Merge collectors

[Gary Smith]

Looking for experienced comparisons between Stainless Works MCL line against Burns B-Tec and Kooks Shootout merge collectors...pros-cons vs cost.. working with 2" ID primaries.

[Alan Roehrich]

Merge collectors are completely application specific. What you're looking for is who knows what dimensions you need for your application. Primary size is one small aspect, and it has to be correct in both diameter and length for your application before you can design a merge collector with most formulas or software.

[Gary Smith]

The ones I'm looking at are off-the-shelf part numbers, and there aren't really any specified dimension differences between these brands except primary/reduction/collector diameters. I know Burns has the most options with length and collector design (including the different outlet shapes etc.).

[Alan Roehrich]

I am not at all a fan of merely grabbing a shelf stock merge collector, especially not just because the primary size matches. It is entirely possible, maybe even very likely, that you'll end up with something that does not work with your combination at all. It may do much more harm than good.

The length, minor and major diameters, and even the taper of the megaphone are very critical to tuning.

[GTX JOHN]

Gary: I have to agree with Alan as usual.

Talk to Perf. Welding about your engine combo as he is pretty
up what everyone is running and will work with you to get you
in the ballpark. Find out what people with the same combo have figured out.

Next time I see you we can chat about your combo and I will give you my opinion in private.

[Ed Wright]

Has everybody else found those to be faster?

So far, my car is faster with straight collectors. Tried two sets built for a friend's LT1, best set made no difference, he found the same. Other set also slowed mine down. I was told that was because I had too much exhaust lobe, I only have 4 degrees more than the intake @ .050", less than 4 at .200" lift.

Ditto step headers. Mine likes straight 1 7/8" primaries, straight 3 1/2" collectors. I am doing something wrong. Seems like I have wasted a lot of money on trick parts. I must be doing something wrong. When looking at Cour's & Decker's times, something very wrong. smh

[Alan Roehrich]

Ed,
Step headers and merge collectors are similar to 4-2-1 headers, you need to do a serious amount of tuning and probably cam testing. When you use either, or both, you significantly alter your exhaust tuning, with an exhaust lobe that is large enough for a set of single diameter headers and a merge collector, it is very likely that you can create a serious "over scavenge" condition. If that is the case, you can see what happened with the right dyno data. The solution most often is a smaller exhaust lobe, as much as 4-6 degrees. You may also need to spread the LSA a degree or two. But what you may gain from all of that is the ability to run a large(r) intake lobe.

The short version of that is: if you have a correctly matched and tuned set of basic headers and collectors and cam, it is likely you will find no power gain, or a power loss with a set of stepped headers and merge collectors.

So, when/if you buy a set of stepped headers and merge collectors, and you spend $1500+, expect to buy at least one cam, and maybe spend money on a couple of dyno sessions and a track rental, so another $2000 is easily possible. It's just another example of "HP cost money, how fast do you want to go?"