Intake/exhaust valve diameter ratio on older OHV8s

[PackardV8]

Let's take as a given the old SBC 2.02/1.6 I/E valve diameter ratio of .792 is the norm/golden mean. It's a given a larger intake valve usually produces more high RPM power than a larger exhaust valve.

I work primarily with Studebaker and Packard V8 engines. The Studebaker V8 used a .92453 I/E ratio and the Packard V8 used a .84375 ratio.

Is it possible that in the bad old days, a larger exhaust valve was seen as a way to reduce pumping losses at relatively low RPMs and thus increase efficiency and fuel economy.

If not, what other reason might Studebaker engineers have had for such a large exhaust valve?

jack vines

 

[140Airpower]

Marquis and Pat, it appears fairly clear that exhaust flow optimization gains in importance with supercharging and turbocharging and that cam phasing should be different than for NA applications. Also, that efficiency could benefit greatly from VVT on-the-fly optimization under computer control in turbo setups.
Which brings up another question about exhaust flow. Early exhaust opening helps breathing, but costs expansion pressure and efficiency. When you consider the difference between mechanical vs turbo supercharging it appears this can be more of a help for a turbo, as stated, but does it hurt efficiency more or less in the turbo and how much does this effect contribute, if at all, to the reputed efficiency advantage of the turbo?

 

[thruthefence]

And going a little further back in time, we have this:

http://xroads.virginia.edu/~music/blues/tb.html

 

[KeithDyer]

I have a recent set of Big Block Chevy heads from MBE in the Charlotte / Mooresville area. Study up on them. These guys are some of the best in the High Performance head market.

Dart Iron Eagle castings, CNC ported (both ports and chambers). Intake valve size is 2.350" and exhaust diameter is 1.800".

We have found on different race car applications that if we hurt the exhaust flow in some fashion (valve size, rocker ratio, camshaft exhaust profile, etc.) or pick up intake flow using the same methods, overall performance would pick up. Methanol engines seemed to really respond to this treatment.

Not sure if it was due to keeping heat in the motor or filling or what, it just seemed to work well.

Take care, K

 

[Lou Scannon]

"We have found on different race car applications that if we hurt the exhaust flow in some fashion (valve size, rocker ratio, camshaft exhaust profile, etc.) or pick up intake flow using the same methods, overall performance would pick up. Methanol engines seemed to really respond to this treatment.

Not sure if it was due to keeping heat in the motor or filling or what, it just seemed to work well."

Supercharged?

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[140Airpower]

David Vizard's observation about intake vs exhaust flow was that a 25:1 ratio existed such that a 1" decrease in intake pressure drop would overcome up to a 25" increase in exhaust back pressure. I suspect that there is a range over which this is true and that this ration applies to high performance applications.