increasing flow with chevy valves steem size

[Nacho-RT74]

a chevy guy ( and friend ) told me one trick to increase flow on my heads... use the chevy size steem ( adding valve guides on heads ) and will increase some flow... ( dunno remmeber the chevy steem size he told me... 5/16 I think )

worths the effort/spend ? does exist 2.08 and 1.74 chevy valves AND with same Mopar length

[BrianShaughnessy]

Edelbrock heads already come with 5/16 chevy stem valves standard.

Not sure about the stealth / 440source but I'd assume so.

[aifilaw]

Edelbrock heads already come with 5/16 chevy stem valves standard.

Not sure about the stealth / 440source but I'd assume so.

checked, they are 11/32

[firefighter3931]

Fwiw, the Eddy heads use an 11/32 valvestem which of course is slightly thinner than the stock 3/8 diameter. That being said, upgrading to thinner valves is not the most cost effective way to increased cylinder head flow. 

Stock 452/346 castings respond very well to a simple bowl port.....easy 25-30 cfm increase and 50hp bump in power. This is with stock valves as well. 


Ron

[Nacho-RT74]

ok, GREAT, thanks Ron... as usual

thats what I thought...

[BrianShaughnessy]

Edelbrock heads already come with 5/16 chevy stem valves standard.

Not sure about the stealth / 440source but I'd assume so.

checked, they are 11/32

I stand corrected.    I know they were Chevy sized, but temporarily forgot what Chevy size is.  It only makes sense for Edelbrock to use Chevy valves due to the economics of the whole situation.     

 
A friend of mine wrenches on some little british motors for a race team that runs places like Lime Rock, etc.    One of his trcks is to use the thinnest valves available.    He went on and on about how the little motors turn ridiculous rpms and the power they make but everything has  a trade-off. 

[Ghoste]

Which brings up another good point.  If the valve size isn't having a huge impact on port flow, what about it's effect on rpm ability and valvetrain harmonics and so forth?

[b5blue]

Good to hear from Ron about this! Bowl job is planned for my 346's end of next year (part of phase 2  )

[Nacho-RT74]

Which brings up another good point.  If the valve size isn't having a huge impact on port flow, what about it's effect on rpm ability and valvetrain harmonics and so forth?

[b5blue]

Hey wile we are at it what about swirl polishing them?

[aifilaw]

Wow, too many topics for one thread.

Valve size reduces the restricted area in the port, yes. But overall port shape has a far greater impact. A valvetrain with the least amount of friction is obviously the best at making power. and reducing the friction is gone about in a variety of ways. Little engines making little power (and larger now due to material enhancements) eliminate a lot by going to single-overhead and dual overheat cam designs linked to the crank through a chain. Still more have skipped the entire process and gone to solenoid controlled valves making the timing completely computer controlled throughout the RPM range. But this is all pointless to our application because we have push-rod motors, unless someone decides to go off the deep end and start making geared overhead cams for us, et cetera. I'm on my lunch break, so if the question of what's best to reduce friction a long valve stem in a long valve guide, and a wide diameter guide/stem vs. a small guide/stem hasn't been answered I'll waste time on that.

The easier question is polishing; Exhaust ports is a no-brainer, always a good decision, always time well-spent, the faster and cleaner you can get the exhaust gas out the more power you will make and efficiency you will have. It is also important to remember that, if you have ever looked at an exhaust port, it gets caked with carbon very quickly, teflon coating has had some results.
The intake is a harder question to answer, because with a perfectly smooth, or imperfectly smooth intake port fuel and air as it goes past the walls of the port will have the tendency to seperate. The term for this escapes me, but take an air compressor with a blow-tip and stick it into a plastic tube and just vent it for a while after the compressor has been fully charged on a humid day. You will notice alone the walls of the tube little eddies of water appear and streak in the direction of the output. This will happen with your A/F, except at a much higher rate because of the 14:1 ratio and the fact that air does not naturally contain fuel, they will attempt to separate. In certain scenario's completely defined by the cam geometry, heads, bore, stroke, et cetera, polishing the intake port can be good. But generally having a somewhat rough intake port will actually help as a slight turbulent flow will help further atomize the mixture on its way into the cylinder for combustion.

[firefighter3931]

Which brings up another good point.  If the valve size isn't having a huge impact on port flow, what about it's effect on rpm ability and valvetrain harmonics and so forth?

Larger valves will increase flow as long as the cylinder head bowl and port is properly sized/shaped. Traditionally, Mopar BB head castings have smallish bowl dimensions relative to the valve diameter. That is where the old Direct Connection porting templates came in. The templates were designed to enlarge the bowl just enough to work well with the stock valve sizes. The bowl should be no more than 90% of the valve diameter. The last thing you want to do is make the bowls too big because this will hurt low/mid lift flow numbers and actually reduce power....a step in the wrong direction.

Obviously, using a larger diameter valve will create more weight in the valvetrain....larger valves are heavier than smaller ones. Generally it's a non issue as long as the valvesprings are properly matched to the cam profile and installed correctly.


Ron

[Purple440]

So without doing any bowl/port work, increasing the valves sizes simply adds weight?

[firefighter3931]

So without doing any bowl/port work, increasing the valves sizes simply adds weight?

Exactly ! 



Ron