custom made expansion chamber makers

[stirlinggaz]

hi,
im looking for recommendations for someone to build me a custom made expansion chamber for a project im working on.
its nothing too complicated, just a little single cylinder 180cc 2 stroke engine combined with a dellorto vhsb 34mm carb or maybe something bigger...
theres nothing available ready made, that would be suitable, apart from the usual 125cc exhausts which would just restrict it.
its not for racing so it would need a useable power-band & be capable of making peak power at around 12500rpm but still be useable below 7000rpm.
would this be prohibitively expensive? even in mild steel, without an end can? (I have a few that could just be welded/bolted on.
I know there are programmes/guides out there that can assist in designing them yourself but I think that might be outwith my skill-set. (im willing to look into this though)

anyone actually done anything like this & can point me in the right direction?

cheers,
GAZ

[chris-red]

These guys near me still do.

https://gibsonexhausts.co.uk/page_8.php?pgenme=2stroke

I've never used them mind.
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[P.addy]

Wouldn't a 200cc enduro exhaust suit the "needs" to a degree. As in it won't restrict it but still gives you something to work with.

[stirlinggaz]

[stevo as b4]

Hi Gaz.

Paddy is thinking the right way IMO, but if it's not just to get a motor running in a bike cheaply, then while cutting and shutting a 200cc bike's exhaust to fit the new engine/bike/vehicle should get you closer to what you need than a 125cc pipe will, it's worth spending more on a custom pipe to get the most out of a non std motor/bike build if it's feasible?

I'm having a 125cc pipe made up in a months time for a KMX 125. I'm led to believe it will cost in the £300-350 region, for my application, but with any decent custom job your paying for the time and expertise in measuring, calculating and educated guess work from experience, much more so than the price of the materials and labour to fabricate it IMO.

Oh and what engine is it, curiousness needs satisfying!

[Suntan Sid]

Honda MTX200R

https://www.motorcyclespecs.co.za/Gallery%20B/Honda%20MTX%20200R%2083.jpg
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[Iain.]

Why not use the factory expansion chamber and re-package it as per the motocross engine RS50 conversions?

https://www.apriliaforum.com/micahupload/Apriliasaki%20Upload/BuildingPicsTop.jpg

https://www.apriliaforum.com/forums/attachment.php?attachmentid=81192&stc=1&d=1207240431

[bladerunner]

Mick abbey is worth talking to. He tunes and makes pipes to suit the bike. 12.5k peak power is pretty high up the range to be pulling well from 7k if your after sporty levels of hp
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[stirlinggaz]

[UnknownStuntm...]

[Suntan Sid]

Before you attack the MTX spanny, is there an easy, non destructive, method of fitting it on the engine and seeing what's what?
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[stirlinggaz]

[Kickstart]

Hi

Expansion chamber design is a real black art, and far more to it that just down to matching engine capacity. Needs to be designed for port timing, etc.

How well designed is the porting on the BBK? Which BBK was it that Performance Bike used in the article (about 20 years ago) on playing with the NS125?

All the best

K
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[stevo as b4]

I wouldn't cut up an MTX 200 pipe.

So rare, and sellable on Ebay too. Even then id want to measure all the dimensions so I'd have something to base another MTX200 pipe on or pass on the details to other MTX owners trying in desperation to get exhausts for their MTX's.

If the guy doing the custom pipe makes it for your engine (with big bore kit) and for your chassis or something very similar, then buy it at that price, it's a steal especially if it's been dyno tested/developed.

My pipe will be more than that, but I'm going stainless (thanks to Knacker and his DT125RE with the sexy shiny pipe).

Matching pipes from cc to other engines is of course very simplistic, but it does seem to always be the case that bigger engines/cylinders need more volume in the pipe than they did as a 125cc engine.

Look at all the Aprilia RS125 owners that complain of poor top end performance when fitting the 150/160? big bore kits. If Polini or whoever makes the kit supplied a pipe with it specifically for the conversion, I bet the results and power gains achieved would be far more pleasing. As it stands the forums are nearly all against bigger cylinder conversions and regard them as backwards step.

[stirlinggaz]

[stevo as b4]

Don't forget Moar pics either!