Runner length
Turbo Mini Forums

Here is the calculation based on a 1293 with 35mm bore runners:



What is bothering me now is the potential for the reflected positive pulse from the inner cylinder inlet valve opening to be destroyed by the negative pulse from the outer cylinder inlet valve opening as they pass in the port. The same thing would also happen to any pulses from valve closure.

In which case this all goes out the window and we can just make them as long as possible to achieve maximum ram effect.

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."

Rusty by nature

The same pressure differential exists under boost conditions.

As the wave speed is unaffected by pressure or density, then I think the theory holds for boosted conditions.

A high inlet temperature would alter things as this has a bearing on the speed of sound.

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 have been to a technical class today (in Renault) about turbochargers and I now believe what you are saying.

Edited by Advantage on 27th Nov, 2010.

Rusty by nature

Had a chat with my vibrations lecturer today about the work I'm doing. He's convinced me that Helmholtz has very little impact. It is in fact the closed-end organ pipe theory that seems to hold well. I will be doing some research over Christmas to find out.

Basically WAVE gives me a plot of the pressure wave in the inlet runner. If I do an FFT of this I can find the frequency spectrum and validate the idea.

theory here

and results here



The poor performance (as said on last page) was from the blue 10,000rpm curve because its period is 6ms (or 360 crank deg) hence the approximate 420 crank deg between valve shutting and opening caused low pressure at next valve closing point

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

I think that there is more to it than simple harmonics. The closed-ended organ pipe equation gives a simple linear relationship, close to the Engleman equation.

The latest work on this has been done by Winterbone & Pearson at Loughborough.

This book will be going on my CP list:

http://bookshop.blackwell.co.uk/jsp/welcom...&awcr=&src=awin

Edited by Paul S on 26th 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."

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."

Its an extract from A Bell's book, relating to runner lengths, interesting that he recomends around 400mm as per Paul, and also that going too long kills the top end off as per John Ks findings on the wet manifold SC setup,

Thanks Joe.

It all adds to the understanding.

I wonder if BL realised the potential and made the turbo inlet manifold runners longer as a result?

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 doubt BL thought about it, I reckon the change was just for packaging, but you never know with BL,

I'll have to do some calcs and see if the stuff I posted pans with the posted equations.

The Helmholtz equation also give some very interesting results for the exhaust manifold.

It certainly seems to agree with the conventional wisdom with regard to LCB lengths.

So, if we carry through the theory that it works on the inlet of a turbo engine, why not the turbo exhaust manifold?

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."

Yep,

after seeing pauls clubby on the rollers compared t other cars I definatly think remote turbos are the way to go, just make sure you lag it well, lost heat is lost energy.

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."

Just to bring this thread up to date with my latest findings.

I got the Winterbone & Pearson book for Xmas. I could have bought a set of pistons for the same money, but the book is very enlightening. I quickly realised that you cannot develop a spreadsheet solution for runner length.

The book is a very good read if you want to know about the application of starred Rhieman variables to the homentropic flow of gas in a pipe and the asociated wave dynamics.

By chance, I was also able to acquire some engine simulation software that appears to be based on the same theories. Helmholtz is very much relevant to both the intake and exhaust runner length.

So after much work with the software, first of all baselining with some known engine builds and the 998Ti, I applied the already purchased items such as the 33/29 12G295, GT1752 and the custom ground scatter cam. I then optimised the exhaust runner length using the 998Ti inlet manifold and then went back and made further improvements on the inlet.

The plots below are based on the optimised runner lengths. You can see how at valve overlap, it is possible to tune the exhaust pressure to be below that of the intake pressure. This then leads to an average VE that peaks at over 100%.

Outer Cylinders:


Inner Cylinders:

Note the charge robbing as the inlet valve closes. Also the shock wave caused by the siamese exhaust port.

Both the above are at 6000rpm

Predicted power curve:


The job now is to get the manifolds and engine built and on the NMS dyno to see if the theory works.

Edited by Paul S on 9th Feb, 2011.

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."

Plots?

Plots now added.

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."

So you have 90%+ VE from just under 4000RPM to about 7400RPM and close or above 100%VE for close to 1000RPM? That's quite impressive. And is it with both intake and exhaust within the engine bay?

Jean

http://www.jbperf.com/

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."

Does this devellopement gives a new understanding of that :

Edited by Advantage on 17th Feb, 2011.

Rusty by nature

It does indeed. Particularly as they used it in a heavy car that needed more low down torque.

Not sure you could use it in a Mini without the dashpot through the bonnet.

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."

Maestro/Montego manifold?

Could be interesting to try this out with it all sticking out the bonnet!

If something is worth doing, it's worth doing half of.

yep

How far up would it stick? Should be easy enough to lift the bonnet up a bit on the hinges

carb goes over the top of the engine so pretty high i would imagine

If something is worth doing, it's worth doing half of.

A very interesting thread this. As it happens my runner length is currently to be around 160mm, way shorter than any predictions here would suggest is optimal.

What interests me is how the reflection is reflected, and how this affects the results.

For instance, if you had open inlets then there will be no reflection and thus runner length will not be critical. But in a plenum you'll get a reflection.. How far the plenum 'wall' is from the trumpet mouth is will surely have an effect.

Also, what is the length of a standard alloy manifold?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

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