<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:<hr /><font size="1" face="Verdana, Helvetica, sans-serif"><strong>Anyone have any thoughts on the cheap bhp booster advertised on ebay - 10-15bhp for less than £50 - sounds too good. Is it an air intake mixer or something. Would appreciate any thoughts.</strong><hr /></blockquote><font size="1" face="Verdana, Helvetica, sans-serif">The cheap eBay bhp booster is actually a 5p resistor plus instructions. You fit it between the Air Flow Meter (AFM) and the Engine Management Unit (ECU). This changes the value sent back to the ECU and makes it think that the engine is pulling in cooler and denser air, it adjusts the fuelling (i.e. increases it) to match this false reading. The mixture is richened slightly and you'll get more power at the expense of fuel economy. I doubt you'll get anywhere near 10bhp extra and the running of the engine may be compromised in certain climates (extremes of temperature in either direction). It is a very crude form of chipping without the associated timing and rev-limiter changes that you get with a proper chip.
My advice, save your money and go to your local electronic component shop, buy a variable resistor and put that in instead. Then you'll have a tunable system for even less money!
In all seriousness though, it's definetly not worth it and the increases that it claims would be easily attainable by cleaning your AFM mesh (with carb cleaner), swapping in a decent cone air filter and checking the throttle body butterfly alignment to ensure that WOT really is wide open.