General Cylinder Head Flow Numbers discussion

[SSDiv6]

Originally Posted by Glenn Briglio

Got to be pretty destructive application and not for roller lifters.

Just on restricted travel and solid lifters. As long you have good quality lifters and checked the spring pressure often you are good. Prior to the allowance of aftermarket roller rockers, you needed to have a box of spare OEM rocker arms because the tendency of the pushrod to go thru the rocker arm cup.

[Stan Weiss]

Originally Posted by SSDiv6

Just on restricted travel and solid lifters. As long you have good quality lifters and checked the spring pressure often you are good. Prior to the allowance of aftermarket roller rockers, you needed to have a box of spare OEM rocker arms because the tendency of the pushrod to go thru the rocker arm cup.

Been there done that.


Stan

[Adger Smith]

-Head A stock completly untouched
-Head B has flow characteristics that make me feel like it will be okay (.5 under)
-Head C has flow characteristics the make it a record setter

IMHO
And Head C has correct port volume, but probably has a larger CSA at several key places in the port.

[HawkBrosMav]

Let me add a little more specific question to this:

.444 valve lift cam.

Lift -------- Head A -------------- Head B

.050 -------- 50.8 -------------- 35.1
.100 -------- 81.0 -------------- 57.6
.150 -------- 108 --------------- 88.2
.200 -------- 129.9 ------------ 117.12
.250 -------- 142.3 ------------ 136.6
.300 -------- 157.0 ------------ 158.0
.350 -------- 161.8 ------------ 172.6
.400 -------- 166.8 ------------ 175.6
.450 --------- 166.4 ----------- 175.6
.500---------- 165.8 ----------- 174.5

Which head would you rather have? Head B is a bit better up top but Head A is substantially better down low. I would still say looking at it from an area under curve stand point that Head B would be slightly larger but very small difference.

[Billy Nees]

Low-lift flow is very important in a "restricted" engine.

[SSDiv6]

Originally Posted by HawkBrosMav

Let me add a little more specific question to this:

.444 valve lift cam.

Lift -------- Head A -------------- Head B

.050 -------- 50.8 -------------- 35.1
.100 -------- 81.0 -------------- 57.6
.150 -------- 108 --------------- 88.2
.200 -------- 129.9 ------------ 117.12
.250 -------- 142.3 ------------ 136.6
.300 -------- 157.0 ------------ 158.0
.350 -------- 161.8 ------------ 172.6
.400 -------- 166.8 ------------ 175.6
.450 --------- 166.4 ----------- 175.6
.500---------- 165.8 ----------- 174.5

Which head would you rather have? Head B is a bit better up top but Head A is substantially better down low. I would still say looking at it from an area under curve stand point that Head B would be slightly larger but very small difference.

You need to take into consideration the intake manifold and throttle body flow also. No matter how much air flow you have on the cylinder heads, the intake manifold and throttle body/carburetor, can become a restriction.

[FED 387]

exhaust port flow is going to come into play in this too

[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

[HawkBrosMav]

Originally Posted by SSDiv6

You need to take into consideration the intake manifold and throttle body flow also. No matter how much air flow you have on the cylinder heads, the intake manifold and throttle body/carburetor, can become a restriction.

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.

[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.