Superflow 110
instructions section 1.0
page
Flow-testing 110
1.1
ting heads test 1.5
1.6 Tes
data sheet
tes testin ting • test ample
t data
1.7 A nalyzing t th he Avoiding
1 2 2 3 4 6 8 9
2.0 2.0
Air Flow Through Engines
3.0
HP &
4.0 4. 0
Intake Int ake Port Area rea
5.0 5.0
Valve Seats
18
6.0 6.0
Valve Sizes
18
7.0 7.0
Valve Lift
8.0
Combustion Combu stion Chambers
22
9.0 9.0
Dynamic
23
10.0
Inertia
11.0
Test Pressure Conversion Conversi on Chart
26
Suggested Suggested Additional References
27
& CFM
Shape
Flow
Flow Effects Supercharge Effect
10 12 16
19
24
1.0 Flow-testing 1.1
Superfl ow 110 description The Superflow 110 is designed to the air-flow resistance of engine engine cylinder cylinder hea ds, intake intake manifolds, velocity and restrictor plates. For intake testing, air is is drawn in through the cylinder head into the through the air blower, and exits through the orifice plate at the top of the Superflow Superflow 110. 110. Fo re xh au st testing, the path of the the air-flow air-flow is reversed by a switch on the front control panel.
The test pressure meter (manometer) measures the pressure or vacuum at the the base of the the test test cylinder. The test pressure is adjusted to a standard standard valu e, for instance instance 15.0 inches of wat er, by turning the flow control knob on the lower front panel. Separate knobs control either the intake or exhaust flow. The amount of flow is read from the inclined flow meter (manometer). The flow measures the pressure difference across the 5 flow orifices at the the top of the Superflow 110. By selecting different combinations of or ifices ifi ces, , the flow meter can be used in any of 9 different ranges to obtain high accuracy over a wide range of flows. The flow meter reads 0 to 10 0% of any flow range selected selected with the rubber stoppers. A separate test test orifice with a .312" and a 1.875" diameter hole is included for calibration of the flow tester. The machine requires 110 VAC, or 110 and draws draws 15 amps .
electrical power
1.2 1.2
What Is a flow test? In its its simplest form, flow testing testing consists of blowing blowing or sucking air through a cylinder head at a constant Then the flow rate is measured at various valve lifts. A change can be made mad e and and the head re-tested. re-te sted. Greater air flow indicates an im. If the tests are no corrections for atmospheric conditions or machine variations are required. The results may may be compared directly. At the other other extre me, it is possible to adjust and and correct for for all variations so that test results may be compared to those of any other head, tested tested under any conditions on any other other Further calculation s can can be made to determine valve valve efficiency and and various recommended port port lengths lengths and and cam timing. •• The calculations are very without a calcu lator , preferably with a square root key. The calculations are not essential to simple flow testing. Adapting heads for for testing testing Cylinder heads are mounted onto the Superflow by means of cylinder adaptors adap tors. . The adaptor consists of a tube tube 4" long with the same same bore as the engine and and a flange welded on each end. The lower flange is bolted to the flow tester and the upper flange is bolted or clamped to the the test cylinder head. The flanges flanges must be flat or gasketed to make an airtight seal. The adaptor adaptor tube may be 1/16" 1/16" larger larger or or smaller smaller than the the actual actual engine engine cylinder. In some cases cases it is convenient to make the upper flange of the adaptor about wider than the test cylinder head so that the head will be supported when it is offset for testing the end cylinders.
.
A device must be attached to the cylinder head to open the valves to the the various test test positions. The usual method is to attach a threaded mount a arm end of a bolt contacts the end end of the the valve stem. As the bolt is rotate d, it pushes open the valve. valv e. A 0 to 1" x .001 dial indicator be mounted to the the same same fixture with its its tip tip contacting the the valve spring spring retainer to measure the amount of valve opening. The standard standard valve springs should should be replaced replaced with light springs springs for testing . See the photos in the Superflow brochure for various types of valve openers. On the intake side of the cylinder head, is strongly recommended that a radiused entrance guide be installed to lead the air straight into the the head. The guide should should be about one port port width in thickness and be generously radiused on the inside all the way down to the the head. The intake intake manifold can also be used. The exhaust flow flow may exit directly from the head.
rt
1.4
Flow test preliminaries All test data may be recorded on the standard Superflow form test data sheet, (see samp le) . Before beginning a test, record the head and measure the stem and valve The net valve area is the valve area minus the stem area in square inches. net valve area = .785
-
)
Before installing the test adapter, install only the test orifice plate onto the Superflov. Install all the rubber stoppers in the orifice plate on top of the Superflow and set the direction knob to Close the intake and exhaust flow control knobs lightly against their seats. Zero the and and zero the flow With only the small .312" diameter test orifice open, turn on the machine and slowly open the intake flow control until the test pressure reaches 10. 0" of wate r. The flow meter should now read approximately 45% on the 10.0 range orifice open on top). This indicates a flow of .45 x 10 cfm 4.5 If flow is within 1 cfm of this reading, the machine is worki ng properly. Now all the rubber stoppers the top orifice plate (185 cfm range) and open both the .312" and the 1.875" diameter holes in the test orifice. Adjust the intake flow control again until the test pressure reads 10 .0". Allow the machine to warm up for several minutes until the upper thermometer reads about higher than the lower Multiply the flow meter reading times 185 cfm to obtain the test orifice flow. It will be 153.2 cfm under standard conditions . If the flow meter does not read 153.2 cfm, the flow readings will all have to be corrected by a correction factor. This factor is equal to:
Test flow correction factor -
test orifice flow
This factor compensates for machine variations and all atmospheric conditions. Enter this information on the test data For best acc uracy, this factor should be determined before each day's testing. It does not need to be re-determined before additional tests on the same day. Multiply the flow ranges on line C by the correction factor to obtain the corrected and enter these in line D on the data sheet. The corrected flow ranges may be used for all tests made on the same day.
If Superflow wil l not draw 10" due to low line voltage, use 8" test pressure .
Then:
Flow correction factor
flow
All tests should be performed at the same ratio of valve lift to valve diameter, or L/D ratio. Then the flow efficiencies of any valves can be compared, regardless of size. Multiply the valve diameter by each of the six L/D ratios to obtain the valve lift test points . Fill these in on lines A and of the data sheet. Choose the proper
pressure for the intake valve diameter
the exhaust valve at the same test pressure. in on line 3 of the data sheet. Valve diameter 2.1" to 2.3" 1.6" to 2.05" less than
Fill the test pressure
Test pressure 5" 10" 15"
This completes all the preliminary preparations. While they are very time they will insure that the test results are valid and Most of the preliminaries will not be required for subsequent tests of the same head. .. . . 1.5
Performing a flow test
'
Remove the test orifice plate from the machine and install the test head, cylinder ad apter, and valve opener onto the flow tester for the actual flow tests. Set the dial indicator to read 0 with the valve closed. Install either the intake manifold or an air inlet guide on the intake port.
inclined flow meter. Close the intake and exhaust flow control valves lightly against their seats (do not force or they will be damaged). Place the rubber stoppers into orifices 5, 4, 3 2. Turn the mode selector switch to intake. Turn on the Superflow and adjust the intake flow control until the test pressure meter reads the test pressure you intend to use. Determine the leakage flow from the and Because only the #1 orifice is open, the flow meter reads at A reading of would indicate a leakage flow of .47 x 10 cfm 4.7 cfm. Leakage will usually be from 1 to 10 cfm. If there is no leakage, the test pressure may rise to the top of the meter. This does not matter as long as the flow meter reads zero. The leakage not affect the test provided that you correct for it in your results. Turn off the Superflow, Repeat this test before the exhaust tests. Enter the leakage on line 8 of the data sheet to be subtracted from the chart cfm. Open the valve in the head to a lift of .20 valve diameter. Remove all four rubber stoppers from the flow orifices and turn on the Superflow. Adjust the flow test pressure to 10.0" and allow the machine to warm up for 5 minutes. This step may be omitted if the Superflow has been warmed up previously.
The
is designed with multiple ranges so that the flow For accuracy, use the orifice ranges which give readings above 70% of the scale. If the reading exceeds 100%, switch to the next higher range shown on the flow chart by changing the combination of orifices open at the top of the Superflow. If you have previously determined the proper flow ranges, fill in line 5 and skip the next step. If no t, open the valve to the first of the six lift points. To select the proper flow range, begin with the largest stopper and re-install the stoppers in the flow orifices until the flow meter reads above This is the proper of orifices for this test pressure, head , and valve lift. Always use the same combination for future tests at this point. From the chart on the front of the machi ne, determine the full scale range value, then record the corresponding corrected range from line D on line 5. Re-adjust the test pressure to the recommended value and record the readings of the and the temperature difference between the top and bottom thermometers onto the Superflow data sheet. Turn off the machine. Go to the next valve lift and repeat the above steps. (Each valve lift may require a different flowmeter rang e.) Continue this procedure until you have reached the maximum lift test point.
and close the intake flow control valve . Move the valve opener and dial indicator to the exhaust valve and repeat the above procedures. This completes the test. — . For intake manifold tests, remove the radiused inlet air guide and replace it with the intake manifold. Repeat the intake tests and compare the results to determine the effect of the intake
T E S T
Test
D A T A S H E E T
Description: ''
/VLB
valve
area:
Exhaust valve
area
Test Operator Test orifice flow at 10" test
Test flow correction factor:
7 = /•
.30
Valve lift/diameter A. (in) B. Exhaust valve
.
/So
Flow range (cfm) 10.0 '•
1. Test Number
/SO.
1 40.0 1 '8-3
1
2
|
4
3
59.0
105.0
5
6
185.0 2 '
1
fcO.O
7
8
9
10
n
12
/C
4. Valve lift (in.)
•375
485
5. Corr. flow
'S3
6.
.9/°
7. Chart cfm Leakage cfm
•
• 7/8
335 ,S
9. Test cfm (L7-L8) 10.
difference
So
So
4i'
45'
11. Temp. diff. factor
•/£
570
12. Corr. tes t 13 Corr Potential (from 15. 7. rating Test
Z2.C
3
/Si
Z73
47o 79
84
r/
7c
eg
7/
74
Test valve
valve
a
T to $ >
I
<
Valve diameter
1.7
Analyzing the test data For simple analysis of the test results, it is only necessary to calculate the test line 9. First calculate the chart cfm, line 7 by multiplyin g the flow meter reading, line 6, line 5, the corrected flow Then subtract the leakage cfm , line 8, from line 7. The result is the test cfm, 9. This can be compared to other tests without further calculations.
-
.
To correct for the temperature difference caused by the air passing through the blower moto r, the test cfm must be multiplied by the temperature difference factor shown below. The temperature is the difference between the upper and lower thermometer
• -•
Temperature Difference Correction Factor Diff. Intake
5° .996
10° .992
15°
20°
25°
30°
35°
40°
45°
50°
55°
.988
.984
.981
.977
.973
.970
.966
.962
.958
Exhaust 1.004 1.008 1.012 1.016 1.019 1.023 1.027 1.030 1.034 1.038 1.042 The result is line 12 the corrected To obtain the valve efficiency, it is necessary to calculate the flow in c_fm square inch of valve area and then compare that to the best yet achieved. Divide line 12 by the valve area in square inches to obtain line 13. Then fill in line 14 from the chart in section 7, figure 6. Divide line 13 by line 14 and multiply by to obtain line 15, the flow rating. The percent flow rating can be used as an indicator of the room left for futher improvements in flow. These results can also be plotted on each test data sheet (see samp le) . scale to which the data is plotted. intake test points and triangles for
the graph printed on the back of The arrows shown indicate the Circles are used to indicate the the exhaust test points.
Many additional factors and relationships are discussed in sections 2.0 through 10.0 which follow.
1.8
Avoiding Test Errors
.
Each test you involves considerable effort on your part, but this effort can all be wasted if you allow undetected errors to creep into your test program. Always check the following points to reduce the chances of mistakes. 1. 2. 3. 4. 5. 6.
8.
Always use the same orifice range at the same test point. Keep the leakage CFM to a by making a good seal all surfaces, including the valves in the head. If light valve springs are used, make sure the valves are not sucked open by the vacuum of the intake tests. Always level and zero the meters before each test. Always use a flow inlet guide on the intake side of the head and always use the same guide and cylinder adapter. Try to conduct your tests when there are no frequent changes in line voltage. Voltage changes will not affect the accuracy of the Superflow, but they will cause it to surge and be unstable used in the same way and at the same temperature. When in doubt, repeat the tests. If you don't get the same
2.0
AIR FLOW THRO UGH ENGINES The horsepower of an engine is directly proportional to the amount of air drawn into the cylinder and retained until ignition occurs. By reducing the air flow resistance of the intake and exhaust tract, cylinder filling is and engine horsepower is increased directly. The average airflow through each engine cylinder can be estimated as follows: Average airflow
= 1.6 x HP per cylinder
The intake airflow rate for a single cylinder will be about 2.5 the average airflow for the cylinder because the intake occurs during only
of the total cycle.
For example, if a Chevrolet V-8 engine produces 440 HP , the HP per cylinder is 55 HP. Avera ge Airf low Intake Rate Peak Intake Rate
= =
1.6 x 55 HP = 88 cfm 2.5 x 88 cfm = 220 cfm 2.5 x 220 cfm 550 cfm
When an engine is ope rati ng, the pressure drop across the cylind er head ranges from 0 up to about 145 inche s of water at the 550 cfm flow rate. (This is equiva lent to the test pressure reading on the
The average pr essure drop is about 23 inches of water (or about 2" of merc ury) at the 220 cfm flow rate. When testing with the Superflow it is not important whether a test pressure of 5 or 10, or 15 inches of water is used, provided the same pressure is used for each subsequ ent test that will be compared to the origina l test. A head that meas ures 10% better at 5 inches of water test pressure will also measure better at 10 or 23 or 145 inches of wate r. The exception to this rule is at lower valve lifts or through small, long passage s. Then the test pressure must be kept above a certain minimum to insure that the turbulent and down and become lami nar. The mini mum recommended pressures are as
Min imum
Lift .050" .100"
. 2 0 0 " .300"
Conveniently, the bigge r the opening , test pressure
Mil 15" water 8" water
5" water V' the lower the required mini mum
11
Beginners in flow-testing are frequently confused by carburetor flow ratings. Presently in the U.S ., most carburetors are rated in flow capacity at a test pressure of 20.4 inches oi: water (1.5 inches of mer cur y). An 850 carburetor is one that passes 850 cfm of air at a test pressure of 20.4 inches of water. Ho weve r, if you observe a manifold vacuum gauge on a racing engine at full throttle, you will see that it only reads about 0.5 inches of mercury (7.8 inches of wat er ). At a test pressure of 7.8 inches of water, the same carbureto would only pass 490 cfm of air. This is why carburetor ratings appear to be all out to engine Large carburetors may be tested and on the Superflow, but only at a reduced test pressure. At a test pressure of 1" of wate r, the carburetor will flow 22X of its rated capacity at 1.5 inches of mercury. For example, at 1" test pressure, a 660 cfm carb will flow .22 x 660 = 145 cfm. AIR FLOW THROU GH ENGINES (Cont'd) The amount of power to be gained by improved air-flow depends on the engine's efficiency (the percent the cylinder is full). An engine with 60 % volumetric efficiency can be improved more than an engine with volumetric efficiency.
4000
5000
The volumetric efficiency of a gasoline 1.
can be estimated as follows:
Volumetric Efficiency = 5600 x
RPM x
100%
where CID is the dis plac ement of the engine in cubic i nc he s. Be sur e you use ac cur at e HP fi gu re s. If the volumet ric eff ic ie nc y on an un-supercharged engine exceeds th e HP or RPM figu res ar e pr oba bly
For an al coh ol burning engi ne, 2.
Volumetric
the formula i s :
12
HP &
&
&
H P, RPM, CID and engine air-flow capacity are all related in a definite fashion. With the wide spread use of accurate engine and it has become possible to measure the air-flow potential of a racing engine and then to predict its potential HP and the RPM at which the HP will peak. The effect of porting and manifold changes c an be anticipated in advance and proper changes made to take full advantage of the differences. The total air-flow thru a gasoline engine its maximum HP. At peak power, a racing engine will use 1.67 cubic feet of air (cfm) per minute for each HP it develops. For example, a 100 HP engine will use 167 cfm. This will hold true for any four-cycle gasoline burning racing engi ne. Alcohol burning engines will use 1.47 cfm per HP developed. To increase the power outpu t, either the air-flow capacity of the engine must be increased, or the air-fuel charge be burned more effecti vely. Racers have tended to concentrate primarily on increasing the air-flow. To put more air thru an engine, the flow resistance of the carburetor, intake manifold and cylinder head must be reduced. This need has led to hundreds of after market carburetors, manifolds and ported out cylinder heads, all designed to get more air thru the engine. The flow-bench is a measurement device designed to measure the air-flow capacity of various engine components. Air is or sucked, thru the intake system at a standard pressure, and then the air-flow capacity is measured. In this man ner , different parts can be compared and the effect of changes can be quickly evaluated. These flow tests are conducted at a constant peak air velocity at the va lv e, usually between 100 and 400 feet per second. While the flow-bench air velocity is not varying as it does in an operating engine, experiments have shown that flow-bench tests actually simulate engine operation closely enough. This is why flow-benches have become a major development tool for engine manufacturers and racers alike. But what is the relationship between the capacity on the flow bench and the horsepowe r of the engine? Tests have shown that if the complete intake system air-flow is measured at maxim um valve lift and at a test pressure of 10" of water, a well developed racing engine will produce the following HP per cylinder: 3.
|
HP
=
x (cfm at
of water)
Of course to reach this leve l, the engine must also have the the right cam, and a tuned exhaust system. In shor t, it be a well-tuned racing engine. With this formula, a head-porter can see that if he improves the maximum flow thru the intake system by 1 cfm, the engine will gain .43 HP per cylinder. (The formula is only for gasolin e engines without super-chargers). The intake flow lso determines the engine will develop peak H P:
at which the racing
(cfm at 10 " at wa ter)
CID
where CID is the engine displacement in cubic inches per cylinder. For super-stock and engines which are not all-out racing engines, peak power will occur at 10% RPM than formula 4 indi cate s, so use 2200 instead of 2000. Now, let's try out these formulas on an examp le. If you have a "220 HP" small-block 292 Chevy which runs in super-stock, what will be the maximum HP at what RPM? Tests show that at a test pressure of 10" of wat er, this intake system will flow 105 cfm of air . The CID per cylinder is one-eighth of 292 or 36.5 CID. .43 x 105 cfm
45.1
or for all 8 cylinders HP The RPM for 2000 for racing
=
8 x 45.1
=
H P
.
power will be (2200 is for super-stocks,
RPM
=
105 cfm
6330 RPM
So the engine has a potentail of 361 HP at 6330 RPM. But remember, this is the maximum potential HP . The engine will only approach this if everything else is optimized. Now, let's try another example to show how changes in the intake system will effect the engine performance. For this examp le, we wil l use a small block Chevy 30 2, displacement 37.75 CID per c ylinder. Head
Stock, 2.02" valve Normal ported, 2.02" valve Best ported, 2.02" valve Westlake, 2 x valves
Intake System Flow
12 0 1 43 cfm 16 0 cf m 17 5 cf m
Power
413 492 550 602
HP HP HP HP
@ @ @ @
6360 7570 8470 9270
RPM RPM RPM RPM
14
The "Normal ported" head is about the best that can normally be achieved, even with careful flow-bench testing. However, it is possible to improve the head up to the "best ported " level, though welding might be required. For the last two hea ds, the engines be wound up to 8500 and 9300 to take full advantage of the additional flow. This brings us to the need for another guideline. If the engine must hold together for more than a couple runs down the drag strip , the peak power should not be developed at a piston speed in excess of 3700 feet per If a few runs down the strip are you want , this may be raised to 4600 but the engine will need super internal parts to last even one
These rules can be reduced to a formula for the RPM for peak HP (remember, your shift points may be 1000 RPM or more above peak H P ) :
Safe peak power RPM
Maximum peak power RPM
27,600 in. stroke
Returning now to the example of the 302 engine, a well ported head would be adequate for most road-race applications for the 302 because the peak power is already being developed at slightly more than the 3800 piston the power peak was pushed to an even higher RPM, the engine would frequently fail to finish the race. To take full advantage of the extra breathing of the head , the power peak would have to be at 9270 RPM (4630 fpm) and engine life would be short. Without super internal parts, it would probably not survive even one run down the drag strip. The shift point would be up around 10,500 RPM. A lot for any Chevy!
To use the graph, the per cylinder of your engine and then you can read the RPM required for any particular HP and the CFM of flow capacity that will be required on the flow-bench at a 10" test pressure.
Intake System
For an examp le, suppose you have a 427 V-8 engine which will hold together up to 7500 From the graph for 53.4 CID (1/8 of the power per cylinder would be 85 HP if you can improve your intake system to 196 cfm on the flow bench at 10" of water test pressure. For all eight cylind ers, the engine could produce 680 HP at 7500 RPM. Of course it's not enough to simply calculate the flow capacity required . The engine must achieve it, and so let's talk about how to improve the engine airflow, and how to judge the flow potential of any engine. Intake Port Area and Shape For maximum flow, the ideal intake system would have a single carburetor per cylinder with a slide-plate throttle and a venturi equal tc .85 times the intake valve diameter. Below the venturi , the carburetor bore should gradually open up to the size of intake valve at the intake manifold entrance and gradually taper down to about .85 times the intake valve diameter at a point about 1/2" below the valve seat. The optimum length for the port will be discussed in Section 9.0.
17
In practice, this ideal is never achieved, but it does provide a guide-line for what an efficient port would be like. When porting out a cylinder head for flow, k eep the following points in mind. 1. 2. 3.
4.
6.
Flow losses arise from changes in direction and decreases in velocity (port bends and ex pansions). Port area should be between 65 % to 100 % of valve area. Remove material primarily the outside of port bend s, not the inside. This will improve flow by increasing the radius of the bend. Port length and surface finish are not important flow. The greatest flow loss in the intake port is due to the expansion of the air out of the valve. This makes the area from 1/2" below the valve to 1/2" above the valve the most critical part of the port. The valve seat shape has a substantial effect on the flow.
caused by port may wonder why the port should be necked down below the valve seat. The reason is that the air must both turn 90° and expand as it flows out of the valve into the engine cylinder. "Humping" the port inward just below the seat allows the air to make the turn outward toward the valve edge more gradually, reducing the total flow loss. Unfortunately, many stock ports are too large in this area already. The chart below shows approximately where the flow losses occur in a stock Chevy head with a 1.94" diameter intake valve. Note that the flow losses are negligible in the straight part of the port where it is easy to grind.
Bend at valve guide .4- Expansion behind valve guide .5 Expansion, 25° Expansion, 30° .6 .7 Bend to exit valve Expansion exiting valve For sand-cast surface.
Would be
fo
polished
As manufac tured, this head flows about 837, of its potential for a wedge-co mbustion chamber head. The best head porters are able to increase the flow to about of its potential with the aid of careful flow-testing. Further improvements are difficult without major surgery and welding. Grinding and enlarging the first in the Chevy port where it is easy to reach has very little effect. Valve Seats The valve seat has three purpose s: to seal the port, to the val ve, and to guide the air thru the valve. Sealing and cooling are promoted by a fairly wide seat between .060" and Maximum flow is frequently achieved with a narrower seat, usually around .030" wide. Multiple angle to fully radiused seats are essential for good air flow. A typical competition intake valve seat will consist of a 30° top cut .100" wide, a seat .040" wide , and a 70° inside cut .180" wide. An exhaust valve will work well with a 15° top cut .060" wi de , followed by a 45° seat .060" wide, and a 75° inside cut .100" wide. The O.D. of the valve should coincide with the outside of the 45° seat. Flow-bench experimentation will frequently uncover a superior shape for any particular head. A three angle seat will out-flow a simple 45 seat by up to 2 5% at lower valve lifts. 6.0
Valve Sizes
The total flow thru the engine is ultimately determined by the valve diameters. well-designed smaller valves will out perform larger valves on occasion, a good, big valve will always out-flow a good, smaller valve. Valve size is limited by the diameter of the engine bore. For wedge-shaped combusti on cham bers , the practical maximum intake valve diameter is .52 times the bore diameter. permit intake valves up to .57 times the bore diameter due to the extra space available in the combustion Four-valve heads are best of all , but the engine must operate at very high-speed to take advantage of the extra valve area. The present trend in racing engines is to keep the exhaust system flow to or of the intake system flow. This may be more than is Tests indicate that there is generally no power improvement as long as the exhaust flow is greate r than 607° of the intake flow. This would dictate an exhaust valve diameter .77 to times as large as the intake valve.
7.0
Valve Lift and Flow
The air-flow thru the engine is directly controlled by the valve lift. The farther the valve opens , the greater the flow, at least up to a point. In order to discuss a wide variety of valve sizes , it is helpful to speak in terms of the ratio of valve lift to valve diameter or ratio. Stock engines usually have a peak lift of 1/4 of the valve diameter, or .25 d. Racing engines open the valves to .30 d or even .35 d. The graph in figure 4 shows how flow varies with lift for a welldesigned valve and port . Up to .15 the flow is controlled mostly by the valve and seat area, but at higher lifts the flow peaks over and finally is controlled by the maximum capacity of the port. intakes have lower flow at full lift due to masking and bends, and are at a 1 5% lower level.
Fig. 4.
Valve potential air flow at a test pressure of 10" of water
::
ft -
y
50 -
±
X
-
-
20 -
z
10 t
*
.20
-
•
g
•u
Figure 6 can be used as a guide for judging the performance of any valve. To get the flow rate cfra for a particular valv e, simply multiply the cfm per square inch the chart by the valve area minus the valve area. The flow rate you get is not the "expected" flow rat e, rather the potential flow rate for a particular head at the test pressure. The maximum potential flow for some of the popular heads are shown in the comparison chart in figure 5 at 10" of water test pressure. These figures represent the maximum air-flow which can be expected under optimum conditions of port and valve seat design. Even well modified . heads will generally only obtain 80 % to of these figures.
5
Potential Air Flow
ve Lift/Valve Diameter
8 9 1 9 9 8 106. 0
.20 .25 .15 test pressure 56.6 53.0 46.2 76.5 102.4 109.2 81.2 108.7 115.8 91.5 104.8 112.0 127.6 146.3 156.2 153.0 218.4 159.2 182.6 195.0
106.0
159.2
.10
Intake Valves
i
VW 1.24" D. Norton 1.50" D. Yamaha TX 650, 1.62" D. Chev. Small Block, 1.72' D. Chev. Small Block, D. Chev. Westlake, 2x1.5" Ford 302, 2.25" D. Chrysler 2.25" D.
15 . 3 25 . 4 26 . 9 30.3 42 . 3 52 . 8
30. 50. 54. 60. 84.
213.2
58 . 9 11 2 . 5 11 9 . 0 11 6 . 7 162 . 7 22 5 . 0 20 3 . 1
227.2
If the flow reaches a maxim um value at a lift of about .30 you may wonder why some cams are designed to open the valve farther, even high as .37 d. The answer is that in order to open the valve more quickly and longer at lower lifts, it is necessary to "over-shoot" the maximum head-flow point. The extra flow is gained on the flanks of the lift pattern, not at the peakThe head-flow figures shown in Fig. 4, 5 and 6 are for the cylinder head alone with just a radiused inlet guide on the inlet port. When the intake manifold is installed the total flow will drop off from 5% to 30%, depending on the flow efficiency of the manifold. By measuring the flow at each valve lift with and without the intake manifold, it is possible to accurately measure the flow efficiency. Frequen tly, the intake manifold will have even more room for improvement than does the cylinder head. It is the total flow with the intake manifold installed which must be used in formulas 3 and 4 described on pages 12 and 13.
6
Valve flow
For hemi-intake and all exhaust valves
Valve Lift/Diameter Test Pressure
.05
.15
.20
.25
.30
cfm per sq. inch valve area
7.4
3" 5" 8" 10" 15" 20" 25" 28" 36"
.10
9.6 12.2 13.6 16.7 19.2 21.5 22.8 25.8
15.0 19.3 24.4 27.3 33.4 38.6 43.2 45.6 51.8
22.5 29.0 36.7 41.0 50.2 58.0 64.9 68.6 77.8
30.0 38.8
49.1 54.9 67.2 77.6 86.7 91.8 104
32.0 .41.4 52.3 58.5 71.6 82.7 92.5 98.0
33.0 42.5 53.8 60.1 73.6 85.0 95.1 101 104
.25
.30
For wedge intake valves
Valve Lift/Diameter Test Pressure 3" 5" 8" 10" 15"
20" 25" 28" 36"
.05
.10
.15
.20
cfm per sq.
7.4 9.6 12.2 13.6 16.7 19.2 21.5 22.8 25.8
15.0 19.3 24.4 27.3 33.4 38.6 43.2 45.6 51.8
22.5 29.0 36.7 41.0 50.2 58.0 64.9 68.6 77.8
area
25.7 33.2 42.0 47.0 57.5 66.4 74.2 78.5 89.0
27.5 35.5 45.0 50.2 61.5 71.1 79.5 84.0 95.3
28.6 37.0 46.8 52.3 64.0 74.0 82.6 87.4 99.2
From a flow stand-point a combustion chamber has a clear advantag e over the wedge. Until the valve lift reaches .15 valve diameter, there is little difference, but at higher lifts the is usually less shrouded. In most designs , the is also straighter due to the valve angle . These two advantages add up to an average flow advantage of at higher l ifts, even with equal valve diamete rs. When you consider that a chamber also generally permits the intake valve to be greater diameter than a wedge, it is easy to understand the success of the racing engine.
u s
i o n
~
•
—
In most eng ine s, it appears that the combust ion chamber design was dictated by the choice of valve geometry. Perhaps it should be the other way around. Most combustion chambers just don't combust as well as they should. and pent-roof combustion chambers are generally the best with wedge chambers being 5% to 1 0% worse. Most gasoline burning racing engines use a compression ratio of between 12 and 13.5 to 1. If the cylinder is completel y filled, you would expect that the torque per cubic inch of engine displacemen t wo ul d be the It and the are mostly due to combustion chamber effectiveness. One way to a is to measure the torque output per cubic inch of engine displacement. At the RPM of peak torq ue, a good chamber will develop 1.25 to 1.30 pounds of torque per It may be possible to raise this as high as 1.5 foot-pounds per CID, though not without an outstanding combustion chamber design and ram-tun ing. Most racing Detroit only reach 1.15 foot-pounds per CID. There is plenty of room for improve ment. A second guide line for judging efficient burning is the required spark advance for maxim um power. The efficient combustion chambers have higher turbulence and require less spark advance. A turbulent combustion chamber substantially reduces the "ignition delay" time between when the spark fires and the charge begins to burn rapidly. For example, a Chevy with a normal combustion chamber shape might require 42 maximum spark advance (35° ignition delay), while a highly turbulent combustion chamber might only require 33° BTDC advance (27° ignition The more turbulent chamber will also burn more rapidly and produce up to greater power from the same initial charge. Combustion chamber is more of an art than a science and so trial and error methods are frequently the only choice. In gen era l, strive for high turbulence and minimize the distance from the spark plug to the farthest part of the combustion chamber. At times combustion chamber burning complexities can make it very confusing when trying to compare cylinder heads on an engine. For instance, it is difficult to a cylinder head on a Chevy 302 and then on a Chevy 330. While the same head will bolt onto both engin es, the compression ratio, and combustion chamber effectiveness, and RPM range will all Even the degree of turbulence will change. These factors can mask differences due to the flow capacity of the heads and confound even the experienced engine builder.
Dynamic flow effects
"
Engine volumetric efficiency and power can be increased considerably by taking advantage of the natural dynamic effects which occur during the intake Both the kinetic energy and the resonant pulses can be harnessed to fill the engine cylinder at volumetric efficiences up to Without these dynamic effects, volumetric efficiency is limited to 1007=, without supercharging. When the inlet valve closes, a pressure pulse bounces back out the intake tract, and then in again toward the valve. By making intake tract the proper length, the returning pulse can be timed to arrive at top dead center of the next intake cycle, shoving extra air in and keeping exhaust gases out of the intake port. To visualize what occur s, imagine that one end of a steel bar is placed against a hard surface. If the other end is struck with a a strong pulse (tne hammer blow) will travel down the bar to the other end, and then back to the hammer end. The pulse will actually cause the bar to jump back towards the hammer! While the bar (or the air in the port) moves very little, a strong pulse has been transmitted through it. To use this pulse, the intake port must be the correct length. The pulse will help only through a narrow range of RPM. Above or below a certain range the pulse will actually decrease power so proper synchronization is essential. There are actually several pulses which can be used, corresponding to the 2nd, 3rd and 4th time the pulse arrives at the valve. The 2nd pulse is bes t, the others being weaker and shorter. Fig. 7
Inlet pulsation chart
Harmonic
Length formula
Lower RPM
2nd 3rd
897. 917. 937.
74,000/RPM *
Upper RPM
1087. 1047. 1047.
Pulse strength varies with inlet
Pulse Strength* + + +
107. 77. 47.
valve opening
The chart in Figure 7 shows the pulses which can be used. To obtain the inlet system length, divide the number shown by the RPM for peak HP as determined by the flow measurements (see Section 3. 0) . For exam ple, at 8000 RPM for the 2nd harmonic; length =
132,000 8,000
16.5"
This is the desired length from the intake valve to the air inlet entrance. For engines with a plenum chamber type intake, the length is from the valve to the plenum chamber. The pulse in the example will benefit from 89% up to 1087= of 8000 RPM, or from 7120 RFM up to 8640 The greatest benefit will occur at about below 8000 RPM. Below 7120 RPM or above 8640 RPM, the pulse will actually work to decrease engine power .
24
10.0
Inertia-sup ercharge effect When the intake valve starts to clo se, the fast moving air column tries to keep itself into the cylinder. If the inlet valve is closed at just the right instant, the extra charge will be trapped in the cylinder (called inertia-supercharging). Volumetric efficiencies up to can be obtained. To determine the proper valve timing for maximum inertia-supercharge, it is necessary to determine the inertia supercharge index, Z,and then the valve closing timing can be determined from Figure 9. Z depends on the average inlet valve area, so this must be First determine the inlet flow vs . valve lift for the complete intake system. Next determine the cam lift profile at the valve versus the degrees of engine rotation. From these two pieces of data , construct a graph, as shown in Figure 8, of engine flow in versu s degrees of engine rotation. This is a plot of the total engine flow considering both the intake system and the cam.
Count the number of squares under the flow curve and divide them by the total number of squares beneath the 87 cfm line. The number obtained is the intake flow rating Area under flow cur'
The will general ly be between 0.35 and 0.45 for good engine s. This is a total rating of the intake system flow for any engine. The higher the the better the engi engine. The average inlet val
area is th
average inlet area
times the intake
x Valve area in sq. inches
Now this data can be used to determine the inertia-supercharge index, Z, from the formula
z -
126,000
V
x Inlet Length t area
'
where CID is the displacement of one cylinder in cubic inches and the inlet length is in inches. Z will usually be between 0.9 and 1.2, and is also a measure of the strength of the inertia-supercharge which will be obtained. When Z has been determined, use Figure 9 to obtain the correct intake valve closing angle where the valve should be closed down to a lift of .10 x valve
10°
20°
Intake Valve Closing
30°
Angle at
50°
40°
.10
11.0
TEST PRESSURE CONVERSION CHART
Want flow at:
3"
1 .00
5" 8" 10" 12" 15" 18" 20" 25" 28"
774 612 548 500 447 408 387 346 327
1.29 1.00 .791 .707 .645 .577 .527 .500 .447 .422
1.63 1.26 1.00 .894 .816 .730 .666 .632 .566 .534
1.82 1.41 1.12 1.00 .913 .816 .745 .707 .632 .598
2.00 1.55 1.22 1.09 1.00 .894 .816 .774 .693 .654
2.24 1.73 1.37 1.22 1.12 1.00 .912 .866 .775 .732
2.45 1.90 1.50 1.34 1.22 1.09 1.00 .949 .802
2.58 2.00 1.58 1.41 1.29 1.15 1.05 1.00 .894 .845
2.89 2.24 1.77 1.58 1.44 1.29 1.18 1.12 1.00 .945
3.05 2.37 1.87 1.67 1.53 1.37 1.25 1.18 1.06 1.00
If is 65 cfm at a test pressure of 5", what would flow be at 15"? 65 cfm x 1.73 - 112.5
FLOW
Test Pressure 1"
3" 5"
8" 12"
28" 65"
VS TEST PRESSURE
Peak Velocity 66.2 fps 114.7 148.0 187.2 209.3 229.3 256.4 296.0 350.3
thru a perfectly streamlined orifice with an area of 1 sq.
in
37
12.0 Suggested Additional Reference Gas In te rn al Combustion Engine Annand and Roe, Haessner Pu bl is hi ng Go. (En gin eer ing Librajry)
•
.
The Internal Combustion Engine in Theory and Practice, 2nd edition, Vol. 1, Pre ss 1966 (Engineering Lib rar y) The Sports Car Engine, Colin Campbell Robert Bentley, I n c . , (Pu blic Library) Research and Development of High-Speed, Small Displacement Honda Engines. SAE Paper 700122, 1970 of Automotive Engineers, Dr., PA The Theory and Practice of Cylinder Head Modification David Vizard, 1973, Classic Osceola, 826-6600 Desig n Refinement of In du ct io n and Exhaus t Systems Using Steady-state Flow Bench Techniques. SAE Paper 720214 Society of Automotive Engineers Commonwealth Dr., Warrendale, PA
Colorado Springs. Colo 80907
