What is a safe RPM limit for 66 x 96 1911

[Lo Cash John]

Looking for experience and maybe opinions here.

I'm helping a buddy build a 66 x 96, 1911 cc engine. It began life as a 1.8 from a Porsche 914 and now has moderate cam, mildly worked heads with dual springs, chromoly pushrods, blah, blah, blah. Rods are stone stock and the cooling fan is stone stock. Pistons are KB from European MotorWorks and I don't know the weight off the top of my head.

Is this combo safe to 6200RPM without the stock rod bolts letting go or the fan scattering?

Thoughts?

[twodollardoug]

That's a great question. After your question gets answered I would like to know how is the rev limit determined on any high performance type 4 engine. Is it valve float? Where hp drops off on the dyno? I can't imagine it's trial and error.

[Lo Cash John]

That's a great question. After your question gets answered I would like to know how is the rev limit determined on any high performance type 4 engine. Is it valve float? Where hp drops off on the dyno? I can't imagine it's trial and error.

There's no point revving the motor past the point of maximum power so that's a very important thing to know. I expect this motor to make power up to 6000 based on cam and head work. It has enough valve spring pressure to control the valves so my next concern is the rods and/or rod bolts.

[Clatter]

Rod bolts are supposedly next.
50-year-old stock bolts?
Heavy rods like ARP bolts.
Never really explored the limits with stock bolts, but can say with the ARP bolts they will tolerate short bursts to 6500 at least a few times.
How well the lower end is balanced might play a role as well.
Factory redline was 5600, IIRC?
Heavy pistons might not be helping.