At what point is it a manifold and at what point a header? Any specific distance from exhaust valve to collector, or what?

Its basically a cast manifold, designed like a header. Bonus side, is you get header like performance, without all the welds to fail and get water in your engine.

They are probably the best manifold for N/A engines. I'd like to see a dyno test of them up against the Stainless marine GEN III's with 5" tails on some 1000+hp forced induction engines, or up against some CMI Big Tube 2.25+ primary full length headers on a healthy N/A big block, like say 750+hp. Its been proven they outperform most marine exhausts on 500hp engines.

The exhaust primary ID requirement gets pretty large when you get into those big N/A engines and forced induction engines. Like in the neighborhood of 2.25-2.375. Just like in the automotive world, full length headers almost always outperform a shorty header. Especially in low and midrange torque. Gil manifolds, imco, eddie marine, etc, are basically shorty headers , and these are more like a full length header.

I think these are what your looking for Joe, you said 1000HP plus 750HP right?

I'm seeing stainless headers on them now ?

Hardin headers to be exact, along with injection. My point was I don't think the short runner (elbow top style) of the SS marine gen 5s would out run the KE headers being longer runner.

The Gen 3's, are massive though. They have shorter runners, but a 5 inch collector, and 5 inch tail option. The lightnings are 4 inch collector ? On a big forced induction deal, I would think the runner length would get trumped by overall size. The 170+mph fountain had the Gen 3's on it. I'd have to imagine, if a 900HP N/A 632ci , wants a 4.5 to 5 inch collector diameter, a 1200hp forced induction deal would like it to.

I used a set of these on my first twin turbo setup. We made 1200 hp and ran them for 4 years with zero issues.

Are we saying girth over length? but she said size doesn't matter....

Depends on what application you're dealing with

Im not big into the race car scene, but I still like looking at some of the stuff those guys are doing. Heck, many years ago, a set of 2 1/8 headers with 3 or 3.5 collectors were considered big. Nowdays, they are running 2.5 ID primarys, 5" collectors, etc. Stuff is friggin huge. Of course nowdays they have engines that are making alot more power, and need more exhaust. The 454 in my chevy dually, certainly doesnt need the exhaust my 800hp 468's in the boat do lol. Im sure if I strapped the stock manifolds from my truck on my boat engines, and made some dyno pulls, I'd see the boost skyrocket, and power take a dump.

My buddy made 1298hp with an M4 procharger setup, and Edelbrock performer rpm heads. Impressive, but, I wouldn't say the edelbrock heads are better than a CNC dart, afr, brodix, etc. Unless you direct comparisons back to back, its just too hard to say whats "better". Whether its exhaust, intake, heads, cams, etc.

I run the old Stellings "green" headers. They are cool old headers, but they were designed for a 575hp 540ci engine 30 years ago. They have 1 7/8 primarys and 4 inch collectors. I'm sure I'd benefit a bit from a better exhaust, but ..........wish I had more time on the dyno. i would have liked to unbolt my stellings and bolt on icdedppl's gen 3's, and see if it made any difference. That would have been cool test. Or bolt my stellings on his 900hp engines and see.

I was hoping Full Force would have dyno'd his 540s again, and tried endeavor32's lightning manifolds he offered up. That would have been really cool. I think the lightnings would have kicked the standard SM's azz on a 650-700hp NA 540.