Header Shrouding On 351W

danny clemens

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May 4, 2005
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I'm putting a 351W block in my 66 FB. I bought the Hedman engine swap headers mainly because I didn't want to put out the cash for a set of Hookers or JBAs.

I have a set of AFR 185 heads and upon measuring the exhaust port I found that it is about 5/32nds wider than my header opening. I have plenty of area on the top and bottom so it is the sides that are the problem. The header is going to overlap the exhaust port a little over a 1/16 of an inch on each side. I'm going to grind the edge of the header some (can't do much without making a hole in the 18 gauge steel) where the corner meets the head to make the exhaust transition as smooth as possible.

Is this a problem with headers on aftermarket heads because there isn't much space in between where the bolt attaches to the head and the header tube? There just isn't much room to spread the header tube out.

The car is going to be mostly a weekend cruiser and not really needing max performance but I'd still like to know is this going to cause some really bad turbulence in the exhaust port?
 
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yes it's a problem with heads. i have stepped headers because i have the standard flange. however my headers are squared at the flange and just slightly larger than the port.

they make adapter plates that allow you to mate headers with the wider bolt pattern to a head with the standard pattern.
 
I don't know what the negative impact of these headers will be but whatever it is I'm stuck with it at least for awhile. If I'm not satisfied with the performance then I might check into the JBA or Hooker headers later on. There just aren't too many engine swap choices out there for headers on my car.
 
That's why I made my own. That being said, I'll never do it again. It was a friggin nightmare. For me, maximizing performance was the priority so 1 5/8" or smaller primaries was out of the question. But that meant shock tower mangling and difficult-to-reverse modifications. If you're concerned with original appearance, or maintaining your sanity, take it from someone who did it (poorly).

As far as power goes, your situation isn't optimum but likely won't affect torque too much. And if it's mainly a streeter, torque is what's important. If you were building an 8000rpm screamer where port velocities were much higher, that'd be a different story.
 
This isn't going to be a screamer and is being built with the main priority being torque which I think I'll have plenty of. The headers could have been widened a little bit at the factory to take care of the problem but I guess production numbers is key on a cheap part.

I think I'll grind the flange at an angle to neck it down to the secondaries and if I get the metal too thin I can always mig it back up on the outside.