just making it bigger or I am making the runner more efficient. When looking at getting a CNC ported head, I have to ask the question, whose work did they duplicate, or did they just tell the program to make the ports 15% bigger and keep the same contours? The guys that ask me to help them build engines, most of the time bring me a pile of accumulated parts, wanting me to build a GOOD engine. As far as bolting it together I can make sure all the clearances are sound,and it assembled correctly, but they have to realize they determined what the HP output was when they were walking the swap meet getting all those good deals. When somebody asks me to help and we use a computer program to select the components to meet the HP goals they have set the results are much better. Many times a quick CC check of a head runner tells me those super trick good deal heads are at the swap meet because they have huge ports that are lazy and they made no power.
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Re: Port CCs
[Re: LowDeck451]
#2268051
03/12/17 03:21 PM
03/12/17 03:21 PM
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Joined: May 2008
Posts: 5,399 Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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As mentioned, the port cc's are mainly useful when comparing two of the same type of heads. Different models of heads may have different runner lengths. The McFarland formula relates minimum port cross-section area to the engines peak torque RPM where the port velocity reaches a sonic choke point. The original formula uses velocity of .5 Mach, but others have reported that that is a bit low, and use a higher velocity. Speed Talk has a good thread on it here: http://speedtalk.com/forum/viewtopic.php?t=771Also, there is differences in port shape and taper angle. On some heads, you can fill the ports in places like the floor reducing the port volume, without hurting the total flow of the head, and get better velocity.
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