Joe, what will it take to get 207 cfm on the intake/w 1.94 valves @ .450 and 155 cfm on the exhaust/w 1.54 valves @ .450? How much can be taken off the heads without shrouding the valves? At what lift is notching the cylinders required? Thanks.
 I looked at Mummert's "Street Port" numbers; intake meets/exceeds my goal, but exhaust less than 75% of intake flow. He did get 169 cfm exhaust flow with "Performance Port," but he used 1.60 exhaust valves for both.

If you have six inch carbides in diamond oval, or flame shapes that are 7/16" or 1/2" diameter, then clean up the entire ports from valve seat to intake manifold.  Match the intake to a Fel Pro gasket size and clean up around the valve guides so that you end up with a taper to the stem.  The valves should not hit the cylinder at less than .535" lift, and you may get by with more with the 1.94" valve.  The exhaust valve is not an issue.  On the pushrod wall, work that down a bit, and the cylinder head bolt wall.  A good multi-angle valve job and you should be close to your goal.  Work the tops and sides of the ports more than the floor. I personally use stones on 3 1/2" mandrels in various sizes to get a better radius around the guide, pushrod tube wall, and cylinder head wall.  Those are hard to find but work really well on iron heads.  The exhaust port just needs a clean-up and square it to the gasket size.  Don't try to take down the guide area very much, or you will find water.  A radius valve job on the exhaust with a 45* seat angle works well for street duty.  I would not worry too much about the combustion chamber at your performance goal.  210 cfm is easy, but 150+ is not.  Nature of the head.  Joe-JDC 
  

  

  

  

JDC

JDC

Thanks for the photos. I see you used Beehive springs. I will use Pac 1283 Viper Beehive springs. They are Beehives that are closest to cam manufacturer's recommended installed height and seat/open pressures. I realize that the heads will have to be cut for same. 

Watch beehive springs, when they break (and they will) there is nothing to hold the valve up (heavy damage), I have seen this a lot in 6.2 scrubys

So far, they have been run to 7300 with 5/16" valve stemmed valves and titanium retainers on many dyno pulls.  The springs that are designed for the LS engines seem to be trouble free---so far.  I have a new set of PAC double springs for the race heads that will be going on the dyno soon.  They will be used with titanium retainers, and hollow stem valves.  Shooting for .675" lift at retainer.  Joe-JDC

JDC

Look here (gm service bulletin)

https://gmauthority.com/blog/2020/09/new-service-bulletin-addresses-valve-spring-issues-in-gm-v8-engines/

I like to think I've done my homework and have selected the best components for my application. I'm not building a race engine, valve lift under .500, and not likely to see 6,000 rpm. No matter how good your components are/how much work goes into building an engine, if you push it to/over the limit, sometimes things break. 

I agree it is an issue to be considered.  I also like that Ted always puts a heat cycle into every dyno test on start up where the engine is run in for 20-30 minutes and got the rings seated, then lets the engine completely cool down before repeating dyno testing.  That seems to let the valve springs temper properly and have no further issues under normal engine operation.  Joe-JDC

JDC

Interesting information on the Beehive style springs with failures. In the racing engines I design and assemble I recently went to that style after finding a livable pressure at nearly 2” installed height; they under a Howard’s listing and since LS are so much shorter I’m not worried. The smaller top design with retainers are a relief after using 1.550” diameter springs with rocker arm interference which has been a problem for years. There are no commercial available roller rocker arms available for the engine in question. The ones I have were designed by me made by a machine shop before I needed to go to a larger diameter spring. Thanks for sharing.. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.