2-stroke Exhaust Fabrication
Over the past couple of years, the 2-stroke motorcycle has become increasingly popular again. Of course, for some this has always been the case. It is the 250cc to 500cc sized bikes that have seen a marked increase in second hand values. Hence, more people are now looking at restoring and tuning these bikes.
As a result, we see a number of customers come to us asking for producing copies of the standard expansion chambers, or bespoke sizing and fabrication of one-off pipes for a specific tune of engine. The most common request for bespoke pipes comes from the RD350LC engine variants. With the pleathora of bolt-on parts available mainly from the USA due to their fondness of Yamaha Banshee quad racing, a seemingly unlimited number of bore/stroke engine combinations are possible.
While many try an existing set of pipes for these engine combinations, we've only seen limited success. A far more effective approach is to use the engine specification to calculate the optimum dimensions for the exhaust chambers. We have now done many dozens of these, and the results have been exceptionally good.
One of the first in the UK to create a 535cc Banshee engined race bike was the 2-stroke tuner extraordinaire Stan Stephens. After several attempts of trying use US sourced Quad pipes, he came to us to produce one-off pipes. You can read more on that story here. Suffice it to say, that the results were good enough to get his bike banned from racing, and we now produce all his pipes for him.
Our 2-stroke exhaust fabrication services can be catergorised into the following stages:
- Reproducing an existing set of pipes
- Sizing of expansion chambers based on engine characteristics and subsequent fabrication to fit the bike
- Full engine simulation to identify improvements beyond just the exhausts
Reproducing an existing set of pipes
This is the simplest of services as it consists of essentially copy what is already there, or fabricating and fitting a set of pipes to customer supplied specification. Costs will vary depending on the complexity of pipe runs, but usually are about:
- £175-200 per pipe in mild steel, or
- £220-250 per pipe in stainless steel
Silencers are in addition and can be supplied in either carbon fibre or brushed aluminium sleeve. We usually require to have the bike in our workshops for this service.
Sizing of expansion chambers based on engine characteristics and subsequent fabrication to fit the bike
This is next step up and is particularly suited to people who have a tuned engine where no existing pipes provide adequate performance. In order for us to undertake this service, we either measure the pertinent engine parameters ourselves, or supply a worksheet for the customer to take his own measurement. This service is only supplied in conjunction with pipe fabrication as detailed above.
- The cost for this service is £250 per specification (usually one per bike)
Full engine simulation to identify improvements beyond just the exhausts
This is the most comprehensive service we provide for extracting the maximum performance from tuned 2-stroke engines. It involves obtaining an extensive data set from an engine, mainly by hand measurements. It goes far beyond the sizing of expansion chambers and creates a model of the engine from airbox to silencer. The resulting outcome can be any of the following examples:
- Increase inlet taper between carburettor and reed valve block by 1.5 degrees.
- Increase flow coeefficient of transfer ports by 12%.
- Lift exhaust ports by 2.4 mm.
- Decrease carburettor throat diameter by 3 mm.
This service provides for a nearly unlimited analysis of the entire engine and typically produces over a hundred torque/power curves for customer consideration. As an example, we employed this process during the tuning of our ER-6 engined 95Racer and produced over 200 torque/power curves just for the exhaust section.
- While the cost of this service is quoted on an individual basis, it is FAR cheaper than shaping metal. It simply wouldn't be possible.