General Cylinder Head Flow Numbers discussion

[Stan Weiss]

Originally Posted by Ralph A Powell

You need to read the gray area part of rules. Most of the heads are ported( acid and others ways the camouflaged) to pass tear downs!

Ralph,

Thanks. Didn't I hear a couple of years ago NHRA got something like a FARO, touch probe / laser scanner for checking stock ports?

Stan

[Dissident]

Folks,

One should realize a few points in a cylinder head discussion of NHRA stock eliminator head and manifold components. "trust but verify" is a good methodology to follow.

1) The rule book might state one thing but in practice the "passed tech" cylinder heads are quite another and many examples of ported/reshaped and covered up have passed with abandon. That includes manifolds. It is sometimes a discretionary call as it states in the rulebook. Methinks that there was (is) at least one lawsuit that reflects same.

2) Cylinder head rules indicate that the valve job is "legal" all the way down to the valve guide. This area can be very creatively used by something like a single point cutter that can re-contour the area described. Other methods can also be used.

3) Starting off with primo castings is the best beginning, but not totally necessary if one goes the route mentioned in 1) above.

Regards to All that like this kind of stuff,
HB2
Dissident

[SSDiv6]

Originally Posted by Stan Weiss

Ralph,

Thanks. Didn't I hear a couple of years ago NHRA got something like a FARO, touch probe / laser scanner for checking stock ports?

Stan

With core shift and with the high number of different cylinder head part numbers for the same engine combination, it would make it very difficult.

This is a true story...
Many years ago I got a call from NHRA asking me about technology to shrink metals, especially cast iron. The reason was that there was a particular engine combination that every time the engine went through tear down, the cylinder heads were compliant and at the next race, the car would go faster.

So, NHRA purchased a pair of the suspect cylinder heads from a junkyard, sends the cylinder heads to a trusted shop to have them built to the rule book guidance and when they poured the cylinder heads, the port volumes were bigger than the suspect cylinder heads!

I explained to NHRA that during the casting process, a temperature differential or the abundance of Ferrosilicon will cause shrinkage of cast iron. The reason why many racers check and flow lots cylinder head castings. ...or the cylinder heads were spray welded to add more material.

[HawkBrosMav]

Originally Posted by Ralph A Powell

You want a port that continues to flow well past your max lift point and not go turbulent and is quite on the bench!

Ralph not being in the room when the heads are being flowed and not owning my own stuff to do it... is there a way to know if the port is quiet by looking at CSA and port velocity? Do I just need to ask the head guy if they were quiet?

How far past max lift would you like to see it "flow well" .050?.0100? more? and by "flow well past" do you mean the CFM should still be increasing or just not backing up a lot? if it just holds the peak CFM from say .350-.500 at a fairly constant CFM but isn't gaining anything or dropping off at all is that okay?

Thanks
Brad

[SSDiv6]

Originally Posted by HawkBrosMav

Ralph not being in the room when the heads are being flowed and not owning my own stuff to do it... is there a way to know if the port is quiet by looking at CSA and port velocity? Do I just need to ask the head guy if they were quiet?

How far past max lift would you like to see it "flow well" .050?.0100? more? and by "flow well past" do you mean the CFM should still be increasing or just not backing up a lot? if it just holds the peak CFM from say .350-.500 at a fairly constant CFM but isn't gaining anything or dropping off at all is that okay?

Thanks
Brad

Brad,

It needs to be on the flow bench and the quietness is the sound of the air. Usually test 0.100" ~ 0.150" past your required maximum lift and don't worry about the behavior past that limit.

[Dissident]

Folks interested in flow bench testing:
These days I can't hear worth a dip, but I do know a fair amount about flow bench testing and there are multiple ways to discern the stability of airflow in the cylinder head or manifold without hearing....
The cylinder head should be tested with the manifold and carb/throttle body attached so the "real" flow test is indicative of what the system is doing. That kind of testing is a bit more difficult, but much more meaningful. From that flow data, potential power can be predicted as can the rpm at which peak power will occur. Measuring a load of intake manifolds is worth the effort. Unless one follows the outline that I posted previously. You might find some worthwhile tips in HPBooks, Engine Airflow

Regards,
HB2
Dissident

[Billy Nees]

You guys might want to take a look at the "odd" little rule change that's in the 2020 to 2021 rule changes. It just might have been put in there for a reason.

[SSDiv6]

Originally Posted by Billy Nees

You guys might want to take a look at the "odd" little rule change that's in the 2020 to 2021 rule changes. It just might have been put in there for a reason.

Saw that...inconspicuously and discreetly placed...

SECTION 11A: STOCK CARS: 1, BLUEPRINTING (Page 2) (12/3/2020)
Permitted per NHRA Specifications available from NHRA Technical Services
Department headquarters. Stock factory OEM Components (unless otherwise
specified) must be retained and remain unaltered (i.e., cylinder heads,
connecting rods, pushrods, crankshaft, etc.).

Clear as mud especially when aftermarket cylinder heads are allowed.

[HawkBrosMav]

Originally Posted by SSDiv6

Saw that...inconspicuously and discreetly placed...

SECTION 11A: STOCK CARS: 1, BLUEPRINTING (Page 2) (12/3/2020)
Permitted per NHRA Specifications available from NHRA Technical Services
Department headquarters. Stock factory OEM Components (unless otherwise
specified) must be retained and remain unaltered (i.e., cylinder heads,
connecting rods, pushrods, crankshaft, etc.).

Clear as mud especially when aftermarket cylinder heads are allowed.

I guess I don't how that wording changes anything with the way the rules were written before... It already spells out what can be done and what can't be done as far as "alterations" so that would fall into "unless otherwise specified" meaning that all the heads that passes last year will pass this year just the same..

[SSDiv6]

Originally Posted by HawkBrosMav

I guess I don't how that wording changes anything with the way the rules were written before... It already spells out what can be done and what can't be done as far as "alterations" so that would fall into "unless otherwise specified" meaning that all the heads that passes last year will pass this year just the same..

"unless otherwise specified" refers to the NHRA approved aftermarket cylinder heads.