General Cylinder Head Flow Numbers discussion

[HawkBrosMav]

Originally Posted by Dissident

When doing comparative testing, it is imperative to use the same radius inlet guide (not rolled up clay method) as the specific entry has influence on results. On the exhaust side, one should always use a short length of pipe for the same reason.

The methodology of area under the curve is best evaluated by graphics and using the cfm/sq in rating. One should have a graph of the cam / valve lift for that evaluation as well. It is in these types of details that gains are sqeezed out of otherwise run of the mill components.

After the heads are evaluated, then one can begin sorting out manifolds and carbs and placement of same.
Notes, lots of notes so you can take a look at what items worked the best. This is particularly important when you are evaluating valve jobs.
Lots of patience, study, and thoughts with coffee will help get the job done.

Regards,
HB2
Dissident

I'm playing with those curves now. That is one reason I am asking the questions I'm asking. Trying to determine if area under the curve if just area under the curve and doesn't matter where it is.. obviously where the curve moves will determine other pieces like cam and timing events, possibly converter as well and potentially effect header lengths and sizes, but I have to choose a set of heads first to match those things to the flow curve.. If area doesn't matter as long as the other parts are matched well to the system as a whole... great.. if having the flow low but giving up some up top is better.... great... if wanting the great numbers around peak lift while giving some up early is best... great.. just thought I'd pick the brains of others that have had to think about this stuff before I did.

[Billy Nees]

Velocity is your friend.

[SSDiv6]

Originally Posted by Billy Nees

Velocity is your friend.

Correct.

[Brad Hawk]

I don't know how much of their experience comes from working w/ lower-lift Stocker heads, but cylinder head guys like Darin Morgan and Chad Speier emphasize port designs that remain stable w/o any backing up in flow at lifts well above the actual valve lift used, even if it reduces some of the flow #s seen at lower lifts.

However, those recommendations are when they're talking about ports remaining stable to 1.0" when the valve lift might be .700". They're saying this, IIRC, based on findings from flow testing well above the standard 28" H2O pressure since the higher test depressions can reveal different flow behavior than seen at 28". How that might need to be "adjusted" (as much as can be w/in the constraints of the class guidelines) when the peak lift is .400"-.500", I dunno... just throwing that out there for consideration. Thx

[SSDiv6]

Originally Posted by Brad Hawk

I don't know how much of their experience comes from working w/ lower-lift Stocker heads, but cylinder head guys like Darin Morgan and Chad Speier emphasize port designs that remain stable w/o any backing up in flow at lifts well above the actual valve lift used, even if it reduces some of the flow #s seen at lower lifts.

However, those recommendations are when they're talking about ports remaining stable to 1.0" when the valve lift might be .700". They're saying this, IIRC, based on findings from flow testing well above the standard 28" H2O pressure since the higher test depressions can reveal different flow behavior than seen at 28". How that might need to be "adjusted" (as much as can be w/in the constraints of the class guidelines) when the peak lift is .400"-.500", I dunno... just throwing that out there for consideration. Thx

Both Darin and Chad know very much about low lift flow and they not only understand it from the science, but also from the flow bench and racing.

By the way, Darin's stepdad was Kip Martin and he got his feet wet with him doing Stock and Super Stock heads.

Chad has been doing cylinder heads most of his life and worked at Patterson and MadCap racing engines along with Nick Ferri.. Chad is still doing Super Stock cylinder heads, both cast iron and aluminum.

[SSDiv6]

One reality to deal with is that there are lots of cylinder heads that have been maximized and the guys that build them, charge accordingly based on the R&D and time they put behind them.

Too many times there is no other option than to pay the money if you want to go fast. The other option is to do it yourself, which entails a big learning curve, asking the right people that are willing to share and investing on the right tools and equipment and at the end, entails lots of money too.