ENGINE TECH - MB Clubman x

We're not going to tell people how to make a Clubman Exhaust. Its not a secret, here's a insight to the amount of time and effort that has gone into the latest developments in Clubman designs by Mark Broadhurst.

One exhaust may suit an engine which doesn't suit another! This could be based around port timings, gearing or how someone rides their bike and other factors. Mark's been making Clubman style exhausts since the early 80's when his Standard exhausts and a very old 50mm Ancillotti Clubman kept cracking and because of this Mark wanted to know how to weld and fabricate as he was sick of asking work colleagues to weld this and that. And that's how he can weld, self taught through help with work colleague's. If you're going to learn - do it the hard way, learn on rusty bits and pieces of metal.

Anyway, its a long period of time to learn how Clubmans work or Big Boxes as they have become known since our MBgm Clubman was produced. These days Mark doesn't offer a Clubman hand made service as he's too busy. Mark has made hundreds of Clubman exhausts often getting mistaken for another certain person within Doncaster. But this is no problem. Marks always liked the wolf in sheep's clothing approach to all things Lambretta and engineering......... a fast impressive quiet bike over a noisy hard to ride peaky monster.

Years of making and trying slightly different Clubman designs lead to lots of dyno developments in 2010 to find the ultimate Clubman. This started by taking various Clubmans and comparing results. Days, weeks and months of testing and reworking these exhausts Mark learnt so much more about them. Even 2-10mm here and there can transform an engine. Mark tested everything, tailpipe lengths and diameters. Baffle designs, front cone and U bend lengths and diameters. When he first set out he totally expected to get the results required by making an expansion hidden by the standard box! The results we totally unexpected even though a multi tapered Clubman gave 28bhp on a TS1...! There's not much Mark doesn't know about these Big Box Clubmans - its a total science and different to all his Expansion knowledge that he has learn't through testing over the 30 year period.

Here's the start of many months and years of testing, the end result is the MBgm Broadie Big Box Clubman.

SIL Indian big bore exhaust, showing a small cone leading into the main exhaust box and a strange angled U bend which makes fitting the main exhaust difficult


The very popular AF or KBA Indian Clubman, although not a bad Clubman and good as a budget pipe it is not the best on the market. The Indian big bore can show a better power spread and is much quieter

This is the Italian Casa Clubman with a really wide stubby cone, this are known to fall apart


This is a AF / KBA Clubman, these are made by the same firm KBA Auto's. AF Clubmans are made exclusively for AF and the company then floods the Uk with their version.... Exclusively! Right. This is a version we modified at the front and inside to improve this version


We have modified all types of Clubmans this is the Italian Sito version, providing all the modifications are done correctly they all work.... within reason


You can use any standard 150 type box and convert it to a Clubman. We have used Indian, Sito, Casa and any others that comes along


The Italian Sito Clubman is very popular, sometimes a pig to fit and as with lots of Standard style exhausts may need some persuading! This exhaust gives a high peak power of 7500rpm + and a low torque figure. Its ok, better than the AF KBA version but the torque drops so quick it makes pulling 4th gear hard especially if you over gear it. This ones had some internal mods tested


Here's a fact, the best power comes from a gutless exhaust body.... but the noise is beyond a joke so to reduce it, we tried lots of ideas. This silencer is really complicated, its hidden under the bike and is not visible! Does it work?


As part of finding ways to reduce noise we tried lots of ideas, at the end of the day it needs to be simple, reliable and fit, not like this. This one had lots of boxes added onto the side to test area and volume


We originally started life with multi tapered down pipes using our Expansion chamber knowledge, which we expected to develop an exhaust crushed into the box, we even made expansions the correct size to fit in the space, but moved on


This shows the amount of times we have cut and modified the internals just on this one pipe


These are just some of the pipes we tested over a 3 month period........ no one can tell us how to make an Clubman exhaust but we could tell you. Without the testing, development and experience, all you can do is try, try and try again and keep trying, without time and a dyno you could not learn what we have done. Whatever you do will always be a compromise somewhere! and we know that as well.




We've explained it's swings and round abouts with Big Box Clubmans and a lot depends on port timings, shapes and sizes, compression ratios and carb sizes. Some Clubmans like the KBA/AF Clubman gives a real nice low down power ideal for an engine working around town and cities, put on a bike on the open road and the power uns out of steam. Others like the Sito Plus has less power low down but gives higher revs, it revs but the torque drops as the revs go up so the bike is fine in most conditions but add some weight, wind or a hill and it looses power. The upshot was Mark has a found a design that is quiet and works like no other exhaust. Our MBgm Big Box Clubman is designed to give a nice wide spread of power to work on as many unknown engines as it is fitted to. This spread can be improved if the port timings are corrected and you can make a nice engine even better. Done correctly you can give a flat topped torque curve giving revs and torque at the same time......... That was until others read this article and over time have taken our Clubman and developed their own one off designs. But it is always swings and rounds abouts, these expansion type exhausts only really work on high exhaust ports therefore loosing that all important low down rideable power spread that our MBgm Clubmans are designed for. 





And there it is........ hundreds of hours of development, and 30 years of experience making Clubmans 

If you have a question ask Mark mark@mbscooters.co.uk