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Old 06-16-18, 11:18AM   #1
Nascar-TA
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Default Pontiac Head Port Length

Hello, I hope this is the right area for asking these questions. I am looking for "Length from intake port in head to valve seat" of a pontiac cylinder head. I have searched this site along with other pontiac sites and found nothing. It may be that I am searching it the wrong way, but I found out that the Small Block Chevy has a port length of 6.125. I had a friend measure a head and he found it to be 4.3125 inches. I used this in my calculations but now would like comfirmation because I recently found the Chevy Port length. I figured the chevy would be shorter than the pontiac. My second question is concerning port injection machining on a pontiac intake, but I will get into that one later. Thanks in advance, and any help would be appreciated.
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Old Yesterday, 12:24PM   #2
Steve C
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First, is the reason for the length for use as input for computer evaluation ?

I cannot add here what the exact length is or was on a actual factory head. But for conversation I have a copy of a old 'corrected flow data sheet' on a iron head done by Dave Bisschop at SD Performance, on it he lists the intake length as 4.5" and the exhaust as 4.8". I also have a copy from about 15 years ago for the input used on the Performance Trends Engine Analyzer program for one of Jim hands combinations with his iron heads, the program input requires intake length only and it was listed at 5".

A post from years ago by Jim Hand....

My Performance Trends PRO engine analyzer states: "Port length" is the port length of the intake port (down the center of the port) from the intake valve to the end of the head port (the start of the intake manifold runner.)

All stock iron heads I have measured are 5.0", and all stockers I have measured have 153cc volume. And I just remeasured a 6X and it is 5" in lenth. Depending on how centered you can keep the measuring hose/wire and where you terminate the valve end, you could see a slight variation but no more then 1/4". Incidentally, my current 6X-4's measure 171 cc port volume and flow 266 cfm @ .550 @28" pressure with 2.11 valves. Also, you can assume that all 8 are equal length.

Personally I thought my old Performance Trends Engine Analyzer program stated 4.7 inches. But I will assume Jim's information could be more accurate for the use in the EA program.


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Old Yesterday, 03:19PM   #3
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On a Edelbrock Head itís only 4Ē just measured. The intake measues 5Ē from meeting flange to just inside plenum.

For some reason I thought you measure the overhall length. Iíve been told street car application likes a long runner for good low end and mid range. Were as all out race application likes a short runner, how much shorter I donít know. Hope this helps more then confuse.
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Old Yesterday, 03:26PM   #4
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On the Performance Trends PRO you can play with port length. Know one thing way back when I played with Torker 11 intake vs Torker 1 the car would lose a .1 tenth. Canít remember which one has the short runner. But Torker 11 would lose a tenth. This was with a roller cam application as near as I could tell on the dyno Torker 11 would lose bottom end so Iím thinking it had the longer runner.
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Old Yesterday, 03:46PM   #5
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"The intake measues 5Ē from meeting flange to just inside plenum."

What intake manifold ?

The average intake runner length on a factory '72 HO intake is 5.21". The longest is 6.5" and the shortest is 3.75".

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Old Yesterday, 04:30PM   #6
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The 4.7" port length is what I used to use on my old EA program for the Edelbrock cylinder head. That length I used came from the specs within the Engine Analyzer program library, at least that is what I have written down. The instruction manual states it is the length of the intake port (down the center of the port) from the intake valve to the end of the head port (the start of the intake manifold runner).


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Old Yesterday, 05:37PM   #7
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Thatís measuring my Victor intake, yes you are correct, been a while since I used the Pro program. Thanks for refreshing my memory
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