connecting rod strength
connecting rod strength
(OP)
I understand that as pistons reach top dead center, their inertia is trying to pull them through the top of the combustion chamber. At that point, the rods and rod bolts are the only things keeping this from happening. At some point, there is a speed at which the inertia of the piston is enough to break either the connecting rod, or the rod bolts. What I want to know is whether or not higher compression ratios (or higher boost levels in forced induction engines) will decrease inertial loads exerted on the rods and rod bolts allowing the engine to turn higher rpms before the rods let go. If so, how much of an increase in engine speed can be expected for each full point that compression is raised?





RE: connecting rod strength
Rod
RE: connecting rod strength
This cushioning effect might be for real, but remember that at TDC it is mostly combustion pressure, not just the compressed intake charge, so CR is really a secondary consideration. If the original poster wants to claculate this out then he needs to work out the piston acceleration (ivymike has posted on how to do this), and then find out the interaction between cylinder pressure and piston acceleration, and some cylinder pressure diagrams at different CRs.
This doesn't get around evelrod's point - at some time in an engine's life you have to back off the throttle and then this small cushioning effect will evaporate, shortly followed by your engine.
Cheers
Greg Locock
RE: connecting rod strength
A description of the type of work I have done can be found here
http://www.fea-uk.co.uk/connecti.htm
RE: connecting rod strength
Inertial forces are a factor of speed and mass, so either lighten the reciprocating mass or slow it down... neither lend themselves to speed, power or reliability.
RE: connecting rod strength
RE: connecting rod strength
Inertial forces are a factor of speed and mass, so either lighten the reciprocating mass (poor reliability, due to the nature of the weaker design by having less material available to structurally support the load that is being distributed over the surface of the piston) OR slow it down (poor power, due to the design of the internal combustion engines need to have more cycles per unit of time to create power - made evident at the extreme amounts of hp in high revving engines, found typically in motorcycles and the like)
RE: connecting rod strength
RE: connecting rod strength
With a max effort at reducing reciprocating weight, grind and bevel the crank counterweights and change to the lightest, strongest flywheel clutch assembly you can buy.
Lotta work!!!but your engine will rev faster and decelerate faster. Along with cam and top end work, this is a basic formula for building just about any performance engine. It is often cheaper in the long run to BUY custom made parts for a performance engine. Take your choice.
Rod
RE: connecting rod strength