Intake runner length ...

[TRD Man]

Has anyone done any research into intake runner lengths and their effect on performance. If so, do you have links to literature, articles etc... ?

[Adamal]

2 words come to mind.

Helmholtz

and

Redmist

[RomanV]

And in other, more relevant news:

Here's a simple calculator to give you a rough idea on where to start:

http://www.bgsoflex.com/intakeln.html

(Only unfortunate thing is that it doesnt tell you where the 'anti' or undesirable resonant ranges are)

And here's a more indepth article on intake length:

http://www.team-integra.net/sections/ar ... icleID=466

My only gripe with this is where it says that helmholtz resonance doesnt apply when you dont have a plenum wall for 'reflection' because it isnt true.

[KinLoud]

Ages ago I was experimenting with a couple of different intakes for my racecar.

See my next post below for the thread I started...
Basically swapping to a shorter runner length meant I lost all my midrange torque but the top end was similar.

Here are some sites I found when I was doing some homework on this topic

http://www.velocity-of-sound.com/
http://forums.evolutionm.net/engine-tur ... hread.html
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.physicsforums.com/archive/in ... 80364.html
http://www.allpar.com/history/memories/bob-scott.html
http://www.freepatentsonline.com/5176114.html
http://forums.hybridz.org/showthread.php?p=652337
http://www.engr.colostate.edu/~allan/fl ... age7f.html
http://hyperphysics.phy-astr.gsu.edu/hb ... e3.html#c1
http://www.glenbrook.k12.il.us/GBSSCI/P ... 11l5c.html
http://www.phys.unsw.edu.au/jw/Helmholtz.html

Basically either go short... i.e. trumpets
Or go long, i.e. runners

Length of runners affects tuned frequency
Diameter of runners affects air velocity
Plenum size affects many things, helmholz, throttle response...

[KinLoud]

This is a repost of a thread I started ages ago...
viewtopic.php?t=57312&highlight=resonance

This post covers a bit of research I am doing into factory vs modified intake manifolds on my racecar.
It's a pretty long post but this info might help someone designing or modifying an intake.
Feel free to give me feedback and suggestions - including how to present the results of my investigation more clearly in this post and if it is in the wrong part of the forum.

INTRODUCTION
Early 2005 I put the gen3 3SGE into my 1983 AA63 Carina.
I used a W57 gearbox.
To adapt the 3SGE to rwd I had to modify a few things (I will post info about this later).
The engine is mounted upright using factory SA60 crossmember and engine mounts.

INTAKE
I used the factory intake but had to adapt it to rwd. I had to blank off where the original throttle body bolted to as the throttle body would have hit the top of the firewall.
I got part of a V6 camry intake welded to the intake so the throttle body pointed towards the front left of the engine bay.

As the engine is mounted upright, part of the intake sits higher than the bonnet. A hole was cut in the bonnet and hump riveted on to cover the hole. This hump looked a bit ugly!

When I bought another 3SGE to keep as a spare I got a nearly completed MODIFIED 3SGE intake.
Halfway through last racing season (2006) I decided to fit this intake to see how it went. Wayne (vvega) kindly finished the modified intake off for me.
When I raced using the intake I found that I had lost a lot of midrange power. When you changed to the next gear you had to wait until the revs got up to the power band. This resulted in slower lap times.

This is an investigation as to why I lost power.

INTAKE DESIGN PRINCIPALS
Intake design is a complex process. The intake has to fit within the factory engine bay, fit within the manufacturers budget, be durable and give good engine performance (and economy) over a wide rev range.

The length and diameter of the intake runners (individual tubes from the plenum to each intake port in the head) affects the torque (and therefore power) at various rpm.
The LENGTH of the intake runner affects it's "tuning" i.e. the resonance frequencies. This resonance can help increase the amount of air that flows into the cylinder. It can also DECREASE the amount of air if not designed correctly.
A long runner will generally help lower rpm performance, a shorter runner will help higher rpm performance.
Runner length is most often used to even out the torque band of the engine rather than provide a large peak at a particular rpm. This helps provide smooth acceleration.

The DIAMETER of the intake runner affects the speed of the air as is flows towards the intake valve and cylinder. I will give a very simplified explanation.
Small diameter runners leading to a large volume cylinder will give better low rpm performance but at high rpm the diameter will restrict the flow.
Large diameter runners leading to a small volume cylinder will give poor performance at low rpm and average performance at high rpm.

Plenum volume also affects the engine performance. I think this happens in 2 ways:
1 - The volume of air between the throttle and the cylinder affects throttle response. A large volume means it will take longer for the pressure to rise when the throttle is opened. A small volume means it will take a shorter time for the pressure to change. You will hear this described as "throttle response".
2 - The plenum chamber acts as a resonator. This will affect the resonance of the runners and the whole intake system.
Usually the plenum volume is between 50% and 200% of the engine displacement.

FACTORY INTAKE -

The factory gen3 3SGE has a complicated intake manifold. It is made in 2 parts. The shorter part is uncomplicated and bolts to the head. The longer part of the intake is more complex and bolts to the shorter part.

Runner diameter is approx 45mm. The runner cross section changes to an oval shape where it meets the head, approx 55mm x 32mm.

NOTE
The total length of the intake runner includes the distance from the intake valve to the intake manifold face of the head, 100mm

It has a plenum of approx 1.3L and 4 long runners 430mm in length (530mm total).
At about 1/3 distance from the plenum, 4 very short runners join the long runners. This is the ACIS part of the intake.

These short runners connect to another plenum or resonant chamber (I will call this the ACIS plenum).


This ACIS plenum can be blocked off by butterfly throttle type plates.


The effect of this ACIS plenum is to effectively shorten the intake runners length to 310mm (410mm total).

PLENUM VOLUMES - both the plenum and the ACIS plenum have volumes of approx 1.3L each.

When the ACIS plenum is closed off (ACIS closed) the resonant effect of the intake runners favour low/mid rpm performance.


When the ACIS plenum is open (ACIS open) the resonant effect favours higher rpm.
The ACIS opens at 5000rpm (according to http://toyotaownersclub.com/forums/inde ... 38590&st=0)

FACTORY INTAKE PERFORMANCE
Power delivery with this intake is good and even thoughout the rpm range.

MODIFIED INTAKE
This intake uses the shorter part of the 2 part factory intake. A plenum has been welded on the the end of the runners. The plenum has a flange to mount the throttle body. Runner length 200mm (300mm total).
Plenum volume - approx 2.2L




MODIFIED INTAKE PERFORMANCE
Power delivery is poor below 5800rpm. Above 5800rpm the power delivery is similar to the factory intake.

INVESTIGATION
I decided to do a bit of investigation into the resonance of the factory and modified intake. I hoped to understand why the modified intake performed so poorly in the low and mid rpm range.
Method.
I measured the length of the various runners and the volume of the plenums.
I placed a speaker very close to one of the intake runners and blocked off the other runners to simulate the valves of the other cylinders being closed. I then placed a microphone inside the plenum next to the active runner.
Using ToneGen program I played sinewaves of varying frequency through the speaker.
AudioXplorer was used to analyse the signal from the microphone.
The data was entered into an Excel spreadsheet.
A test was also conducted without any intake (microphone and speaker only) to get data on the natural resonance of the room. These measurements were subtracted from the intake data to give more correct results.

You can see that all 3 lines have a broad peak from approx 80Hz to220Hz. The modified intake has a much larger peak than the others in this frequency range. I suspect this might be due to the larger plenum volume (2.2L) vs the factory plenum (1.3L)
The factory intake shows another peak around 310Hz for both ACIS Closed and Open, this is due to the basic resonance of the long runners.
At around 570Hz there is another peak for the ACIS Open, this will be caused by the effective shorter runner created by the ACIS butterfly valves opening up the ACIS plenum.

The testing I did on the resonance of the intakes was as scientific as I could easily manage. I made an effort to reduce errors and outside effects.
I have not investigated the effect of different size plenums as this would have made the process much more difficult.

COMPARISON WITH FORMULA TECHNIQUES
As a comparison I entered the intake runner lengths into a formula.

Resonant rpm for intake runner:
RPM = k/L
where
k = 79200 (constant), L (inches) http://pweb.jps.net/~snowbum/InExTuning.htm
OR
k = 84000 (constant), L (inches) http://www.allpar.com/history/memories/bob-scott.html

INTAKE LENGTH TUNED RPM
Intake runner length - Resonant RPM
530mm ACIS closed - 3796 to 4025 rpm
410mm ACIS open - 4907 to 5204 rpm
300mm Modified intake - 6706 to 7112 rpm
I understand that for best overall performance the tuned RPM should be approx 1000rpm lower than peak power rpm. This will give a wider power band and improve overall acceleration.

CONCLUSION
The short runners of the modified intake create a powerband at high rpm and much lower power at mid rpm.
I will be better off using the factory intake. Acceleration out of corners will be much better.
Possibly I could modify the factory intake by shortening the runners so the power bands with ACIS Closed and Open are raised by approx 1000rpm. This could improve power in the rev range that I use when racing.

Great description of intake design
http://www.team-integra.net/sections/ar ... icleID=466

Good comments on runner length and plenum size: look on page 120,
http://books.google.com/books?id=ze_w0i ... zrQT44LMws

BACKGROUND
In August 2002 I bought a dereg AA63 Carina with an almost dead engine (barely ran, loads of smoke!)
The AA63 Carina had from factory an early 4age (bluetop bigport), T50, 4 wheel disk brakes and independant rear suspension (IRS)
With full interior and aircon it weighed 1060kg.
After removing interior and sound deadening, replacing side and rear windows with polycarbonate and installing a full rollcage it weighed 960kg.
I raced it with the 4age and T50 for 2 seasons. I won my saloons group 3 clubracing class at Taupo in my second season (2004).
During 2004 I bought a crashed 1995 Toyota Curren with gen3 3SGE, E56 lsd gearbox, ABS, Superstrut suspension with the bigger brakes.

Ken

[neo]

Excellent as always Ken...

You really need to get out more

[Crampy]

http://forums.neons.org/viewtopic.php?f ... ner+length

I like this article. They guy just chucked on different lengths of pipe in his ITBs and saw what it did on the dyno. Straight pipes aren't ideal, bellmouth on the end would be better, but it illustrates what the longer intake does to the power delivery. VERY nice gains in the mid range.

[matt dunn]

When we built my intake (even though it's turbo'd)
we applied some of the stuff dad got from when he was in aussie.

We were pretty limited on space for length, but there is way more than just length to worry about,
shape, dia, the radius of the curl on the end opening and area behind the bellmouth are all just as important.

[RedMist]

Did an absolute tonne of work on Helmholtz with the race 4age. In the end the calculations only give you a reasonable starting point. I ended up using a mixture of calculators and a spreadsheet that unfortunately is long gone. Helmholtz is complex, do not underestimate it, it's also MASSIVELY beneficial. A calculator that doesnt take into account valve timing, runner geometry, exhaust back pressure, even fueling will not give you accurate results.

Also aim to have the Helmholtz frequencies boost your mid range by having it hit your low gear shift RPM. (shift gear, instantly in high torque range) It's considerably more beneficial than having it higher in the RPM range.

I developed trumpets that made the entire intake lenght 19.5 inches from valve face to bellmouth (if I recall, then again I could be miles out!). It was however a bluetop head (radical head work with ports considerably smaller than that of the redtop smallport) a 40mm adaptor plate, stock silvertop TB's and manifold, and 80mm trumpets (with 180 degree returns) Then went .25 inches either side (three sets of trumpets) in order to dyno test. Calculated results gave our best curve. The 20 valve intake gave us a beautiful transition from the 16 valve head so we didn't bother to replace it. The adaptor also pushed the injectors further out into the runner, which was another goal. I would have liked to push the inside wall of my airbox out further to butt onto the back of the 180 degree return, but offroad racing would have simply snapped all the trumpets off.

Don't forget that you have two Helmholtz frequencies. One in each intake runner and one the intake to the plenum.

Matt's also very correct. There is a tonne to think about once you have decided on a theroetical runner length.
Bellmouth shape, airbox volume, airbox shape, injector bosses and location, filters, distance from bellmouth to back wall of airbox, distance from bellmouth curve to front wall of airbox, shape of airbox. ALL count, ALL can give drastic improvements in a limited class, ALL deserve a tonne of study, and if at all possible, as many combinations as possible deserve dyno time.

Turbo's aren't so effected by Helholtz as each turbo blade creates it's own pressure wave. For the 350z turbo offroader we didn't bother calculating Helmholtz, just concentrated on getting the flow correct.