7.3 IDI head flow numbers
Senior User
Joined: Mar 2008
Posts: 225
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Flow bench numbers are ok for a base line but really dont truly tell you your overall flow in an engine. Air flow at max lift is only a small part of the intake event. To maximise the intake event you must look at the complete valve travel from first opening to max lift to last closing. If you port to max lift only and ignore the rest of the valve travel you will only gain top high reving performance and sacrifice the bottom end and mid range. Most ports ours included are to big in critical areas. The turn down area just ahead of the valve for example should be reduced slightly to accelerate the air before the valve, by doing this you can maximize the air entering the cylinder thru out the intake event. It cuts a minute amount off the max valve lift flow but adds greatly to all the rest of the valve travel flow. Below is a picture of roughly what I am talking about.
<a href="http://s1252.photobucket.com/albums/hh562/anderson352000/?action=view&current=PortingSideView3.gif" target="_blank"><img src="http://i1252.photobucket.com/albums/hh562/anderson352000/PortingSideView3.gif" border="0" alt="Photobucket"></a>
<a href="http://s1252.photobucket.com/albums/hh562/anderson352000/?action=view&current=PortingSideView3.gif" target="_blank"><img src="http://i1252.photobucket.com/albums/hh562/anderson352000/PortingSideView3.gif" border="0" alt="Photobucket"></a>
Last edited by xcite; Sep 26, 2012 at 07:10 PM. Reason: link
Elder User
Joined: Aug 2007
Posts: 589
Likes: 2
From: Nutter Fort,West Virginia
good news is that since we have the precup we don't have to worry about swirl as much (if at all?)
do you plan on adding material to increase the radius?
and any idea how thick the runners are?
do you plan on adding material to increase the radius?
and any idea how thick the runners are?
Thread Starter
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Postmaster
Joined: Dec 2004
Posts: 2,941
Likes: 30
From: Maple Valley, WA
Flow bench numbers are ok for a base line but really dont truly tell you your overall flow in an engine. Air flow at max lift is only a small part of the intake event. To maximise the intake event you must look at the complete valve travel from first opening to max lift to last closing. If you port to max lift only and ignore the rest of the valve travel you will only gain top high reving performance and sacrifice the bottom end and mid range. Most ports ours included are to big in critical areas. The turn down area just ahead of the valve for example should be reduced slightly to accelerate the air before the valve, by doing this you can maximize the air entering the cylinder thru out the intake event. It cuts a minute amount off the max valve lift flow but adds greatly to all the rest of the valve travel flow. Below is a picture of roughly what I am talking about.
Im not so much worried about getting peak flow from these things, I am concentrating on sub-.400" flow, and area under the curve. The Port volume of these heads is rediculous to begin with with the exhaust being the worst... Either way, there is no hope for velocity in these heads turning regular RPM's.... However, we can make improvements in flow regardless of velocity, and not effecting it negatively...Thats my main goal...
Now my question is... Is the red in your pic what you would want to take out, or what you would want to add???
I am of the opinion (as well as what I am going to try first) that keeping the highest port floor, combined with the largest short turn radius, is going to equate to the best flow, both low and high lift, regardless of what it does to velocity... Basically what I am getting at, is gaining the best flow you possibly can, while taking out as little material as necessary to get there. The valve job is going to add a ton on these heads as it is, the porting is just to complement the VJ essentially...
Anyway, well see what the numbers end up being, and go from there... Ill know where to start when I see the numbers first hand.
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Postmaster
Joined: Dec 2004
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From: Maple Valley, WA
As far as the runners go, everything I have heard says they are not thick at all, so I guess we will find out....
Senior User
Joined: Mar 2012
Posts: 125
Likes: 2
From: terre haute IN
do you have a valve grinder? i have one i would be willing to donate to the cause if you know how to use it. i got a great deal on it a couple years ago with the intention of learning but only used it once on a set of lawn mower valves. it works and is stout. its old skool black n decker.
Senior User
Joined: Mar 2008
Posts: 225
Likes: 2
Your exactly right.
Im not so much worried about getting peak flow from these things, I am concentrating on sub-.400" flow, and area under the curve. The Port volume of these heads is rediculous to begin with with the exhaust being the worst... Either way, there is no hope for velocity in these heads turning regular RPM's.... However, we can make improvements in flow regardless of velocity, and not effecting it negatively...Thats my main goal...
Now my question is... Is the red in your pic what you would want to take out, or what you would want to add???
I am of the opinion (as well as what I am going to try first) that keeping the highest port floor, combined with the largest short turn radius, is going to equate to the best flow, both low and high lift, regardless of what it does to velocity... Basically what I am getting at, is gaining the best flow you possibly can, while taking out as little material as necessary to get there. The valve job is going to add a ton on these heads as it is, the porting is just to complement the VJ essentially...
Anyway, well see what the numbers end up being, and go from there... Ill know where to start when I see the numbers first hand.
Im not so much worried about getting peak flow from these things, I am concentrating on sub-.400" flow, and area under the curve. The Port volume of these heads is rediculous to begin with with the exhaust being the worst... Either way, there is no hope for velocity in these heads turning regular RPM's.... However, we can make improvements in flow regardless of velocity, and not effecting it negatively...Thats my main goal...
Now my question is... Is the red in your pic what you would want to take out, or what you would want to add???
I am of the opinion (as well as what I am going to try first) that keeping the highest port floor, combined with the largest short turn radius, is going to equate to the best flow, both low and high lift, regardless of what it does to velocity... Basically what I am getting at, is gaining the best flow you possibly can, while taking out as little material as necessary to get there. The valve job is going to add a ton on these heads as it is, the porting is just to complement the VJ essentially...
Anyway, well see what the numbers end up being, and go from there... Ill know where to start when I see the numbers first hand.
Red area is added material.
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Senior User
Joined: Dec 2011
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okay are these just the numbers for a 7.3 or are we looking at both the 6.9 and and the 7.3. i am very curious about this now considering i am thinking about doing a cam job on my truck so question being at the point for me is whats the "stock" numbers on a stock cam "brand new". i was just on ebay and everything i seen was the same numbers on open size of being a .253 and the duration on them was not much different between the intake and exaust side i believe being a 184 i wanna say are there any better cams i could get and if so where or would i have to have something custom made for the "dino" considering what everyone would call these things a lost cause because of "new" vehicles now days
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Postmaster
Joined: Dec 2004
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From: Maple Valley, WA
I'm still waiting on the head, shop got behind, and I told him no rush, so when he gets to it, he gets to it... ill update as soon as I find out.
As far as the cam being available, its available right now.
As far as the cam being available, its available right now.