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Discussion Starter · #1 ·
This may sound like a dumb question but I'd really like to know the answer. When comparing intake port volumes and exhaust port volumes in a cylinder head are these figures/measurements taken with the valve installed or are they measured by plugging the guide hole and manifold flange then filling from the valve seat? Is there a standard proceedure used by all head makers for measuring this?

Or do they do a mold of the port then measure that? If the valve is installed or not installed there would be a great deal of port size differences.

The last set of heads my Son and I did had a published intake port size of 156 and with minimal grinding we ended up at 171 with the valve installed and it raised some question as to how everyone is measuring this, I didn't measure the port size before we started cutting.

I guess somebody that does alot of port measuring will know the answer if they do a lot of comparisons to manufacturer's specs. Bob
 

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I don't own a flow bench, but all the flow bench sessions i've seen included figures with the valve at 0.100", 0.200", etc., so there has to be a valve in the port to measure them at different lifts, right? I know the standard head of vacuum is 28 inches of water.
 

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Discussion Starter · #4 ·
Yeah flow tests are done with the valve open at diffent amounts but what i was questioning is the actual port volume and how it is measured-with valve or without. The valve can take up about 15 cc's I'm guessing whith could make it tough comparing cylinder heads if some companies measure it with and without the valve installed. I'm surprised nobody has chimed in and offered a definate answer on this already. Maybe I should talk to Brodix, AFR, Dart, etc.... No big deal really but if we're comparing heads it could make a difference for sure.
 

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baddbob said:
Yeah flow tests are done with the valve open at diffent amounts but what i was questioning is the actual port volume and how it is measured-with valve or without. The valve can take up about 15 cc's I'm guessing whith could make it tough comparing cylinder heads if some companies measure it with and without the valve installed. I'm surprised nobody has chimed in and offered a definate answer on this already. Maybe I should talk to Brodix, AFR, Dart, etc.... No big deal really but if we're comparing heads it could make a difference for sure.
Oh, I see what you mean now. Yeah, it might be like cams, one company giving their timing at 0.006" tappet lift and the other company giving theirs at 0.020". That's what was happening in the 60's before everyone standardized on 0.050".

I would think that the most honest way to measure the port would be to grease up the valve stem and seat so that liquid wouldn't run out, then pour the measuring liquid in from the intake port opening. Like you're thinkin' though, some unscrupulous individuals are gonna seal off the guide and seat somehow and pour the port that way to show a larger port volume.
 

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(Bob, your PM box is full.)

Every head we have done has the valves in it, and whether measuring port volume or chamber volume our valves seal perfectly and no grease is needed to keep the liquid in.

Ports are measured by using a graduated accurate cc burrett (long tube container) and filled with windshield washer fluid (to see it, blue) with one drop of dish washing liquid in it to break the surface tension of the water for accurate readings.

Just pour the port or chamber full and see how much liquid was used.
 
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