Calculation For Intake runner length?
Calculation For Intake runner length?
(OP)
Hello all,
I'm currently working on an Individual Throttle body intake for my Car. I was wondering what to use to calculate the optimum runner length for the intake, before the throttle bodies. Better if there was a way to choose which Rpm the power would be coming on full. If anyone has any advice let me know... Thanks in advance, Stephen
I'm currently working on an Individual Throttle body intake for my Car. I was wondering what to use to calculate the optimum runner length for the intake, before the throttle bodies. Better if there was a way to choose which Rpm the power would be coming on full. If anyone has any advice let me know... Thanks in advance, Stephen





RE: Calculation For Intake runner length?
Every individual body setup I've seen for racing on-road or off, has runners just long enough to get the bodies nicely situated. In other words, very short.
RE: Calculation For Intake runner length?
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RE: Calculation For Intake runner length?
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Make sure you go to page two of that post, as well.
One source I've come across as I work on modifying my Kawasaki GPz1100 is the MegaSquirt forum. There is an interesting thread on there with good technical input.
http://www.msefi.com/viewtopic.php?t=21144
The discussion about which pulse you are tuning for is interesting. I'm going to have to research this more.
RE: Calculation For Intake runner length?
RE: Calculation For Intake runner length?
84,000 / tuned rpm = runner length
The runner length is measured from the back of the intake valve to the start of the radiused entry of the runner. Most people use the max. torque rpm as the "tuned rpm".
Also, as a general rule of thumb, the port cross section area should be ~83% of the valve area in the intake port and taper out at a 3.5 degree angle as it goes toward the entry of the runner.
There are more exact formulas that use the compression ratio, engine displacement, and cam timing, but this one is close.
RE: Calculation For Intake runner length?
RE: Calculation For Intake runner length?
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculation For Intake runner length?
This is the qoute from the team-integra site... that was the info that i was taking into consideration.
I understand that lenth of the runners as well as the lenth, diameter, and volume of the velocity stacks, will be used for tuning the setup. Thats the information that I'm trying to find. What factors do I need to take into consideration when "tuning" the ITB setup? What length of the runners will provide maximum velocity and power, and at which rpm band? How do I calculate the optimum velocity stck length and taper? This is basically what i ment. My apologies if I filed to state my question correctly.
Thank you for the responses. This is great information.
RE: Calculation For Intake runner length?
Have you looked on sites like Kinsler, Crower, Enderley and Hilbourne (Fuel Injection Enterprises I think).
I can find the URLs and correct spellings later if you can't find them from this.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculation For Intake runner length?
This incidentally is why you are not deafened by tailpipe noise.
Incidentally they banned variable length manifolds on F1 cars, which have ITBs, I hardly think they'd bother if they didn't work.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Calculation For Intake runner length?
http://www.wallaceracing.com/runnertorquecalc.php
however also try performance trends engine analyser pro free download, it will allow you to model the cam.
RE: Calculation For Intake runner length?
For a first order harmonic, the length of the runner is something like 12 feet...
Now if I understand this correctly, the longer runners are very particular about the rpm range over which they resonate. That 12 foot runner for instance might only provide that "forced induction" for +/-50 rpm until the second harmonic (rpm) is reached
If that's true, then short runners don't provide a whole lot of the compression effect, but do it over a much broader range.
Anyone care to comment on that conjecture?
I know that saying "short runners are good for high RPM use and long runners are good for low end torque use" is too broad a description... Just like how you can hit 2 or more notes on a recorder with the same fingering if you blow hard enough.
RE: Calculation For Intake runner length?
Regards,
MB
RE: Calculation For Intake runner length?
I think the author of the quote is confusing recovered energy from a Helmholtz device (pressurized plenum) with simple wave resonance, which, of course, relies for the strength of the pulse the difference in X-sectional area between the tube and the atmosphere (~). IIRC the expension ratio should be at least 625% to use all available energy and avoid any secondary wave causing superposition etc.
RE: Calculation For Intake runner length?
Pressure waves reflect from open ends just as strongly as from closed ends, except that they flip their sign at open ends.
RE: Calculation For Intake runner length?
No it doesn't. It is rubbish. The reflected wave goes back down the pipe, otherwise it wouldn't be a reflection.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Calculation For Intake runner length?
P.S> I'm not trying to sell or promote his software. I'm just a satisfied user of this program.
Scott
RE: Calculation For Intake runner length?
Degrees=(.012*L*N)/C
L=runner length in mm
N=RPM
C=speed of sound (around 334m/s)
and you want to set the runner length as to get a degree value of 80-90 degrees of crankshaft revolution.
all of this info is out of a book im reading for my FSAE class written by Hienz Hessler (sp? i'll check it later ).
where the degree value is when the pulse 1st returns to the intake valve. as it continues to return to flow/velocity/amount of charge ( or whatever u want to maximize) this value reaches a max just as the valve closes.
my question is, if anyone followed me through that, is WHY 80-90 DEGREES?!?!?1
i've been trying to figure this out all damn day and i can't figure out why...the only reason the book states is 80-90 degrees is through trial and error
but i was wondering if anyone has any hard fact as to why this is...
thanks, sorry for the sloppy post, i kinda got excited!!!
~Michael Pal
RE: Calculation For Intake runner length?
For anyone out there genuinely interested in truly understanding the "unsteady gas dynamics" effects that explain the tuning of intake and exhaust ducts then read Blair's two books on the subject. They contain the definitive explanation of this subject - heavy reading in parts, but worth it!
htt
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RE: Calculation For Intake runner length?
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculation For Intake runner length?
hahha
~Michael Pal
Pal's the name, FSAE race cars are my game.
Terps Racing
RE: Calculation For Intake runner length?
The sonic wave starts at the inlet valve opening, travels to the end of the track, to reflect back as a positive wave, meets the piston 80/90* down the stroke. The closed pipe, reflects the positive wave back to the open end of the tract, a reversal takes place to reflect a negative wave back into the cylinder as the piston is slowing at BDC. The negative wave is reflected back from the piston, through the cylinder dropping the pressure to increase filling. The wave finally reflects back from the open end of the tract as a positive pressure, to increase the external pressure on the inlet gas to assist filling and prevent charge reversal.
Harvey.