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Posted: Mon Aug 30, 2004 5:14 pm
by Smuz
I'll have to dig that stuff out at home.
Uhhhhh, do ya need a bigger shovel? I'm kinda interested in this. I got sum pieces of stainless pipe and I'm setting my TIG welder back up this month.

Gimme sum more info, Steve.

Posted: Tue Aug 31, 2004 9:40 am
by stevec
Thanks for the reminder Smuz. I've been busy with relatives, the kids birthdays, etc. and it slipped my mind. The folks are leaving tomorrow, and I'll try and check tomorrow night!

Posted: Fri Sep 03, 2004 10:29 am
by stevec
No, I still haven't got that info out. I left myself a phone message so I can check it tonight, but I'll be gone all weekend, so you're gonna have to wait until next week! :roll:

Posted: Tue Sep 14, 2004 3:52 pm
by stevec
Well I finally dug it all out, looked it over again, changed a few things slightly, and wrote it all out. I know a picture would help greatly here, but this'll have to do for now. I've converted everything to inches since most of us will be dealing with that, especially when getting pipe.

The chamber I'm envisioning would be a "two-stage" expansion chamber, which would essentially have two cones at the engine end, instead of just one.

Here are the spec's I've come up with. These are based on an LJ20 engine, but should be the same for an LJ10 as well. There are a total of six sections, consisting of the header, 1st divergent cone, 2nd divergent cone, belly (the largest diameter part of the chamber), convergent cone, and stinger.

1. Header - this is the part that comes directly off the exhaust port. In most cases, it begins with the exhaust manifold. For a true two-stage expansion chamber, a custom header would need to be built, as this section should only be 2.5" long, and use 1 5/8" pipe. The pipes coming out of each of the two ports should be exactly the same length, so it'll need to be a true "Y", not angled backwards. (note: better check for clearance issues here!) If one is longer than the other, then one piston will have more power than the other, and will thus be forced to "pull" the less powerful one.

2. 1st Divergent Cone - most, if not all, of this would likely need to be incorporated into your header, as the 2.5" isn't even enough to converge the two pipes into one. The length of this section is 10", and it is a very slight angle: the pipe diameter would only go from 1 5/8" up to 2", a difference of only 3/8" over a 10" span. It may work to have the cone only 6" long, with a 4" long piece of 2" flexpipe at the other end (remember that flexpipe?), I'm not sure how much effect that would have on power output.

3. 2nd Divergent Cone - This cone would take the diameter from 2" to 3", and be 3.5" long (measured longitudinally, not by measuring a side of this cone!

4. Belly - the belly of this chamber is simply a 2.7" length of 3" pipe.

5. Convergent Cone - This cone brings the diameter from 3" down to 1 1/8" (1.125"), and the total length would be 5.9". Again, this length is measured not by a side of the cone, but the length from the center of the middle hole to the center of the output hole. In other words, the measurement would be taken with the large hole flat on the ground, and your measuring stick inside the cone measuring the distance to the smaller hole.

6. Stinger - This is a 5.9" length of 1 1/8" pipe on the end of the convergent cone. The small diameter of the stinger allows the backpressure necessary for the expansion chamber to work. This backpressure creates a denser environment for the sound waves in the chamber. Behind the stinger, you can run whatever exhaust you want without affecting the power, as long as it is not more restrictive than the stinger.

The overall length, measured from the center of the pipes/cones and including the bends for the exhaust manifold, would be about 24.5". Based on my calculations, this exhaust would allow an LJ10/20 engine to create 39hp (as opposed to 27-28 stock), with an average exhaust temp of about 700*F (380*C), assuming your LJ engine is perfectly tuned and ported and your carb is perfectly jetted for this chamber. That's doubtful, but I would expect at least a moderate gain by using a two-stage chamber, as well as a much broader power curve. (Remember, even an additional 3hp is a 10% improvement!). My thinking is to run 1.5" exhaust behind the chamber, which is about stock, and just run it all the way to the convergent cone, thus covering up the stinger completely.

I should point out that this is purely theoretical; I've never tried it, but the formulas are similar in the various books and websites I've read, so according to theory it should work. I'm hoping to put one of these together over the winter, but I can already see that time will be an issue getting the V ready for next year's get together in Colorado, so I'm posting it here in hopes that someone else has more time to try it.

Finally, in response to other questions, everything I've read indicates that it doesn't matter what you put behind the stinger, as long as it is less restrictive than your stinger. Thus, if you cut the rest of your exhaust completely, your LJ might be a little louder but the power output should be about the same.

I'll see if I can make up a diagram and scan it, as it would probably make this much clearer!

Posted: Tue Sep 14, 2004 6:42 pm
by russmehl
Nice description, thanks...

Posted: Wed Sep 15, 2004 11:16 am
by Idahopaul
awesome! that took a lot of work!

Posted: Sat Sep 18, 2004 11:07 pm
by Smuz
This looks do-able. The configuration I'm imagining is:

1. Header: A 3/8" header plate with the 1 5/8 tubes coming down at an angle, smoothly converging into one 1 5/8 pipe.

2. First div. cone: incorporate a 90 deg bend into this to point towards the rear.

3. The rest is as described.

Notes and questions:

1. By incorporating a 90 deg bend in the first div. cone, one should be able to hold the distance from header plate to centerline of the exhaust run to a minimum of about 4-5 inches. This sounds about right, from what I remember of the drop on Wilson. I dunno how much clearance there is directly under the two exhaust ports on Wilson, but I'm reasonably sure that it's at least 4 inches to allow for the manifold and heater air box.

2. Steve, several questions about the header immediately occur to me: To smoothly converge the two 1 5/8 pipes, there will be approx. 1.5 inches of convergence. Would the 2.5 inch header length be measured to the beginning of the convergence, the end of the convergence, or the middle? Does it really take two 1 5/8 pipes to converge into one 1 5/8 pipe? Two 1 1/8 pipes have about the same area as one 1 5/8 pipe. Seems to me that the total area of the two header pipes might should be the same as the small end of the first divergent cone.

3. Suzuki's original design doesn't seem to follow this methodology very well at all. Makes one wonder just how much horsepower increase the original expansion chamber gives.

4. If I build one of these for Wilson, I can kiss my heater set up goodbye. If one were to add fins and an air box to the header and first divergent cone for a heater, how would the decreased exhaust gas temperature affect the chamber design. Not that I'm gonna go to THAT much trouble for a heater that's pathetic at best, but it's an interesting question.

Steve, puts yer thunking cap on and see if ya can come up with sum ideas on the questions outlined in number 2. This looks like a fun little project for when I get bored.

Posted: Sat Sep 18, 2004 11:16 pm
by Smuz
Holy cow!

I just got the calculator out and 39 horsepower out of Wilson iz a 62% increase!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Man, I GOT to make one of these!

Posted: Sun Sep 19, 2004 10:36 pm
by stevec
That's the spirit, smuz!

You will want a 1 5/8" pipe coming from each cylinder, converging into one 1 5/8" pipe. And yes, a 1 5/8" pipe will have a greater area than the area of the exhaust port. The length would be the total length of the header, so basically the convergence will likely be part of the first cone.

I've actually thought about that heater question, putting the fins on to dissipate heat. It would obviously reduce the exhaust temp, which is a good thing mostly, but it may lose a little power. I can't tell how much from crunching numbers; the exhaust temp is more of a by-product of other calculations. I would think that any power loss would be slight, based only on the changed (reduced, I think) density of the air. The perfect 2-stroke engine would be ported, jetted, timed, etc. to match a specific expansion chamber, thus optimizing the engine's power - if we could do that, we could probably get 80+ hp out of an LJ10 motor! Just look at some of those enduro motorcycles! It'd be easier to just build a new engine from scratch though...

Posted: Wed Mar 23, 2005 2:57 am
by Idahopaul
well smuz, are you still gonna try this on wilson?

Posted: Wed Mar 23, 2005 6:01 pm
by Smuz
dunno yet. Not 'till after the meet, aniways.

Posted: Wed Mar 23, 2005 7:36 pm
by russmehl
Found this while doing a LJ20 web browse. ... D%26sa%3DN

So how much is 65,000 yen?


Posted: Wed Mar 23, 2005 7:40 pm
by Sluggo
Only about $612 :!:

I couldn't see the link but that's a great price for something that no longer exists :!:

I'll take it if you don't want it.

Posted: Wed Mar 23, 2005 7:44 pm
by russmehl
Link fixed, Try again!


Posted: Thu Mar 24, 2005 5:41 am
by Jimny
The bottom one looks like the original one of course so I wonder if the top one helps to add more HP?

On the 20 I just got it has what looks like a 21" Glass-Pack muffler that they used for the expansion chamber(EC). I will take pics of it as soon as I can get in at a decent time so I can unload it from my truck and take pics.

Russ is there another page that describes the EC's?

Posted: Thu Mar 24, 2005 9:42 am
by stevec
In the picture, the top piece is their redesigned expansion chamber, and the bottom piece is the muffler/tailpipe. Still, compare their expansion chamber with a stock one, and you can see how much the design has evolved over the years!

Posted: Thu Mar 24, 2005 6:44 pm
by Jimny
They have big time since the ole can style that they started out with. If I had the cash I would buy one to see what the sound is like and the power difference. :cool:

Posted: Mon Apr 04, 2005 3:22 pm
by stevec
Found some more info on this, and I think my calculations need to be changed a bit:

My overall length was off (I was measuring from the wrong point). The diameters are all ok, but a few lengths need to be changed:

1. The stinger length needs to be doubled (11.8", not 5.9")

2. The header should be much longer. I had the total length of the header plus 1st cone at 12.5"; The header only should be this length! I should point out that this length begins at the piston wall - thus the first inch is taken up by the cylinder wall and exhaust manifold plate. I should also mention that this is an estimate, and many articles I've read indicate that you'll almost surely need to adjust this to fit somewhat. This is the "tuning" part. If you can, make as much of this part "sliding" if possible, (like a trombone) so that you can adjust the length at first. Once you have the optimum length, you can then weld it. With the bends in the header, this may not work out as well as I would hope, but this is, after all, just a starting point.

3. The belly is less than 3", but this is based on the engine putting out max hp at 6000 rpm. If you want peak hp at a lower rpm, it appears that all you need to do is lengthen this section. I think changing it from 3 to 6" would lower the peak rpm from 6000 to 5000. I didn't try it any lower, but if you REALLY had a lot of time, you could play around with this.

Remember, these are hypothetical numbers, based on mathematical formulae I have found regarding two-stroke engines, and thus have not been tested. If you do decide to try this, please let us know how it goes!!!

Posted: Mon Apr 04, 2005 4:53 pm
by Jimny
You keep mentioning this "math" thing. What is it? :wink:

Man that's mind boggling, I think I will buy that one from Japan for $600.+

Posted: Tue Apr 05, 2005 8:58 am
by stevec
The biggest problem with designing an expansion chamber is that there are so many variables with the engine. If you design one for a racing engine, you're designing it for a certain rpm, and for one specific engine, that mostly likely you built yourself. For a mass produced engine, every one will be slightly different, and they will not all be timed and tuned the same. This gives us a guideline, but there will likely be some trial and error when you actually build one. If I had the tooling and parts, I could make one in a day, but I'd want to test it, change the lengths a little, test it again, etc. until I found the best specs. That's what takes the most time, and is why I haven't actually tried it yet.

Posted: Thu Jan 19, 2006 3:46 pm
by Demomike

this is what I happen to be doing at work today (see attached), kinda look familar? Maybe I should have the guys make an extra?

edit: image updated below...

Posted: Thu Jan 19, 2006 5:12 pm
by stevec
Cool! Is that for your LJ, or something else?

Posted: Thu Jan 19, 2006 5:19 pm
by Demomike
Just something I'm doing for work, but it reminded of the expansion chamber pic from Japan in this thread. A little tweaking though and we could have some flat patterns....

Posted: Mon Feb 20, 2006 6:07 pm
by Jimny
russmehl wrote:Found this while doing a LJ20 web browse. ... D%26sa%3DN

So how much is 65,000 yen?

Found a couple more places today that has the same LJ20 expansion chambers, Here is what one said translated:

"Presently the chamber of LJ20 is sold only, it purchased from free solo.

Exchanging simultaneously with the muffler, the highest speed raised 10 kilometers or more.

It became the way which the highway inserts. (Laughing)"

Mmmhhh raises the top end huh? Interesting.

Posted: Sat Mar 04, 2006 7:32 pm
by Jimny
I can't get any reply out of them so....

Steve, email the dimensions of what you came up with and I will build one for the LJ I am restoring and we will see how it works.