Racing flow benches

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PRH

PRH

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I was reading thru the SB Head flow thread(which has gone totally off the rails of what it was intended for IMO),
and there was some discussion on flow numbers being different from different benches.

I just had another chance to experience this last week.
I’m not even going to mention what kind of head it is...... cuz it doesn’t really matter.
The heads weren’t here for porting work anyway. There was an issue with how the intake valve seats were cut for bigger valves, and a resulting installed height issue.
I knew the heads had been flowed and had the customer tell me which port had been tested, and I would test the same one.
Interestingly(to me anyway), the “big number” isn’t very much different between the two benches, although it happens at a slightly different lift.
However, the mid-lift numbers are rather different from each other.

Intake flow(same port, same head):
Lift———A———B
.200— 163—— 138
.300— 220—— 199
.400— 270—— 249
.500— 319—— 290
.600— 347—— 333
.650— 336—— 346
.700— 334—— 329

Exhaust:
Lift———A———B
.200— 124—— 101
.300— 169—— 139
.400— 210—— 177
.500— 242—— 211
.600— 265—— 237
.650— 273—— 244
.700— 275—— 253

So, if you’re only looking at the “big number”...... the intake ports are within 1cfm....... 347 vs 346.

The head didn’t get better on the one bench, or worse on the other bench....... that’s just how the benches interpret what the head is doing at the various lifts.
Which is why I always say....... you can’t compare numbers from different benches as “apples to apples”.

I’ll say it again.......Those two sets of numbers that look so different.......are the same port on the same head.
 
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PRH said:
I was reading thru the SB Head flow thread(which has gone totally of the rails of what I was intended for IMO),
and there was some discussion on flow numbers being different from different benches.

I just had another chance to experience this last week.
I’m not even going to mention what kind of head it is...... cuz it doesn’t really matter.
The heads weren’t here for porting work anyway. There was an issue with how intake valve seats were cut for bigger valves, and a resulting installed height issue.
I knew the heads had been flowed and had the customer tell with cylinder had been tested, and I would test the same one.
Interestingly(to me anyway), the “big number” isn’t very much different between the two benches, although it happens at a slightly different lift.
However, the mid-lift numbers are rather different from each other.

Intake flow(same port, same head):
Lift———A———B
.200— 163—— 138
.300— 220—— 199
.400— 270—— 249
.500— 319—— 290
.600— 347—— 333
.650— 336—— 346
.700— 334—— 329

Exhaust:
Lift———A———B
.200— 124—— 101
.300— 169—— 139
.400— 210—— 177
.500— 242—— 211
.600— 265—— 237
.650— 273—— 244
.700— 275—— 253

So, if you’re only looking at the “big number”...... the intake ports are within 1cfm....... 347 vs 346.

The head didn’t get better on the one bench, or worse on the other bench....... that’s just how the benches interpret what the head is doing at the various lifts.
Which is why I always say....... you can’t compare numbers from different benches as “applies to apples”.

I’ll say it again.......Those two sets of numbers that look so different.......are the same port on the same head.
Click to expand...
Thanks for doing that. Just numbers on a chart you can use as a guideline, baseline or bragging rights. Good info to have when picking out a cam though. No reason to go with .650 lift if the ports fall off after .550. :lol:
 
Yep. When Yellowrose ported my Eddy RPM heads we put them on the bench, got the numbers and really listened to how they sounded, they were loud and ugly stock. Then Tim ported them as much as possible with a burr finish. Flowed them on the same bench, got way better flow numbers and the sound changed, smoothed out and was crisp. This was before we picked my Howard’s cam. The heads, cam and intake are going on my J headed 340 .30 over currently in my car. This motor was on broke in / dynoed, so we know the base line of where it’s at before this changes. Motor is coming out in the next month or so. Fun times...
 
The main point I was making, was as PBR often says........
You need the “before” numbers........ from the same bench..... to really know how good the “after” numbers are.

To say a head flows “x”, without the proper context...... is just a number.
And....... it’s best to look at the whole curve..... not just the big number.
 
The fact that the numbers bounce around versus being a percentage high or low thru out the range makes one wonder how valuable of a tool is a flow bench .
 
I’m not sure if I was clear in the first post......
The two sets of numbers are the same port, on the same head....... tested on two different benches.

The flow bench is a tool to gauge your progress.

Flow it before you start working on it....... make changes..... see if it helps or hurts.

The numbers don’t need to be absolutely correct to be valuable....... but they do need to be repeatable.
 
This is what I was saying a while back with my two separate head flow numbers from two different people in two different states on two different flow benches.

My guy came back lower numbers. He still complimented on work and flow rates and told me I’d make the power I’m looking for and then some.
 
Along that train of thought.......
I didn’t know what the numbers were from the other bench when I did my test.
Based on how the bowl, valve job, and short turn were configured .......... the numbers from my test were consistent with what I was expecting to see.
The numbers weren’t some kind of anomaly for me.
 
PRH said:
The main point I was making, was as PBR often says........
You need the “before” numbers........ from the same bench..... to really know how good the “after” numbers are.

To say a head flows “x”, without the proper context...... is just a number.
And....... it’s best to look at the whole curve..... not just the big number.
Click to expand...



if you read any of my posts on porting my first target and I’ve repeated it 100 times is over [email protected] and build from there. On my moved pushrod heads I posted I sacrificed my high number (332) because I wasn’t happy with my mid lift numbers so I reshaped the short turn to make a big improvement there because my cam was only .650 lift. The only time I ever charged for flowing heads was when I flowed two Hemi heads with different part numbers that a customer was afraid to run if they were to far off ( they weren’t). I learned something almost every time I flowed and tested a head so before and after numbers were always free of charge. As far as seeing differences at different lifts calibration plates are available from .100 up to verify this. My three plates cost less than 100.00
 
Flow benches are like dyno's. Their output are just numbers and unless there is someway to calibrate them, you will get waht you get from that particular machine.
 
pittsburghracer said:
As far as seeing differences at different lifts calibration plates are available from .100 up to verify this. My three plates cost less than 100.00
Click to expand...
There's your calibration. How can you "adjust" your bench to hit the calibration plate numbers?
 
John, I have 5 PTS plates.
100, 200, 300, 350, 400

I don’t want to get off on some long winded tangent about why different benches may produce different numbers.
I’m merely bringing it back up again that there’s no denying that different benches can produce numbers different enough from each other, that you don’t even recongnize the numbers as coming from the same head.
And, IMO....... these two sets of numbers are a good example of that.
 
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Regards flow benches… i had a set of W5 heads that ended up making good power.
Ryan ported and flowed them. They peaked in the high 320’s, just like he later posted on his website under the W5 section. This was his first W5 head. He was schooled by another guy on what to do, and if i remember right, copied and exhaust and intake and copied that work onto mine.
An extremely well known Mopar engine builder flowed them as well, peak number they got was 297. Best Machine.
Another very well known head porter, Mopar guy, later flowed another set of W5 heads on his bench, which if anything, likely were a bit better than mine.. that set went 299 or so as i recall.
Neither set of heads went remotely close to 320 xx on two different benches, yet, they worked. 700 lift roller.
 
toolmanmike said:
There's your calibration. How can you "adjust" your bench to hit the calibration plate numbers?
Click to expand...


When I finished building my flowbench and loaded the info on my laptop you go into calibration and (choose your plate size) I started at 300cfm. after it’s in place start the flowbench. If by chance it was 298-301 you lucked out. If not you go to the configure screen and raise or lower your number to dial it in. Then I checked my 100 plate and it was dead nuts on. So now you write that config number down so your have it for the future. Then you switch over to exhaust and do the same thing and write down that configuration number because it will be different. That number has the be switched (takes 45 seconds) when going from exhaust and intake. Now if you have a pilot style flowbench with fluid manometers calibration will change with the weather, mine won’t and is why I built it after having both style benches before.
 
My perspective is....... the only numbers I know are really comparable to numbers that came off my bench are.......numbers that came off my bench.
 
Speaking of numbers look at what showed up just now. Now if I can Leala to let me play. Lol
BA313A7F-9796-4255-9A62-1E01D2C9D89A.jpeg
 
PRH said:
I’m not sure if I was clear in the first post......
The two sets of numbers are the same port, on the same head....... tested on two different benches.

The flow bench is a tool to gauge your progress.

Flow it before you start working on it....... make changes..... see if it helps or hurts.

The numbers don’t need to be absolutely correct to be valuable....... but they do need to be repeatable.
Click to expand...
This happens all the time.
People either misinterpret or just read out of it what they want.

I flowed the same port on two different benches... The other gave better .100-.400 lift numbers by about 6cfm and flowed the same peak but by maybe .030 lift earlier.
My thinking is unless they use the exact same module/hardware/manometers that the only diff left is the operator, bore size and its alignment, blower motor winding milage.. just a few things. Lol
 
PRH said:
The main point I was making, was as PBR often says........
You need the “before” numbers........ from the same bench..... to really know how good the “after” numbers are.

To say a head flows “x”, without the proper context...... is just a number.
And....... it’s best to look at the whole curve..... not just the big number.
Click to expand...
I think you can see through the numbers once you seen enough and worked enough with a bench. Whenever I see some really high numbers that I don't ever see ..I just assume they're probably about 8 cfm lower in actuality. I don't believe any of us would literally "race another flow bench".
If I'm just close.. it's there enough for me in my filter of 'it's probably a little less than that'. Call me assuming, we all are sometimes. I know you played with the flow bench enough to move that cylinder head around and learn how important it is to line up that chamber on the straight side. Bore size and alignment can change the number drastically on a just fits bore adapter, like 4".
I think there are things the reader just doesn't understand Iike the operator does.
 
PRH said:
I was reading thru the SB Head flow thread(which has gone totally off the rails of what it was intended for IMO),
and there was some discussion on flow numbers being different from different benches.

I just had another chance to experience this last week.
I’m not even going to mention what kind of head it is...... cuz it doesn’t really matter.
The heads weren’t here for porting work anyway. There was an issue with how the intake valve seats were cut for bigger valves, and a resulting installed height issue.
I knew the heads had been flowed and had the customer tell me which port had been tested, and I would test the same one.
Interestingly(to me anyway), the “big number” isn’t very much different between the two benches, although it happens at a slightly different lift.
However, the mid-lift numbers are rather different from each other.

Intake flow(same port, same head):
Lift———A———B
.200— 163—— 138
.300— 220—— 199
.400— 270—— 249
.500— 319—— 290
.600— 347—— 333
.650— 336—— 346
.700— 334—— 329

Exhaust:
Lift———A———B
.200— 124—— 101
.300— 169—— 139
.400— 210—— 177
.500— 242—— 211
.600— 265—— 237
.650— 273—— 244
.700— 275—— 253

So, if you’re only looking at the “big number”...... the intake ports are within 1cfm....... 347 vs 346.

The head didn’t get better on the one bench, or worse on the other bench....... that’s just how the benches interpret what the head is doing at the various lifts.
Which is why I always say....... you can’t compare numbers from different benches as “apples to apples”.

I’ll say it again.......Those two sets of numbers that look so different.......are the same port on the same head.
Click to expand...

Where are the .100 lift numbers?
Those might say something.
 
pittsburghracer said:
When I finished building my flowbench and loaded the info on my laptop you go into calibration and (choose your plate size) I started at 300cfm. after it’s in place start the flowbench. If by chance it was 298-301 you lucked out. If not you go to the configure screen and raise or lower your number to dial it in. T
Click to expand...

I would to have a bench. What does it take to build one?
 
Last edited by a moderator:
In my humble worthless opinion, flow benches are like engine dynos and chassis dynos. Absolute numbers aren't worth much, especially if you don't know the operator, the equipment, and the conditions.
Bottom line to me.... how does it run all put together in the combination.
I would rather have a dyno proven 400 hp that runs hard than a car with "dyno proven 700 hp" that won't fall out of a tree.
 
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