I was just wondering how people come up with those numbers. Like 270/190 and so forth. Do you measure each intake and exhaust port, the average all the intake ports together and average all the exhaust ports together? How do you know if each port is exactly the same? If they weren't the same, wouldn't this throw the balance of the engine off?

 

in short you have to take it to a shop that has a flow bench and they measure how much air can flow through the heads at a given valve lift.

 

ok, but do they measure each of the 8 intake ports and each of the 8 exhaust ports seperately?

 

Most people use one of these: http://www.timgilles.com/photogaller...wflowbench.jpg

Rich

 

How can all of you read the post and still not realize what this guy is asking??? I wish i could tell you, but i dont really know the answer.

 

ok, since no one seems to be actually reading my question, here it is again...

 

Measurement is from one port.They try to get them as close as possible.

 

Some people measure all the ports, some do one of them. Most times the ports are all pretty close, same porter does each port so the dimensions are the same, valve job is the same etc...

Bret

 

When having my heads flowed I had the option of the machine shop just doing one intake and one exhaust port, or for an extra charge they would flow all of them and give me the numbers. I ended up just having them do one of each.

 

Seeing how the human cannot make an exact duplicate of anything, it seems like it would be a better idea to get heads ported by machine. Having just 1cfm more in one port seems like it would completely throw an engine off balance.

 

Well considering that Pro Stock and NASCAR motors have hand finished ports and they don't always have equal runners that doesn't hold water.... Hell look at a BBC, a good ported set of standard BBC heads vary a lot of CFM from good port to bad port.

Bret