Pacific Muscle Cars

I have read a lot about exhaust flow with aftermarket valves vs. stock valves. The prevailing thought is that the stock 1.55" valve flows better than the aftermarket pieces because of the back cut angle. What about the intake valve? Is there any flow advantage to an aftermarket 2.00" or 2.02" valve, or is the stock intake valve also superior due to the back cut angle?

Also, what is the RPM limit of the stock valves in a naturally aspirated application?

Thanks!

ROGERSPERF.

The rpm range depends on the weight of the valve and valve train as far as what flows better agian it has to do with valve margin and back cuts the more air you can get thru a port with out increasing valve size is a much better deal.Volicity is what you are after.

Pacific Muscle Cars

I understand the goal of velocity, but I'm inquiring specifically about the comparison between intake valves. Let's assume we're talking about a stock head with stock valves vs. Manley. I have seen data supporting that a stock exhaust valve flows better than Manley because of the angle. Is the same true for the intake? If so, does increasing to a 2.02 Manley show any improvement in flow over the stock valve?

As for the RPM limit, I am interested in hearing how hard people have reliabliy pushed the stock valves. The reason for the question is because I'm trying to weigh my options. I'm installing a large cam that will require high RPM shifts. I am willing to sacrifice some flow for reliability, but only if it's absolutely necessary.

ROGERSPERF.

If you compare two valves of the same dia but had diffrent back angles yes it is possible one valve would flow better then the other but since you are comparing 2.020 to the factory 2.00 it would flow more just do to the size increase but you may not increase in flow at upper lifts do to valve shroulding or not enough port to supply valve opening.I would have no way of being able to tell you if the stock valve would live at say 7500 rpm for any lengith of time.By putting a back cut of any kind on the ex. valve would increase flow but it will also increase ex. reversion witch is not good.ex. gasses coming back into the chamber.



mike