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When I bought my original CT70 it came with a short homemade STE which I removed. I tried fitting it the other day to my clone bike, which is fitted with a Lifan 110cc engine. It sounds really nice and more like a 250 two stroke with the exhaust fitted. Am I going to mess up my engine leaving the pipe on there? It's made from a CT low level pipe I think, and is about 18" long, it terminates in line with the rear wheel about 4" ahead of it.
AFAIK prematurely burnt valves perhaps, engine will run hotter... also most exhaust systems are designed with a certain amount of back pressure inherent within the system/design, straight pipes negate that.
I have seen a lot of street legal bikes with very short straight through pipes, so I wonder if the builders have made any alterations to the engine components to increase their lifespan? I have now fitted a longer, larger diameter straight through pipe. It's a 28mm ID bore and around twice as long as the old home made one. The bike definitely accelerates faster through the gears but there is no increase in top speed. It's quite noisy and if you shut the throttle quickly it's pops quite a lot. I think I will stick with this exhaust for a while and see how I get on with it. I am thinking of fitting a 125 to the Lifan over winter so if the exhaust valve does burn out it won't be the end of the world.
The idea that straight through pipes somehow make a bike magically quicker is actually a myth. Scientific data shows that in some cases it is possible to gain a few more hp if the bikes fueling system is properly set-up, correct fuel map or correct jetting with a carb bike. However doing this will certainly rob your bike of torque which is in the real world what makes the bike accelerate on the road, and in fact your 'seat of the pants' feeling that your bike is now quicker is simply a psychological trick caused by more noise.Quote:
Originally Posted by trexuk
the pipe should be the correct length to reflect a negative pressure pulse back into the engine and help start the inlet charge moving. Because the engine revs are always changing this is usually accomplished by a tapered section so the negative pulse is spread over a wider range of revs. After the taper it doesn't really matter what the pipe does as long as it doesn't reduce to a size below the header diameter. But in the real world we should run it into a muffler so our neighbours don't hate us.When it comes to building exhausts one should
spend more time with a calculator than a hacksaw.
When it comes to building exhausts one should
spend more time with a calculator than a hacksaw.
from knurl on the aprilia forum
the exhaust pipe formulahere it is, been around for a long time
the formula;
Length= 850 x Exhaust opening [degrees bbdc+180]/rpm[power peak]
the Exhaust opening is effective opening ie; 0.040-0.050
Diameter, the pipe must hold, from the valve to the end of the head pipe twice the cylinder volume.