Expansion Chambers for DMH

[sam]

Expansion chambers lend themselves quite well to the loop scavenged engines (all new PRO alky engines). ...... Bottom line, if you want to run expansion chambers, you need a looper. -Paul Fuchslin

Paul, that does not address why expansion chambers on loop charged C Mod Yamatos don't blow away non chambered C Mod & cross over C Stock Yamatos. Its not just the loop charging it is the exhaust port timing/angle/area issue combined with the pipe (or more precisely - not combined).

I have a couple of over ported 20H blocks that are considered junk because of the excessive porting work done to them ... I am going to see if bolting on an expansion chamber will "redeem" them. Bringing the exhaust port timing into the range commonly seen with motors that are responding well to an expansion chamber may be seriously close to cutting into the water jacket on a Merc. Your dad may have already determined this to be the fact with a straight mill drop into the cylinder, but I am guessing that there may be some hope with an angled cut.

[jeff55v]

Come to Rochelle!

Bottom line, if you want to run expansion chambers, you need a looper.
Unfortunately, there will be noise pressures from some sites and not others. -Paul Fuchslin

Well said Paul. I recall this past summer, driving into the pits at Rochelle,IL. We held the DMH NAC's there. Sunday morning at about 7am... there were already several Dmods out testing! It was great! Who needs coffee?
(No offense Kevin)

[alky6]

Paul, that does not address why expansion chambers on loop charged C Mod Yamatos don't blow away non chambered C Mod & cross over C Stock Yamatos. Its not just the loop charging it is the exhaust port timing/angle/area issue combined with the pipe (or more precisely - not combined).

I have a couple of over ported 20H blocks that are considered junk because of the excessive porting work done to them ... I am going to see if bolting on an expansion chamber will "redeem" them. Bringing the exhaust port timing into the range commonly seen with motors that are responding well to an expansion chamber may be seriously close to cutting into the water jacket on a Merc. Your dad may have already determined this to be the fact with a straight mill drop into the cylinder, but I am guessing that there may be some hope with an angled cut.

Sam - time/area, you and I are saying the same thing there. There are many other factors involved - it is an air motor and any restriction to getting the air in and out of the engine is a hindrance. The reed system on the stock yamato is terrible. Add to that the fact that you want to increase the RPM (more air) over stock and it won't matter how big your ports are. Further, and correct me if I am wrong but, I believe there are restrictions on how much one can advance the ports on the C-mod yamato (hence the time-area problem). In this case I would expect that a megaphone would probably run better than the expansion chamber.

One can look at it this way, as opposites:
megaphones = lots of suction, little plugging
expansion chambers= little suction, lots of plugging

You need to know if the air is free to move through the engine or if there are bottlenecks. If you have bottlenecks, the expansion chambers probably won't help much; looper or crossflow.

As for your Mk 30 at least you are using a reed block that will flow the same amount of air as a 44 (50% more). Have fun playing with the chambers on the C, I know that was one that my dad always wanted to play with. Good luck, keep me in the loop on your progress.


Ken, - no offense taken. I'll just pick and choose where I race while I still can. Business decisions undoubtably will need to be made by the conducting clubs. Most likely, I will always be able to run the six at DePue. - Sorry for hijacking your thread with engine discussions, just can't help it.

-Paul Fuchslin

[mercguy]

Paul, a WORLD of knowledge!!

Sam - time/area, you and I are saying the same thing there. There are many other factors involved - it is an air motor and any restriction to getting the air in and out of the engine is a hindrance. The reed system on the stock yamato is terrible. Add to that the fact that you want to increase the RPM (more air) over stock and it won't matter how big your ports are. Further, and correct me if I am wrong but, I believe there are restrictions on how much one can advance the ports on the C-mod yamato (hence the time-area problem). In this case I would expect that a megaphone would probably run better than the expansion chamber.

One can look at it this way, as opposites:
megaphones = lots of suction, little plugging
expansion chambers= little suction, lots of plugging

You need to know if the air is free to move through the engine or if there are bottlenecks. If you have bottlenecks, the expansion chambers probably won't help much; looper or crossflow.

As for your Mk 30 at least you are using a reed block that will flow the same amount of air as a 44 (50% more). Have fun playing with the chambers on the C, I know that was one that my dad always wanted to play with. Good luck, keep me in the loop on your progress.


Ken, - no offense taken. I'll just pick and choose where I race while I still can. Business decisions undoubtably will need to be made by the conducting clubs. Most likely, I will always be able to run the six at DePue. - Sorry for hijacking your thread with engine discussions, just can't help it.

-Paul Fuchslin

Paul, thanks for the very good info. It confirms alot of my questions on expansion chambers, etc vs. megaphones. I always kind of wondered myself, why a Cmod Yamato (with expansion chambers) does not BLOW AWAY a stock Yamato. I will stick with my Cmod Merc (hmm expansion chambers on it??).

looking forward to seeing (and hearing) that alky6 of your going again!

PS: if you dad wants to "play" with a Cmod Merc, I would be more than willing to lend you mine for a donor, as long as I got it back FASTER!!!!

[Denice Medeiros]

I agree with you pual ive been looking for chamber for cmod yamto and can not find one or one that would work on a 302. so i put a megaphone on and it ran all most as fast as the 30h me and your dad build only to find that you cannot ran a megaphone on a 302 85-c

[Fast Jack]

Pipes

Have you ever tried to find a new race sight? I have , we now have 2 new sights in Maine and with the efforts of Steve N, one in NH. The problem of noise is one of the first objections you will get when you start the process of puting a new race together. Stock cars now have to run mufflers at many tracks,Try to find a field to run RC aircraft? Land for recreation is geting very expen$ive,and the people that can afford it can also out spend you when you try to lobby for a new event. I love the sound of a good merc with megs. ( I have a vintage Castercraft with a 44 on it). The future of boat racing is based on the availability of sights to hold events. Perhaps we may have to eliminate megs, as a consesion to hold future events. I think you will find a C yamato can run fast with the right pipe. My 302 has a pipe I designed from a long standing karting profile, I was told by a top engine builder it would not work.. Check the CMH points to see this years results.. I have never been one to put all my eggs in one basket, I run stock ,mod and PRO, I know I will have a boat or 2 to run at any sight based on what there local restrictions may be. To boycot a race because you can't run open pipes will help put an end to our sport,local clubs need all the entrys they can get to cover the coast of an event.

[alky6]

Have you ever tried to find a new race sight? ....To boycot a race because you can't run open pipes will help put an end to our sport,local clubs need all the entrys they can get to cover the coast of an event.

Yes on new race sites. Boycott - no. It's tough to run at a race with equipment one doesn't have (our Merc alky 6 doesn't work with expansion chambers). Again a conscious decision. In the future, when we no longer have race sites to run megaphones at, we will have to decide if investing in new technology for 1100R is what we want to do. Until then, the nastalgia of the old technology will prevail.

-Paul Fuchslin

[nbass]

I love this topic

73.95 MPH Class 05030 - BMR Saturday, March 26, 1994 Record Type KILO Location WATERFORD, CA Driver J. W. MYERS Owner J. W. MYERS Boat FARLEY THE BIG WHEEL Hull Type WILLIAMS Engine YAMATO

59.04 MPH Class 05030 - BMR Saturday, September 25, 1993 Record Type 3 MI/3 LAP Location YELM, WA Driver J. W. MYERS Owner J. W. MYERS Boat REMEMBER WHEN Hull Type WILLIAMS Engine YAMATO

I love this topic. I wish we could get together and share experiences.

I agree with all that an expansion chamber on a deflector piston engine generally does not work. We have done some wild testing with a 44 by cutting the block and pistons to get enough port time, but the reed block then becomes the restrictor. I have made an expansion chamber work well on other engines including a Yamahato 80. I believe J.W. Myers still holds the B-mod runabout straightaway and some course records with my expansion chamber. He worked with me to fine tune the initial design. I have attempted to make chambers for Yamahato C-engines with limited success. Limited intake may be the problem, but for the most part, the owner-driver does not understand how the chamber works and they fail to work with the initial design to make it work. I think it was Ron Anderson that said “if the pipe is so long you have trouble mounting and keeping it in place, you are getting close”.

I would like to add to the things that can be wrong with your 302 C-mod pipe design, 102 and 202 similar comments.
1. Overall length too short. From the piston face to the mid length of the reflector (tail) cone should be 4-feet or longer.
2. The elbows from the cylinders should not be larger than 1.375-inches ID, 1.25-onches ID may work better. Maintain uniform cross sectional area as best possible.
3. Leadout, the length from the piston face to the first megaphone should be about 1.5-feet.
4. The mid section should be about 4-inches in diameter.
5. The engine cannot be too lean or too rich. Especially too lean, but in either case the pipe will not work.
6. Keep in mind that a pro-engine at 12,000 RPM can make a big length adjustment within 2-inches of pipe length change. A stock engine at 6,000 RPM needs twice that or 4-inches of length change. Keeping a fairly flat tail cone section (maybe 8-degrees) will help distribute the power over a wider range.

Just some fun starting information. There is a lot more but this should get you started. All comments and experimental results greatly appreciated.
Thanks,
Neil Bass

[T Chance]

Back in 1970 I drove a B-Mod Champion Hot Rod for a guy. Now, remember the first 4-cylinder Konig's with the "Tin Can" exhaust. This is the type of exhaust he had on the Hot Rod. Basically it was standard megaphone exhaust exiting into a closed cylinder, kind of like a jumbo coffee can with a bleed off pipe. I think the water outlet was dumped into the can too. It was very quiet and it ran as well, or better, than with just megaphones.

On the same subject I had a 500 cc Konig with the "tin can" exhaust. It was quieter with the water in the can but faster without. I also slid the can on the elbows. But when I switched to expansion chambers it really made it go.

I too, have been in discussions about expansion chambers on crossflow engines and have been told they just don't work like they work on a loop scavenged engine.

By-the-way I personally prefer the sound of expansion chambers to megaphones.

[Dave M]

A Point To ponder

Since those who know, and there are many of who know, that chambers are not the most effecient means of exhaust on a deflector engine, what should we do ?

THis is being asked of those who know, not those outside looking to kick in some opinion without knowledge.

In my opinion it is a lost cause trying to make chambers work on a deflector. It works to a point on certain race courses. But they are few and far in between. Ultimately the law of average have the megaphone winning.

Givin this information, perhaps it is time to develop new engines into the class that are true loopers. THis would end the debate and phase out the 44 mercs in about ten years. Since Mod is changing all the class names to be more like the alkies, why not live by it. Make it "X" CC engines, no open megaphones, have at it. It took years upon years to develope the Mercs into what we race today. It takes time to figure out the engines and what porting works, what chambers work, etc.

And by the way, you put a megaphone on a 102 yamato, you better hold onto your hats. It is wicked fast. Just ask Tim Schultz who races one with a megaphone in NBRA. It is the same boat he races 125CCH at the USTS races. SInce I never seen a GPS speed or radar gun speed, I am guessing it is into the low 80's maybe high 70's.

[dcrabtree]

And thats odd due to the millions that love nascar and car racing period.Everyone knows there 10 times louder than mods will ever be.And your right Dave exspansion chambers don't work on every engine and yes you have to work with them to get them to work.I don't know whats wrong with the people in those few communities that detest mods. And its probablly the same communities that have excessive loud semi truck traffic or a factory or two that pound away all day.It doesn't make sense and I'm sure glad its the opposite here in Quincy.Its the noise of the pipes that bring the fans down to the race site. Thats almost as bad as a couple lakes around here that don't allow any boat racing but two are three times a year they allow 50 to 100 bass boats loose to tear the water up.Whats the difference.The complaint was the fuel leakage would cause an ecological problem.Like bass boats don't leak fuel out there exhaust.And I think the noise is just a cover for what the real reason is.

[David_L6]

...phase out the 44 mercs...

Thems fightin' werds!

And by the way, you put a megaphone on a 102 yamato, you better hold onto your hats. It is wicked fast. Just ask Tim Schultz who races one with a megaphone in NBRA. It is the same boat he races 125CCH at the USTS races. SInce I never seen a GPS speed or radar gun speed, I am guessing it is into the low 80's maybe high 70's.

Old AOF 102 Mod class.... 400 pound minimum, any gear ratio lower unit and a (supposedly) stock 102 powerhead with a megaphone = slightly faster than the good C Mod Mercs and a little slower than the 40" D Mod Mercs. I ran one on my 83 model B&H. Only had one prop that was big enough for 12:15 gear ratio and was about 35 - 40 pounds over minimum and it still ran 1.5 - 2 mph faster than my C Merc. That's with very little set up work for the 102 and a lot of set up work and lots of props for the C Merc.

[alky6]

A potential Solution?

Dave has asked for it - A potential solution:
Don’t crucify me here (I have run a lot of MOD stuff and still hold some FER records) but…a potential solution would be to phase certain MOD classes into their PRO equivelant (and under PRO rules) and eliminate the CMOD, DMOD, FE from MOD. The DMOD classes are equivalent to 250/350H and 350R. CMOD= 175/250H and 250 CCR (of course these comparisons are debatable). They all run expansion chambers (silencers can be added). Engines are widely available. The cost is about the same when you consider all the work done to get a DMOD to run competitively. The engines are fairly competitive out-of-the box. Parts are available. You can tweak to your heart’s content (bore and stroke requirements only). The fuel is a “green” fuel along with a “green” lubricant (methanol and castor oil). Fuel costs are about the same if you have to run high performance gasoline in your MOD engine.

The above, in all probability, might just happen eventually on its own; as there are fewer and fewer race sites that support the noise (noise - aka beautiful music: which I love by the way), and with the growing lack of new engines and parts (again debatable) racers will look for other venues to quench their thirst for working on two-strokes and fierce competition on the water.

Please do not take this as an attack on MOD, just an outside-of-the-box idea from one with "knowledge on the subject" as Dave would say...

I am sure the "fur will fly" now; so-to-speak.

[dcrabtree]

They Work ,We Ran Them

Before we quit racing that is just what we were doing is trying exspansion chambers on our 30 and 40ci deflector mercs and they worked just fine. I guess it helps when you have someone in your corner that knows what there doing. The last time we ran we put the 40 into E hydro at the nationals and took two straight seconds so I would say were on the right track.And it doesn't matter if it was 25 years ago are yesterday,the mercs haven't changed. And thats real nice just because we can't get something to work we throw it away.Sounds just like the opposition and comments we ran against in the early 80's.To bad some of you can't get them to work because it doesn't take that much.Have a nice day.

[Morris85C]

I want to buy a set of chambers for my d mod where do i get them from.