MaxRaceSoftware,

No I meant maximizing flow around 28 inches or 2 in hg across the head only. I would want to see almost 0 manifold drop or as low as possible. I want high pressure dense air in my manifold!

I meant that flow around 28 inches is a fair predictor of hp with a good port because that will usually develop sufficient airspeed to cause turbulence that if fixed will return more power and airflow through the engine. Fixing turbulence at 36 inches say and up sometimes only results in a bigger port with maybe a longer power band with less average power so you have to watch out.

If like you said you had ports of equal sections and volumes but one was stable and kept going to higher drops it should be a better head for sure. I'm only saying that if you have to make it appreciably bigger to kill turbulence at these higher drops sometimes you don't make any more power and can sometimes drop power.

 

Just for additional information
-and not for argument sake-

typically, an engine will make its "BEST" Peak HP at
.7 tenths to 1.2 inches Hg. of plenum vacuum

also, like in a resrictor-plate example or like a 2-Barrell resricted Class Rule engines....an engine can make Peak HP at for instance
7.0" inches Hg. of intake manifold plenum vacuum, but it won't be the "Best" possible Peak HP/TQ its capable of.

however, if the restrictor-plate or 2-Barrell Carb was removed and replaced with higher CFM unit.....you would discover that
at end of all your Dyno testing , the "BEST" Peak HP amount would usually always occur between .7" to 1.2" inches Hg.
never yet have seen an engine make its very "BEST" possible Peak HP at 1.5" inches Hg its capable of

Here is Dyno test results a few days ago on Chevy BBC 540 cid engine

RPM-------TQ---------HP-------Vacuum
5500----726.9-----761.2--------0.7
5600----726.8-----774.9--------0.7
5700----721.1-----782.7--------0.7
5800----734.1-----810.7--------0.7
5900----728.2-----818.0--------0.8
6000----728.8-----832.6--------0.8
6100----726.0-----843.2--------0.9
6200----724.6-----855.4--------0.9
6300----719.0-----862.4--------1.0
6400----713.3-----869.3--------1.0
6500----707.1-----875.1--------1.0
6600----704.1-----884.8--------1.0
6700----705.3-----899.7--------1.1
6800----697.4-----902.9--------1.2
6900----686.2-----901.5--------1.2
7000----679.2-----905.7--------1.2
7100----660.5-----892.8--------1.2
7200----649.4-----890.2--------1.3
7300----638.9-----888.1--------1.3
7400----629.5-----886.9--------1.4
7500----621.4-----887.4--------1.4
7600----610.9-----884.1--------1.5

best peak HP was at 7000 rpm = 905.7 HP and 1.2 inches Hg

7000=905.7 HP and 1.2 inches
7600=884.1 HP and 1.5 inches
--------------------------------------
21.6 HP difference in this example

the above is typical of results i see when vacuum is hooked up to plenum area in the intake manifold ...its also very possible to make "Best" Peak HP at lower than .7"inches Hg with
great carb booster signal/ plenum shape and size


Vacuum inches Hg------inches Water
1.5"-----------------------20.43

.7"------------------------9.53

1.0------------------------13.6195 @ 20 deg C

1.2"-----------------------16.34

2.0"-----------------------27.24 (almost 28 inches H2O)

7.0"-----------------------95.34"

A misconception about Flow Testing heads is to look at your Intake Manifold 's Plenum vacuum and think that you should flow develope your Cylinder heads at only or around that value in Inches of Water test depression.

but Peak Intake Port depressions are much higher than this
inside each individual runner near max piston velocities,
even though at the same time you only recording 0 to 2.0 inches Hg inside Intake Manifold Plenum

if 28.0 inches of test pressure was the "actual only direct correlation" to actual live engine operating conditions between Peak Torque and Peak HP points ....then there would be absolutely no chance on earth of a port going into Sonic Choke
....also there would be hardly any chance of any engine making more than 106.81 PerCent Volumetric Efficiency

All the millions of dollars and time spent in Research/Developement by Detroit, Japan, Germany, etc
all the SAE Papers and articles published on Sonic Choke and Inlet Mach Index subjects would be useless !

Books like ;
1-Scientific Designs of Exhaust and Intake Systems"
by Phillip H Smith page 237 chart 13:5 ....would not apply

2-The Internal Combustion Engine in Theory and Practice
Vol 1 by Charles Fayette Taylor
page 173 Z-Factor ...would not apply

3-Dynomation ....would be wrong

4-Engine Expert-Alan Lockheed ....would be wrong

5-David Vizard ...would be wrong

6-Buick Motor Division (V6 Race effort) ..would be wrong

7-Chevy Race Shop ...would be wrong

8-Ford ...would be wrong

9-Darrin Morgan (Reher-Morrison)...would be wrong
Darrin states some of Chevy Indy Racing League (Chevy IRL)
Cylinder heads were Flow developed at 150 inches of water
...also states in same interview he is planning to go to 50 to 60 inches test depression when flow developing cylinder heads

From my personal experience....i've fixed a lot of Cylinder Heads
that other HeadPorters missed when they only Flow tested those heads at only 28 inches or less .

36",48,50 or 60+ inches of Test Pressure
you use these higher test pressures to find out
if flow will stop gaining or reduce as you do your Flow Tests in Valve Lift increments on the FlowBench

maximum intake port velocities inside intake ports will be
usually 600 to 700 feet per second before going into Sonic Choke

Flow_Velocity_FPS = ( Test_Pressure ^ .5) * 66.2

where Test Pressure can be FlowBench Test depression or can be Pitot Velocity Probe pressure ...all in inches of water

^.5 = same as square root

66.2 = factor

FPS = feet per second


28 inches = 350.3 fps....approx 1/2 of Port Limiting Velocity in live engine ......also = 106.9 % Volumetric Efficiency


600 fps = 82.15 inches of water ...also = 120.16 percent Ve
700 fps = 111.81 inches of water...also = 127.44 percent Ve

.55 Mach = approx 616 fps ..also = 121.25 percent Ve
616 fps= 86.59 inches of water

 

MaxRaceSoftware,

No I meant maximizing flow around 28 inches or 2 in hg across the head only. I would want to see almost 0 manifold drop or as low as possible. I want high pressure dense air in my manifold!

I meant that flow around 28 inches is a fair predictor of hp
============================================


racer7088 (Erik) ...i definetly agree with you that 28 inch Flow numbers are a very good indication of potential HP to expect ;

heres a little more info ;

Peak_HP = Flow_CFM * .257 * Number_of_Cylinders

is estimated potential Peak HP to expect
you multiply .87 percent times cam's theoretical max lift , round off to nearest .050" in Flow Test, then see what CFM is at 28 inches

example=> .700" Lift cam
.700 Lift times .87 percent = .609" Lift
Flow head at .600" Lift , then take CFM at 28 inches and calculate HP potential with above formula

.257 Factor = for beginning engine builders and engines near 10.0:1 Comp Ratio

.285 Factor = would be for Professional engine builders with wet sump pans, lightweight rotating assemblies, low tension great sealing rings, deep oil pans, etc.
excellent use of inertia/wave tuning with 9.5 to 11.5:1 Comp Ratios or
11.5 to 13.0:1 CR ranges without fully utilizing inertia/wave tuning effects

.300 to .310 Factor = Current ProStock Technology with dry sump, unlimited carburetion, Hi Comp Ratio, ultra lightweight rotating assembly, etc, max use of inertia/wave tuning, etc, 14:1 to 17:1 Comp Ratios
(usually no better than .3200 efficiency or no worse than .2980 eff %)

all factors are just baselines

major errors will be from no 2 FlowBenches or Dynos read the same

and there are people with bogus FlowBenches and bogus Dynos out there ..that makes above Factors appear to be incorrect

but if dyno or flowbench is honest,
those Factors will be very close to reality

but its still bench racing
just gives you a ballpark guesstimate of what to expect.

---------------------------------------------------------

Darrin Morgan of Reher-Morrison
has SpreadSheet online at his website

in that SpreadSheet, Darrin's HP prediction is
1324 HorsePower which is 165.5 HP per Cylinder

which is about .2982 Factor

pretty close to .3000 Factor i came up with for Pro Stock technology

Reher-Morrison
1.025 " max approx Lift range times .87 percent
equals = .892" lift, rounded to .900" Lift

at .900" lift heads flow 555.0 CFM at 28 inches

.2982 Factor

 

Erik

You make a good point about increasing size.

I just want to emphasize that shape is a better method and area to work on to control intake port turbulance ( which you did not disagree with).

The shapes I use work at 7" 28" 45".

MaxRace has more Time dragging air thru ports than I do!

 

I just want to emphasize that shape is a better method and area to work on to control intake port turbulance ( which you did not disagree with). SBC
-----------------------------------------------------------------

SBC,

yes you use the "Port Shape" not the "size"
to correct turbulence or flow separation

you use the higher test pressures "ONLY" to verify that
the "PORT SHAPE" is correct !!

the reason to flow test at higher test depressions than 28 inches
is to find out what "SHAPE" will work at the "Live engine's"
port velocities

 

700 fps Sonic Choke ?

I thought the speed of sound is roughly 1120 fps depending on the air temperature?
=========================================

1120 fps => yes, you are roughly correct for mean sea level
and Standard Temperature and Pressure conditions (STP)

but also the speed of sound is "zero" in vacuum !!

so at a point or certain amount pressure differential, the actual speed of sound is

much less in live running engine on Intake side

its been known for many decades or almost a Century now, by many researchers like

Ricardo, Heywood, MIT, Ford, GM, Chrysler ,Honda etc along with many SAE papers on

Sonic Choke conditions in Intake and Exhaust ports

recently many engine builders and headporters have used terms like
1-Port limiting Velocity
2- Inertia Block
3-Flow separation

to describe Sonic Choke conditions

Common sense tells you that its "not possible" to run the engine higher and higher in

RPMs to Infinity and continue to make infinte power with infinte port velocity !

Sonic Choke occurs in all engines at a certain port velocity
and sets the point where power will ultimatelty fall off
and where pumping losses skyrocket

in larger Short Turn radius heads with straighter shot at valves like ProStock

technology ..Sonic Choke can be delayed to near .70 of speed of sound (STP referrence

point)

in heads like older 23 deg valve angle with more abrupt turn into bowl area ..Sonic

Choke conditions will occur near .50 to .60 speed of sound (STP referrence point)

if all Ports could be made perfectly straight , then Sonic Choke conditions could be

delayed to .80 to 100 percent of speed of sound

supposedly research papers have shown Wankel engine design to approch .80+ speed of

sound port velocity before Sonic Choke condition occur

FlowBenches are steady-state flow measuring devices

4 Stroke engines are "Batch Processors"
"Inertia Block" with pressure differentials induce Sonic Choke conditions

 

Holy F...

This thread has more "over the head factor information" than the
Caramilk secret!


#1. Sonic Choke in a nutshell = The point where intake runner
velocity is so high, that acoustic tuning is no longer possible?

#2. Flowing a head at 36 inches of water is dynamically outside
of *most* street/strip engine capabilites.

My Meaning: To enable enough air flow through the runner to
maintain a 36 in. H20 reading would require massive amounts of
air movement dictated by large engine displacement, RPM, etc.

Such engines would have poor low RPM efficiency (VE), but would
begin to create decent port velocity at high RPM.

Perhaps a Pro-Mod engine would fit this category?


#3. If manifold vacuum increases to more than 1.2 in./hg. this means
that the carburetor or Throttle Body is too small. The pistons
drawing down are creating a differential of pressure between
the intake valve and throttle blade.

< 1.2 in./hg. means venturi or Throttle Body is too big

= ~ 1.2 in./hg. means venturi or Throttle Body is just about right

> 1.2 in./hg. means venturi or throttle body is too small



Yes, No, maybe so on all assumptions?

 

#2. Flowing a head at 36 inches of water is dynamically outside
of *most* street/strip engine capabilites.

My Meaning: To enable enough air flow through the runner to
maintain a 36 in. H20 reading would require massive amounts of
air movement dictated by large engine displacement, RPM, etc.
========================================

Zero_to_69....you were doing OK until you got there !!

"Scientific Design of Exhaust and Intake Systems"
by Phillip H Smith was written/published => 1962

in Morrison Pressure Indicator charts in book
you can calculate that even way back then ,
on the 2000 to 3500 RPM engine examples Smith
talked about ...that max intake port depression
correlated to well over 36 inches of water (84 inches +)

and thats with old low rpm. small valve , small port engine pure street technology of 1950's to early 1960's

a 14 cid lawnmower 1 cyl engine can have much higher than
36 inches of water max intake port peak flow depression
at or near max piston velocity to max cyl volume
-------------------------------------------------------------------------------

#2. Flowing a head at 36 inches of water is dynamically outside
of *most* street/strip engine capabilites. -Zero_to_69

Zero_to_69......the car you drive...its engine will have more than
36 inches of water depression between peak torque and peak hp points

bone stock car's engine cruising down highway at 21.0" inches Hg. = 286.01 inches of water depression in intake manifold plenum

 

Zero_to_69

Here's a little more Info

Post from another website ;

Quote =>

In the gas industry laboratory where I used to work, where precision gas flow measurement is required for revenue purposes, positive displacement flow meters are always used. These either use a bellows that fills and empties, or a partly submerged turbine where inverted buckets on a paddle wheel fill and empty as the thing slowly rotates. These are highly accurate and have low pressure drop and work right down to zero flow.

For laboratory (high) air flow references we used sonic nozzles. What you do is have an accurate calibrated nozzle, and increase the depression across it until the flow goes sonic. Any further increase in pressure differential across the nozzle gives no further increase in flow beyond that point.

You connect up the sonic nozzle to a monster vacuum pump and open the valve. You hear the air rushing into the hole with a mighty roar. As you open the valve further the roar gets louder, then suddenly it goes dead silent ! ! As the air rushing in gets to the speed of sound, no sound can escape back out. Fascinating stuff.

You then know exactly how much air volume is rushing down that hole, and you can put your test piece in front of it and know the flow will not change from the exact sonic nozzle calibration figure as long as it remains sonic.

 

Hey, two out of three isn't bad!

I'm having a tough time understanding this "Inches of Water"...

One of these days, I'll grasp it. After a few more replies here
and chapters of Dr. Morrison's/ Dr. Smith's book, I might surprise myself and
some of you as well!

I'm on chapter six at the moment. Getting even more interesting
as I flip every page.

Thanks for the guidance,
Tino

 

I'm having a tough time understanding this "Inches of Water"...


like OldSStroker said =>

GOOGLE is your friend. Visit him.

you probably benefit from Freeware Units Conversion software
or Conversion Charts

Pressure Conversions

1 psi = 27.7296 inches of water at 20 deg C

1 psi = 2.0360 inches Hg (Mercurcy) at 0 deg C

1 inch of Mercury (Hg.) = 13.6195 inches of water

do searches for rest of units you are interested in ?

 

It's not the unit conversion that I need to grasp, it's how the
numbers are related to head flow.

For example, the flow bench construction and measurement points.

In my head, I see a flow bench with a cylinder head bolted to it.

A valve and a dial gauge

The intake port of the head is fitted with a standard flow device.

The chamber is sealed to the bench to a calibrated cylinder.

Air is sucked through the intake port, through the chamber at a
valve lift of x.xxx inches.

The manometer reads 28 inches of water ... or when the air flow
is sufficient to pull 28 inches of water, the data is reported.

IE: 200 CFM @ 0.500" valve lift @ 28 inches of water

IF we were to increase the flow of air through the flow bench until
the manometer read 36 inches of water, I would suspect the rate
of air flow to increase to maybe 250 CFM (same valve lift).

Or...if the valve was slightly closed at the same rate of air flow (250 CFM):

The manometer reading would go higher if the intake port could flow
the air (IE: 40 inches of water).

The manometer reading would fall if the intake port choked air
flow.

That's the picture in my head at the moment and maybe that's
the reason I can't grasp the concept.

I would have no issue reading web links if I knew they were credible.

I could read something over my level of comprehension and think
it was correct just because it sounded cool. I'd rather make mistakes
here and be corrected before I flap my mouth in the real world

 

A 28 inch tall and one square inch base water column weighs one pound. So does an identical 2 inch column of HG (Mercury). When you create a one PSI drop you can support that much water in a manometer. You are reducing the pressure under the head or in the cylinder under the head to one PSI LESS than what is in the intake port so air rushes in to equalize with this and it is measured in terms of flow at that particular pressure drop.

One PSI drops generally correlate with about 145 cfm/ in^2 which is right at 350 FPS average velocity in a straight pipe and less or more at the valve and over the short turn in areas of mismatched velocities and turbulence. Most all out ports are developed around 100 M/S average velocity on intake to develop peak power or are sized similar to that when initially sized. At higher average velocities than this power tends to drop off. I used to live with two engine designers at Ilmor now and I know about how they size stuff there too but again they test stuff at different drops too to uncover turbulence issues that can hurt the port a little at peak instaneous depression. The weird thing is that sometimes fixxing this by going much bigger than the cross section to create the approximate 100 M/S velocity will actually hurt the engine if it involves significantly bigger cross section to slow the air down there locally.

 

Zero_to_69 ,

picture of screen with flow test inputs

http://www.maxracesoftware.com/Flow_Max_Intake_1.jpg

basically,

you start flow tests with valve open
for example, at .200" Lift (or whatever starting point)

you adjust intake flow control **** to increase test depression to 28.0 inches of water ..on vertical manometer

you then look at inclined manometer which is calibrated in percent ...for flow percent reading of a certain orfice flow


the percent reading is multiplied times orfice CFM @ 100.0 percent
to get Flow CFM


you open valve to .300" Lift ....as you do..the test depression on vertical manometer drops
so you turn flow control **** till you again are back to 28 inches

then again read Flow PerCent Scale (inclined manometer)

usually, everytime you increase valve lift, the vertical manometer level drops

and when you adjust back upwards to 28 inches you see PerCent of Flow (inclined manometer) increase likewise if flow is also increasing


link to picture of flow steps
http://www.maxracesoftware.com/FlowMax_1.gif

http://www.maxracesoftware.com/flow_bench_pictures.htm


this head had small short turn shape problem
which was later corrected
which netted better flow at all lift points


try SuperFlow..and download SF-600 or any other .PDF file
FlowBench manual

just because you don't have a FlowBench doesn't mean you can't download any of their manuals which show you how to flow heads (Basics 101)

 

The monometer simply shows how much pressure drop is being applied to that port to make it flow what it is flowing.

The higher the pressure drop the higher the flow rate will be as it is related to the square root of the difference in the new to the old pressure drops.

The thing is, that the port or whatever you are actually flowing also can go turbulent and flow only a LITTLE MORE or the SAME or even LESS at a higher pressure drop very easily instead of continuing to flow more and more.

If you increase the pressure across this port even more eventually the port starts to back up from the chaotic and disorganized flow that results from turbulence and now at this point even though you are putting more "suction" or pressure drop on the port it is now flowing LESS than it was in true and in mass airflow than it was earlier with the lower drop across it!

All these pressure drops are caused by the shortblock which is essentially the supercharger or "blower" underneith the heads that make them flow what they do. WIth more cubes and/or higher rpm the pressure drop on a head is increased and you can keep turning more and more rpm untill you cross that airspeed limit in the heads we are talking about where true mass flow drops and then you are on the downside of your powerband and have to shift because spinning the engine higher is not allowing you to burn any more fuel and air.