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A Question for two stroke people

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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 08:17 - 12 Mar 2010    Post subject: A Question for two stroke people Reply with quote
Hello,

I remember recently that I stumbled across the site of a company (I think it was UK based, but it might not have been) who custom build expansion chambers for your two stroke bike. They claimed to use computer aided design to match the spanny shape with your engine. Has anybody got a link to it?

The reason I ask is that all of the reasonably well known spanny manufacturers just make copies of old designs and don't design new exhausts from scratch. I'm told that both Lomas and Nikkon use old kit pipe designs (which won't be matched to the tune on your bike) and Gibson/Allspeed just use ancient allspeed designs which appear to have been developed by trial and error rather than maths.

Any ideas?
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Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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MaybeGuy
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Joined: 12 Mar 2007
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PostPosted: 08:41 - 12 Mar 2010    Post subject: Reply with quote
sounds like a gimmick to me.
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!! Mr. Green
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 08:47 - 12 Mar 2010    Post subject: Reply with quote
mattsprattuk wrote:
sounds like a gimmick to me.


Well to some extent it does, yes but also what they say makes a lot of sense. Why would a set of Allspeeds work with every possible iteration of porting, port timing, bore, stroke, ignition timing and jetting?
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Kai.Wilson
Spanner Monkey



Joined: 26 Sep 2009
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PostPosted: 08:56 - 12 Mar 2010    Post subject: Reply with quote
Expansion chamber...Boost Bottles

They don't work on 2stroke with a reed valve...The reed petals stop the extra fuel Wink

Kai
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Kai.Wilson
Spanner Monkey



Joined: 26 Sep 2009
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PostPosted: 09:07 - 12 Mar 2010    Post subject: Reply with quote
They are for rotary disc valve induction 2strokes.

Sorry meant to add that

Kai
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 09:24 - 12 Mar 2010    Post subject: Reply with quote
phantomkai wrote:
Expansion chamber...Boost Bottles

They don't work on 2stroke with a reed valve...The reed petals stop the extra fuel Wink

Kai


Apologies for being harsh but...

You're talking bollocks. You clearly don't know what you're talking about. A boost bottle is very different to an expansion chamber. Please don't contribute to a thread unless you know what you're talking about.

An expansion chamber is the bulge part of the exhaust which helps to scavenge gasses from the exhaust port. Their shape and length basically defines the characteristics of the engine, but they have to be mapped to the shape and size of the exhaust port and to some extent the inlet ports. Gavin (on this forum and the RD forum) has run a back to back dyno test of Jim Lomas, Nikkon and Allspeed exhausts on a standard valve, and he found for example that Nikkon exhausts gave the best power, but not enough torque for the bike to rev out in top gear. This meant a gearing change was required to get the best from the engine.

Stan Stephens has told me that he thinks Allspeeds are the best match out of the three for my engine (as he tuned it) but I was just idly speculating about getting something made. I probably won't do it, and I'll probably end up getting Allspeeds but I'm interested to read their site and see what they say.

A boost bottle is similar to an expansion chamber in the sense that its size and shape helps to determine the flow of gasses into the inlet port. But, as you say with reed valve induction this is pretty irrelevant. But a Boost Bottle and an Expansion chamber are quite different, so I'd prefer it if you didn't just spout nonsense you've read on a scooter forum.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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MaybeGuy
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Joined: 12 Mar 2007
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PostPosted: 09:39 - 12 Mar 2010    Post subject: Reply with quote
i always thought the exhaust was down to displacement per cylinder, then from there its how you want the power delivery.
Shorter spannies are peaky at high revs and vice versa.
I doubt that company do anything more than just have a cad drawing for reference
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!! Mr. Green
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 09:48 - 12 Mar 2010    Post subject: Reply with quote
mattsprattuk wrote:
i always thought the exhaust was down to displacement per cylinder, then from there its how you want the power delivery.
Shorter spannies are peaky at high revs and vice versa.
I doubt that company do anything more than just have a cad drawing for reference


I don't think its quite as simple as that. Length is important yes but the gradient of the cones and angle of joins etc also makes a lot of difference.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 09:57 - 12 Mar 2010    Post subject: Reply with quote
Hi

I tend to agree with Matt.

From articles many years ago on 2 squeak expansion chamber I think the maths was just the start. Then it comes down to some trial and error, especially once trying to get the design to fit the bike without too many problems.

Did find this:-

https://www.buildandclick.com/html/more_info.html

Might be interesting to have a play with.

All the best

Keith
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 10:03 - 12 Mar 2010    Post subject: Reply with quote
Kickstart wrote:

From articles many years ago on 2 squeak expansion chamber I think the maths was just the start. Then it comes down to some trial and error, especially once trying to get the design to fit the bike without too many problems.


As I recall they need your bike in their workshop and they use a dyno and some clever software to measure loads of stuff. They were saying that they have eliminated much of the trial and error. I'm sure I didn't imagine it...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 10:28 - 12 Mar 2010    Post subject: Reply with quote
BLUEX5 wrote:
In the past I've heard of a simillar service, although I assume it wouldn't be cheap. I can't see any perceived gains would be useful on the average roadbike.


I'm not really thinking of doing it, I just wanted to look at their site, and I've lost the URL...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Robby
Dirty Old Man



Joined: 16 May 2002
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PostPosted: 10:36 - 12 Mar 2010    Post subject: Reply with quote
From memory, a few years ago there was an article in one of the bike mags (Keith will probably twig and go and fetch it from the loft, at a guess ~2005ish and RiDE or any year and mechanics) where a guy made his own expansion chambers for a mental 2 stroke for the same reasons as you. He worked out the maths and made them himself, but I think he was a maths related PhD kind of guy.

The only custom exhaust place advertising in mechanics is Gibson.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 10:42 - 12 Mar 2010    Post subject: Reply with quote
Robby wrote:
From memory, a few years ago there was an article in one of the bike mags (Keith will probably twig and go and fetch it from the loft, at a guess ~2005ish and RiDE or any year and mechanics) where a guy made his own expansion chambers for a mental 2 stroke for the same reasons as you. He worked out the maths and made them himself, but I think he was a maths related PhD kind of guy.

The only custom exhaust place advertising in mechanics is Gibson.


Sod it, I'm just going to buy some Gibson Allspeeds.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 10:57 - 12 Mar 2010    Post subject: Reply with quote
Hi

No idea on the quality now but would hope it is the same, but the old Allspeeds were well made and lasted well. And on the MBX125 I had they worked well as well.

I know there are a few people around who will make custom 2 stroke exhausts, but think most want a pattern (ie, Rotax can give you drawings of the critical dimensions for their engines from which an exhaust can be made).

All the best

Keith
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Spit-Fire
World Chat Champion



Joined: 24 Jun 2008
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PostPosted: 12:33 - 12 Mar 2010    Post subject: Reply with quote
hey may jay don't know if this help.

but the is a scooter sprint team by the name of team dwarf racing (record holders)

who are in the process at the moment of releasing there own range of scooter exhaust.

from what i remember they have done one off's in the past and they use some form of computer software for the math side of things like you mentioned.

could give them a shout,
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 12:34 - 12 Mar 2010    Post subject: Reply with quote
sPiTfYa wrote:
hey may jay don't know if this help.

but the is a scooter sprint team by the name of team dwarf racing (record holders)

who are in the process at the moment of releasing there own range of scooter exhaust.

from what i remember they have done one off's in the past and they use some form of computer software for the math side of things like you mentioned.

could give them a shout,


I was looking for a specific company. As I said I'm not really trying to get an exhaust made, I just wanted to read their website. It actually comes from a post in the workshop asking if Nikkon exhausts are any good...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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