• Author / Uploaded
• dcapito4017

• Categories
• Carburador
• Medición de flujo
• Motores
• Acelerador
• Volumen

Citation preview

SuperFlow Flowbench 110 Instructions Section

1.0

Page

Flow-testing 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

SuperFlow 110 description What is a flow test? Adapting heads for testing Flow test preliminaries Performing a flow test Test data sheet sample Analyzing the test data Avoiding test errors

1

2 2 3 4 6 8 9

2.0

Air Flow Through Engines

10

3.0

HP & RPM & CIO & CFM

12

4.0

Intake Port Area & Shape

16

5.0

Valve Seats

18

6.0

Valve Sizes

18

7.0

Valve Lift & Flow

19

8.0

Combustion Chambers

22

9.0

Dynamic Flow Effects

23

10.0

Inertia - Supercharge Effect

24

11.0

Test Pressure Conversion Chart

26

12.0

Suggested Additional References

27

13.0

Troubleshooting

29

1.0 Flow-testing 1.1

Superflow 110 description The Superflow 110 is designed to measure the air-flow resistance of engine cylinder heads, intake manifolds, velocity stacks, and restrictor plates. For intake testing, air is drawn in through the cylinder head into the machine, through the air blower, and exits through the orifice plate at the top of the Superflow 110. For.exhaust testing, the path of the air-flow is reversed by a switch on the front control panel. ORIFICE PLATE

PRESSURE HSl M[HR

1

TEST

HEAD

_ _ BLOWER flOW CONTROL KNOB

I

The test pressure meter (manometer) measures the pressure or vacuum at the base of the test cylinder. The test pressure is adjusted to a standard value, for instance 15.0 inches of water, by turning the flow control knob on the lower front panel. Separate knobs co~trol either the intake or exhaust flow. The amount of flow is read from the inclined flow meter (manometer). The flow meter measures the pressure difference across the 5 flow orifices at the top of the Superflow 110. By selecting different combinations of orifices, 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 100% of any flow range selected with the rubber stoppers. A separate test orifice with a .312" diameter and a 1.875" diameter hole is included for calibration of the flow tester. The machine requires 110 VAC, or 110 VDC electrical power and draws 15 amps.

2

1.2

What is a flow test? In its simplest form, flow testing consists of blowing or sucking air through a cylinder head at a constant pressure. Then the flow rate is measured at various valve lifts. A change can be made and the head re-tested. Greater air flow indicates an improvement. If the tests are made under the same conditions, no corrections for atmospheric conditions or machine variations are required. The results may be compared directly. At the other extreme, it is possible to adjust and correct for all variations so that test results may be compared to those of any other head, tested under any conditions on any other Superflow machine. Further calculations can be made to determine valve efficiency and various recommended port lengths and cam timing. The calculations are very cumbersome without a small,electronic calculator, preferably with a square root key. The calculations are not essential to simple flow testing.

1.3

Adapting heads for testing Cylinder heads are mounted onto the Superflow by means of cylinder adaptors. The adaptor consists of a tube 4" long with the same bore as the engine 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 test cylinder head. The flanges must be flat or gasketed to make an airtight seal. The adaptor tube may be 1/16" larger or smaller than the actual engine cylinder. In some cases it is convenient to make the upper flange of the adaptor about 20% wider than the test cylinder head so that the head will be supported when it i~ offset for testing the end cylinders. A device must be attached to the cylinder head to open the valves to the various test positions. The usual method is to attach a threaded DQUnt to a rocker arm stud so that the end of a bolt contacts the end of the valve stem. As the bolt is rotated, it pushes open the valve. A 0 to 1" x .001 dial indicator may be mounted to the same fixture with its tip contacting the valve spring retainer to measure the amount of valve opening. The standard valve springs should be replaced with light springs for testing. See the photos in the Superflow brochure for various types of valve openers.

On the intake side of the cylinder head, it is strongly recommended that a radiused entrance guide be installed to lead the air straight into the head. The guide should be about one port width in thickness and be generously radiused on the inside all the way down to the head. The intake manifold can also be used. The exhaust flow may exit directly from the head.

3

1.4

Flow test preliminaries All test data may be recorded on the standard Superflow form F-120 test data sheet, (see sample). Before beginning a test, record the head description, and measure the stem and valve diameters. The net valve area is the valve area minus the stem area in square inches. net valve area

=

.785 (D 2 valve

D2

stem

)

Before installing the test adapter, install only the standard test orifice plate onto the Superflow. Install all the rubber stoppers in the orifice plate on top of the Superflow and set the direction knob to intake. Close the intake and exhaust flow control knobs lightly against their seats. Zero the vertical test pressure meter and level and zero the inclined flow meter. 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 water. The flow meter should now read approximately 45% on the 10.0 cfm range (#1 orifice open on top). This indicates a flow of .45 x 10 cfm = 4.5 cfm. If flow is within 1 cfm of this reading, the machine is working properly. Now remove all the rubber stoppers from 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 25 0 F higher than the lower thermometer. Multiply the flow meter reading times 185 cfm to obtain the ! l l t orifice~. 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 ---- ----

=

153.2 1f. test orifice flow

This factor compensates for machine variations and all atmospheric conditions. Enter this information on the test data sheet. For best accuracy, 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 range, and enter these in line D on the data sheet. The co~rected flow ranges may be used for all tests made on the same day.

*

If Superflow will not draw 10" due to low line voltage, use 8" test pressur~. Then: 137.0 Flow correction factor - test orifice flow

4

All tests should be performed at the same ratio of valve lift to valve diameter, or LID ratio. Then the flow efficiencies of any valves can be compared, regardless of size. Multiply the valve diameter by each of the six LID ratios to obtain the valve lift test points. Fill these in on lines A and B of the data sheet. Choose the proper ~ pressure for the intake valve diameter from the chart b,elow. It is generally most convenient to test the exhaust valve at the same test pressure. Fill the test pressure in on line 3 of the data sheet. Valve diameter 2.111 to 2.3 11 1. 6 11 to 2.05 11 less than 1.6

Test pressure 511 1011 15"

This completes all the preliminary preparations. While they are very time consuming, they will insure that the test results are valid and repeatable. 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 adapter, 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. Zero the vertical test pressure meter and zero and level the inclined flow meter. Close the intake and exhaust flow control valves lightly aga~nst their seats (do not force or they will be damaged). Place the rubber stoppers into orifices 5, 4, 3 and 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 flowmeter and chart. Because only the #1 orifice is open, the flow meter reads 10 cfm at 100%. A reading of 47% would indicate a leakage flow of .47 x 10 cfm c 4.7 efm. 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 will 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.

5

The flowmeter is designed with multiple ranges so that the flow can be measured very accurately. For greatest accuracy, use only 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 not, 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 70%. This is the proper number 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 machine, determine the full scale range value, then record the corresponding corrected flow range from line D on line 5. Re-adjust the test pressure to the recommended value and record the readings of the flowmeter and the temperature difference between the top and bottom thermometers onto the Superflow F-120 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 range.) Continue this procedure until you have reached the maximum lift test point. To test the exhaust port, turn the mode selector switch to exhaust 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 :\'1let a1r guide and replace it with the intake manifold. Repeat the intake tests and compare the results to determine the effect of the inta"ke manifold.

TEST

Test Description:

fZ. 'I

R.

CII£//Y 1lEt1P, #-3917281,

SHEET

STOCk #2 PtJRT hi/Til

.pO~T OPEN FI&JM 11£19/J.

€;X1I/ltlS T

ItVLET GtJ/PE,

Exhaust valve die •• area l.5'o'~ do, 1,671.;y1.

Intake valve dia •• area: /9.('d., 'ZB6 IAI.2 Tes tOper ator

DATA

Da te .....;;6;...-...;3~-_7.s-.;...._ _ _ _ _ _ __

/y. WIL L / ,4/J?.5 ISO. 7

Test orifice flow at 10" test preasure:

efm

Test flow correction factor: 153.2/ IS(}, 7 - ..&1.......:;0....'1.....:1_ _ __ Valve lift/diameter (LID) .05 A. Intll}l-e valvE' lift (in) .097 B. Exhaust valve lift (in 07~

1

1. Test Number

2. Test port number

2.£

3. Test pressure (in.)

/0

4. Valve lift (in.)

.10 ./94./So

2

3

.291

.20 .38B

.ZZ5"

,306

.15

4

-"'" ,

.~I

5. Carr. flow range (c fm) -I~7 8~s 1a;.9

co

30

11. Temp. diff. factor

.917

12. Carr. tes t c ftr.(J.llxL9) J!,l.

.76~ .~/O

6~tj

.~70

.~Z3

.906

.~I.S

~5G

..fo·

,~.JC.

18.3 -ftJ.7 6tJ.o 85':S 8£5'

.t!8S- ,7.96 .793

1.!o.4 /6:.2 3Z.4- "17'

2,2.0

3Z.5 79."

tl

/"UW

..

35

.961! .966 .970 .973

93. / II?€ 12""'7

f'z..

fX#/'1v,sr

-

215

I.(/'~

,~.O

15. % flow rating

x

I

(cfm at 10" at water)

where CID is the engine displacement in cubic inches per cylinder. For super-stock and engines which are not all-ont racing engines, peak power will occur at 10% higher RPM than formula 4 indicates, so use 2200 instead ot 2000. Now, let's tryout these formulas on an example. 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 water, this intake system will flow 105 cfm of air. The CID per cylinder is one-eighth of 292 or 36.5 CID. HP

...

.

.43 x 105 cfm

45.1

or for all 8 cylinders HP

=

8 x 45.1

0;:

361. 2 HP

The RPM for maximum powe r will be (2200 is for super-stocks, 2000 for racing engines): RPM

...

2200

':r03

x

105 cfm

...

6330 RPM

So the engine has a maximum potentai1 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 example, we will use a small block Chevy 302, displacement 37.75 CID per cylinder. ~

Stock, 2.02" valve Normal ported, 2.02" valve Best ported, 2.02" valve Westlake, 2 x 1.~' valves

Intake 120 143 160 175

S~stem

cfm cfm cfm cfm

Power

Flow 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 heads, the engines must be wound up to 8500 and 9300 RPM 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 minute. If a few runs down the strip are all you want, this limit may be raised to 4600 fpm, but the engine will need super internal parts to last even one" run. These rules can be reduced to a simple formula for the RPM for peak HP (remember, your shift points may be 1000 RPM or more above peak HP): 5.

6.

Safe peak power RPM

I

-

Maximum peak power RPM

22.200 1n. stroke

-

27,600 in. stroke

I I

Returning now to the e~ple 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 fpm piston speed. If 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 Westlake 4-valve 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! Now, if we pull all the formulas together, it is possible to construct a graph for determining the maximum intake system flow required for a particular engine and application. From this graph, you can easily select the required flow for any engine and RPM. Remember that the CFM, CID and HP figures are for each cylinder, not the entire engine. To use the graph, determine the CID 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.

16

For an example, suppose you have a 427 CID V-8 engine which will hold together up to 7500 RPM. From the graph for 53.4 CID (1/8 of 427), the max~ power per cylinder would be 85 HP if you can tmprove your intake system to 196 cfm on the flow bench at 10" of water test pressure. For all eight cylinders, the engine could produce 680 HP at 7500 RPM. Of course it'. not enough to stmply 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. 4.0

Intake Port Area and Shape

For maxtmum flow, the ideal intake system would have a single carburetor per cylinder with a slide-plate throttle and a venturi equal to .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 1:f.ke. When porting out a cylinder head for maximum flow, keep the following points in mind.

1. 2. 3. 4. 5.

6.

Flow losses arise from changes in direction and decreases in velocity (port bends and expansions). Port area should be between 651. to 1001. of valve area. Remove material primarily from the outside of port bends, not the inside. This will improve flow by increasing the radius of the bend. . Port length and surface finish are not important to flow. The greatest flow loss tn 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.

If flow losses are caused by port expansions, not contractions, you may wonder why the port should be necked down below the valve seat. The reason is that the air must both turn 90 0 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 ~here 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 ~t is easy to grind.

1 Loss

Source of Flow Loss .1 Wall friction .2 Contraction at push-rod

Bend at valve guide Expansion behind valve guide .5 Expans ion, 250 0 .6 Expans ion, 30 .7 Bend to exit valve .t:'. Expansion exiting valve

.3

.4-

*

For sand-cast surface.

41 2

*

11 4

12 19 17

31 1001.

Would be 31. for polished surface.

18

As manufactured, this head flows about 83~ of its potential for a wedge-combustion chamber head. "The best head porters are able to increase the flow to about 9S~ of its potential with the aid of careful flow-testing. Further improvements are difficult without major surgery and welding. Grinding and enlarging the first 2~' in the Chevy port where it is easy to reach has very little effect. S.O

Valve Seats

The valve seat has three purposes: to seal the port, to cool the valve, and to guide the air thru the valve. Sealing and cooling are promoted by a fairly wide seat between .060" and .100". 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 comgetition intake valve seat will consist of a 30 0 top cut .100" wide, a 45 seat .040" wide, and a 70 0 inside cut .1SO" wide. An exhaust valve will work well with a lSo top cut .060" wide, followed by a 4S o seat .060" wide, and a 7S o inside cut .100" wide. The O.D. of the valve should coincide with the outside of the 4So seat. Flow-bench experimentation will frequently uncover a superior shape for any partio cular head. A three angle seat will out-flow a simple 4S seat by up to 2S% at lower valve lifts. 6.0

Valve Sizes

The total flow thru the engine is ultimately determined by the valve diameters. While well-designed smaller valves will out perform larger valves on occaSion, a geod, big valve will always out-flow a good, smaller valve. Valve size is limited by the diameter of the engine bore. For wedge-shaped combustion chambers, the practical max~um intake valve diameter is .52 times the bore diameter. Hemi-heads permit intake valves up to .57 times the bore diameter due to the extra space available in the combustion chamber. Four-valve heads are best of all, but the engf.ne 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 SO% or 901. of the intake system flow. This may be more than is necessary. Tests indicate that there is generally no power improvement as long as the exhaust flow is greater than 60% of the intake flow. This would dictate an exhaust valve diameter .77 to .80 times as large as the intake valve.

19

7.0

Val ve 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 lid 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 d, 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. Wedge-chamber intakes have lower flow at full lift due to masking and bends, and are port-limited' at a 15% lower level.

Fig. 4.

Valve potential air flow at a test pressure of 10" of water

70 IP M- It lim ~t

60

'/

/

v

, ~

....

~~

so

.... ~

.... ~

~

,M-

~

.. .... ,

..", ~

~'f"

J

.-c.40

... tl'.

~

u.E 30 ~ .~.

••

,

~

~'I' ~

IJ

,

20

~

~

.

,

10

.,

I~

r-

IJ

.10

--

.20 Valve lift II10 lame t , er

..

.30

~.

r- - -

.40

20

Figure 6 can be used as a guide for judging the performance of any valve. To get the flow rate cfm for a particular valve, simply multiply the cfm per square inch from the chart by the valve area minus the valve stem area. The flow rate you get is not the "expected" flow rate, but rather the maximum 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 ~btain 80i. to 90i. of these figures.

Fig. 5

Maximum Potential Air Flow

Intake Valves VW 1200, 1.24" D. Norton 850, 1. 50" D. Yamaha TX 650, 1.62" D. Chev. Small Block, 1. 72" D. Chev. Small Block, 2.02" D. Chev. Westlake, 2x1.5" D. Ford 302, 2.25" D. Chrys ler Hemi, 2.25" D.

.05 15.3 25.4 26.9 30.3 42.3 50.7 52.8 52.8

Valve Lift/Valve Diameter .20 .25 .15 .10 cfm ~ lU" test pressure 56.6 46.2 53.0 30.8 76.5 102.4 109.2 50.9 54.1 81.2 10B.7 115. B 60.9 91.5 104.8 112.0 127.6 146.3 156.2 84.9 101.8 153.0 204.B 21B.4 106.0 159.2 182.6 195.0 106.0 159.2 213.2 227.2

.30d

5B.9 112.5 119.0 116.7 162.7 225.0 203.1 233.4

If the flow reaches a maximum value at a lift of about .30 d, you may wonder why some cams are designed to open the valve farther, even as 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 maxtmum head-flow point. The extra flow is gained on the flanks of the lift pattern, not at the peak. The 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. Frequently, the intake manifold will have even more room fOf 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.

21

Fig. 6

Valve flow potential at various test pressures For herni-intake and all exhaust valves Valve Lift/Diameter Test Pressure

.05 7.4 9.6 12.2 13.6 16.7 19.2 21. 5 22.8 25.8

3" 5" 8" 10" 15" 20" 25" 28" 36"

.10 .15 .20 .25 cfm per sq. inch valve area

.30

15.0 19.3 24.4 27.3 33.4 38.6 43.2 45.6 51. 8

33.0 42.5 53.8 60.1 73.6 85.0 95.1 101 104

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 98.0 111

For wedge intake valves Valve Lift/Diameter Test Pressure

.05

3" 5" 8" 10" 15" 20" 25" 28" 36"

Valve area

7.4 9.6 12.2 13.6 16.7 19.2 21.5 22.8 25.8

=

.10

.15

.20 .25 cfm per sq. inch valve area

.30

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

28.6 37.0 46.8 52.3 64.0 74.0 82.6 87.4 99.2

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

2

.785 (D\a1ve

From a flow stand-point a herni-shaped combustion chamber has a clear advantage over the wedge. Until the valve lift reaches .15 valve diameter, there is little difference, but at higher lifts the hemivalve is usually less shrouded. In most designs, the hemi-port is also straighter -due to the valve angle. These two advantages add up to an average flow advantage of 16% at higher lifts, even with equal valve diameters. When you consider that a herni-combustion chamber also generally permits the intake valve to be 10% greater diameter than a wedge, it is easy to understand the success of the herni-head racing engine.

22

8.0

Combustion Chambers

In most engines, it appears that the combustion 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. Hemi and pent-roof combustion chambers are generally the best with wedge chambers being 54 to 10~ worse. Most gasoline burning racing engines use a compression ratio of between 12 and 13.5 to 1. If the cylinder is completely filled, you would expect that the torque per cubic inch of engine displacement would be the same, regardless of engine design. It isn't, and the differences are mostly due to combustion chamber effectiveness. One way to judge a combustion chamber's performance is to measure the torque output per cubic inch of engine displacement. At the RPM of peak torque, a good combustion chamber will develop 1.25 to 1.30 footpounds of torque per CID. 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-tuning. Most racing Detroit V-8's only reach 1.15 foot-pounds per CID. There is plenty of room for improvement. A second guide line for judging efficient burning is the required spark advance for maximum power. The more 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 smell-block Chevy with a normal combustion chamber shape might require 42 BTDC maximum spark advance (35°.ignition delay), while a highly turbulent combustion chamber might only require 33 0 BTDC advance (27 0 ignition delay). The more turbulent chamber will also burn more rapidly and ,produce up to 10% greater power from the same initial charge. Combustion chamber improvement is more of an art than a science and so trial and error methods are frequently the only choice. In general, strive for high turbulence and minimize the distance from the spark plug to the f~the~ 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 compare a cylinder head on a Chevy 302 and then on a Chevy 330. While the same head will bolt onto both engines, the compression ratio, and combustion chamber effectiveness, and RPM range will all change. 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.

23

9.0

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 cycle. Both the kinetic energy and the resonant pulses can be harnessed to fill the engine cylinder at volumetric efficiences up to 130%. Without these dynamic effects, volumetric efficiency is limited to 100% 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 the intake tract the proper length, the returning pulse can be timed to arrive at top de.ad center of the next intake cycle, shoving extra air in and keeping exhaust gases out of the intake port. To visualize what occurs, imagine that one end of a steel bar is placed against a hard surface. If the other end is struck with a hammer, a strong pulse (the 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 best, the others being weaker and shorter. Fig. 7

Inlet pulsation chart

Harmonic 2nd 3rd 4 th 0

*

Length formula

Lower RPM

l32,000/RPM 97,000/RPM 74,000/RPM

89% 91% 93%

Upper RPM 108% 104% 104%

Pulse Strength*

-++ -+

10%

no

4%

Pulse strength varies with inlet flow and inlet 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 example, at 8000 RPM for the 2nd harmonic: length -

132,000 8,000

a:

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 108% of 8000 RPM, or from 7120 RPM up to 8640 RPM. The greatest benefit will occur at about 3% below 8000 RPM. Below 7120 RPM or above 8640 RPM, the "pulse will actually work to decrease engine power.

24

To obtain benefits from the pulsation, it is also necessary that the intake valve be open to a lift of at least .02 times the valve diameter by 150 btdc. Openings of 20 0 to 40 0 btdc are usually preferable. The intake flow rating (see Section 10.0) must also be 0.3 or greater for significant benefits. 10.0

Inertia-supercharge effect When the intake valve starts to close, the fast moving air column tries to keep ramming 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 1301 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 measured. 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 A construct a graph, as shown in Figure 8, of engine flow in cfm/in~ versus degrees of engine rotation. This is a plot of the total engine flow considering both the intake system and the cam •

.rI

80

-.•.

,

:R:1:-: :--1:-- _,1- -! -. ~ ... -:- •..

I '

", -.'. -,. ~-:

0

.

ic 60

.

.'

.

I

"

,.

I ..

, ...

\'

------ -.... . -- - - - --.

- -'

I I

;

I

---~-T-" :-+-I ~'-T'''-- t -- "-':' ----:.. , .

I

..

i'

I

.;-...

! .

I

-

!

I.

u

40

~

-t-

r

-"" 0

I

.

"

I

. ,c

20

1

. ,

--------l - - - -

i~ak. ~w

-.. -...,. ... --i --.

- - I -.-- -

I

e., I

:.

I

I . I

~

c(

--I. ----- '--

I

- - - - -+ ... - ----.~ ..

I

E

,

.--+-;"';';:--~~---f--""';'---+--TD•• I .dU~.tion ~:---'----------~ . ,. I ~1--_+___1r_~--+_-~--+----__~-_1-1- - - .~---

.......

-

~.

--,.----+- - ... ---~---... . -

-

.,c;.

,.1.

!

- - . - --- - ..... - -

.. ~

'

.

.;

..,I

I

j

I . I ' t:::c I;:

+----~>---~-~+-I--

I . J . .I .

I

+--I~~-~..,q.....-+-_-+--_~--+"-'_-_-_·+I_~_:-:+j-.-·-+-----~r-.--I . . :•i;·:·-··+-:-Ir.~~:-t-~:··-~ .. ~.

. ,. : . ~ .:.

----r

.. i .'

. I' .. : ... 1 .

I'"

.

.

.

t

°6·0~0~~~--~T-D~C--~--~---------9~00~--------------B~D~C----------~6~00~~ Fig. 8

Crank Angle

25

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 system flow rating Cv.

-

Area under flow curve Total area under 87 cfm line

The C will generally be between 0.35 and 0.45 for good engines. This is a ¥otal rating of the intake system flow for any engine. The higher the Cv, the better the engine.

Cv

The average inlet valve area is the

7.

average inlet area

E

ttmes the intake valve area.

Cv x Valve area in sq. inches

Now this data can be used to determine the inertia-supercharge index, Z, from the formula below:

8.

CID x Inlet Length average inlet area

RPM

Z

IC

126,000

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-supercnarge 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 diameter.

'

r

1.4P-------~--------~1----~--~--~----~--~----~1--~~--~ 1.3

.--::--!--~ i -_:- __ 1- .- ---- ---'1'-'-

l

' .-TI : ;--: -J.. 1.1 --:. -+-

!

,

1.2

~ -~ ---'--~+~~-:-'1-~-~~~"~- i

I

1

1.0

ij

-.

j'

.,

I"

I

-

j.... t~:.. ----~l-----

-

-~

-- --

-

-'-

~.

'.

I

I " -: I - ,1~~~~: -"~-~~:-~~---.

.-I",: - ..

I,!

-.

1':-~~ L;~~-;

.

~i

t

l

' :.

'-J .

i

f

• , - ,-

-I

I ------;

,

N; : --

-

. I

I

-

t---:----'--:--·

I ' ;

---'1---;----

I

,.

j: . - I

i -!

:.. I

~~j---

j

-. . .,' -., -, ' t' '.,' - 1 . I .. . 'TT i -, , '. .. 1 • ... f~"'i -; . .:. -. .:_._. . +-1-'--·~.....---~+

I

j,

.9

•

-

,

I

~

-4-

•

___ , ..

- j.,

. L ____ .

I

•

.--,-..•

,

• • -+- ....

'

-~ ... : 1: :

-+

.

--~.

i

- ... j

'"

~

•..~

..j- ~-

.. -..

~

.8~0~~----~~~----~~--~--~~~~--"~--~--~~0~~----~0

o

Fig. 9

0 100 20 300 Intake Valve Closing Angle at

400

LID •

50 .10

60 abc

26

11.0 FLOW-8ENCH TEST PRESSURE CONVERSION CHART Want Flow At:

...« ~

-0 u.

CII

>

10

:I:

3" 5" 7" 10" 12" 15" 20" 25" 28" 30" 35" 40" 45 11

3"

5"

7"

10"

12"

15"

1.00 .774 .655 .548 .SOO .447 .387 .346 .327 .316 .293 .274 .258

1.29 1.00 .845 .707 .64S .577 .SOO .447 .422 .408 .378 .354 .333

1.53 1.18 1.00 .837 .764 .683 .592 .S29 • SOD .483 .447 .418 .394

1.82 1.41 1.12 1.00 .913 .816 .707 .632 .598 .577 .535 .SOO .471

2.00 1.55 1.31 1.09 1.00 .894 .774 .693 .654 .632 .586 .548 .516

2.24 1.73 1.46 1.22 1.12 1.00 .866 .775 .732 .707 .655 .612 .577

20"

25"

28"

2.58 2.89 2.00 2.24 1.69 1.89 1.41 1.58 1.29 1.44 1.151.29 1.00 1.12 .894 1.00 .845 .945 .816 .913 .756 .845 .707 .791 .667 .745

3.05 2.37 2.00 1.67 1.53 1.37 1.18 1.06 1.00 .966 .894 .837 .789

30"

3S"

40"

45"

3.16 3.42 3.65 3.87 2.45 2.65 2.83 3.00 2.07 2.24 2.39 2.54 1.73 1.87 2.00 2.12 1.58 1.71 1.83 1.94 1.411.531.631.73 1.22 1.32 1.41 1.50 1.10 1.18 1.26 1.34 1.04 1 .12 1.20 1.27 1.00 1.08 1.15 1.22 .926 1.00 1.07 1.13 .866 .935 1.00 1.06 .816 .882 .943 1.00

Example: If flow is 65 cfm at a test pressure of 5", what would flow be at 15"? cfm

= 65

cfm x 1.73

= 112.5

cfm

FLOW RATE VS TEST PRESSURE Test Pressure 1" H20

3" 5"

8"

10" 12" 15" 20" 28" 30" 35" 40" 45" 65"

Peak Velocity 66.2 fps 114.7 148.0 187.2 209.3 229.3 256.4 296.0 350.3 362.6 391.6 418.7 444.1 533.7

JfCFM/In 2 27.6 cfm 47.8 61.7 78.0 87.1 95.6 106.9 123.4 146.0 151 .1 163.3 174.6 185.1 222.5

*Flow thru a perfectly streamlined orifice with an area of I square inch.

27 12.0

Suggested Additional References Gas Flow in the Internal Combustion Engine Annand and Roe, 1974 (out of print.) Haessner Publishing Co. (Search Engineering Library) The Internal Combustion Engine in Theory and Practice, Charles Fayette Taylor, 2nd edition, John Wiley & Sons, N.Y., NY. (Search Engineering Library) Internal Combustion Engines, Edward F. Obert, 2nd Edition, International Textbook Co., Scranton, PA. (Search Engineering Library) The Sports Car Engine, Colin Campbell Robert Bentley, Inc., (out of print, Public Library) The Theory and Practice of Cylinder Head Modification David Vizard, 1973, Classic Motorbooks, Osceola, WI, call (800) 826-6600 to order. Tuning BL's A-Series Engine David Vizard, 1985. Haynes Publishing Co., 861 Lawrence Drive, Newbury Park, CA 91320 (805) ~98-6703, F~14-$19.95. S.A.E. Technical Papers S.A.E. Technical Papers may be obtained by contacting Society of Automotive Engineers, INC. 400 Commonwealth Drive Warrendale, Pennsylvania 15096 (412) 776-~841 Request a Current Year Catalog or state by number and author and paper title listed below. Send along a fee of $3.50 for each paper requested. 700122*

Research and Development of High-Speed, HighPerformance, Small Displacement Honda Engines 1970

720214*

Design Refinement of Induction and Exhaust Systems using Steady-State Flowbench Techniques 1972

790484*

by S. Yagi

by G.F. Leydorf, Jr.

An Analysis of the Volumetric Efficiency Characteristics of 4 stroke Cycle Engines Using the Mean Inlet Mach Number. Feb. - March 1979

by Itaru Fukutani & Eiichi Watanabe

28

820154*

AirFlow through Poppet Inlet Valves Analysis of Static , Dynamic Flow Coefficients Feb. 1982

820410*

by Itauru Fukutani & Eiichi Watanabe

A Study of Gas Exchange Process Simulation of an Automotive Multi-Cylinder Internal Combustion Engine Feb. 1982

by Masaaki Takizawa Tatsuo Uno , Toshiaki Oue Tadayoshi Yura

Bosch Automotive Handbook from SAE Publications, $12.95. *All papers belonging to S.A.E. are covered by u.s. Copyright laws and cannot be reproduced without paying a fee or obtaining permission to reproduce from S.A.E. Publishing Division.

SuperFlow reserves all rights for these instructions worldwide. Reproduction or translation of this work beyond that permitted by Sections 107 and 108 of the 1976 o.s. Copyright Act without permission of copyright owner is unlawful. Request for permission or further information should be addressed to SuperFlow Corporation.

D

,... ,

r, I

I

I

I ,

I I

, I I I I

I

,, I

•

,

,

I

, I l.. J

I ' l...J I

-rNiltu

.

~

11

C

I~

I

r.

J

··S' ..

I

I

1 '"

1I II',

I

: 01 ,

J

f , I

I

,4

-1

I I

-1-

I

, I

-

'" I

ALL

JOIN

:

1-•.

I

..

t-..L

: I

I '

I

-

-

I

-1

I

r-/i--

Sac. ....EN r