Suction & Friction Losses, Engine Performance V Speed

Here You Go John,



Eddie

Thanks Eddie!

I looked at my `Sent´ copy of the e-Mail and it was a mess, too large and twice itself plus a pic I´d thought I´d deleted -- you must have done quite a bit of editting, Eddie.

Right name for the job -- Eddie the Editor! well done that man!!

Pity the top diagram was only up to 4500rpm -- in the bottom graphs the Losses Curve can be seen to loop up really viciously to meet the drooping Suction-Loss curve at maximum No-Load speed.

These are realistic curves for an engine without reed-valve and resonant exhaust. The torque and bmep are typically flatter than the curve above `e.h.p.´ but similar in shape in that both rise with increasing engine speed to a maximum of bmep & torque and then droop off with the increase of speed. The object of the auto engineer is to design the transmision to have a `cruising speed´ at that best bmep & torque speed to obtain optimum specific fuel consumption... With racing engines it is to have that maximum occuring where it gives the maximum acceleration -- relative the gear ratios available, of course.

The dream of the auto engineer is to produce a flat torque curve.

The upper diagram shows that A, the bearing friction increases as a straight line -- so what bad bearing friction you have at 1,000rpm only gets worse at 11,000rpm proportionately -- whereas B, the induction losses increase at an exponential rate with speed -- so the faster the engine revs the much-worse become the losses attributable to gas flow -- and worst of all come C, the piston & ring(s) friction losses which increase at roughly the square (v²) of the engine speed.
Merckle, `Air-Cooled Auto Engines´ gives the percentage of Losses attributable to piston&rings as 57% of Total Losses...

.. but of course, he is not talking of a single ring Bantam...

I still think a lot can be done in this area....

Fact is, most Bantams are unique -- relative any other form of racing vehicle. That is, in relation to the useable torque. It is well above 7 -- 8,000rpm. The gain in performance seems more -- these days -- reducing the Losses by as much as possible even if those reductions look ridiculously ed piston small.

Cheers!

Christmas PS to newcomers -- re the bullshine diagrams above -- in the upper diagram:- get all three right and you might win a race....?