Runner length
Turbo Mini Forums

Anyone got any formulas to calculate the optimum runner length?

The manifold on the 998 Turbo is 220mm from the inlet trumpet to the manifold face. This gives a good torquey engine off boost, but may limit the top end.

The new manifold for the Miglia is designed at only 155mm from trumpet to manifold face. As we are looking to go to 8K, then this may be about right.

Just wanted to check before I cut the runners.

I've got plenty of room in the Miglia to make it much longer, but I don't think it would be of any benefit.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I found this site:

http://www.team-integra.net/sections/artic...p?ArticleID=471

Anything form 300-350mm from valve to trumpet should give peak VE at 7000rpm.

But with the siamese inlet port you want the wave from the outer cylinder inlet valve closing ramming the inner cylinder inlet valve. Hence you want a shorter runner with a siamese inlet port........

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I spoke with someone who knew their stuff after showing them my triple-injector manifold design a few years back (which had 12" runners) and he reckoned the design wouldn't work too well (after he understood why there were three large injectors being used). Instead, he believed a very short (read 2" or so) tapered runner is needed to minimise the siamesed port effects.

Incidentally, the guy worked for Ricardo, and is now at Ford, and knows more about CFD stuff than any of us will ever know... One of those folks that guestimates stuff in his head and is close enough to right all the time LOL - so I was going to simply do what he suggested out of the box!

Edited by TurboDave16V on 27th Sep, 2009.

tapered which way?

That would be tapered at the inlet to reduce the pulse energy. Reducing the pulse energy by openening up the inlet and running a very short runner would just minimise the pulse effect and shift it right up the revs out of the operating range.

That would be missing a trick in my opinion. There are benefits to be had, but not by the conventional approach due to the siamese port.

Now I reckon that the runner length needs to bring the pulse back 180 degrees earlier than the normal single port & cylinder configuration.

The reason for this is that the inner cylinder inlet valve closing will not create a pulse as the outer cylinder inlet valve opening maintains momentum in the port. Hence we want the outer cylinder inlet valve closing to give a reverse pulse at the opening of the inner cylinder inlet valve. 180 degrees earlier.

So instead of the pulse coming back 540 degrees later, we want it back in 360 degrees, 66% of the normal time. This assumes a 180 degree inlet cam duration. If you use 280 degrees in the same calculation, the answer is only 60%.

So, in my opinion, the inlet runner needs to be 60-65% of the length normally calculated for a single port and cylinder setup.

So total length needs to be around 180 to 230mm, which is quite short.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Here is a power point presentation which goes through some of the theory: http://not2fast.com/gasflow/Lecture08/Lect...v3_document.htm.

Jean

http://www.jbperf.com/

Where do you define the runner finishing and the port starting, especially on the siamese setup ???

From your openning statement you say the manifold face, but why specifically there ???

Edited by Rod S on 27th Sep, 2009.

Schrödinger's cat - so which one am I ???

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The info I gave above is assuming turbo stuff BTW - including a plenum of reasonably large volume.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Dragging this up again.

In this video Vizards states that the longer the runner the better.

http://www.youtube.com/watch?v=DCIwAJboZuE

He specifically states that inertial ramming has a far greater impact than pulse tuning.

So should we be aiming for the longest runner that we can get under the bonnet, whatever the rev range?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I would think that you'd run into drivability issues at some point due to the volume of the runners.


Jean

Edited by jbelanger on 21st Nov, 2010.

http://www.jbperf.com/

What about building a set of runner extenders and check ?

The inlet I used is standart but is sat on a set of 10 mm slightly wedge shaped spacers (on the head side).

That was to get clearance, "downdraft" and more straight before the valve.

I know it is a little naive but every little helps ...

Rusty by nature

My existing manifold has a runner length of around 240mm. On both the 998 and the 1275 it seems to provide a lot of torque off boost.

Even though the runners are quite large in diameter at 35mm bore, this does not seem to create any problems. I've managed to get rid of the lean tip-in just off idle with a bit of acceleration enrichment.

I've done a layout that will allow another 100mm of runner length and still fit under the bonnet, although clearance is tight. That is going to add around 30% to the inertia ramming effect. I can't see how that could have any negative effects at the top end with such large diameter runners.

The potential to bring unwanted pulses into play is always there though.

I'm tempted to go longer. I can always cut it back if it does not work so well.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Interestingly I've been doing some modelling of runner length in Ricardo Wave these last couple of weeks.

The model is of a Yamaha FZ6 engine.

I've used Heywood's formula to good agreement with the Wave models.



By using a 500mm runner (from plenum to valve head) there is a high volumetric efficiency at 8700rpm with a steep drop just after due to the wave reflection timing in the runner. Basically the reflected wave causes a low pressure at the valve and doesn't recover in time before the valve shuts.
Ve drops from 110% to 70% and results in a 20bhp loss.






Having the runner 240mm long tunes for the red line at 12300rpm. This removes the dip at 10000 rpm and retains the performance fairly well up to the tuned length.




The results make sense with the theory used. Also, as a form of validation I've compared the bhp and torque curves to yamaha data. They correlate well.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Great stuff.

I'm assuming that unlike exhaust tuning, intake tuning is about avoiding pressure pulses ocurring whilst the inlet valve is open.

Now the reflected negative pressure wave in a non-siamese port engine is presumably caused by the positive wave from the intake valve closure reaching the end of the runner and being reflected back.

So what we have to consider is that the inner cylinder inlet valve closure will not necessarily cause much of a pressure wave because the outer cylinder inlet valve is opening at the same time.

However, the closing of the outer cylinder inlet valve will cause a wave. Furthermore, it has far less time to reflect back without causing a drop in VE as it only has around 300 degrees of crank rotation before the inner cylinder inlet valve opens again. That is instead of the normal 480 degrees approx. based on an effective inlet duration of say 240 degrees.

So a shorter runner than optimum is required for an A Series.

Just need to work out the longest length you can get away.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Paul: Sounds fair enough.

I'll try and model a Siamese head over the crimbo break if I get time.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

That will be very interesting.

I've just been reading up on Helmholtz, but I still dont get the reasonance to pulse relationship.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

v quick post as in a rush but : -
http://www.turbosport.co.uk/showthread.php...4-power!/page15

veeeery long runners on a screamer of an M10, apparently it works!

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Am I right assuming the wave tuning is not that sensible on a boosted application ?

Rusty by nature

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

I just found some basic explanation in Wikipedia:

http://en.wikipedia.org/wiki/Manifold_(automotive)

Looks like the intake valve opening has a more significant effect than I origianlly thought.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

A lot of the early work on this was carried out by H.W.Engleman.

Lifted from elswhere:

"Engleman postulated that the main peak of the Power/Torque curve is caused by the pipe and cylinder volume tuning as a Hermoltz resonator with a pressure peak occurring at bottom-dead-centre (bdc). This lead to the relationship:

N = ( (15 * a) / pi ) * ( (F / ( L * V ) ) ^ 0.5)

N rev / min
F meters squared
L meters
a meters / second
R Joules / Kilogram * Kelvin = 287 J/Kg K
T Degrees Kevin
V meters cubed

Where N is the engine speed in rev / min, F is the pipe cross-sectional area, L is the pipe length, a is the speed of sound in the gas, R is the Universal Gas Constant, T is the gas temperature, and V is the mean cylinder volume, which was taken by Engelman to be half the cylinder swept volume plus the clearance volume. Engelman also found that the exact correlation between the engine speed and the natural frequency of the resonating system is dependent on the engine valve timing.

a is the speed of sound, the equation is given by

a = ( (gamma * R * T) ^ 0.5 )
a ---- Speed of Sound ---- Meters/Sec
gamma ---- Ratio of Specific Heats
R ---- Universal Gas Constant ---- J/Kg K
T ---- Gas Temperature ---- Kelvin (K)
Gamma is approximately 1.4 for air and 1.35 for exhaust fumes
R is equal to 287 J/Kg K"

I'm very quickly coming to the conclusion that we do not need to factor the length of the runner due to the siamese port.

This is because the main benefits are to time the positive pressure pulse returning from the plenum to arrive as the inlet valve is closing and the piston has started the compression stroke.

More here:

http://seit.unsw.adfa.edu.au/ojs/index.php...iewFile/180/142

Edited by Paul S on 23rd Nov, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."