Header Question...

[Catnip]

What your asking is do the High Velocity Merge Collectors help. Yes they help scavanging a good bit, in a comparison we did on an engine dyno we saw a 5Hp gain across the board and 7 peak using a burns HVMC (no spike) versus a standard stamped 4 into 1. This was on a 10.0:1/CR 2.3L. As Mike said, primary length and size are the biggest part, but I believe that the way the header comes off the head plays an important role too. Its just a theory of mine, one day I'll be able to test it on the flow bench. Like your second picture posted, that comes off the head very nicely. You dont want to just go 90 degrees out the head. The larger primaries are required once you start moving more air like going up in displacement.

I'm thinking about just modifying my DC 4-2-1, with longer primaries (I have no A/C, so the space is there) and then adding a megaphone and reverse cone. I'll be making the megaphone/reverse cone and just using 1 7/8" piping from the flange to the existing primaries. With the "stock" primaries flared to where the 1 7/8" pipe from the flange, will slide in, the transition shouldn't be choppy and pretty smooth.

Obviously, this it just until I can get a real header or at least a decent one, but I don't want to do random things that aren't at least good ideas... lol

[Vteckidd]

I'm thinking about just modifying my DC 4-2-1, with longer primaries (I have no A/C, so the space is there) and then adding a megaphone and reverse cone. I'll be making the megaphone/reverse cone and just using 1 7/8" piping from the flange to the existing primaries. With the "stock" primaries flared to where the 1 7/8" pipe from the flange, will slide in, the transition shouldn't be choppy and pretty smooth.

Obviously, this it just until I can get a real header or at least a decent one, but I don't want to do random things that aren't at least good ideas... lol

What size are the primaries on the DC USDM? they should be close to 1 7/8th almost all B series headers nowadays are close to that or 1.75in etc bloh blahb blah

You would be surprised how much a 2.5in collector makes. Chop off the last 8in of your USDM header and weld in a 2.5in pipe like my Narrow header and youll see good gains.

[Catnip]

What size are the primaries on the DC USDM? they should be close to 1 7/8th almost all B series headers nowadays are close to that or 1.75in etc bloh blahb blah

You would be surprised how much a 2.5in collector makes. Chop off the last 8in of your USDM header and weld in a 2.5in pipe like my Narrow header and youll see good gains.

I think you're right on the size, although I haven't measured for sure. I already did the 2.5" collector mod, but I can see how it could be improved... especially if I'm going B20 bottom end.