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Old 2nd October 2007, 22:57   #31
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Default Hi

Thats OK.
Now after realizing that mine is a 250 Single Cylinder what do you think.

My assumptions

One Cylinder =
Exhaust Gases leave the ports at same time =
Gases from one port reach the expansion chamber earlier than the gases from the other port ( Lenght of one hedder pipe is longer than the other remember!!.) =
The exhaust from the longer pipe push the gases from the smaller pipe out of the expansion chamber & eventuly get themselves out of the exhaust tip before the gases from the next cycle are released.

This is my assumption. what do you think?.
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Old 2nd October 2007, 23:47   #32
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Quote:
Originally Posted by Shreeram View Post
The exhaust from the longer pipe push the gases from the smaller pipe out of the expansion chamber & eventuly get themselves out of the exhaust tip before the gases from the next cycle are released.
This may be true but it does you no good in a two-stroke. With a 2-stroke, it is not about exhaust flow. It is about pressure wave timing and intensity. In other words, it is about controlled backpressure. I dont think your current design will cause any engine damage, however it is theoretically wrong because of two reasons:

1) One of the header pipes does not make use of the divergent cone and therefore your engine gets only half the scavenging effect that it could otherwise have with that same expansion chamber.

2) You have twice the optimum area that the tailpipe needs to have. This means that any pressurized activity in the expansion chamber is negated because the pressure is bled too soon from the tailpipe.

I still stand by my original solution. Make both the header pipes join into a single one before they enter the divergent cone, and have only one tailpipe with one muffler coming out. You wont be disappointed. Also, try to make the header pipes just a little bit shorter (cut off ~40-50 mm) than stock. That center cylindrical section seems a little small to me now. Make sure it is atleast 100 to 110 mm in diameter. Bigger center diameter= hard hitting powerband.

I have seen some yezdis wherein the second exhaust port is completely blocked off with a plate. The other one is ported and some metal removed to optimize the duration and port area. Then a single expansion chamber is fitted. This does make sense to me because the yezdi is a fairly low-rpm design that doesn't require much exhaust port area.

I see you're already running the 28mm pacco carb. Good choice. Also, good work reinforcing the frame just ahead of the rear shock.

Here's something that we built back in 2003. Just to fire the imagination a little bit. There is no component on this motorcycle that has not been modified in some way.


Last edited by ananthkamath : 3rd October 2007 at 00:00.
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Old 2nd October 2007, 23:51   #33
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Quote:
Originally Posted by Shreeram View Post
The exhaust from the longer pipe push the gases from the smaller pipe out of the expansion chamber & eventuly get themselves out of the exhaust tip before the gases from the next cycle are released.
Important thing to note here: Gasses don't push/move each other, they mix and cause turbulence. Its the pressure difference which moves gases.


Ok lets try to work out what will happen for single cylinder engine. Lets call the two exhaust ports and header pipes A and B where B is the longer one connected to the belly.

Here is what I think will happen:
- Exhaust pulse will leave both A and B at the same time
- Pulse A will enter the diffuser and a -ve pressure pulse will start sucking used gases from the cylinder
- This -ve pressure pulse will not be acting on B. Suction will only happen at port A, decreasing pressure in cylinder and reducing the speed/pressure of exhaust gases in header B. This may even cause a reversal of flow of gases in header B.
- Pulse B will enter the belly and will cause turbulence in flow
- Some exhaust gases will still remain in header B
- now +ve pressure pulse will be started by the baffle cone, this will push the exhaust gases in header B into the cylinder
- as the tailpipe is separated before the baffle cone ends the +ve pressure pulse will be weak and will fail to push most of the input charge from header A into the cylinder

All of the above depend on various parameters e.g.
- difference in lengths of header pipes
- where the header pipes merged
- engine RPM
- belly length
- cone angles of diffuser and baffle
etc.

This will hurt both the performance and the engine.

I think most of these problems will be solved if you do the following (most of this is already suggested by Ananth in greater detail):
- keep lengths of headers pipes exactly the same
- merge the headers at least 50mm before the diffuser cone starts
- Keep a single tailpipe
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Old 3rd October 2007, 00:42   #34
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Quote:
Originally Posted by Steeroid View Post
You could also make a LONGER rounded tank so that you have less area to cover up with spare metal.

I just have to say this - you need a LONGER fuel tank. At least a longer-looking tank. You can weld stuff onto the existing tank and make it look longer than the actual tank is, so you dont have to rebuild a tank.

Think about it. Oboy - this is turning out to be a fantasy for all of us!
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Old 3rd October 2007, 14:32   #35
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Default Hi

Thanks Ananthkamat & Vabs78

What you people say makes sense.

But as per the suggestions by most people here, I will be using the Original Twin Shotguns.

But will certainly impement what you people say on the expansion Exhaust. Lets try that too. Theres no harm in trying.
Thats how one LEARNS.

@Steeroid - Thanks Will make the Tank look longer.
But my Heart still goes with the Boxy original Tank.
Anyways i will be painting both tanks & using one of them
as i wish as i can change it anytime.
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Old 3rd October 2007, 15:19   #36
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SHreeram was this bike reg in Mysore?
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Old 3rd October 2007, 17:52   #37
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Quote:
Originally Posted by lohithrao View Post
SHreeram was this bike reg in Mysore?
Why do you think so?. No It Was not.
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Old 3rd October 2007, 18:21   #38
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Quote:
Originally Posted by Shreeram View Post
Why do you think so?. No It Was not.
Hey cause the number plate read s as "MYM" so just took a wild guess

Anyway the bike is looking good and am sure it will look fab once completed.
i like the tank...keep it going
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Old 3rd October 2007, 19:27   #39
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just one request. Keep the technology new in it, but keep the look old school. the charm of old school is nostalgic.

off topic : this is my 427th post. heheheh

cheers.

Last edited by ac 427 : 3rd October 2007 at 19:28. Reason: addition.
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Old 3rd October 2007, 19:40   #40
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Quote:
Originally Posted by lohithrao View Post
SHreeram was this bike reg in Mysore?
AFAIK, the factory is/was in Mysore. God knows what happened to factory.. Looking at the way things are going, probably has some IT park !!
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Old 4th October 2007, 09:52   #41
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i agree with ac427,do retain the old world charm of the bike, pls dont try to make it look like a pulsar or any other new age bike,yezdi is a classic please do retain that.[just a request]
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Old 4th October 2007, 10:06   #42
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Quote:
Originally Posted by lohithrao View Post
Hey cause the number plate read s as "MYM" so just took a wild guess
Actually it must be MVM, very much a pune regn.

Nice going, Shreeram......got me curious even though I'm not much into bikes....eager to see what the finished product looks like!

This may be OT but I did have plans of having a lambrteta chopper once....
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Old 4th October 2007, 10:41   #43
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Default Hi

One person has made a lamby chopper. Heres the pic

@#2#
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Old 4th October 2007, 19:06   #44
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Another Yezdi lover !!

Sorry for hijacking your thread....but I have a Yezdi Roadking but the engine bore is out of shape and it's already at the maximum oversize, so reboring isnt an option.
I am looking for a new engine.... please let me know if you have any info.

I am from Bangalore.

And really nice work. I'll be following this thread closely
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Old 4th October 2007, 19:24   #45
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The Lamby chopper belongs in the Wild and Wacky thread!

Shreeram - great job at modding the Yezdi, do show us Punekars the finished product in the flesh!

Superavi
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