The Society shall not be responsible for statements or aptmansadvanced in papers or in discussion at meetings of the Society or of its Divisions or Sections, or printed in its publications . Discussion is printed only if the paper is published in an ASME ;ournal or Proceedings . Re lea sed for general publication upon presentation. Full credit should be given to ASME, the Professional Division, and the author (s). $3.00 PER COPY I TO ASME MEMBERS ~~f;~·c;~-11 RESEM~CH STP.FF FORD MOfOH COMPM.'Y Design of a Tuned Intake Manifold H. W. ENGELMAN Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio Mem. ASME This paper summarizes a long-term study of intake manifold tuning. It includes the results of several graduate research projects. A ration al mathematical model is developed which defines the modes of resonance in a manifold for up to four cylinders, and affords a method of design for peak ram supercharge at a desired engine speed. A specific example of the design of a manifold is included. Contributed b y the Diese l & Gas Engine Power Dh•ision of th e American Society of '\1eehanieal Engineers for presentation at the Winter Annual Meeting, Detroit, Michigan, November 11 - 15, 1973. Manuscript r ece i,•cd at ASME H eadquarte r s .Jul y 18, 1973 . Copies will be available until August I, 1974 . ... , .... t AfiERICAN SOCIETY OF MECHANICAl. ENGINEERS, UNITED ENGINEERING CENTER, 345 EAST 47th STREET, NEW YORK. N.Y. 10017 the oscillations can be extremely beneficial. is compressible. and the air in the cavity volume is the spring of a simple spring-mass system . of a Tuned Intake Manifold w. means that resonances will exist . a welltuned intake manifold will give maximum torque at some desired value of rpm by utilizing resonance effects to produce supercharge. the air in the pipe is the osci llating mass. This paper describes an accurate mathematical model for the design of certain multicyli nder intake manifolds to get the best possible breathing. Give n an eng ine. A principal finding o f the original work (1. For the fixed resonator of Figure 1. Thus th e Ricardo patent (3) sets forth equations which bracket the optimum length within a ratio of 3 to 1. or e l astic . 1 Helmholtz Resonator The cylinder of an engine with its intake pipe with the valve open constitutes just s uch a Helmholtz resonat or as shownin Figu re 2. in cran kshaf ts and valve trains we seek to avoid resonant oscillation~. At ics fundamental res onance. That initial work established the Helmholtz resonator as a model of the cylinder and its intake pipe with t he valve open dur ing the intake stroke . The tuned design may not be much better . However. Previous analyses were all based on organ-pipe theory. it was still the Oil and Gas Power Division. study at th e University of Wisconsin (1)1 resulted in a paper (2) presented to this division in 1953. whereas in manifolds. and the peak will not be sharp . so does every intake manifold. using the resonances which are always present to obtain some supercharge.·Design H. some tuning effects will exist and may produce some supercharge. but even this may be twenty percent plus or minus . BACKGROUND Improved breathing wi ll almost always improve the combustion in a diesel engine. Just as crankshafts and valve trains have resonances. The air flow and charge density will be above the values for the engine with open ports over a speed range greater than two-to-one. The characteristic feature of this resonator is that its dime nsions are small compared with the wavelength of a sound at its resonant frequency . like all gases. th e resonant frequency. which gives the tolerance in inches. It is not generally possible to say j ust how much gain can be achieved in a particular engine by intake tuning. Less indefinite is the equation given in the Pla tn er patent (4). ENGELMAN ABSTRACT This paper summarizes a long-term study of intake manifold tuning. when ll. However. A specific example of the design of a manifold is included .D. f 0 . The fact that air. and the equations do not include them. It is not uncommon to f ind that a better air su pply may actually reduce peak pressure at a given power level. since any manifold on the engine will have resonances.umbers in parentheses designate References at end of Paper . and affords a · method of design for · peak r am supercharge at a desired engine speed. A rational mathematical model is developed which defines the modes of resonance in a manifo ld for up to four cylinders. for a typical engine. PRINCIPLES The basic Helmholtz reso nator is shown in Figure 1. It would be well to define just what a properly tuned manifold is or does. It includes the results of several graduate research projects . The reason for these t olerances is simple: variations of pipe area or cylinder volume do affect the optimum pipe length. It will be of the order of a twenty percent increase i n charge flow over the open port. The design calculations set forth in this paper are the result of a very long-term study. It is not at al l unusual to encounter air distribution problems in a new engine development. which simply does not provide a way to inc lude the effect of pipe area and cylinder volume. Fig. is given by fo = Cs • ~ 21T " ~ (1) . but not recognized as such . A Ph.2) was how piston movement affected the resonance. The greatest percentage increase will be in the middle of the range. These are most commonly resona nce effects. Modeled as The second principal fi nd i ng of the original work is that the tuning peak will occur wh e re the nat ural Helmholtz resonan ce of cylinder and pipe is roughly doub le the piston frequency . The idle pipes with their closed valves simply comprise a volume de noted by v 2 . provides 0 for convers1on of units and sets the Helmholtz resonance a t 2 . the carburetor would comprise par t of L2 /A 2 . Np = 162 C Resonant electrical circuits . and i ts pipe to the branch point has dimensions 1 1 a nd A1 . especially in communi(4) cations wo rk . s ~hompson at The Ohio State University in his M.D. 5 depending largely o n valve timin g . L. That is. dissertation. 77 . 1 times piston frequ e ncy . Unfortunately. The elect rical analog is shown in Figure 4. Eber hard studied threecylinder groups a nd Schwa llie studied the four-cylinder manifold . the cylinder on its intake s troke is denoted by vl. This study also cover ed the effect of standing waves in the organ pipe mode when the valve closed. The basic acoustical model of three-cylinder and four-cylinder manifolds is shown in Figure 3 . I and V are in cent imeters. in consis tent units.l i where K is the ratio of frequencies .wltere.0 to over 2 . ~I Fig. suddenly was not ha lf good enough as of December 31. (3) where Np is the rpm at which the tuning peak occurs. An important result is that the composi t e pipe may be treated on the basis that (~L) eff 11 = A 1 (5) where VD R piston dis placement compression r atio Substitution of this Veff fo r V i n Eq uation (1) gives the resonant f r equency of the cylinder and pipe with a moving piston. From these findings the equation published in 1953 (1. a nd a factor Q wh ich i s essen- ~ r. Consequently. 3 Acoustical Model of I ntake Manifo ld thesis (5) continued the st udy of singl e pipes and the r esults were presented in a DGP paper (6) in 1969 .::-: ~ 2 . Cs is t he velocit y of sound in t he pipe in fps. and showed that the effect is not large unless the pipe itself is quite large . The constant is 642 for metric units . For metric units the constant is 1348. The acoustical model can now be hand l ed easily by Equation (3) is rewritten (for English units) a mathematical method used for electrical resonant circuit s . and A. The basic concept is present ed in the early work (1) but without 1 experimen tal confirmation . Their organ pipe mode resonance frequencies will be substantially higher than the tuning or Helmholtz frequency . Thus VD 2 ( ~) (2) R .S c . 9) i nvestigated the tuning of manifolds. The cons t a n t. are generally treated in terms of resonant K sl ~l~ freq uency or freque ncies . 1970 . the pe riod of a resonant cycle takes approximately 180 degrees of crank rotation. and v are in inches. and pipes consisting of two sections of diff erent c ross-sectional area. 2) is Np 77C s ~ ~~ ~ "'V LVD "'V R + 1 where the subscripts refer to the individual sections of the pipe . theses (8 . their effect is that of a plenum at the branch point . Eberhard and Schwallie in the M. The improvemen t in economy and l ow-end torque led Ka uff ma nn (7 ) to undertake th e r eduction of gasoline engine emissions by application of tuned manifolds as his Ph. In a gasoline engine. For simplici ty. one-half the displacement plus the c l earance volume. However . Flow e nters the bra nc h point through a feed pipe of dimens i ons L2 a nd A2 . each barrel feeding fou r cylinders which fire at uniform intervals . A manifold was then built for a V-8 gasoline engine and t es ted as an undergraduate laboratory experiment in The Ohio Sta t e University Internal Comb ustion Engine Laboratory . and may vary from 2. 2 Cylinder and Intake Pipe a Helmholt z Resonator . the Clean Air Act of 1970 was passed during his i nvestigation. ! Fig . L. cs A L v velocity of sound pipe c r oss-sectional area pipe length cavity volume I The e f fec t ive engine cylinder volume is that at mid-stroke (1).Sc. The stock two-barrel carb uretor was used. A treme ndous improvement whe n he started . wh ere C i s in M/sec a nd A. where the end of the pipe is open . The study also included th e effects of bends. and further. the designer can define the manifold configuration which optimizes resonance for his operating conditions. this mathematical model pre dict s the re so nan ces ver y well. To design a manifold having certain frequency characteristics it i~ not necessary to carry any loss or resistance terms in the calculations . 3 . To simplify the solution. Figure 4 shows no resistances in the electrical analog. an inductance ratio is defined for both the analog and the acoustical model: (L/A) 1 1 (L/A) 2 (6) 1 Similarly. and 1 2 to the L/A of the inlet. With this mathematical model. The ide nti f i cation of the r esonances was emphasized in the expe rime ntal work. the voltages on c and Cz are in phase. ~ (ab+a+l ) 2 - (ab+a+l) - l (R+l) Then the characteristic equation for the ana log circuit becomes 0 (10) p which is analogous to equation (1) . What the equations presented here will do instead is also useful. however. At the lower resonance the pressures i n the cylinder and at the branch point are in phase.. The solution for the resonant frequencies is re adily carried out on the basis of series r esonance. in terms of the freq uencies that will be found. or supercharging. It is readily shown that the electrical analog in Figure 4 has two resonant frequencies. a capacitance ratio is defined v2 2(R-l) VD ~ (ab+a+l/ c (8) . It is recognized that the designer want s to be able to predict the performance of the engine on his drawing board. and the two frequencies are found t o be (ab+a+l) + 2abL 211 f Electrical Analog of Intake Manifold. At the lower frequency. including the carburetor. 1 1 to the L/A of th e intake pipe. According l y . It should be emphasized that these equations do not define engine performance or performance gained by tuni ng. and at the higher resonance they are out of phase . Similarly. The fact that any flow losses will degrade breathing is well known. Then two frequenc y ratios may be defined for the analog circuit (11) and (12) For the intake manifold. 1 while at the higher frequency the voltages are of opposite phase . if any. X 1 Nl = - N (13) p and (14) Figures 5 and 6 give the values of x and x respective1 2 ly for the ratios a and b most likely to be encountered. such that the voltage across the current source in the analog is zero. It should be pointed out that this analog is valid only if the intake periods have little or no overlap. As will be shown. A1. c1 corresponds to the effective cylinder volume. and L1. c2 to the volume of the other intake pipes and log at the branch. and needs the e quations which will e nabl e him to do so . The frequency of the tuning peak is quite independent of the losses.4ab (9) 1 1 where f is the lower and f the higher resonant fre1 2 quency. but their elimination is quite separate from the design for a particular Np. one higher than and one lower than that calculated for Np from e quations (3) or (4) using Vl. that one of these will be higher a nd one lower tha n the resonant frequency of 1 1 and c1 taken alone. -tially the reciprical of the losses. It should therefore be a very useful de s ign tool . generally up to four cylinders only. It is quite convenient to treat the tuned manifold in the same way. rather than specific prediction of e ngine performance . The confirmation of this model is considered the mos t important of th e experimental results whi ch f ollow. or t o accept the losses due to high runne r velocity for mixture d istribution in a gasoline engine . The resonant frequency of L c alone is 1 1 '1 4 4ab 211 1 Fig. The losses reduce the gain. in the tuned manifold there are two resonances. but the designer may elect to accept a l oss to obtain swirl in the cylinder in a diesel e ng ine. ::: :::::f:::±::-.----- N ~2.0 1. and is typi cal of all. Induct a nce Ratio a 1 and Capacitance Ratio b .0 I - 2.-.- : ." tl1 oo " H t lC ~ 95 > 0 90 }.8 2.LB 1.4 manifolds is th e length L . "{_ ~ 0 ~ I I ~'(\ I I ! ~: .2 j I I 120 I I .A-4-1. In Fig..1"--. 9: s tandard 2-inc h/copper water tube.1.0 i:i ! I ' \ · I- --! I I I\ 1\ .~r.. 6 - · ---- ------ 2. . 8.j ~ l I .. I o.'\. The B.6 1. 5 Frequency Ratio X vs . For single pipes.. 2 i I ' • i ' 0 .. ~1 05 . but l ess gai n or supercharging effect.cy lind e r pipe s we re 1-1/2 inch conduit bends .0 - ! \ i\ t.. .\\\V<~ ~0. I I I I ! I'- I I \ \ 1\ : l I 1'\ ' - ...0 vs.. depend on t he flow velocity.2. I I I I I I I 0. • ' CAPACITAN CE RATIO b ~ I ! I x2 I ! I I o. Fig . Inductance Ratio a and RESULTS Some of the results fr om Eberhard ' s thesis are shown in Figs .. and the resulting supercha r ge... I 1500 DI GIJB SPIED. and a gain of some 18 percent over the stock manifold for the B-4 configuration... -. with long-radius solder ells connected to a large "lo g.2 1000 ------ I 2. I I I 0 I "N ~ ~ I ~'\. \ I 'i'-. N-.6 1." The difference between the B-3 and B-4 manif olds is in the leng th L .. The primary cause of this difference is th e crosssectional area of the pipes."l""' "'~""-~ ~"'-1 T-.4 0 . Meas ured va lues of vo lumetric effi ci ency for four of his manifolds are compared with 4 2000 2500 Fig. I II L il ~ I . The st oc k 2 manifold i s a log bolted directly to the head . 1. ._.2 . The other manifolds show similar peaks._ o . from Reference (8) -. 7 Comparison of Four Tuned Ma nifolds with St oc k Intake Manifold. 0 I I ~~ '-.. The A-3 and A-4 configurations 2 were simil a r. 0.L t... 6 Frequency Ratio Capacitance Ratio b I ! i I I \ I 0.PACI'I'AlfC! RATIO b\ N .180. I lr-~ --.t- I 0.2 115 I 1.e 1. but the log-t o. ---Q-B-}.. data from many sources i ndicates that max imum supercharge occurs when t he mean induction velocity at resonan ce is approximately 200 fps . -·. RPM ----· . The Platner equation as found in the patent (4) gives the same pipe length as equation (3) if the mean induction velocity co rresponds to a Mach number of 0. ~--'---' --r.8 I I I I i I I those of the s t ock manifold in Fig ..6 : I I " \\\~'\ ~ ).. Ricardo (3) found the optimum at 180 fps for his configuration . 5 0 I I ' ~\\\\'\... ili o._ 12 --v.rl- -----. the magnitude of the oscillation.__ I I i i ! : .2 IMDUCTUCE RATIO a 1. 9 i I 0 .2 1 ... 8 ! r.6 I I ! i I 0 .e 2 . ~ 1-~~ I I 0. 7 represents a subs tant ial supercharge.6 I I r-.6 1• • 1.. 7 and 8 .-.~ o.7 .o --STOCI ~ Fig. 4 85 . The volumetric efficiency of almost 116 percent shown in Fig .. That is.\\_~ 0... Again.4 CONFIGURATJ ON --lr.3 and B-4 manifolds of Fig..~t---.A-. The mean induction veloc it y is the average ve l oci t y of a volume of charge equal to the piston displacement flowing into the cylinder during the time requir ed for 180 degrees of crankshaft rotation. 1 I I I CA.0 .e.2 --o-B-4.t- r- I . 9 shows one of Eberhard ' s manifolds. The flow losses affect the value of the optimum . increasing losses t ending to decrease the optimum velocity . 7. 0 0. 7 are shown in Fig . "t--l-.0 1.2 a:._--:.• I : J . which is a velocity of 210 fps for velocity of sound at 1150 fps. \\\1'\1'\.8 1. the theoretical or predicted rpm values of these peaks are compared with the experimentally dete rmined values for a group of manifolds all having the same Np ..__.2 IKDUCTAN CE RATIO a ¥ig. the difference between the A-3 and A.. The two tuning peaks are quit e clea rl y visible.. Schwallie's data (9) on 4-cylinder manifolds produced r esults which were quite similar to Eberhard's. there is oscil l atory flow in the laminar element. This flowmeter added a n additional resonance to the mani f olds which gave the dip shown in air f l ow at 1450 rpm in Figure 12. or 1 . the object being good mixt~re distribution. together with a low-cost laminar flow meter which made problems. piston d1splacement plus 20 percent of the 358 cu in.3 and B-3 c urves of Fig. is 185 fps. 9 Three-Cylinder Tuned Intake Manifold Studied by Eberhard (8). 1 1/2-Inch Series. if allowance is made for flow equal to 20 percent of v t o 2 pressurize v 2 . 7 is in the lower frequency mode of oscillation. the peak at 1100 rpm occurs with only 116 fps mean induction velocity in the cylinder pipes. 8 Comparison of Theoretical and Experimental Tuning Peaks. Overall. 9. 7 indicate. The manifolds had been originally made by Kauffmann (7) for research in gasoline engine emissions . For a manifold such as that shown in Fig.2100 ~ ~ P. almost id entical to that at the B-4 peak. The high peak for the B-4 configuration shown in Fig . with peaks co nsiderably above the l ami nar flow . limits of the element . The manifold is shown in place in Fig. The only cure fo r this k ind of prob l em i s a c han ge of the frequency of the added resonance . In this case. the four cylinder pipes are brought together in an "X" which is horizontal. all of the same general configuration. added to the analog in Fig . which peaks at 113 percent volumetric efficiency at 1200 rpm in Fig. or c3 . 2 Thus. the standing waves du e to or ganPipe-type resonance wer e more evident than the A. the flowmeter elemen t acted 3S a third inductive leg . Howe ver. The solution fo r this engine is a 55. The feeder pipe veloc ity. established the existence of this parti cula r reso nance in an undergraduate laborat ory experiment. 11. John O'Dea and Richard Wagner . optimization of the velocity is more complex.ga l lon drum. the pressure oscillations in th~ cylinder and in the log (or at the branch point) are in phase. and the volume between it 3 and the carbur etor acted as a capaciti ve element . For this lower frequency mode. which the velocity in the feeder -pipe is 186 fps. the flow ~n the feeder pipe consists of the 98 cu in . Similar Units Made with Conduit Bends were Also Used. 4 . and their assistance is hereby gratefully ac knowled ged . The air flow data in the v1c1n1t y of this cond ition are meaningless . from Reference (8) . Two student s . above the optimum. Fig. the cylinder pipe mean induction ve l ocity is 242 fps. RPP'! Fig . Fo r this rea son.. the mean induction velocity in the smaller cylinder pipes at the peak is 161 fps.+---j 1----+-•2 [7 0 500 1000 1500 2000 21 00 EXPERH!EHTAL TUNIIriG PEAK. The difference of 3 percent in the volumetric efficiency with these two manifolds must therefore be attributed to the higher cylinder pipe velocity of the A-4 configuration. and the carbure to r feeds vertically downward into the cente r of the -X as shown in Figure 10. At this condition. total volume of the log and the two idle cylinder pipes . The curves of Fig . in a number of the manifolds. but most of the loss of supercharge is attribu t able to flow loss 1n the feeder pipe. The A-4 peak at almost the same rpm shows the supp r ession resulting from excessive cylinder pipe veloci ty. Made of Copper Pipe and Fittings. a nd did not change th e bas ic Helmholtz peaks . between t he meter1ng eleme nt and the carbu r e t or . It is a fact that any metering element such as a noz zle or orifice will be 5 . In this case. and emphasizes t he fac t that a resonant system will resonate r egardless of the intent of the designer. Eberhard's data covered a total of 20 different manifolds. 1500 "~ i: ~1 000 I/ ii § . At the higher frequency peak of 2300 rpm for the B-4 manifold. In the A-4 configuration. these did not have a major effect on volumetric efficiency. however. 100 /of I 2000 7 ~/ •. 7 are quite typical. 7. and most of the "ramming" effect is provided by the inertia or inductance of the feeder pipe 1 . and between cylinders 3 and 4. .. Reference (9).... 6 " 1- ~ !:--. There will be a resonance associated with that volume.. L _L I I- c- PkOTOTYP E 1 1 -.. 8 times th e diamet er to be added to the actual length to determine the effective length ..-1~--r--. 13 Comparative Compression Data Showing Uneven Air Distribution Due to Tuning Effects.-- .. __ _ /"\.--.' CYLS i 1 " 4 -. 2/ I ~ /jj r- -- STOC K 0. In describing this manifold as a rake type. runner . which would a lso be described as r ake t ype ..2 Fig .sec tional area to the 6 20 ~-t--t--r--r-~~r-1--4--+--+--+--+--~~-- ENGI NE RP!'I Fig . Reference (7).t/" __..-.:.- V f--- . the log is only slightly larger than the ru nners between cylinders 1 and 2 . a commo n value is 0 .Cy linde r Engine with Tuned Manifold and Laminar Flowmeter in Place ...--.. it is necessar y to distinguish it from Eberhard ' s ma nifold s . For the two mi ddle cylinders .. 1 1 ~s larger and V2 ~s smaller. the effective pipes consist of port a nd ~ unn er only . 1 and 4. exact l y like the laminar element .4-CYL AV-.8 PRCTOT'(PE !H h fk li/f VI ~~ \ I .sectional a r ea .. In Ebe rhard ' s manifolds.::::::-< 1__1_ _ _ 1 ·--r.'" . for the e nd cylinders. 1. and so acco un t fo r t he r ather sma ll ga in in breathing achieved with the t un ed manifolds as compared with the stock unit. 2 and 3.. 10 Tuned Manifold Made by Kauffmann. This differe nce could be seen in his compre~sion data for individual cylinders.) v~--"" ../~-1-~4-~-1-~4-~~-b-+-~~ ~ .-.--...~.. } -. 2 10 ' .. ~ ~ 1 ---= . ~''\..._. ~ f:f }5 f-. runner or cylinder pipe c ross.--.0 ~ 0 .. Thu~ .&:- '\ ~\ ~ e: 0 .~. For a simple pipe with the end cu t off square. 40 r--.1--- --l-+. l~ith the drum . For a simple orifice .srocK '- ~}O ~v~ .-1-+ Fig .. than for the middle cylinders. 1 2 Volumetric Flow Data Showi ng Tuning Effect of Fl owmeter. 11 Four .1.STOCK V~"' cns n .-.. /..~-.. up to the adjacent cylinder runner ..... a shift to 10 Hz or 300 rpm is easy .. and representat~ve data are shown in Fig.--. _L _ ..--..·. Data from Reference (9) . from Reference (9 )..-.. The effective cy linder pipes for the end cylinders each co nsis t of port . and part of the log.·-<.1 . and Studied by Schwaii e . and the frequency must be well ou t of the range in which valid data is desir ed .. the logs were quite large.. 0 1000 2000 }000 ~GI N E 4000 RPM Fig..1.followed by a finite volume.. The major difference is the r atio of th e log cross . Mention should be made here of the end correction which applies to Helmholtz resonators and other syst ems involving oscillatory flow in pipe s .. 1--.. 13. I I -·1---.1'-. L... ~-"' 1-. Reference ( 9) . / I PROTO TYPE . as Used by Schwallie . while in Sc hwallie ' s stock manifold.--~~-. Schwallie was able to calculate the r esona nces of the rake type stock manifold for this engine. 6. De te rmi ne ~he volume or capacitance ratio b.3 3 . It will be qui t e obvi ous th at the des ired peak at 2000 rp~ will ·be the lower. or N resonance . b v2 2(R-l) VD (R+L) 47 . 16 i nches. th e idle intake pip es by about 20 percent . for which L1 becomes 5 inches. b will be increased by the volume of the log. Enter Figure 5 . and the individual cyl inder passages provide little ram effect. The L/A value for a ca r bu r eto r must be determined experimentally. Eberhard's r es ult s i ndicate t hat 200 ft . 5 X 16 38 X 10 2 . for b inductance ratio a. and that N2 f rom Figure 6 is only of the o rder of 10 perc ent higher than Np. Calculate Np from equation (3) or (4). It is well established that in mus i ca l instruments like the trumpet or French horn.25 sq. x2 is found to be 1. the effective leng th is usually taken as the diameter of the hole . The fol lowing are some us efu l fac t s in respect to the procedures and configurations described: 1 . and will result in new values of L2 a nd N2. 589 . values of a and b can be chosen to provide the value of 0. I nlet proportions may now be chose n . It i s desirable that all four individual pipes be of th e same L/A value and have equal flow loss es . Then.. pipe and port area are chosen for a mean induction velocity of 200 ft .65 cu in. per second at the peak. giv~ng 2 Step 8. an Np of 6000 rpm mi gh t be chosen. 3 . per seco nd. say. from equation (3). The three idle pipes will have a combined volume V . and slightly reduce the N1 peak. the smaller the radius of the bend may be made without introducing intolerable flow losses. Therefore. To the flow into the cylinder. 0. for which x1 . in 180 degrees of crank travel is 38 x. 13. and b becomes 2 . Since length enters the frequency eq uations (1). or cross. per seco nd. Np becomes 3100. the engine of Figure 10 will be used. Step 3. 1 1 Th~s pip e area will a lmos t eliminate the N2 peak. A 1 2400 This is a diameter of 1 . The data are incomplete for the large l og configura tion. 589. 0 . 3. centerline dist a nces work well.7 inchas . it s value at 90 F. empi rical data must be obtained for any specific configuration . 7 . a total of 152 cu in. length to the inner wall of th e log will account for some rounding of the e ntrances of the cylind e r pipes . the end of the effective l ength is somewhere in the bell (10) . The required area is then 2533 1. The value of A2 should provide for th e mean ind uc tion veloci t y of 200 ft. the centerline length of the intake passage to these cylinders will consist of 4 inches of port. 7 inches from the X to the port. (3). al though the optimized proportions have not been deve l oped . 3 2 X 15 X Then. per second. MISCELLANEOUS CONSIDERATIONS The design proced ur e set fo r th here does not represent the e ntir e picture of tuned manifold design . The higher res onance N is found from Figure 2 N . or 6. and the valve stems are 4 inches from the manifold gasket surface . from Equation (7). Considering the ram compression adiabatic. 9 . Port and pipe area A1 then might be increased to. The X c onfigu ra tion of Figure 10 provides excellent mixture distribution with liquid fuels (7) . 4540 rpm. . 40 30 rpm . 38 cu in. Initially. based on equation (3). tfiere must be added the flow which raise s th e pr essure in v2.82 X 1. 0 . in .6 in. 38 c u in . and L2 will be decreased. 055. the end ports (#1 and #4) are approximately 15 inches betwee n centers. 1. and N2 .33 fo r X1. 2400 in.in the wall of a cavity. For example . The important engine dimensions must be ob ~ tained. although for the small log shown in Figure 9.25 X 15 14.3 rps.4. The smaller the pipe diameter . there fore. t he performance conforms to the proced ur e presented (8). From equation (6) 0. In this case. in . which is to be 2000 rpm or 33. and (4) · as a square root. 0 .055 sq . Step 4 . however. at right angles to its plane.33.30. and a compression ratio of 9 . a nd since round ed entrances are commo n in manifolds to reduce flow losses. 47. Such propo rtion s for individua l intake pipes will be quite fam iliar to r acing buffs . Loss elimination may be benefic ial. For manifolds. The physical layout is now checked.82 Step 6 . It will be obvious t hat inc reas ing L1 will decrease Np. find a . A possibility is the use of the Figure 9 configuration with the log connected by v e ry short pipes t o th e ports . Step 1. The manifold will be of the pattern shown: the inlet enters an X. A tuning peak will be es tablished at 2000 rpm. since the se are physically limiting. 0. if L1 is increased to 18 inches . per second.2 x 33 . DESIGN PROCEDURE As an example of the explici t design of a tuned manifold. 10 . per second ve l ocity in L is near optimum. plus an allowance for the bend to enter the por t. Step 2. 0. per second. a nd x . thi s is 14 pe r cent on volume. Np . displacement per cylinder.5 CU in. The area A2 should then be inc r eased to 1 . 055 Step 7 . as will N2 . The engine has 4 cy linde rs. 1 .0 Step 5. For a given value of L1. 3400 rpm. 2 . Then a .- "~ "~ Np . X2 . For a manifold like that in Fig. 2533 cu in. the value of car r yi ng an end correction throu gh preliminary calculcations is questionable. For most naturally aspirated engines the v e l oc ity of sound may be taken as 1150 ft . 200 ft. including the effect of compression in the lo g .64.165 sq .64 5 . or about 15 inches fo r L1 . From Figure 5. For the X configuration of Fig. x1 becomes 0 . Thus. The cylinder port may be increased in area for this purpose since the N1 resonance has cylinder and log pr ess ure s in phase. 1. L2.. I t will be not ed that this configuration ca lls for l arge values of both a a nd b. 77 x 1150 • ~ • r. will increase volume rati o b. It is informative to consider t his. It may be des i rable to use the configuration shown in Figure 9. in. P . the effect is almost exactly the same as that of a good geardriven supe rcha rger g iving t he same power boost (1 . "High Output Engine.. No r eason is appa rent for believing that t uning should not be applied for a turb ochar ged e ngine . Thesis . .." M. a nd Moore. one configuration shown in the Platner patent (4) consists of a large box in the V of a V-8 engine with short pipes to the individual cylinders . \4. July 1973. 1971. Ohio State University. .11-:}:ngleman. Vol. "Investigation of the Influence of Gasoline Engine Induction Sys tem Parameters on th e Exhaust Emissions. However. Paper 53-0GP-4. R. 6 . 1956. High back pres s ure in the exhaust system is detrimental to breathing. 2.S . Kauffmann.9) . Patent No. J. ACKNOWLEDGEMENTS The support and assistance of the Cummins Engine Company and t he Interna tional Harves t e r Company in providing the engines used in the manifold s t udies is gratefully acknowledged.W. S .E . 4. 1969. Eberhard is acknowledged with thanks. Patent No . Rather . Ohio State University. 766. " M.. " Verification of a Mat hematical Mode l for Intake Manifold Design. and Engelman. A." U. W. 1. P. In fact.D. Ohio State Univer sity .834. 3. no data have been ob t aine d for any conf i guration supplying more than 4 cy linder s . J. Likewise. " Surge Phenomena in Engine Scavenging. "A Mathematical Model of RamCharging I ntake Manifolds for Four-Stroke Diesel Engines.. " Scien tific America n.S of Resonance in Intake Tuning. 229 . S .• 3: Data are not avai l able for the specific cases of siamese ports.B." U. "Internal Combustion Engine. 1. H. the Cummins Fe l lowship which supported the investigation by W. M. Thesis. "Th e Physics of Brasses. D. pp. H. "The Two 1 €5) Thompson. The only significant resonan ce i s then at Np . Schwallie . . 1931 . due t o the overlap of int ake strokes. S.643. or Supercha'rg'ing Without a Blower . 197 2 .S. Thesis . 24-37.8. 5 .E. Ricardo. to good and bad exhaust tun i ng . 4. M.. Further.S. M. Engelman . 8 . H.473. Overall . Platner. Thesis .. H. 5..M. Paper 69-DGP-11. "Non-Mechanical Supercharging of a Four-Stroke Diesel Engine. No . Eberhard. l953. 1953. Typ\." A. there is good reaso n to attribute the wide variation of benefits gained by pulse-charging. REFERENCES 1. .C. 9 . L. 5'1 Thompson. and the system reverts to a single degree of freedom . . That is. C. " M. 1972. Ohio State University . It appears that these short pipes act as · i f they wer e open to the atmosphere. Data are not available fo r a manifold consisting of a fairly large log feedin g six or eigh t cylinders. i t should be helpful.S . 1968 . 7. 7." A. 10. Int a ke manifold tunin g will no t eliminate exhaus t l osses . R ." Ph. the feeder pipe flow is virtually continuous . Bena de . .. Dissertation. Arthur H. as compared with co ns tant pressure systems." Ph. W. The tun ed manifold will use up some of th e engi ne power in the form of pumping work .6. "The Tuned Manifold. University of Wisconsin . W. W.D. 2 .
Report "Design of a Tuned Intake Manifold - H. W. Engelman (ASME paper 73-WA/DGP-2)"