Loop Engine Exhaust Systems - An Analysis

[Frank Volker]

There have been several questions regarding the exhaust configuration implemented on the Quincy Welding (QW) Flathead (Loop) Engines. The siamese exhaust system, in which two exhaust ports per cylinder converge on each side into a common exhaust header pipe, was unique--at least in that time period (1964 - 1973).

Of particular interest is the effect of this port arrangement on the attached exhaust system; that is, the header pipe and megaphones or expansion chambers. Also of interest is the exhaust divider, the design of expansion chambers, and the wave action in the various systems tested. Water injection is also a favorite topic of discussion. Unless you live in Canada, then it's a favourite topic of discussion.

This post is a placeholder to hopefully field these questions in a central location, and may be edited from time to time to provide upfront content info or a general framework for the discussion.

Frank

[smittythewelder]

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Newbie here. Don't know the norms of this site yet, so I'm gonna inflict a long post on you and see what happens. I asked a question of Frank Volker on the Swamp Pit site, but the format here is much better for discussions-in-progress. The topic was Looper exhaust compromises, a blowdown formula, etc.. If you want to read it on the Swamp Pit (www.outboardracing.com) site, it's still not too far from the top.

Frank Volker! Glad to find you here! Do I surmise correctly that you worked at Quincy Welding and/or were in on the development of the Loopers?

I'm interested in your (Swamp Pit) reference to quick blowdown and weak pressure pulses in the split exhaust system of the Looper. When you say quick blowdown, did you measure this (which I imagine is done with a pressure-probe and transducer, and an oscillscope) or assume it based on the formula you described? I ask because it seems to me that the formula only included port-area; it doesn't account for the fact that an exhaust bridge impedes flow. If you have two ports (a split exhaust) with a combined area equal to the area of a single port, they won't flow nearly as well as the single port due to aerodynamic drag. Maybe the loopers (esp. the A and C) had a lot of exhaust AREA by the standard of the time; I'm just questioning the blowdown formula.
I do realize that split exhausts have a lot squarer ports than big single ports, which are oval-shaped and slower opening. Maybe this quick-open aspect gives a crisper pulse, generating a return wave that extracts better, helping the blowdown . . . .

Now, what was the effect of the "splitter" that appeared in looper exhaust ports and pipes about 1969 or so? Was this so you could open the port at less than 90 degrees ATDC without short-circuiting between cylinders? This series of engines had an odd route for the exhaust gasses: a big port window (each side) feeding into a very small, high-drag header, which then dumped into the start of a large, high-volume megaphone. I had a very abreviated talk with Mr. Christner at the time, about upgrading an older model. He told me that splitting the exhaust PORT (each side) was the main thing, and that old pipes would work about as well as the new ones.

(I'm doing this at the library, and am running out of alloted time. I'll go beg for more, and come back . . .).

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04-18-2005, 02:26 PM #26
smittythewelder
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Join Date: Apr 2005
Posts: 24


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(had to go to a different library branch. Policy,schmolicy!!

Frank, you wrote of "running out of wave" as a consequence of the split exhaust. Nearly 30 years ago I fabricated a set of expansion chambers (remember when we called them "bounce-pipes?) for a friend's A Loop. Neither henor any subsequent owner of the engine has ever tried them. They were fairly mild, low-angle, low-volume pipes, as compared to, say, an A Konig pipe. With what I've learned in the years since, I would now give these pipes some kind of heat-retaining coating ("Jet-Hot" is one) and/or some kind of thermal wrap. Given a splitter in the exhaust outlets, don't you think a set of low-volume, heat-insulated expansion chambers could use the looper's attenuated exhaust pulse to pick up some horses?

BTW, please don't take this as any criticism of the original Looper. I thought it was an ingenious compromise, given the limitation of the bore spacing established by the Mercury crankshaft.

[Frank Volker]

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(1)
Frank Volker! Glad to find you here! Do I surmise correctly that you worked at Quincy Welding and/or were in on the development of the Loopers?

(2)
I'm interested in your (Swamp Pit) reference to quick blowdown and weak pressure pulses in the split exhaust system of the Looper.

(3)
When you say quick blowdown, did you measure this (which I imagine is done with a pressure-probe and transducer, and an oscillscope) or assume it based on the formula you described?

(4)
I ask because it seems to me that the formula only included port-area; it doesn't account for the fact that an exhaust bridge impedes flow. If you have two ports (a split exhaust) with a combined area equal to the area of a single port, they won't flow nearly as well as the single port due to aerodynamic drag.

(5)
Maybe the loopers (esp. the A and C) had a lot of exhaust AREA by the standard of the time; I'm just questioning the blowdown formula.

(6)
I do realize that split exhausts have a lot squarer ports than big single ports, which are oval-shaped and slower opening. Maybe this quick-open aspect gives a crisper pulse, generating a return wave that extracts better, helping the blowdown . . . .

(7)
Now, what was the effect of the "splitter" that appeared in looper exhaust ports and pipes about 1969 or so? Was this so you could open the port at less than 90 degrees ATDC without short-circuiting between cylinders?
This series of engines had an odd route for the exhaust gasses: a big port window (each side) feeding into a very small, high-drag header, which then dumped into the start of a large, high-volume megaphone. I had a very abreviated talk with Mr. Christner at the time, about upgrading an older model. He told me that splitting the exhaust PORT (each side) was the main thing, and that old pipes would work about as well as the new ones.

(8)
Frank, you wrote of "running out of wave" as a consequence of the split exhaust.

(9)
Nearly 30 years ago I fabricated a set of expansion chambers (remember when we called them "bounce-pipes?) for a friend's A Loop. Neither henor any subsequent owner of the engine has ever tried them. They were fairly mild, low-angle, low-volume pipes, as compared to, say, an A Konig pipe. With what I've learned in the years since, I would now give these pipes some kind of heat-retaining coating ("Jet-Hot" is one) and/or some kind of thermal wrap. Given a splitter in the exhaust outlets, don't you think a set of low-volume, heat-insulated expansion chambers could use the looper's attenuated exhaust pulse to pick up some horses?

(10)
BTW, please don't take this as any criticism of the original Looper. I thought it was an ingenious compromise, given the limitation of the bore spacing established by the Mercury crankshaft.

Smitty - I divided your questions into the above numbered catagories. Some editing was applied to simplify the list. If you think this captures everything, then we can start from there. I'm going to be away from the computer until about May 2nd, so most of the time now is getting ready for the trip. I'll check back when I return. I'll answer (1) here:

(1) Some Intro Stuff
I worked at QW from 1964 - 1968. I left in '68 to get my BS in Physics and MS in Mechanical and Aerospace Engineering. I worked very close with Chris (O.F.) in developing the Flathead engines. We seldom referred to them as "loop" engines. Early work was done on a simple test wheel. In '66 (I think), we installed a water-brake dyno. The days were long and often Chris and I would unwind by staging stop-light drag races through the streets of Quincy on our motorcycles. I could probably run out of monitor ink telling you what a genius Chris was, and it still wouldn't touch upon the pure brain power of this man.

In '71, as part of my MS Degree research, I instrumented a detuned FA and measured the wave action in the exhaust header pipe for different exh. configurations. This was the source for most of the data in my earlier post on QW Exhaust System History. I returned to QW for a brief period in '72.

Most of my more recent career has involved programming embedded control systems for flight and nuclear power plant simulation and engine (black box) controllers. Most recently, I did the embedded code for an off-highway application (major forklift manufacturer). I'm pretty comfortable with C, C++, and a bunch of other programming languages as well as electronic and hydraulic control systems.

The hardcore engine work that I did with Chris took place about 30 yrs ago. Since I'm not blessed with 100% recall of anything, my answers are always open to question. However, my understanding of Blair's Two-Stroke Simulation text--the definitive work for modern two-stroke design--is sufficiently sound to present a combination of experience with some of his theories, especially in analyzing the blowdown process.

We'll start off with answering questions about the blowdown process, since that seems to be the most glossed over subject in most reading materials I've seen on exhaust system design.

I'll return sometime after May 2.

Frank

[John (Taylor) Gabrowski]

Ever time I look at a Quincy Flathead block, the amount of and the configuration of the ports of that engine back when they first came out must have blown the cans off everyone in terms of here we go! If those were the first halting steps of Loopers / Flatheads and they were it was like starting at the gate with a JATO rocket welded to hydro. It seemed like there was no slow revolution / evolution inside those blocks to think of and who knew what about expansion chambers at that time anywhere? It was pretty much nill.

The blowdown Smitty is referring to? Is the speed at which the engine released the expanding detonation of air/fuel as it approached the exhaust port on that part of the cranks spin? If so the idea was to get the exhaust out of there with such a wave gone from positive to even negative to help suck the next incoming air/fuel charge into the cylinder on the heels of the exhaust wave zapping out the pipe helping pull that new air/fuel charge so as to have a crankcase side pushing and the exhaust pulling making it the cleanest charge possible for the next detonation. Back then, it was conventional racing exhaust wisdom put in a Loop engine.

Its only since the advent of bounce/expansion/stinger pipes have we seen that the Quincy engine would adapt to yet another system not belled. It was only in more recent times with computers and software(s) where it has become clear that the Quincvy Flathead would indeed have benefitted from going to a single exhaust of given area to a single exhaust spec'd made with todays software that many believe seeing it that the Flathead design was not as dated thought. If the engine had changed to that single exhaust port and fed only one pipe, it would not have changed the way the engine looked, sounded yes! But, the performance would be also increased by what some are thinking could be within the 20%+ range in doing so.

I would love to get a Quincy C Flathead block, do the math, change the exhaust to single exhaust port liners and hang a todays modern day expansion chambers from her. I don't think there would be any surprises except to those who said a single exhaust port and expansion chamber exhausts would not go over and only because they said that decades ago.

Things and thinking sure do change but only changed with the times. You guys at Quincy were marvelous and way ahead of your times in your time!

[Mark75H]

John, because of how close the cylinders are placed due to the dimensions of the Merc crank .... there is no way to have a single exhaust port large enough to scavenge the cylinder on a Quincy - that is why Christner split it to each side