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!

I really don't recall talking port size in cc's on Mopar type heads until Trick Flow started advertising them that way. I know it is common with GM heads. Besides, the port size in cc's really does not tell you much about the port design.

measure them with the valves your going to use.....as motors get bigger port volumes need to increase accordingly.

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.

Thanks for the response. I understand, and it sounds like the small difference in valve shape and stem size isn't enough to change port volume much. That raises another question though, 'min. cross-sectional area'. I've wondered if engine builders use a formula (rule of thumb?) to decide what the csa should be for a given cylinder size and the type of engine use,-street, drag only etc. (I'm only concerned with stock type head layout, not raised port). Thanks again. (I promise, I won't bug you guys all the time with this stuff, it's just so interesting!)

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Thanks csk, that helps a ton.

in class racing, we measure port volumes. it tells you if the ports are close to the same size. we have found variations in sizes. since heads are castings, not all can be equal!! same reason for flow testing all ports, find a lazy port? makes a huge difference in HP.

Yeah. Iv'e been a Stock Elim. fan for years and heard things like checking out a stack of heads just to find two 'good ones' to use. Pretty amazing.

also, doesn't hurt to do same with after market heads. as they are cast also.

True. My question came from watching the Engine Masters episode with the 408 Mopar vs 408 Ford dyno test. Freiberger and Dulcich talked about the 170cc Eddy heads on the Mopar being too small, the Ford had 190cc Eddys and should win, which it did. Then I was thinking about how you can't really compare heads from different makes (Ford/Mopar) on just the CCs, and how it seems that CSA would be a better standard to compare port 'size', but I'm not sure. Which led me here. Then CSK steered me to Wallace Racing website, which has lots of info for me to chew on. Anyway, thanks again for the input guys.

You have to measure the length of the port!!!!! A ford port is shorter than a mopar! CSA is another option but that verys through the port! Keep in mind Port Lenghts!!

I know! That's my point!

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.

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=771

Also, 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.

fast68plymouth
X2

Thanks guys. That's what raised my question on the Engine Masters episode where they didn't explain the things we're talking about here. They just said-Mopar 170cc, Ford 190cc. ??? What I'm looking for are some guidelines to use when doing my own heads, nothing serious really, just to have a better understanding of the 'whys and wherefores' of head flow and velocity for whatever engine I might build, street, truck, bracket car, whatever. I'll check out the sites you guys gave me, looks interesting. Thanks again!

The Enginemasters episodes are fun to watch but don't take them as the last word in technical accuracy. It's fun to have two Mopar guys doing a show. I feel that Dulcich's articles are pretty spot-on, technically. The EM videos occasionally use some incorrect assumptions.

They're like the evening news...entertainment with a bit of reality thrown in.

R.

Very true, and don't get me wrong, I've been a big fan of those guys for years, especially Dulcich's articles. My favorite MTOD show in fact. I just used that as an example. I also think I might have over-complicated a simpler question! Thanks!

When I watched that Engine masters, I was thinking they should do a show about port cross section area. Dyno the same engine with the same type of head, but different port cross section size and see how the torque curve changes?