First of all, I posted this same question in the 335 forum about a week ago, and I'm sorry for the double/repeat post, but I need some opinions, and got very minimal response over there, so:

I know the conventional wisdom on this: NO! But I was on the phone with Price Motorsport, about their 4V flanges, and the guy I was talking to mentioned that those flanges had provisions for 1 3/4" tubing at each port. I said that that was great, because I had a set of 1 3/4" 2V headers that I could just swap flanges on, but then it dawned on me, if I'm using the same diameter tubing, and the same mounting bolt locations as a 2V head, how different can the ports be?

I had always been told that the two ports were extremely different, which they are, but that they were so different that 2V flanges wouldn't cover 4V ports. This is not the case. I just went out and did all sorts of measurments, back and forth and back and forth, and the flanges are plenty large enough to seal the 4V heads, bigger in some places than the 4V manifolds in fact. The only part that is questionable as far as fit is the raised section around each port on the header that actually does the sealing, but I could grind that off, and either weld a new, wider one, in the shape of a 4V port, or just mount it all up flush, flange to head.

Does anyone see any reason why this won't work, or has anyone done this, and what is everyone's opinion on 1 3/4 primary tube dia on a 4V head?

AleX
<!-- / message -->

 

Best I could tell you would be to get some cheap gaskets and just see if they will bolt up and see how well they seal.

As far as the size, I run 1 3/4" on my Corvette which only has a 350, should be fine.

 

They do bolt up and seal, the smallest mating surface tolerance is just about 1/4", I've already checked all that, that's why I'm excited. The one thing I will want to/have to work on is the port shape. The header ports are ovals, the head's are pretty square, and I don't want the exhaust gasses just ramming up against the header flange, but I'll deal with that.

What's anyone else think about the tube size? I say fine, but for 4V heads, 1 7/8" is the more standard size...

 

If you could buy a 2v flange that would cover the ports couldn't you just put it in between the header and the head ? That way you wouldn't have to grind the weld off. I'll bet if you ground it off the header would break loose in no time. High rpm will suffer with such a port mismatch though.

 

Not sure whether or not I can buy a 2V flange, never found one, but never really looked.

I see what you're saying though, that weld isn't just a reduced area mating surface to increase sealing pressure, it's how the tubes are fastened to the flanges. I always wonder why they don't weld on the outside. I guess I'll look closer to see how deep the weld is, but if it isn't deep enough I can just reweld it on either side.

 

Not seeing the header, but some of the bolt holes might be too close to to pipes to weld on the outside.