Does anyone have any flow test results about intake manifolds? Specially interested about stock 4V intake and Blue Thunder flowing capacity. How big is the differece between those two?

 Seppo from Järvenpää, Finland
www.hollowheads.net (just click the hole in the head to proceed)

I can tell you from experience, I put one on my Tbird, after taking off the best stock 4 barrel one,  I could really feel the difference, not many times you can say, WOW , that was worth the money !!  

Po ol Davie

Sparta , Tn.

Stock manifold flows approx 175 cfms per runner from a 57 4v. The Blue Thunder flows approx 264 cfms per runner. Big!!! difference. Hope this helps

-Gary Burnette-

Jep, that was just what I was looking for. thanks Gary!

 Seppo from Järvenpää, Finland
www.hollowheads.net (just click the hole in the head to proceed)

                    Ok I would like to add to this, how much increase would it be to port out the stock 4v? or is it not worth the effort? Thanks in advance

Todd Watertown S.D.

It will depend on how long you work on it and how well you port, you can pick up about half the difference if you know how.

Frank/Rebop

Bristol, In ( by Elkhart) 

It is my experience that a stock iron wide base four barrel manifold  will do a very fine job for a small street engine if the plenum is ported.  My engine is 301CID and made +325Hp with a ported Iron manifold and all the other stuff.  I also never ran any faster with the Blue Thunder than the Iron 4BBL manifold and I am a very early adaptor.  It is my opinion that a 320" or larger Y with highly reworked heads, big valves, headers etc would be necessary to utilize all the potential of the BT.

According to conversations with John Mummert and a careful look at a BT next to the porting job I did on my Iron 4BBL the major thing the BT has is larger runners and wider radii in places where the passages under the carb enter the cross passages in addition to the modified plenum discribed below.

I ported the plenum under the carb based on ideas from David Vizzard's book "Performance with Economy" which is an interesting and useful source.  The key is to remove the sharp edges where the 4 holes enter the passages.  These holes are drilled during production of the  iron manifold and provide no transition for flow downward from the carb to horizontal flow in the passages.  By radiusing these areas of the manifold a big improvement in flow profile is obtained.  This is a lot easier to do when the web between the fore and aft holes is removed which also increases volume under the carb, a good thing.  Once you do all this you will see a severe restriction where the fore and aft passage dives down to the lower cross passages.  This restriction needs to be opened up in the floor of the passage which has the corderoy surface.  If you can reach it there is a ridge in the top that can be smoothed as well.  I do not remove the center partition between the fore and aft runners because this has the effect of making the manifold a single plain type. After all this I also fill the area between the holes and outside of the carb flange with a high temp 2 part hardening plastic.

I have run with a 4 hole 1/2" (stock) spacer and a 1" open spacer.  The 1/2" 4 hole idles better and is a little smoother running but the 1" open spacer seems (seat of the pants) to make more power. I have a 1" 4 hole for my truck which also has a ported Iron4BBL but I can't say how that runs at the moment.

Doug T

The Highlands, Louisville, Ky.

Interesting topic.   Good to see the pros in on this one.  A question I have had for a while!

I have the 57 b intake, & I merely did transition work up top for the large 4 hole 1" Moroso spacer.   I also took the spacer & notched the secondary divider to make it mimic the early ford & holey trend of the pattern that resembles sunglasses.  I have also tried an open spacer, similar results to yours with your manifold work.  Smoother with my modified 4 hole, more top end with the open.  I also have a truck, so that could be why I prefer the 4 hole..