General Cylinder Head Flow Numbers discussion

[Billy Nees]

Velocity is your friend.

[SSDiv6]

Originally Posted by HawkBrosMav

I get that, but would you run a set of heads you knew flowed less air intentionally knowing the TB and intake may be a restriction larger than the heads or would you put the "best" flowing heads on regardless?

I think I'm more curious as to what people are more concerned with if area under the curve is similar between 2 sets of heads. Having the larger peak numbers or giving up a little up top to have much better down low numbers. Obviously there are other factors to consider... mainly possible restrictions before the port and then the relation to exhaust port flow as mentioned in the next reply. But at this point for a simplistic questions and answer.. would you prefer a head that peak flows more or flows down low more given the overall "area under the flow curve" is generally equal.

Billy seems to lean towards low flow potentially with his response.

I always flow the intake manifold first and pick the best. Many years ago I flowed lots of Ford 5.0 intakes and the biggest variation was the lower manifold. As I recall, there are 4 different lowers from different foundries with the same part number and the difference was the last revision letter on the casting number. I believe I flowed around 22 lower intakes and picked the best 4 and the remainder I took to the aluminum recycler.

Having the baseline number from the intake allowed me to then work on the heads, knowing the Delta the intake would effect on the cylinder heads. The brand of valves makes a difference the same as the cut and angles.

[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.

[Jim Hanig]

What i know about head flow, the earliest flow number for a 441 chevy .Was 165 cfm the last set i worked on was 235,this was at 28" at 450 lift. was about 35 hun.

[Billy Nees]

Originally Posted by Jim Hanig

What i know about head flow, the earliest flow number for a 441 chevy .Was 165 cfm the last set i worked on was 235,this was at 28" at 450 lift. was about 35 hun.

Gee, I wonder how that happened! They must have improved the flow benches. They couldn't possibly have done anything to the cylinder head, that wouldn't be legal.

[Jeff Stout]

Originally Posted by Billy Nees

Gee, I wonder how that happened! They must have improved the flow benches. They couldn't possibly have done anything to the cylinder head, that wouldn't be legal.

I was thinking the same thing.