Headers and Port Match Question

[HarleyJack17]

Few questions as I am preparing to finally drop the 445 back in the old truck.

Anyone running BBM heads(or similar) and headers in a 3/4 Ton 73-77 F250 4x4? Wondering if I am going to run into issue for certain. It was tight in stock form and just wondering if with the change to modern heads if I will have any surprises.  Looking at it, I do not see a major problem at the point(engine stand), but we know how things can change.

Header and Port mismatch. In a perfect world I know the match would be precise and if any mismatch it would be with the exhaust port being smaller than the header tube/flange opening.
So, what negative effects would one see if there was a minor mismatch with the head port being larger than the header? Is minor mismatch, 1/16 per side acceptable, 3/32 on the top..etc.??
What would be the limit...would like some feed back/input.  Again, I know it is perfect but is this a common reality and not a huge problem? I feel this is one thing that does not get checked by the majority and so many variables that there is a lot of this but we just do "see" it.   

Looking at the Heddmans I have and they are close but not perfect and there will be a "wall" the exhaust will hit. Concern is constantly fighting leaks or burning up a surface.  Really not wanting to drop the coin on custom headers or hit more delays on cutting/welding flanges unless it is a must.   

[Chrisss31]

At the very least I would chamfer the header flange to match the gasket.  A smooth transition into a smaller pipe will be better than a sharp edge.

[Yellow Truck]

Can't say without seeing what you have, but I had what I think were Hedmans (gave them away 3 years ago) on BBM heads (on a 445 going into a '69 F100 4WD) and the beads for the mating surface on the header flange ran inside the ports. Got lots of gasses bypassing the headers.

I'd actually try some Playdoh stuck to the exhaust ports and trimmed to fit the port, test the header to see how bad it is. One little hint I ignored was the old headers were 8 bolt and the BBM, using the CJ exhaust style, was 16bolt.

[HarleyJack17]

 Can't insert quote for some reason, but yes, I thought to try silly putty but do not have any. May pick some up this weekend. I tried with some grease/cardboard. It worked but to many variables. It is very close and may can be made to be even closer by opening the top hole on the headers/little die grinder work. Worst case I can find some flanges and do a little modification.

Yellow Truck-What did you end up doing on yours? Customer headers?

[GerryP]

I have nothing to say about the headers in question.  But, if you do get jammed up on the port to flange dimensions, you don't exactly need a full custom header.  All you would need to do is cut the tubes off at the small flange and weld them to a larger flange.  I know it's not a super easy job but it's a lot easier than fitting up a completely new set.

[gt350hr]

Flange mismatch is not as big a deal as people think. Air is actually "dragging" on the port walls and ID of the tube. The majority of flow is more in the center of the port/tube. Air flow on the walls can possibly be going backwards ( reversion). Jay can probably add more to this subject as he sees it on "the bench".

[Yellow Truck]

HarleyJack17 - I went with Sanderson shorties. First set I had to send back because they hadn't put a dimple in one of the tubes where it turned into the flange and you couldn't get a bolt or a nut in.

I agree with GT350r - I would not have changed the headers because of a little overlap or because I couldn't use all of the bolt positions on the BBM heads. Mine just couldn't seal. The other point is the Sanderson headers are larger diameter.

In the discussion with the guys at Sanderson they made some claims that I can't validate. They claimed that they had taken headers and hammered big dents into them and they found no difference on the dyno. I've seen a video on this subject which seemed to confirm their claim. They also claimed that there was no difference between a short and long tube in their dyno testing.

I don't know about the latter - didn't really matter to me as I wasn't planning on racing my truck, but the former would tend to confirm that a little lip won't really affect performance, although a smaller diameter probably would.

[My427stang]

I agree with everything on here, with one caveat.  Port mismatch is not huge issue (although I don't like it)  UNLESS the gasket doesn't have crush around the perimeter of both the port and header sealing ring.  Both sides of a gasket have to crush and support each other

With a set of common headers, that can be an issue, with an exhaust manifold or fully machined flange-sealing headers it is not.

An unsupported welded ring on a header will eventually leak.

[GerryP]

...
An unsupported welded ring on a header will eventually leak.

True enough on everything.  One thing on header exhaust flanges that I'm sure you know but others might not:  A flat flange with no "sealing" ring is going to get you the best result since you are using a much bigger surface area to evenly compress the gasket.

Expensive headers are welded to the flange on the outside of the flange.  The head side of the flange has no weld and is -hopefully- flat without any protrusions.

Header manufacturers use clever marketing to describe the weld bead on the head side of the flange as being something really good for sealing the gasket.  It's just cover for a cut corner.

[Yellow Truck]

Ross hit the reason I dumped the old headers - the crush crossed into the port area. The Sanderson headers didn't have a welded ring, and they advise against using a gasket and suggest using black silicone that they provide.

My neighbour, who used to build sprint car engines and is still a cornerstone of the local hot rod community, told me that they guy who ran the local engine dyno only used clear silicone, and that is what he uses and he has never had a leak. That surprised me.

[HarleyJack17]

Thanks for all the responses folks. Pretty much all of what I was thinking just glad to hear some opinions. When the day comes I will report back with initial install and then maybe a longer term report. Looked at trying some Remflex gaskets to maybe circumvent the "weld bead" but have yet to hear back from them. Can always try them later if it leaks.  Could just do what dyno rooms do and use high temp RTV  I think it will work on that point. Curious to see if any of the "fit" changed vs. the frame and body, it was close with D2's and the front driveline.

Thanks again.

[67428GT500]

I used Remflex on the Shelby. I have ported Edelbrocks. They are about .250 thick and crush to about .125.  I have used them twice and they are burn and blow-out proof. The graphite material is rated to 3,000 degrees.  I have 6114 Hookers with the welded bead. No leaks what so ever.

[My427stang]

Thanks for all the responses folks. Pretty much all of what I was thinking just glad to hear some opinions. When the day comes I will report back with initial install and then maybe a longer term report. Looked at trying some Remflex gaskets to maybe circumvent the "weld bead" but have yet to hear back from them. Can always try them later if it leaks.  Could just do what dyno rooms do and use high temp RTV  I think it will work on that point. Curious to see if any of the "fit" changed vs. the frame and body, it was close with D2's and the front driveline.

Thanks again.

The floor of the port of the new heads will be approx .250 higher than it was before, no gasket will fix that with a welded bead.  Now, truth in advertising, I have sealed CJ headers against D2 heads, but it's close, depends on really the width of the weld and how deep they went into the port.  You just may get lucky, but I wouldn't buy expensive gaskets to try unless they were some sort of copper or dead soft aluminum that had some strength

[KMcCullah]

When I had the 504 in my '72 Highboy, I modified the poo out of a set of Doug Thorley fenderwell headers to work with the raised exhaust port in my Pro-Ports. Yea it worked. Even won a few races. Then when we put the same engine in the '62 F-100. The only thing different was we built a tuned set of headers. With a merge collector for pan evacs. It made a huge difference in the way the engine ran. The first pass I made was super lean on the AF meter. Like 14.3-14.5. I let up at the 1/8th. We had to go up 3 jet sizes on both sides of the Dom to get back to 12.7-13. Since I didn't make a full qtr mile pass with the lean jetting, I don't have a time slip to prove it. But I'd bet it would have picked up .3 or .4 tenths. Total HP penalty was maybe 80HP with headers and jetting. What a huge cork those fenderwells were. 

I think BBM heads have a pretty good exhaust port. Maybe Ross could do one of his cool Pipemax comparos. I bet a pair of long tubes with 445 cubes is corkin' up some HP.