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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: BradH]
#1711960
12/18/14 04:00 PM
12/18/14 04:00 PM
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Joined: Jan 2005
Posts: 12,422
Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
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Posts: 12,422
Kalispell Mt.
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The picture above of the graph mentions it is at peak TQ, should be obvious that as scavenging goes down at lower RPM then there is less negative pressure at the lower lifts. Even above the TQ peak it is probably less. On an engine with tuned intake and exhaust runners I bet it changes with the helmholtz resonation. IE the magnum beer barrel intake is tuned around 1800 RPM to build pressure behind the intake valve as it opens combined with the negative pressure building in the cylinder makes for a big pressure differential then add on tuned headers for that RPM and you could get very very low pressure, but on the other hand there won't be much scavenging at that RPM if the exhaust is tuned for 4000 RPM. Also if the cam is wrong the scavenging RPM shifts around changing when the pressure differential is greatest. Even on a more finite scale the resonance the pulse may not hit the back of the valve till it is at max lift or even as it's closing. I would say RPM is definitely going to change the depression level and timing. Probably need a super computer to get it near perfect for wide RPM ranges and throttle opening angles. If you were tuning for a single RPM it would be a little easier 
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: MR_P_BODY]
#1711961
12/19/14 02:16 AM
12/19/14 02:16 AM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
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Posts: 4,457
Washington
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Are you specifically talking to me? What did I say about big numbers? I said flow at two different test pressures and consider the results. I can tell from your comments that your time with a flow bench is limited. As for the guy who has never pulled to the line and raced a flow bench...how silly can you be? Every serious shop has a flow bench a dyno. They also have torque wrenches and ring compressers too. Bet you never raced either of those? 
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: madscientist]
#1711962
12/19/14 02:35 AM
12/19/14 02:35 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
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Romeo MI
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Quote:
Are you specifically talking to me? What did I say about big numbers? I said flow at two different test pressures and consider the results.
I can tell from your comments that your time with a flow bench is limited.
As for the guy who has never pulled to the line and raced a flow bench...how silly can you be? Every serious shop has a flow bench a dyno.
They also have torque wrenches and ring compressers too. Bet you never raced either of those?
I use to have a flow bench... but if I wanted to use
a good one I took my heads into work and used the
benches that had in the head lab... I did all my
own porting... but people put way to much into the
numbers.... you can spend months on the bench or you
can race... what do you want to do
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: MR_P_BODY]
#1711963
12/19/14 11:09 AM
12/19/14 11:09 AM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
OP
Taking time off to work on my car
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OP
Taking time off to work on my car
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Posts: 15,439
Val-haul-ass... eventually
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Please, no pi$$in' contests needed on this thread. I think we're all... - aware that raw flow #s don't tell the whole story and... - know of combinations that run way under expectations due to people using heads that flowed better, but had way too large runners and killed the velocity. Carry on. 
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: Duner]
#1711965
12/19/14 11:22 AM
12/19/14 11:22 AM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
OP
Taking time off to work on my car
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OP
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Quote:
Does anybody ever test flow at positive pressures - as it works when in boost?
"Suck" vs. "Blow"... the head doesn't know any difference between them since it's all about the pressure differential during the test.
I do know that some top-level teams working w/ more specialized racing series have the equipment to test upwards of 100" H2O. Perhaps that amount of test depression takes into account boosted induction to some extent. 
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: BradH]
#1711969
12/19/14 02:41 PM
12/19/14 02:41 PM
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Joined: Oct 2007
Posts: 4,210
New York
polyspheric
master
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master
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New York
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Re: "the head doesn't know any difference between them"
Yes, it does, just not a lot - the Reynolds number changes with air density.
IIRC Smokey said (in one of his books) that tests were done at several depressions (pressure differential), but they had the following effects:
1. Low pressure (10") is relatively numb to small changes which will show up as power on the track or dyno - not sensitive enough. Why do they use it? Because their bench is too small to pull a higher depression on a big port.
2. High pressure (above 28") is very sensitive to small changes, to the point of being "nervous" and showing flow changes for mods too small to actually affect power.
3. 28" showed the closest relationship between a change in flow to a change in power - as close to linear as he could get.
How about real-time dynamic testing? He built a fixture with a huge electric motor that turned over a complete engine while testing flow, and found it didn't help.
BTW: the "conversion tables" for comparing flows at different depressions? The math is correct, but the heads do not perform that way and the calculated result is not accurate compared to an actual test at the other depression.
Boffin Emeritus
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: polyspheric]
#1711970
12/19/14 03:37 PM
12/19/14 03:37 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
OP
Taking time off to work on my car
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OP
Taking time off to work on my car
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Val-haul-ass... eventually
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Quote:
...
1. Low pressure (10") is relatively numb to small changes which will show up as power on the track or dyno - not sensitive enough. Why do they use it? Because their bench is too small to pull a higher depression on a big port.
Winner! Winner! It's the old saying "If all you have is a hammer, everything looks like a nail." And I resemble that remark... 
Quote:
2. High pressure (above 28") is very sensitive to small changes, to the point of being "nervous" and showing flow changes for mods too small to actually affect power.
I think the higher pressures today are being used to identify when issues exist that aren't apparent at 28" (or lower). I can't speak to the "nervous" tendency, having not been involved with it first hand (yet?).
Quote:
3. 28" showed the closest relationship between a change in flow to a change in power - as close to linear as he could get.
Right; he stated he found a direct correlation between flow improvements and dyno improvements for results taken at 28"... and that's been the rule of thumb for decades since.
Quote:
BTW: the "conversion tables" for comparing flows at different depressions? The math is correct, but the heads do not perform that way and the calculated result is not accurate compared to an actual test at the other depression.
Understood, which why (even for my amateur efforts) I'm looking into a higher-capacity bench.
FWIW, these are tests on the same two heads on the same bore adapter size w/ the first columns' results being from my SF-110 (w/ BIG correction factors applied) and the second from Dwayne Porter's Saenz S-600 bench tested at a true 28".
Victor test #3 cylinder on 4.375" bore
Lift --- 110 -- 600
.100 --- 73 --- 75
.200 -- 155 -- 169
.300 -- 224 -- 237
.400 -- 282 -- 280
.500 -- 317 -- 318
.550 -- 329 -- 329
.600 -- 343 -- 341
.650 -- 346 -- 347
.700 -- 350 -- 345
Stage VI test #1 intake on 4.375" bore
Lift --- 110 -- 600
.100 --- 68 --- 69
.200 -- 140 -- 143
.300 -- 200 -- 213
.400 -- 250 -- 262
.500 -- 288 -- 293
.550 -- 305 -- 305
.600 -- 305 -- 307
.650 -- 308 -- 307
.700 -- 310 -- 307
The high-lift trend I see is that the peak #s max at a slightly lower lift tested at the higher pressure, plus the Victor started showing signs of backing up slightly at a lift where my 110 still showed small gains.
The improvements in Dwayne's .200-300" #s may be from him having notched the top of his bore adapter... but I'm going from a fuzzy memory during one of our talks years ago.
I know from my own tests on my 110 over the years that even at lower test pressures some ports just sound "ragged" while others are much smoother. I'd like to know how that translates at higher test depressions, too. 
The other thing I need to pay more attention to in the future is velocity profiling.  / /  / 
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: GTX MATT]
#1711972
12/19/14 04:40 PM
12/19/14 04:40 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
OP
Taking time off to work on my car
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OP
Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Quote:
Quote:
2. High pressure (above 28") is very sensitive to small changes, to the point of being "nervous" and showing flow changes for mods too small to actually affect power.
3. 28" showed the closest relationship between a change in flow to a change in power - as close to linear as he could get.
Would this tell us more about what we could expect from a head with ports far too small for the application? Like a 906 head going on a 540 inch engine?
IMO, that's a simple case of the head not having sufficient cross-section area for the cubic inches it's expected to feed ==> CHOKED
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: BradH]
#1711973
12/19/14 06:05 PM
12/19/14 06:05 PM
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Joined: Oct 2007
Posts: 4,210
New York
polyspheric
master
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master
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New York
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The conversion between flow at one depression and another is just simple math.
The change is the square root of the new pressure divided by the old pressure. Let:
C = change
O = original test pressure
N = new test pressure
C = (N ÷ O)^.5
Example: compare 28" to 25".
28 ÷ 25 = 1.12
1.12^.5 = 1.058
28" reads 5.8% higher than 25", so multiply your 25" reading by 1.058.
Remember, this is what a steady-state test instrument will show, not an actual head!
Boffin Emeritus
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: MR_P_BODY]
#1711975
12/19/14 06:49 PM
12/19/14 06:49 PM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
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master
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Washington
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You don't have to spend all day at the bench if you know what you are doing. It's that simple. I don't use higher than 28" test pressures to inflate numbers. If you had as much flow bench time as you say you do, you would get that.
I'm going to race my 9 second torque wrench on Sunday. Whatcha got for that?
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: BradH]
#1711977
12/19/14 06:58 PM
12/19/14 06:58 PM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
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master
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Washington
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Mr P for the flow bench. The rest is for all you who want to call out my bad azz torque wrench (in reference to all the fools who discount dyno and flowbench time because we don't "race" them).
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Flowbench testing heads at MORE than 28" H2O?
[Re: BradH]
#1711978
12/19/14 07:20 PM
12/19/14 07:20 PM
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Joined: May 2014
Posts: 503
Idaho
1320Dart
mopar
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mopar
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Idaho
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I thought that all of us on here were striving for the same things? HAVING FUN LEARNING MAKING OUR STUFF GO FASTER
Greg ----------------------------------------------------------------- Cost is irrelevant, making memories is far more valuable! 
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