merge collectors

[r lane]

I have two engines with two different exhaust systems, one a Bursch/M&K style with a pyramid collector and a RSR/ Georges headers style with a flat triangular collector. A dyno would be the direct way to begin a determination, but thought I would test the waters here to see what info was available. Is there evidence that one of these two collectors has benefits over the other. I have been told the pyramid provides more even flow. There is what I would call 3 dimensional symmetry to the pyramid where as the triangle is linier. Whether any of that translates into how fluids and vapors flow I have no idea. I will appreciate any good info toward this subject. Bob

[Walt Fricke]

The high end exhausts one can purchase all seem to use the pyramid type, which you can purchase from Burns.

[Bill Verburg]

Originally Posted by r lane

I have two engines with two different exhaust systems, one a Bursch/M&K style with a pyramid collector and a RSR/ Georges headers style with a flat triangular collector. A dyno would be the direct way to begin a determination, but thought I would test the waters here to see what info was available. Is there evidence that one of these two collectors has benefits over the other. I have been told the pyramid provides more even flow. There is what I would call 3 dimensional symmetry to the pyramid where as the triangle is linier. Whether any of that translates into how fluids and vapors flow I have no idea. I will appreciate any good info toward this subject. Bob

What you call pyramid is usually called a rotating design, usually w/ carefully designed merges, The other is a splayed design, which can have merge characteristic but isn't as picky

The rotating merge design ala Burns is generally considered best
but there are all sorts of qualifications involved#1 is muffled or non, any header type system designed to extract additional performance from an ICE will be ham strung by almost any muffler that can be fitted, though some mufflers are better than others

extracting additional performance also requires a cam design w/ a fair amount of overlap, the resonances in the header can then be timed to draw additional fuel/air mix into the cc and extract additional spent gas out

it's interesting to map out the flow in these exhausts,

here are some stats for an H6 911 motor at 6800rpm
113rps
57 the # of times each cyl fires/sec
170 pulses/ s into each collector, 0.0059s apart
0.706m distance each pulse travels before the next one enters the pipe
1.3674 pulses in each pipe at a time

here is the mapping for an SC/RS base engine w/ S cams, lots of overlap lats of potential for the 5th cycle gas extraction, there is soo much overlap that the events have to be shown in parallel rather than linearly as in the case of the SC


here an SC, little overlap little potential for 5th cycle enhancement

[Ollies930]

I do not believe that the collector design has all that much bearing on the performance of the engine. There was a dyno test years ago, where merge collectors were compared to simple weld collectors. The merge collectors made a bit more peak power, where the standard collectors had a wider power band. I think that the length of primary has more effect than the collector design itself. Supposedly the angle of the collector has some effect on the width of the powercurve, but as always it is a tradeoff. If there were any measurable benefit to cone shaped collectors vs flat collectors, then I am sure Porsche would have used them on the 934/935/962, etc.
But the Burns stuff sure looks great and is prefabricated, so if you were to start from scratch, then Burns collectors would be a time saver.

[H-viken]

Originally Posted by Ollies930

I do not believe that the collector design has all that much bearing on the performance of the engine. There was a dyno test years ago, where merge collectors were compared to simple weld collectors. The merge collectors made a bit more peak power, where the standard collectors had a wider power band. I think that the length of primary has more effect than the collector design itself. Supposedly the angle of the collector has some effect on the width of the powercurve, but as always it is a tradeoff. If there were any measurable benefit to cone shaped collectors vs flat collectors, then I am sure Porsche would have used them on the 934/935/962, etc.
But the Burns stuff sure looks great and is prefabricated, so if you were to start from scratch, then Burns collectors would be a time saver.

The ones you mention are all turbos. I would think the collector matters less in those cases?

[winders]

I like these:

Merge Collectors

Lot's of options....

[Ollies930]

Originally Posted by H-viken

The ones you mention are all turbos. I would think the collector matters less in those cases?

I think you might be right about mattering less on a turbo, but the dyno comparison I referenced was for normally aspirated engines. However, the 2.7/3.0 RSR racers had the same style collectors. There were no pictures I could find of factory 964/993 RSR headers, so I cannot comment on those.

[H-viken]

Originally Posted by Ollies930

I think you might be right about mattering less on a turbo, but the dyno comparison I referenced was for normally aspirated engines. However, the 2.7/3.0 RSR racers had the same style collectors. There were no pictures I could find of factory 964/993 RSR headers, so I cannot comment on those.

True. Would be interesting when the pyramid collectors came in to use

[Bill Verburg]

before '7 all the 911 factory headers used splayed merges from '75-94 they weren't headers in the traditionally sense but used splayed where there were merges

993 used 2 different exhaust manufacturers, Bischof and Gilette, the Gillete were a first attempt at rotating collector but no true merge function, Back inthe day contemporary dyno tests showed no advantage for one over the other but again, muffled w/o cams that have much TDC exhaust overlap

The 993RSR is the first rotating design, which was continued and refined for 996/997, 991, 992
993RSR



997RSR

[Evan Fullerton]

I would say it matters some but not much. Switching from George early RSR style headers to HyTech rotating collector, tripple steeped, anti reversion chambered headers with an X pipe on stock compression, stock cam 3.2L routinely picked up 10hp when the tuning was optimized for each.

Some rotated collector, stepped headers from a different fabricator with a different bend layout, collector angle, no X pipe and no anti reversion chambers were exactly the same power as the George headers.

That same HyTech header design scaled up for a GrandAm 4.0L 997 motor produced 15hp more then any other GrandAm spec 4.0L according to PMNA at the time running the M&M RSR headers.

It’s a lot more complicated then just how the tubes come together.

[r lane]

Wonderful looking pieces. Heard of an acupuncturist that work exclusively with ears, just ears. An engineer could pursue nothing but exhaust and never get to the end of it. No pun. A picture on my desk of a car designed and built by Tom Meade, early 70s and I remember in the article his relating the number of remakes on the exhaust until he got it close to right. Right may have been sound and looks, don't know, but I wonder what happened to Tom. Bob

[dannobee]

There's a well known exhaust fabricator in nascar Cup circles who fabricates and tests with the top Cup teams and has been doing it for decades. Two step, three step, tri-y headers, every kind of collector ever made, he's tried everything and quantified the results with engineers and dyno tested everything. A set of his headers often cost upwards of $10K for an inconel set. Cup teams ask, "how soon?" instead of "how much?"

When he showed up to a dyno session with a simple log manifold (but with the appropriate sized tubes and stub lengths) just to prove a point, those in the dyno cell thought he was crazy. When tested on the dyno, the 850hp SB2.2 Cup engine made 8 hp less peak power over the best set of headers they had run. The fabricator then said, "40 years of exhaust technology was worth 8 hp."

As others have said, there ain't much there. Get what is convenient and easier for you to fabricate. Tube diameter matters far more than collectors.

[r lane]

In the final analysis, it is not just one piece. And this was mentioned in Bill Verburg's response. All of the pieces have to be happy with one another. Compression, induction, cam design which just by itself is mad science, rod ratio, over and under square. A set of headers that performs on one setup, can fall flat matched with another set of parameters. The tuners that take the time, hours beyond count, to test the myriad of combinations and to come up with real information, are my heroes. A North Ga engine builder's response when a reporter doing a story on his shop (dyno mufflers the size of small silos, a battery of CNCs, billet aluminum heads, on and on) made reference to the builder as a genius, said no, '' we never quit trying different things, we never think we have reached the final solution.''

[Bill Verburg]

Just to illustrate a few points in an overview of what's happening in the collector, this is a 4 cyl collector, unmuffled, even fire very similar to a Porsche flat 6

[Walt Fricke]

I never did hear just how well this setup worked.

[Bill Verburg]

Originally Posted by Walt Fricke

I never did hear just how well this setup worked.

Not sure what the advantage of that would be

stock has left has 1 2 3 each separated by 60° of crank rotation, right has 4 5 6 similarly spaced

that setup pairs 3 & 6 w/ 150° of crank rotation separating them
similarly 2 & 5 and then 1 & 4

You want separation but not that much

90° V8s w/ 90° cranks will often pair cylinders, for instance a Chevrolet V^ will want 1 & 3 paired and 2 & 4 paired on the left and w/ 5 & 8 paired and 6 & 7 paired on th e right

Porsche also did that w/ v3 of 908 flat 8

1-2-3-4
5-6-7-8
they only paired 4 & 8 when a flat crank was used all the others were kept separate

Ford on the Gt40s
L 1-2-3-4
R 5-6-7-8
paired 1 7 6 4 into 1 collector and 2 3 5 8 into the other to get the same exhaust pulse pattern as the modern Ford Voodoo V8 or all Ferrari V8s
w/ no separation between pulses

[faapgar]

This is a black art as far as for tuning.I have been building headers for 40 years.I am never done as far as exploration.I can always learn something new.Keep posting guys.Thanks Fred

[safe]

Originally Posted by Walt Fricke

I never did hear just how well this setup worked.

I bet it was loud and loud is fast, everyone knows that!

[GG Allin]

I spent the good part of my day today at my neighbors shop trying the fab up the gap with cut outs on the loud inlet between my headers and a GT3 muffler. We failed. I didn't like the way it was going from the get go. My headers are just too narrow for this wide muffler.

The plan now is to get a new set of collectors and run an angle right where they merge. Make them wider so to speak. Curious if this seems like a bad idea to those who would know.

This is what I'm dealing with. I don't want to cut up the headers. That actually came up today as an option. It appears the collectors can be easily removed. I believe theses are S Car Go headers or knock offs of.