Ian C Posted March 31, 2012 Share Posted March 31, 2012 The thought crossed my mind, that we don't usually see dyno graphs showing outputs that low down the rev range, but I still wasn't convinced torque would dip. According to *pinch of salt* Wikipedia, this is the torque output for a BMW K1200R (motorbike), and very strange things happen with the torque curve(s!) low in the revs range. Very odd! That's just going to be because of tuning effects in the engine - the power outputs fluctuates due to intake/exhaust tuning effects and who knows what else. The wierd graph posted by the OP is mathematically correct, it just might have been generated by strange numbers reported by the dyno at such low revs. NOthing to worry about Quote Link to comment Share on other sites More sharing options...
SteveR Posted March 31, 2012 Share Posted March 31, 2012 (edited) That's just going to be because of tuning effects in the engine - the power outputs fluctuates due to intake/exhaust tuning effects and who knows what else. The wierd graph posted by the OP is mathematically correct, it just might have been generated by strange numbers reported by the dyno at such low revs. NOthing to worry about Coincidentally, I was reading something earlier about exhaust design and the affect on torque output of an engine. The article I read suggested that the common understanding that engine's 'need' some back pressure in order to perform at their best is nonsense (I never did understand that theory), but that the important thing is to have a system that promotes exhaust gases to be fast flowing, but low pressure (i.e. low back pressure) - which can mean not going too large a bore size as this would reduce the speed of the gas flow, and avoiding harsh pipe angles, restrictive silencers, etc as these would obviously increase the pressure). The idea is that the fast flowing exhaust gasses can help 'pull' the exhaust from the cylinders on that stroke, thus reducing the amount of power/momentum that is lost in order for the pistons to otherwise have to 'push' them out... I've no idea if that's right ether, but it was interesting to read. It sounds more plausible than the common understanding! Edited March 31, 2012 by SteveR (see edit history) Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted March 31, 2012 Share Posted March 31, 2012 I did a fair bit of reading on "the myth of exhaust back pressure" a while ago, interesting stuff, exhaust length shape and even taper can have quite substantial effects on how power and torque are delivered, but as said the predominate message was just that. Quote Link to comment Share on other sites More sharing options...
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