What rpm can you safely run at for a race engine?

[Joseph Upson]

I'd take a second look at the high volume pump, 20W50 and oil cooler combination. I believe 40 weight with a good oil cooler and stock pump should be more than sufficient with oil temps kept in the optimum range, I'd also be concerned about 70 psi oil pressure, as high pressure is more an indication of good restriction to oil flow than good lubrication. Pressure could be high with a low flow of oil across the bearings. I was one of the first to swap the 3.4L motor into a Fiero years ago starting with a core motor in good shape except for an unexplained spun bearing suggesting the RWD block may still have an oiling deficiency. Lubrication trends have changed over the years with more attention to fluid dynamics. Ford recommends 5W20 for many of their production cars for example and I'd be surprised to see pressures as high as 70 psi on a hot modern engine spinning near its rpm limit.

[Driver_10]

Not to jack this thread... But this brings up a question that I once asked a while ago without an answer. For a 3400/3500 thats seeing between 6-7000 rpms for extended periods, what would be a good ideal oil clearance? (this of course, assuming that your'e running a 40w and a good cooler as stated before).

[geoffinbc]

A good rule of thumb for engine bearings is .001 per inch of bearing. So a 2.5" bearing would have a .0025" clearance. Some engines require more. An Olds V8 for example with its flexy bottom end needs about .004" on all its mains in order to survive. NASCAR engines with there super stiff design run a clearance of .001 on all the bearings with thin 20 weight oil.

[Driver_10]

A good rule of thumb for engine bearings is .001 per inch of bearing. So a 2.5" bearing would have a .0025" clearance. Some engines require more. An Olds V8 for example with its flexy bottom end needs about .004" on all its mains in order to survive. NASCAR engines with there super stiff design run a clearance of .001 on all the bearings with thin 20 weight oil.

Thanks for the info. (thread jack now ended)

[NateD4]

I think it largely depends on how rigid the crank is and how rigid the main bearings are. Rules of thumb are ok... but they only work to a certain point. My advice... if you had issues with your engine at 7K... consider the oil you run, the viscosity and adjust the clearances as needed. If you we're running a 20 W oil try a 40 or 50 W. If you were running 40 or 50 try a lower viscosity. Or perhaps try bigger clearances next time around. Without doing a lot of engineering it'll be tough to pin point your issue and the right solution.

I'd say add another 0.0005" to the clearance next time around and run a 40W oil of some sort (10W-40 synthetic for example).....

I'll be contending with the same thing with my 3900 build. Except I'm aiming for 8500 RPM.