IR lengths and plenum sizing for carbs

[user-23911]

I don't recall ever seeing an efi intake manifold 27" long

27 inch would tune peak torque at 6000RPM............Total length.
I've got several which are longer than that. More than 44 inch?
That's from the intake valve so some of it is in the head.

Who's got an LS1?
What's the length?
Easy to measure with a piece of wire.

[digger]

can tell by eye that the LS is nowhere near that, it might struggle to be 20"

[BenE64]

Take a look at pretty much any EFI manifold and the length chosen is the correct length.

If you want to downgrade to carburettors like in your picture above then you need to add intake trumpets to get the length back.
It's easier said than done because the length is similar to that of the primary runners for the exhaust which on an EFI manifold are usually curved.

The chart above is wrong in that only the odd harmonics are used, not the even ones.
Don't know where the chart came from but 2nd, 3rd and 4th are probably (in reality) the odd ones so really the 3rd, 5th and 7th.


edit.......working it out is quite easy........speed of sound 343 m/sec ....... Primary tuned length. That's a half wavelength because the wave flows there and back again.

At 6000 RPM, that's 100Hz or 50 Hz for a 4 stroke single cylinder.
343/50 is the total distance between pulses = 6.86 meters or (6.86/2) 3.43M tuned length.
Nobody ever uses that because it's too long.
The 2nd harmonic is 6.86/4...not used due to fighting airflow instead of helping it.
3rd is 6.86/6.......1.14M (44 inches)
4th is 6.86/8.......not used as above.
5th is 6.86/10......69cm (27 inches)
That's total length, valve to open atmo.

Just ballpark figures but they fit modern EFI engines........not computer simulation gigo.

I must admit I am a bit lost with this. I measured the standard EFI manifold and its total length of runner is approx 41- 46cm average. Which indecently is within 2cm of what pipemax put out for the standard config on the engine, with the advertised HP and rpm specs for my motor.
From all reports the standard motor is nothing inspiring (170hp) and a lot of people gain just by putting an earlier version manifold on and a 350 holley. They are a different beast with boost, but due to laws here I cant legally turbocharge it with the vehicle I am putting it in. Even standard it is 3 times the HP of the original motor so I will be happy for now with a NA version that is hotrodded to the best of my ability.

[BenE64]

Don't think you'd want an airbox for tuning, but for muffling the intake noise. It's not going to be as beneficial for a low end boost pairing three cylinders. You might be able to give it a big mid-top boost but it would be tricky and the carburetors would be confused as heck too.
So, what's the length?

I am not sure I want to muffle the intake noise. I don't even have a stereo I had a L20B in it with a single side draft weber that went really well considering the 150k miles on it, I was happy listening to that. If one was good, wouldn't three be even better?

I will screen dump the specs off pipemax, I have built it to suit aftermarket cams so it is'nt the ideal for the standard ones, but i am not building this stuff twice, well twice more than the twice I already have.

[modok]

edit.......working it out is quite easy........speed of sound 343 m/sec ....... Primary tuned length. That's a half wavelength because the wave flows there and back again.

At 6000 RPM, that's 100Hz or 50 Hz for a 4 stroke single cylinder.
343/50 is the total distance between pulses = 6.86 meters or (6.86/2) 3.43M tuned length.
Nobody ever uses that because it's too long.
The 2nd harmonic is 6.86/4...not used due to fighting airflow instead of helping it.
3rd is 6.86/6.......1.14M (44 inches)
4th is 6.86/8.......not used as above.
5th is 6.86/10......69cm (27 inches)
That's total length, valve to open atmo.

Just ballpark figures but they fit modern EFI engines........not computer simulation gigo.

some of that must be wrong

[modok]

You are calculating harmonics of a pipe closed on both ends.
On the open end, the wave changes sign from positive to negative.
Say you have pressure at the valve.
The pressure travels to the open end 1, then comes back to the closed end as negative 2, this reflects and travels to the open end 3, then positive travels to the closed end again 4.
from positive to positive.....travels the length four times.

Engine harmonics we measure frequency peak to peak, and the harmonics refer to the number of peaks in an engine cycle.
to understand, change harmonic to what the music guys call overtone.

[user-23911]

You are calculating harmonics of a pipe closed on both ends.
On the open end, the wave changes sign from positive to negative.
Say you have pressure at the valve.
The pressure travels to the open end 1, then comes back to the closed end as negative 2, this reflects and travels to the open end 3, then positive travels to the closed end again 4.
from positive to positive.....travels the length four times.

Engine harmonics we measure frequency peak to peak, and the harmonics refer to the number of peaks in an engine cycle.
to understand, change harmonic to what the music guys call overtone.

Waves are either compression or rarefaction.
An open end changes from one to the other as well as changing direction.
A closed end only changes direction.
A wave is stored energy which is only lost through friction .


So at 6000 RPM as an example (easy) it's 50 Hz.......50 cycles per second or 20 mS per pulse.
At 343 M/sec a pulse will travel 6.86M in 20 msec.
It starts at the valve, travels to the plenum as a rarefaction wave, reverses direction and also changes to a compression pulse / wave. If the pipe is 3.43 M long then it travels a total of 6.86M and arrives back at the valve at the perfect time to push air into the port just as the valve is opening again.


If the pipe was 1.715M long, it's still going to travel 6.86M in 20 msec but it will need to go there and back twice (2nd harmonic).
Again it starts at the valve, travels to the plenum as a rarefaction wave, reverses direction AND changes to a compression wave. reflects off the closed valve, changes direction, still a compression wave......back to the plenum, changes direction again but also changes to a rarefaction wave.....back to the valve just as it's opening.......loss of airflow is the result.

Because it's an even harmonic.

[digger]

Take a look at pretty much any EFI manifold and the length chosen is the correct length.

If you want to downgrade to carburettors like in your picture above then you need to add intake trumpets to get the length back.
It's easier said than done because the length is similar to that of the primary runners for the exhaust which on an EFI manifold are usually curved.

The chart above is wrong in that only the odd harmonics are used, not the even ones.
Don't know where the chart came from but 2nd, 3rd and 4th are probably (in reality) the odd ones so really the 3rd, 5th and 7th.


edit.......working it out is quite easy........speed of sound 343 m/sec ....... Primary tuned length. That's a half wavelength because the wave flows there and back again.

At 6000 RPM, that's 100Hz or 50 Hz for a 4 stroke single cylinder.
343/50 is the total distance between pulses = 6.86 meters or (6.86/2) 3.43M tuned length.
Nobody ever uses that because it's too long.
The 2nd harmonic is 6.86/4...not used due to fighting airflow instead of helping it.
3rd is 6.86/6.......1.14M (44 inches)
4th is 6.86/8.......not used as above.
5th is 6.86/10......69cm (27 inches)
That's total length, valve to open atmo.

Just ballpark figures but they fit modern EFI engines........not computer simulation gigo.

I must admit I am a bit lost with this. I measured the standard EFI manifold and its total length of runner is approx 41- 46cm average. Which indecently is within 2cm of what pipemax put out for the standard config on the engine, with the advertised HP and rpm specs for my motor.
From all reports the standard motor is nothing inspiring (170hp) and a lot of people gain just by putting an earlier version manifold on and a 350 holley. They are a different beast with boost, but due to laws here I cant legally turbocharge it with the vehicle I am putting it in. Even standard it is 3 times the HP of the original motor so I will be happy for now with a NA version that is hotrodded to the best of my ability.

pipemax is a great start point and then you can just test different lengths on the dyno

[modok]

Because it's an even harmonic.

This is a pressure trace, fourth harmonic
explain to me what's bad about it

[BenE64]

Pipemax details I am using to build my exhaust and intake.

199.807 Cubic Inches @ 6100 RPM with 103.00 % Volumetric Efficiency PerCent

Required Intake Flow CFM @28 in. = 154.1 to 163.2 at .530 inch Valve Lift
Required Exhaust Flow CFM @28 in. = 123.4 to 133.7 at .484 inch Valve Lift

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 223.8 228.5 231.4 234.3
Peak Torque Lbs-Ft 212.5 218.1 220.4 223.7

HorsePower per CID 1.120 1.143 1.158 1.173
Torque per Cubic Inch 1.063 1.091 1.105 1.119
BMEP in psi 160.4 164.6 166.7 168.8
Carb CFM at 1.5 in Hg. 363 404 425 445

Recommended Intake Valve Lift to prevent Choke = .530 Lift @ 6100 RPM
Recommended Exhaust Valve Lift to prevent Choke = .484 Lift @ 6100 RPM
Recommended Minimum Normal Maximum Time-Area-Duration Lifts
Intake Valve Lift = 0.4705 0.5300 0.5830 0.6304 0.6645 0.6986
Exhaust Valve Lift = 0.4450 0.4837 0.5321 0.5736 0.6095 0.6455
IntOpen= -.50 IntClose= 41.50 ExhOpen= 41.50 ExhClose= -0.50
Intake Duration @ .050 = 221.00 Exhaust Duration @ .050 = 221.00
Intake CenterLine = 111.00 Exhaust CenterLine = 111.00
Compression Duration= 138.50 Power Duration = 138.50
OverLap Duration = -1.00 Lobe Separation Angle (LSA)= 111.00
Camshaft Straight Up = 0.00 degrees Cylinder Ignition Interval= 120 deg.

-- Operating RPM Ranges of various Components --
Best estimate RPM operating range from all Components = 3982 to 5982
Intake Flow CFM @28inches RPM Range from Flow CFM only = 4042 to 6042
Intake and Exhaust Systems operating RPM Range = 3590 to 5590
Intake and Exhaust Time-Area operating RPM Range = 2813 to 4813
Camshaft's Intake and Exhaust Lobes operating RPM range = 3466 to 5466
Intake Valve Curtain Time-Area at 0.474 Lift RPM Range = 3456 to 5456
Exhaust Valve Curtain Time-Area at 0.474 Lift RPM Range = 3977 to 5977

Intake Valve Close RPM = 5565 Exhaust Valve Open RPM = 5171
Intake System RPM = 5552 Exhaust System RPM = 5629
Intake Time-Area RPM = 4586 Exhaust Time-Area RPM = 5041
Intake Mach Z-Factor = 0.542689 Exhaust Mach Z-Factor = 0.651385
Intake Z-Factor Lift = 0.535906 Exhaust Z-Factor Lift = 0.467813

Curtain Area -to- Valve Area Convergence Intake Valve Lift inch= .414
Curtain Area -to- Valve Area Convergence Exhaust Valve Lift inch= .345

Target EGT= 1422.7 degrees F at end of 4 second 600 RPM/Sec Dyno accel. test
Octane (R+M)/2 Method = 89.1 to 90.6 Octane required range
Air Standard Efficiency = 58.83315 % for 8.900:1 Compression Ratio

------- Piston Motion Data -------
Average Piston Speed (FPM)= 3322.47 in Feet Per Minute
Maximum Piston Speed (FPM)= 5405.981 occurs at 75.84311 Degrees ATDC
Piston Depth at 75.843 degree ATDC= 1.4450 inches Cylinder Volume= 241.3 CC
Maximum TDC Rod Tension GForce= 2192.3804 G's
Maximum BDC Rod Compression GForce= 1261.5373 G's

----- Engine Design Specifications -----
( English Units ) ( per each Valve Sq.Inch area )
Engine Size CID = 199.807 Intake Valve Net Area = 2.089
CID per Cylinder = 33.301 Intake Valve Dia. Area = 2.149
Rod/Stroke Ratio = 1.855 Intake Valve Stem Area = 0.060
Bore/Stroke Ratio = 1.102 Exhaust Valve Net Area = 1.413
Int Valve/Bore Ratio = 0.459 Exhaust Valve Dia. Area = 1.491
Exh Valve/Bore Ratio = 0.383 Exhaust Valve Stem Area = 0.078
Exh/Int Valve Ratio = 0.833 Exh/Int Valve Area Ratio = 0.694
Intake Valve L/D Ratio= .287 Exhaust Valve L/D Ratio= .344
CFM/Sq.Inch = 71.7 to 75.9 CFM/Sq.Inch =82.5 to 86.1

Intake Valve Margin CC's Exhaust Valve Margin CC's
1.00 CC = 0.0284 1.00 CC = 0.0409
0.50 CC = 0.0142 0.50 CC = 0.0205
0.25 CC = 0.0071 0.25 CC = 0.0102
0.10 CC = 0.0028 0.10 CC = 0.0041

- Induction System Tuned Lengths - ( Cylinder Head Port + Manifold Runner )
1st Harmonic= 31.713 (usually this Length is never used)
2nd Harmonic= 17.999 (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 12.566 (ProStock or Comp SheetMetal Intake • best overall HP )
4th Harmonic= 9.890 (Single-plane Intakes , less Peak Torque • good HP )
5th Harmonic= 8.025 (Torque is reduced, even though Tuned Length)
6th Harmonic= 6.751 (Torque is reduced, even though Tuned Length)
7th Harmonic= 5.827 (Torque is greatly reduced, even though Tuned Length)
8th Harmonic= 5.125 (Torque is greatly reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
4th Harmonic is used to package Induction System underneath Hood

Plenum Runner Minimum Recommended Entry Area = 1.644 to 1.849 Sq.Inch
Plenum Runner Average Recommended Entry Area = 1.890 Sq.Inch
Plenum Runner Maximum Recommended Entry Area = 1.930 to 2.284 Sq.Inch

Minimum Plenum Volume CC = 466.1 ( typically for Single-Plane Intakes )
Minimum Plenum Volume CID= 28.4 ( typically for Single-Plane Intakes )
Maximum Plenum Volume CC = 3274.2 ( typically for Tunnel Ram Intakes )
Maximum Plenum Volume CID= 199.8 ( typically for Tunnel Ram Intakes )

--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
150 FPS at Intake Valve Curtain Area= 2.463 sq.in. at .474 Lift
172 FPS at Intake Valve OD Area and at Convergence Lift = .414
212 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 1.740 sq.in.
--- 6100 RPM Intake Cross-sectional areas in Square Inches ---
350 FPS CSA= 1.056 Port has Sonic-Choke with HP Loss ( too fast FPS )
330 FPS CSA= 1.121 Port may have Sonic-Choke with HP Loss ( too fast FPS )
311 FPS CSA= 1.189 Highest useable Port velocity ( possible HP loss )
300 FPS CSA= 1.233 Smallest Port CSA ( Hi Velocity FPS • good TQ and HP )
285 FPS CSA= 1.298 Smallest Port CSA ( very good TQ and HP combination )
260 FPS CSA= 1.422 Recommended average Intake Port CSA (very good TQ and HP)
250 FPS CSA= 1.479 Largest recommended average Intake Port CSA ( good HP )
240 FPS CSA= 1.541 Largest recommended average Intake Port CSA (less Peak TQ)
235 FPS CSA= 1.574 Largest recommended Intake Port Gasket Entry area CSA
225 FPS CSA= 1.644 Largest Intake Port Gasket Entry CSA ( Slow FPS )
215 FPS CSA= 1.720 Possible Torque Loss with Reversion ( Slow FPS )
210 FPS CSA= 1.761 Torque Loss + Reversion possibility ( too slow FPS )
200 FPS CSA= 1.849 Torque Loss + Reversion possibility ( too slow FPS )
Note : these are calculated average Port cross-sectional areas and FPS

--- Cross-Sectional Areas at various Exhaust Port Velocities (@ 28 in.) ---
144 FPS at Exhaust Valve Curtain Area= 2.052 sq.in. at .474 Lift
199 FPS at Exhaust Valve OD Area and at Convergence Lift = .345
245 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 1.208 sq.in. at 6100 RPM
--- 6100 RPM Exhaust Cross-sectional areas in Square Inches ---
435 FPS CSA= 0.681 Sonic Choke at Throat Area (too fast FPS velocity)
380 FPS CSA= 0.780 Sonic Choke at Throat Area (possibly too fast FPS)
350 FPS CSA= 0.846 Exhaust Port has Sonic-Choke with HP Loss (too fast)
330 FPS CSA= 0.898 Exhaust Port has Sonic-Choke with HP Loss (too fast)
311 FPS CSA= 0.952 smallest Exhaust Port ( very high velocity FPS )
300 FPS CSA= 0.987 smallest recommended Exhaust Port (Hi velocity)
285 FPS CSA= 1.039 smallest recommended Exhaust Port (Hi velocity)
265 FPS CSA= 1.118 Recommended average Exhaust Port CSA
250 FPS CSA= 1.185 Recommended average Exhaust Port gasket area
240 FPS CSA= 1.234 Recommended largest Exhaust Port gasket area
225 FPS CSA= 1.317 Largest Exhaust Port Exit gasket area (Slow FPS)
210 FPS CSA= 1.411 Largest Exhaust Port Exit gasket area (Slow FPS)
190 FPS CSA= 1.559 Torque Loss + Reversion + Scavenging loss (too slow FPS)
180 FPS CSA= 1.646 Torque Loss + Reversion + Scavenging loss (too slow FPS)
Note : these are calculated average Port cross-sectional areas and FPS

Valve Intake Exhaust Curtain Area Cross-Sect Area Minimum Flow
Lift Choke Choke Square Inches 280FPS 280FPS CFM @ 28 In
inches RPM RPM Intake Exhaust Intake Exhaust Int Exh
.050 576 630 0.260 0.216 0.125 0.100 14.5 11.6
.075 863 946 0.390 0.325 0.187 0.150 21.8 17.5
.100 1151 1261 0.520 0.433 0.249 0.200 29.1 23.3
.125 1439 1576 0.650 0.541 0.312 0.250 36.3 29.1
.150 1727 1891 0.779 0.649 0.374 0.299 43.6 34.9
.175 2014 2207 0.909 0.758 0.436 0.349 50.9 40.8
.200 2302 2522 1.039 0.866 0.498 0.399 58.1 46.6
.225 2590 2837 1.169 0.974 0.561 0.449 65.4 52.4
.250 2878 3152 1.299 1.082 0.623 0.499 72.7 58.2
.275 3165 3468 1.429 1.191 0.685 0.549 80.0 64.0
.300 3453 3783 1.559 1.299 0.748 0.599 87.2 69.9
.325 3741 4098 1.689 1.407 0.810 0.649 94.5 75.7
.350 4029 4413 1.819 1.515 0.872 0.699 101.8 81.5
.375 4316 4729 1.949 1.623 0.935 0.749 109.0 87.3
.400 4604 5044 2.078 1.732 0.997 0.798 116.3 93.2

Valve Intake Exhaust Curtain Area Cross-Sect Area Minimum Flow
Lift Choke Choke Square Inches 280FPS 280FPS CFM @ 28 In
inches RPM RPM Intake Exhaust Intake Exhaust Int Exh
.425 4892 5359 2.208 1.840 1.059 0.848 123.6 99.0
.450 5180 5674 2.338 1.948 1.121 0.898 130.8 104.8
.475 5467 5990 2.468 2.056 1.184 0.948 138.1 110.6
.500 5755 6305 2.598 2.165 1.246 0.998 145.4 116.4
.525 6043 6620 2.728 2.273 1.308 1.048 152.6 122.3
.550 6331 6935 2.858 2.381 1.371 1.098 159.9 128.1
.575 6618 7251 2.988 2.489 1.433 1.148 167.2 133.9
.600 6906 7566 3.118 2.597 1.495 1.198 174.4 139.7
.625 7194 7881 3.248 2.706 1.558 1.248 181.7 145.6
.650 7482 8196 3.378 2.814 1.620 1.298 189.0 151.4
.675 7769 8512 3.507 2.922 1.682 1.347 196.3 157.2

Cylinder Ignition Interval = 120 degrees 6100 RPM Hertz frequency = 50.8 Hz
Target EGT= 1422.7 degrees F at end of 4 second 600 RPM/Sec Dyno accel. test
199.807 CID Exhaust System operating RPM Range from 4100 to 6600 RPM

--- Single Primary Pipe Specs --- ( Low to Mid-Range RPM Torque and HP )
Diameter= 1.482 to 1.607 Total Length= 29.5 to 32.1 inches long
--- 2-Step Primary Pipe Specs --- ( Low to Mid-Range RPM Torque and HP )
1st Step Dia. inches= 1.482 Length= 14.7 to 16.1
2nd Step Dia. inches= 1.607 Length= 14.7 to 16.1
--- 3-Step Primary Pipe Specs --- ( Low to Mid-Range Torque and Hi RPM HP )
1st Step Dia. inches= 1.482 Length= 14.7 to 16.1
2nd Step Dia. inches= 1.607 Length= 7.4 to 8.0
3rd Step Dia. inches= 1.732 Length= 7.4 to 8.0

--- Single Primary Pipe Specs --- ( Mid-Range TQ to Higher RPM Horsepower )
Diameter= 1.682 to 1.807 Total Length= 29.5 to 32.1 inches long
--- 2-Step Primary Pipe Specs --- ( Mid-Range TQ to Higher RPM Horsepower )
1st Step Dia. inches= 1.682 Length= 9.8 to 11.2
2nd Step Dia. inches= 1.807 Length= 19.7 to 21.0
--- 3-Step Primary Pipe Specs --- ( Higher RPM Horsepower, possible TQ loss )
1st Step Dia. inches= 1.682 Length= 9.8 to 11.2
2nd Step Dia. inches= 1.807 Length= 9.8 to 10.5
3rd Step Dia. inches= 1.932 Length= 9.8 to 10.5

--- Conventional Straight Tube Collector Specs ---
( TQ ) Diameter= 2.264 to 2.514 Best Length= 17.7 and also 35.3 inches
( HP ) Diameter= 2.514 to 3.014 Best Length= 17.7 and also 8.8 inches
--- Megaphone Collector Specs ---( Diffuser or Diverging Cone Shape )---
( TQ ) Diameter= 1.514 taper to 2.514 Best Length= 17.7 or 35.3 inches
( HP ) Diameter= 1.764 taper to 2.764 Best Length= 17.7 or 35.3 inches

H-Pipe= 17.7 X-Pipe= 70.6 distance behind end of Primary Tube ends

-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 17.7 , 35.3 , 70.6 , 141.3 inches long
Worst HP/TQ Loss Collector Lengths= 26.5 , 53.0 , 106.0 , 211.9 inches long
Note=> measured from where the Primary Pipes end inside the Collector to
the point the Collector or tailpipe exits into the atmosphere.

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 128.1 inches long ... typically never used
2nd Harmonic = 48.9 inches long ... longest recommended
3rd Harmonic = 29.5 inches long ... highly recommended , best Torque Curve
4th Harmonic = 20.7 inches long ... shortest recommended
5th Harmonic = 15.7 inches long ... typically never used
6th Harmonic = 12.5 inches long ... typically never used
7th Harmonic = 10.2 inches long ... typically never used
8th Harmonic = 8.5 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 141.3 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 70.6 inches long ... longest recommended with Mufflers
3rd Harmonic = 35.3 inches long ... more bottom-end Torque
4th Harmonic = 17.7 inches long ... highly recommended , best Torque Curve
5th Harmonic = 8.8 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.4 inches long ... reduced Torque , not recommended

The coloured sections are the measurements I am going off for the intake. I have made the primaries to the merge collector for the exhaust already using the highlighted measurements above. I have erred on the small side in pipe size due to lack of room and it will be primarily a street car for the time being. I plan on going 2in from each merge for the lengths specified to the H pipe 17in if I can, (or 35in otherwise) where I will join the 2 pipes into a single 2.5in out the back.

This lot of specs is for a bigger cam than is currently in the engine, I have put smaller 34mm venturis in the IDFs for the current cam, will probably go up in size to the 36mm ones once the cams have been changed. Will just need to suck it and see for the manifolds / exhaust in the meantime as I cant afford to build those twice, lets hope cams come along quickly

[user-23911]

Makes just as much sense as getting data out of the bible.

[BenE64]

Makes just as much sense as getting data out of the bible.

For your calculations above I tried 4000rpm which would be more likely around peak torque for my motor.

3rd harmonic is 1.66M ? I would need to ditch my "down graded" carburetors, make a new efi system, then position the throttle body some 2 feet outside the side of the car or coil up the runners?

By your method the closest i can get would perhaps be 14th harmonic. Still ditch the carbs i have now and go side drafts or efi?

I am not saying that because the world being round doesnt suit my needs i will believe the theory that it is flat because i can make it fit.

Looking at it from my point of view as a relative new comer to designing these things, on one hand there is a program that a lot of people smarter than me recomended and have had good proven results. Or a set of calcs that recommend my intake be 3 times longer than the OEM manifold which chokes power completely by 4500rpm?

When I said I dont understand I meant I dont get how your runner lengths are so much longer than everyrhing i have seen or read?

[ptuomov]

Maye you can get nics "Stef" or "induction apprentice" to give you some pointers on the runner length, runner diameter, taper, and the number of plenums and volume in each. You could PM them, or google some threads by them, read them, and then respond?

Google searches that might be useful:
stef intake site:speedtalk.com
induction apprentice intake site:speedtalk.com

[modok]

12" is a fine choice. I don't know that that's actually going to be in the third harmonic or not, but pipemax's recommendations are actually a LOT more useful than they are truthful to physics.

[BenE64]

12" is a fine choice. I don't know that that's actually going to be in the third harmonic or not, but pipemax's recommendations are actually a LOT more useful than they are truthful to physics.

Im not smart enough to understand everything that is posted so i spend a lot of time reading a post and then even more time researching wtf half of the terms mean in an individual post.

I would assume that all the calculations in the world are fine, then i go cut a taper into the tube and put a slight radius in so the ports line up, then the port transitions have a step and it all means nothing.

Got to start somewhere and dont want to make something that is complete crap.

I have been looking at air boxes. I like the ideas people have put forward so i will see what i can make fit. I need the bottom of the filter box to extend to the mount face of the carby otherwise the float chamber will see different pressure right. So then i need to see what i can do with "chambers" in the plenum/airbox. Porsche style airbixes have the benefitof being along way apart, i may be able to put a dividing wall down the crank centre line to seperate the left and right banks, that would give more separation between consecutive firing cylinders.

Need to drink more beer and come up with a plan.