[A26B]

Todd,

I'm going to school here & havve a couple of questions.

Originally Posted by tpepmeie

In my opinion, valve size becomes the limiting factor (and with valve size goes port size, per my previous post). Using a stock stroke length, with the biggest valves known to fit in the LT5 chamber, the mean velocity at the valve head approaches 80 m/s at 8000 rpm. That is pretty inefficient, as even F1, etc. are typically 73-75 m/s.

If the LT5 has higher port velocity than the typical F1, then should cylinder fill be more efficient from the inertial ram effect.....or....is the velocity higher but total flow volume lower because of port restriction?

To achieve the real big rpms, you would need a more oversquare engine (shorter stroke:bigger bore) and intake valves around 34% of bore area. And ports to match, of course. That would allow more reasonable air velocity as revs increase.

I've read a number of articles regarding port size and it's a generally respected opinion that larger port size is not necessarily always a good thing. More Hp can be realized with higher port velocity in many cases, as a result of more efficient cylinder fill and a/f mixture. I'm assuming your comments are directed to the full-out, purpose built race engine which will operate nearly continuously in the top 20% of the rpm range.

Then, finally, I am told that the ladder-frame sump allows the crank to "walk" in its journals at higher RPMs. Perhaps that is solved with studding the bottom end, though.

Wasn't this an issue with the 375 Hp engine design that precipitated the 405 Hp bottom end design?

Jerry