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Funduro air filtors

6K views 15 replies 9 participants last post by  BrickMan 
#1 ·
Hello folks,want to bin the standard air box and put on some single filters,anyone else done this and what sort did you use.
Jon
 
#5 · (Edited)
WHY because I had a mighty back fire which set fire to the foam filter which melted the airbox,also I'm probably gonna built a bigbore engine so the stock jetting ain't gonna work,also I ride offroad so single filters will make it easier to get the carbs off if I need too and yes because I can.
Jon
 
#13 ·
Hello chaps, I've just joined. Like the chap above I want to fit some pod filters to my funduro, can anyone give me a supplier and recommend which type is the best ? Also will I need to mess with the jets etc. I'm not useless with a spanner but when things go away from the norm I get a bit lost. Any help will be most welcome.
 
#14 ·
Aha, the airbox

Earleir Pegasso version that used this engine made a further 5hp, with some different parts. The BMW airbox is huge, to keep down the inlet noise. It takes up a lot of space to balance the spaced pulses from the engine. If you have a dyno, you could measure sucessive changes to as they are made. otherwise you have no way of knowing if it makes more or less power. it would be louder no doubt, but may have nasty peaks/troughs in the power curve. -without a dyno, the noise might make you think it is more powerfull.

A new BMW airbox to replace the burnt one would be tricky to fit too.
If you do fit two can-shaped filters, I would think, as large as possible would be better, very firmly fitted, with perhaps metal gause to prevent them being sucked into the engine!. and some protection form water ingress.
You could fit the BMW airbox, to give water protection, and put two large can-type filters inside. then open up some bigger hloes at the back of the airbox.
 
#15 ·
Earleir Pegasso version that used this engine made a further 5hp, with some different parts.
My undersatnding wasthat the original Aprilla engines /Pegasso had 5 valve heads, when BMW took basic design they put an extra spark plug inplace of one of valves. When design went from carbs to injection, single spark versions had decomprssion valve inplace of one of spark plugs, twin spark versions did away with this or ina diferent form on existing valves?
Believe original versions had roller bearing big end, bmw changed to shell? These changes(improvements?) also gave added reliability and longer life engines, why these versions great for round world trips, clocking up 100,000 miles without major over haul if serviced ok. Seen articles that Aprilla engines need major attention after 40K-50K ?
More knowledgable out there will put me right please
 
#16 ·
Yes airbox/inlet plenum design is very considered on a variety of engines, but especially larger singles where the pulses are significant.

I worked on a formula student development of the Suzuki 610cc big single, stock I think peak power was around 45hp? With aftermarket injection, light head work, exhaust work, uprated valves (originals approaching end of life anyway), springs it produced around 70/75hp, however in the vehicle it was almost undriveable. Huge throttle lag, ECU really struggling to hold a workable AFR and power band came in too severely and too narrow for much use. Ended up spending most of our R&D time and dyno time playing with inlet manifolds, injector configurations but most of all, developing a huge plenum. The chosen design was something like 25 litre capacity with internal baffles, all made from carbon. Peak power remained the same, but torque was up dramatically, especially in the lower rev range and driveability was very good.
 
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