exaust options

[Sonny]

aaaaahhhhhh

I think I have a pretty good idea how these fortunate few are making this work. The answer is in the elbow, The motor will make the horsepower that it's going to make based on compression. On a small chevy we would use a smaller valve with a smaller lift cam to develop low end torque, and a huge lift cam with a monster valve for rpm's, same horsepower but we had to decide were we could make it work by deciding how fast to let the exaust out. 4 strokers and 2 strokers have there obvious differences but this is a pretty basic principal, and from the little I know about pro motors seems to be true with two strokers as well, big compression=hp lots of air=sick rpm's, by reduceing the diameter of the elbow I should be able to bring the torque curve to a useable rpm??? Now back to the front, and I'm guessing this is were it will get trickie, to increase the exaust wave I have to get more air in. Enter the "KC" carb's, Again changing the torque curve and rpm's. lots of work to do here. There is an answer it's just hideing. What do you guy's think???

[fred tyson]

low end horsepower

hate to disagree on the small block theory but afer seeing it on the dyno on several comonations best for low end , was increased compression, increase intake vave one size, stock size exhaust and stepped headers, now on my old 350 cc yamato that we ran for years, we picked up bottom end and increased mil per hour by using specs that Zak supplied for the elbow for the headers to expansion chambers, these headers alone allowed me to run a larger wheel , thus increasing top end

[bh/]

pipes

Sonny's post of pipe dims and dyno curves were some of Frank Volkers work on a 250cc Quincy 'looper' , a flat top, , ie; non-deflector piston motor.
If u look closely at the curves, comparing megs to the expansion chamber,
it in fact supports what Schmidt, Bass, Fuchslin, et al say, in that the power increase comes on too late to be usable in a short course motor. The HP curve is way below the curves for the three megs all the way through, and only equals them at 9500rpm. At 8500 the 'pipe' is making 25% less than the meg. I imagine this effect would be more pronounced with asthmatic breathing deflector piston motors.
I have this pic of a Merc C-mod motor equipped with sliding expansion chambers, which are purported to 'work', and I assume are Gollers[?]

[Doug4N]

Does anyone have a copy of Jennings formula for expansion chambers? I am using the formulas derived by Blair and am curious to compare the two.

[Merc55H]

If you search for expansion chambers on Google you will find several webpages that have formulas posted. Whether they are Blair's or Jenning's I don't know. There also is a guy by the name of Hepperle who has an interactive pipe design program on the internet. There is also a Swedish site that sells an Excel based chamber design program. I suspect that somewhere in some motorcycle mfr's engineering department there is a kickass program light years ahead of what is available to the public in the way of chamber design.

[David_L6]

http://www.mh-aerotools.de/airfoils/..._header_en.htm


http://www.hpt-sport.com/tunedpip.htm

[nbass]

Replay to sam's comments

I fully agree with Sam's comments about changes to expansion chambers to make them work at a different RPM range. We did try different chamber designs on a 44 (MK 500 block), all sliding chambers. We concluded that overall the engine did not develop enough exhaust pressure to maintain a supersonic wave through the elbows. Part of the problem is that the port arrangement makes the port to pipe transition too large for the port area. Energy is therefore lost at the ports making the problem even worse. Pipe shape and stinger size did not help the problem. Another part of the problem is the limited transfer port capacity. A functioning expansion chamber will draw air and fuel through the transfer ports, if it is available. If not available, there will be little or no gain from an expansion chamber. Coupled together, the chamber did not work effectively. The Mean Effective Pressure (MEP) for a 44 is about 85psi, whereas the MEP for a 250 Yamahato is about 150 PSI. From this you can see that the energy from a 44 is prety low and any inefficiencies in the port exit or the elbows can loose it all. The was a minor noticable boost at high RPM, but it occured way beyond the HP peak. That boost could not be duplicated at lower RPM with longer pipes. We did not experiment with a MK 30 engine. That may be another story.
Neil

[ANZANI-QUINCY FREAK]

Mark 30 Expansion Chambers a Different Story

I hear ya and went through the same thing cutting and pasting my way through 4 sets of 4 chambers (16 pipes) to find out that they just would not work on a Merc 44 the way you said they did yourself even changing the filler block, squeeezing the inner dimensions down to match the ports and roundd edging the exhaust port outside to flow rearward better with that pressure wave. I abandoned trying that on a Merc 44 right after that going back to Quincy pipes.

With the Mark 30 it was a different story. Used leBanco filler block and elbos and a new set of two expansion chambers. Retained a set of fireslot older design pistons and tested that way and found an imprvement thought the pipes are fixed length and no cutting and pasting yet. Tried a set of newer flatops but that was not as good so went back to the old fireslots. Exhaust ports are top squared and radiused. The engine seems to be producing better power with the expansion chambers making me wonder if its the small bore and weak crankcase pressure of the Mark 30s getting something out of this so far? Looks promising but that is all at this point. There are C-Mods responding well to these kinds of pipes but why and what future cutting and pasting maybe required I am not thre yet.

[hshawwpba]

hshawwpba

I hope this comes through large enough that it can be read. It is the horn or bell dementions for the alky merc motors and the horsepower spec's in relation to rpm's. I can e mail the full size image to anyone who is interested in having it. But the info suggests that a stinger pipe is a home run. This water injection deal sounds pretty interesting too. Does anyone have any photo's of a working water injection opperation??

Please email me a larger copy of pipe info that is readable for old eyes!

hshaw@hmausa.com

[alky6]

The Mark 30 is a very different animal. Imagine all the real estate one could utilize in a block the same size as a Merc 500, yet have the almost 50% less area taken up by cylinders. Not to mention the same reed blocks, etc. Lots of room for ports... But back to Bass, you need the BMEP to establish a good initial wave to get the pipe to "huff and puff". If you enjoy playing with engines, want to learn a whole lot about thermodynamics, and are ready for an aweful lot of disapointments continue trying to acheive the same or better performance with expansion chambers over megaphones on the Mark 55 or 58 blocks. If you do plan to play you will need to invest in a dynomometer as boat testing is time consuming and difficult to get an instant change not to mention hanging all kinds of crazy shaped pipes off of.
-Paul

[crankbearing]

before it reaches the ports

I see a major difference between merc deflectors and konig, yamato, yamaha(cycles) etc.... there is one major difference, we all taper our cranks to dump or unstuff the crankcrase and all the above two strokes stuff more crankshaft in there as to not dump that much so there is just plain more to draw out.

Has anyone tried expansion on a looper (not quincy) but on a scavenged block, we had a 44 that was loop scavenged that was a real mid range bandit. It would burn totally clean and worked very well. We never did try expansion chambers on that motor.

Regards,

[nbass]

To Paul

Good comments, and no I do not intend to waste more time and destroy more engines. I made my analysis and decided to leave it at that.
Moving on,
Neil

[jeff55v]

Pipes that work on a Merc...

If you search for expansion chambers on Google you will find several webpages that have formulas posted.

I did a google search looking for drawings of a pipe that will work best on a Merc. Or any age old deflector piston motor. The only thing I could come up with was a megaphone.

[seagull170]

More pipe info

If you can't get a copy of Jennings & can't translate prof Blair into laymans speak have a look at Two-Stroke Performance Tuning by A. Graham Bell
ISBN 1 85960 619 9 published by Haynes.
It seems very similar to Jennings just a lot newer.

[Sonny]

loopers

The chart I posted, (someone elts's research). shows a stinger pipe diagram for a gen 3 looper. There seems to be room for research and development as far as tuning a crossfire exaust wave. It seems the failure to the model is port configureation and piston shape. Maybe the time is better spent trying to develop a variable venturi carberator?? or maybe variable port timing??