Merge collectors
 

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.

Re: Merge collectors
 

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.

Re: Merge collectors
 

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.).

Re: Merge collectors
 

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.

Re: Merge collectors
 

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.

Re: Merge collectors
 

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

Re: Merge collectors
 

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?"

Re: Merge collectors
 

Alan, I've been telling the same story for years but nobody seems to want to listen. There are advantages to being able to take exhaust lobe away from the engine though. If a conventional header is "properly" sized to a combination, the average Racer should be satisfied. IMHO, most Racers buying off-the-shelf headers are buying too large a primary tube for their application and then being sold the merge collectors as the fix.

Re: Merge collectors
 

Billy, that's what I'm seeing as well. If your headers are too big, you can "crutch" them by using a merge collector with a small minor diameter, and even better, the longer of the two common correct tuned lengths. For example, if you had 2" primaries, and you should be running 1-7/8" or 1-3/4" primaries, you could use a merge collector that had a 1/4" smaller than normal minor diameter ( say 2-5/8" instead of 2-7/8"), and if the first tuned length was 7", you could go with 14".

Unless you buy your headers from someone who really knows what they're doing (there are not too many guys like Jere Stahl selling headers these days) or you have good header software (PipeMax is what I use) most people end up with 1/8" or more larger primaries than they need. In order to compensate for that, they need to add 3-4 degrees at 0.050" to the exhaust lobe. If you can't or don't spread the LSA out, that really limits you on the intake lobe and/or the ICL.

Here's a good example. On a Stock Eliminator engine, we did the preliminary dyno testing with a set of 2-1/4" dyno headers. Then we swapped to the 2" - 2-1/8" Stahl headers with Jere's semi merge collectors. We immediately gained well over 25 ft/lb of torque, but we also lost well over 10HP at the top over a 600 RPM spread. Then I looked at the dyno data closer, and realized that at the same place I lost over 10HP, the engine flowed almost 20 cfm more! Guess where the 10+HP went. Right out the exhaust as an "over scavenge" condition. The correct fix for that is around 4 degrees off the exhaust lobe, and 1-2 degrees more LSA. The reason for the whole thing was the engine previously had a set of Hooker headers that should have been on a Super Stock engine, the primaries were too big and too short. A set of Mark Lelchook's merge collectors were used to help "crutch" that. But even that was not enough. What we know about that, is that this particular car, with that cam and Stahl headers is a killer in the 1/8 mile, but a little off in ET in the 1/4, and down around 2MPH at the top. It's getting a different combination, but Jimmy Bridges and I had decided that, if we kept running that one, it would get 4 degrees less exhaust lobe, and 2 degrees more LSA. I'm pretty sure Jimmy is ten times smarter than I am.

Re: Merge collectors
 

Interesting read. What would be the tell tale signs that a engine may be over scavenging? Anything noticeable in the tune up that would be an indicator of this condition?