Cylinder head geometry has been a bigger player in hp output over the last 20 years  than air flow.  The C302B is a classic example.  Although capable of carrying a bigger valve and more airflow numbers than the Yates  head  it cannot achieve the power numbers of the Yates head.  Even the 20 year old low port versions of the Yates head from the 90's  were significantly better.
 As Joe pointed pointed out our angle mill head flows a tick better than highly ported regular version,  but they run significantly better,  as long as the fundamentals are there.
  When you are playing with the port on a head,  you are only playing with half of the runner.  The everyday average guy will try and view the head as the head, and manifold as the manifold.  
Classic example  many engines  have a different intake manifold flange angle   Sbf  90*  Sbc 80*   Y block 75* .   You will have to look at your manifold and see if the runners are coming perpendicular the flange face itself.  If it  is you can achieve decent results  if you try and R&D the head by itself.
 The Y Block lower port can be finicky by itself, but if you bolt a manifold to it, (or the other half of the runner)  it gets very stable and predictable.  Years ago when developing our angle milled race head  we played with a few different manifolds  cast and fabricated to see how the ports as whole responded.  I think the funniest thing we saw was that ports that were the touchiest by themselves were a couple numbers better, when the manifolds were installed  (Which one do you wanna pick, to spend 2 weeks making a CNC program out of )
  These days, rates of chamber fall away top angles on the valve job, different runner tapers ,  placement  of the MSCA  in the runner ,  Low lift Flow in relation to camshaft duration  or  FLOWRATION as I call it  are things  that I see actually affecting how the motor runs.  

 
 


  
 

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Since this discussion has moved beyond just flow numbers, I've read in the past about "turbulence & "quench" in cylinder heads. How much effect do those factors have in performance?  And, particularly how do Y-Block heads fair, both stock "G's, or 113's  & Mummert's?  
P.S.- I suppose turbulence involves the intake manifold also?   


Paul

Quench or squish velocities are a tuning aid for adjusting meter per second  burn rate.   Its semi complex and some of it may actually seem backward.  Squish (or piston to head clearance),  squish pad area in relation to bore area, engine rpm, and rod/stroke ratio are key factors to adjusting burn speed.
 The next thing people ask is why would I try to adjust this.  At the end of it all your trying to achieve the highest rate of SAFE combustion speed you can. 
  Without having this turn into an overly drawn out out explanation,  if you have a low compression engine,  a low rpm engine, poor cylinder head  design.  In general poor cylinder heads have air fuel separation problems.
 These things will cause slow or erratic burn speeds.  Tightening your piston to head clearance, and looking for heads with high squish to bore area will help force air and fuel into the chamber more completley and at a higher rate of speed. 
 Heres where slope gets a bit slippery. When searching for heads with high squish to bore ratios, this usually indicates the combustion chamber footprint is small, valve area and shrouding can be a problem. 
 As things start going the other way, compression starts getting high, cylinder head geometry improves, rpm starts rising, the need to try and do thing to increase the rate of burn speed dont become as critical because they are getting faster naturally.
 Just remember that the rules come through experience in working with certain engines. Some engine with 10.0:1 compression and 89 octane are on the edge of detonation while others are very safe at 12.0:1 compression with 87 octane.  Some engine are at the end of there rev range at 6000rpm  and others cruise at that speed.







 
 
 

 

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

John with this in mind how do you think an engine like the early Chrysler Hemi compares to a good wedge cylinder head when running on gasoline such as the stuff available in the 1950’s?

We all know that a Hemi is great at stuffing cylinders full of exotic fuels especially under the pressure of a blower.

I’ve kinda always wondered cube for cube how efficient is a hemi compared to other head designs when thinking in terms of their targeted purpose which was a powerful and efficient passenger car engine.

Heck these early hemis were even used in industrial applications with low compression and lazy camshafts.

What if anything did Chrysler have on the competition, or what did they do I wonder to make a pure Hemi chamber perform on the street?

Cylinder heads don't work on any one function.    I guess you can break a cylinder heads performance down into about 4 main functions. They are related though.

1.  Airflow:  Everyones favorite,  Its measurable,  its easy to throw out a number during a bench racing session, and there is math to project power levels of a given cfm.  Based on a particular efficiency. When the efficiency changes the math changes.

2. Velocity:  This is a good indicator of incoming port energy, this must be backed by a cfm number relative to the power level you are looking achieve to have truly have energy.  One without the other doesn't work.

3.  Efficiency:  This is where you start to here crickets.  This where all the magic is. The secrets.  The heads that make high horsepower and torque. The ability to handle high amounts of compression, on minimal octane.  

4. Valve train:  It seems a little out of place with the others. But if it is not up to task than the rest is a waste of time.


   Others may disagree, but the old hemi's of the 50's and 60's weren't really exciting naturally aspirated.  I do feel that the particular weaknesses they had as naturally aspirated engines were not drawbacks as blower engines.
1. Enormous combustion chamber, hard to get high compression without the ugliest top heavy piston you've ever seen.
2. Huge low velocity exhaust port,  not exciting for naturally aspirated.
3. Mediocre flowing intake port,  but its placement far away from the cylinder, the port being very straight would keep swirling to a minimum as it would keep fuel separation to minimum.   
(Connie Kalitta went into extreme detail on why the valve cants Ford puts into there Boss 429 to try and make a better naturally aspirated Hemi were a complete disaster in a Top Fuel motor.)
4. Very heavy exhaust rocker arm, but a roots blown nitro motor doesn't have to turn a bunch of rpm.

 I think its safe to say you can make just about anything work if you put the time into it.  But you will have to understand what the strengths and weaknesses are of whatever your building, and attack the weaknesses first.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Thanks John, excellent explanation of cylinder head and induction science. I always thought Ford really pushed technology forward in the areas you described above especially during the Total Performance era.

The 1954 Lincoln 317 cylinder heads I have on the docket for my next build (thanks Ted) look like they have an “active” combustion chambe. Lots of quench pad and the chamber looks to have surfaces which concentrate the fuel charge near the spark plug. It looks purposeful and thought out.

To my eyes this is unique and unlike most 50’s inline valve engines. I’ve read that the Y-block cylinder head development was largely misunderstood by most hot rodders. The turbulence and swirling that looks like it was built in from Ford was somewhat rejected and the simpler basic wedge engines like the Cads, Olds and scrubs were more accepted.

This Engine Masters Challenge is an excellent opportunity for the Y-blocks to shine.

Good luck to all the competitors.

The Hemi may well have been the best with nitro and a blower, the Ford Cleveland head was the  engine that made the  most 
HP per Cubic inch in a naturally asperated  engine!  All the teams in NASCAR are running a Head copied from the Cleveland. The  LS series scruby is a Copied version  of a Cleveland head.