Racing flow benches

[PRH]

Though not stated, I'm gonna assume the "b" numbers are from your bench Dwayne.

Correct...... my numbers are bench B.

I’ve tested several heads that come CNC ported from the manufacturer, where they have published flow numbers.
Sometimes the flow numbers from my bench are pretty close from top to bottom.
Other times........ close for some of the curve.....not all that close for other parts of the curve.
Once in a while, my numbers will be a little higher than the advertised numbers......... although that doesn’t happen very often.

I’m on my second bench.
I bought the first one at the end of 1992, and the current one in August 2007.

As for the phrase, “racing flow benches”, it’s something I say to people/customers who are trying to compare numbers they have gleaned from different sources, off different benches.
I tell them......... you’re just “racing flow benches”.

Same situation as “racing dynos”.

 

[PRH]

I had a customer who was doing his own porting on a set of these same kind of heads as the test here.
He had them flowed locally(to him) and was pretty unhappy with the results.
And the results were pretty low numbers......... lower than I would have expected for the description of the work.

I asked if he had the head tested before any work was done, and he had.
From about .400 and up, the “before” numbers were a solid 20+cfm lower than I’d ever seen from that type of head before.

Adding 20cfm to his ported numbers put them in line with what I would have expected to see on my bench.

 

[justinp61]

Dwayne, did you flow the port after making the correction to the intake seats?

 

[33IMP]

If i had to make a guess..... budget aluminum rat heads.

 

[PRH]

Dwayne, did you flow the port after making the correction to the intake seats?

The reason they were here was to cut the intake seats to restore the valve tip heights to what they’re supposed to be.
Larger intake valves had been installed and the new valves were sitting a fair amount proud in the chamber, and the installed height was a solid .030-.035 short........ and that extra height was needed for the cam/spring combo.

Without doing something to compensate for sinking the valve into the chamber that much........it almost always reduces the flow in the lower lifts........ and this situation was no exception.

After recutting the seat, and just doing a minimal amount of deburring the new “lip” that was now around the intake seat resulted in this:

Lift———flow
.200—— 133
.300—— 197
.400—— 256
.500—— 307
.600—— 343
.650—— 351
.700—— 329

 

[MOPAROFFICIAL]

Not all ports are equal either.

 

[polyjohn]

Great thread and very enlightening indeed!

I have read many, many articles on iron heads over the years.
I guess folks don’t want to spend 40-50 hours on a head to get worse flow?
So benches can be (possibly) manipulated to show good numbers (for a customer) lol.

200cfm @ 300 lift is my new mantra lol.

As they always say “the valve only sees max lift once”
Everywhere else it sees Twice...

 

[PRH]

I guess I never finished this story......
The owner asked if he thought I could get a little more out of these heads after re-cutting the seats.
I didn’t want to get into a lengthy porting session with these, but thought a back cut on the valve would help down low, and a better form on the SSR would help up top.
That resulted in:

Lift—— In
.100—— 75
.200——155
.300——207
.400——264
.500——314
.600——349
.650——361
.700——339

VS as rec’d:
Lift———In
.100—— 74
.200——138
.300——199
.400——249
.500——290
.600——333
.650——346
.700——329

 

[pittsburghracer]

I guess I never finished this story......
The owner asked if he thought I could get a little more out of these heads after re-cutting the seats.
I didn’t want to get into a lengthy porting session with these, but thought a back cut on the valve would help down low, and a better form on the SSR would help up top.
That resulted in:

Lift—— In
.100—— 75
.200——155
.300——207
.400——264
.500——314
.600——349
.650——361
.700——339

That dive at .700 would make me go back and find more area at the short turn and flow it again. Now I gotta go back and see what head this is.

 

[pittsburghracer]

I guess you didn’t mention what head it was not that it really matters. Did you hear any turbulence at .700 lift?

 

[PRH]

I never said what head it is....... but it’s one that I see this situation occur on often.

It’s a turbulence issue, that can be a challenge to fix.

As a reminder......... these heads didn’t come here for porting work. They came here to correct a seat depth/installed height issue.

They were already ported........ and had there not been an installed height problem, would have been run as-is.

 

[polyjohn]

This raises another question?

Total flow against maximum flow.

The infamous 906 has less flow than a 452 at .600, but the 906 has a better area under the curve...

Horses for courses...

This backs up PBR’s quote, 200@300-lift...

Nice work @650 PRH ‘361’ seems a BIG number to me...

 

[33IMP]

This raises another question?

Total flow against maximum flow.

The infamous 906 has less flow than a 452 at .600, but the 906 has a better area under the curve...

Horses for courses...

This backs up PBR’s quote, 200@300-lift...

Nice work @650 PRH ‘361’ seems a BIG number to me...

Polyjohn, you are assuming a big or small Mopar head. Wasn't specified, matter of fact he made sure not to tell us what head.(I'm guessing cheap bb chevy)

 

[Rat Bastid]

This raises another question?

Total flow against maximum flow.

The infamous 906 has less flow than a 452 at .600, but the 906 has a better area under the curve...

Horses for courses...

This backs up PBR’s quote, 200@300-lift...

Nice work @650 PRH ‘361’ seems a BIG number to me...

And that right there is one flaw of the flow bench. What test pressures are we comparing. A port that looks good at a static 28 inches may suck at 40 inches. And it’s still static flow, at way less pressure drop than 40 inches. And there is no piston in the way at TDC where low lift occurs.

I’ve said it so many times I may have to make a video about it. Flow is a low priority when looking at a port.

 

[polyjohn]

That’s right Ratty!

A flow bench is nothing like a moving piston in the ‘down stroke’ cycle of an 4 stroke engine.
But everything is a compromise in life...lol...

So with hours of reading David Vizard books, I am going to use his “cheap as chips” engine bench for my first err bench?

I will fit a vacuum supply to floating piston in the bore and see what flow differences there are with the ‘valve opening’ and piston height?

There is little or no vacuum at the start of a cycle, only the exhaust gas firing out off the exhaust port, following many others on their way to freedom...lol

I believe someone has designed such a bench to discover what the exhaust pressure escaping, does to the start of the intake charge?

So the initial downstroke takes quite a while before the maximum vacuum is created, somewhere between half stroke, to ‘full’ with the inertia of intake charge following on behind.

 

[polyjohn]

I heard with blown top fuel engines and the design of the infamous ‘hemi head’, more fuel goes out the exhaust than goes into the cylinder lol...

 

[PRH]

One thing I forgot to mention in the beginning of this thread is……..
Both of the flow benches used are the same make and model.
A Saenz S-600, which is essentially an Argentinian built copy of a Superflow SF-600.