Piston speed and RPM limit

[Mensan]

When calculating a rev limit using piston speed as my determining factor, what do I want the piston speed to be? This engine will most likely have forged rods/pistons with a cast iron crank. As far as I know, there is not a forged crank available that I can afford. Is 4500 out of the question? It will have a 3.9 inch stroke. TIA.

[Dave1647545494]

you need a bunch more measurements

 

like piston weight rod weight etc.

 

I went 7500rpm on a cast crank in my buick with a good balance

 

I have a cast crank in my 2.2 chrysler turbo too it sees 6000plus rpm on a daily basis

[Mensan]

Right, but piston speed will vary depending on stroke and RPM. The piston speed in engine "A" could be 4000 at 7500RPM, and in engine "B" it could be 6300 at 7500RPM. All I want to know in this thread is piston speed limit.

[SPLN SUX]

keep the average speed below 140mph and you should be fine if every thing is forged. Im running a 3.75 stroke and 7k isnt out of reach if i need it. Im running a 4 banger so theres a bit less weight to throw around but the physics is the same.

 

Your real concern should be your rod pressure angle. Keep your rods long and the piston waaaay up in the cylinder or youll build up an awful lot of heat real quick. If you need to, grind out slots in the base of the cylinderwall to provide a lil extra clearence for your rods... a rod kissing the cylinder wall at 6k wouldnt be too pretty.