From David Reher (of Reher-Morrison).

The most important characteristic in a cylinder head is the ratio of the throat size to the valve size. That’s never mentioned in ads and articles that focus on flow numbers, and it’s not even considered in engine simulation programs. The fact that a port moves a certain amount of dry air in a steady-state flow bench test has only a tenuous connection to real world operating conditions. In a running engine, the flow is constantly in a dynamic state as the valves open and close and the piston rises and falls. The fact that a port flows X cfm at a predetermined depression has little relevance; the true test is whether the port develops a signal quickly in real time as engine rpm increases. And that can’t be measured on any flow bench.

A software program may calculate that an engine needs bigger valves, and the flow bench might confirm that larger valves indeed produce more airflow – but the engine may not care. In fact, it might not even accelerate as well as it did with small valves. Why? Because stuffing bigger valves into a cylinder can pinch off the airflow between the valve heads and the cylinder walls. The valve sizes must be in proportion to the bore diameter. Increasing the diameter of the valve 10 percent to pick up a 5 percent increase in airflow is never a good bargain.

Like I said, you can have a valve that is too big.

Rich

 

True enough, nice quote. I'm just curious if 2.10" is really beyond that threshold of dimishing returns or if it's just close enough (and costly enough due to the required seat replacement) that no one bothers.

I'd never consider a 2.10" in the stock seats, but with larger seats, an aggressive cam profile, and some chamber porting I wonder where the threshold really is.

Interesting.

 

In a stock casting,don't believe the CSA of the port and the size of the throat are large enough to support a 2.100 valve.
Ya can put 'um in but ya are throwing your money away 'cause the would probably hurt more than help.
A 2.0/2.02 valve in a stock casting can be made to flow over 300CFM and that's 'bout 600FWHP.
Need more? Bring your checkbook.

 

Do you realize that the aftermarket castings usually only get 2.080 valves?

One vendor has several car up in the 500rwhp range NA couple are through unlocked automatics, with 2.00/1.56 valves in GM castings. I think people are way too fast to jump on the "bigger is better" bandwagon for almost everything.

 

easy guys... I never said it was smart bang-for the buck investment. Sometimes poeple are willing to accept very small gains for large investments in time/money. I was just curious if anyone has some numbers to put difinitive limits on this relationship in LT1's.

Is 2.10" in the area of "diminishing returns" (as in still shows a small gain), or is it past that point and actually "detrimental" to performance.

Just curious if anyone knows for sure (I'm sure SOMEONE out there has played with this enough to know).

 

Yea,that BIG of a valve hurts performance in a stock casting. Ask any big time builder. Refer back to earlier posts as to the max per bore size and imagine the CSA and throat size it will take to support the valve. The CSA is large(2.5+) That is also getting into MAX effort/flow areas for a given CSA/port size on a trailer queen.