Thanks for the explainations bonkers Buell fans!
Sorry you think I'm taking the piss! Maybe I'm just a bit thick?

For some reason I expected to see a more linear graph.

I also should have typed air speed, (in the filter housing before the throttle body)not air flow!

Anyway, I was always under the impression we measured Volumetric efficiencey in CFM or litres per minute. (as we do when a head is on the flow bench)

Also the graph shows the race filter to give 100% efficiencey. That can't be right, unless you have forced induction. I recon 80% maybe?

We sometimes do some quick sums for calculating the vetilation systems for yacht engine rooms.
(I know it's right if I have to push the engine room door open )

If I use the numbers for my bike at 6200rpm (from the owners destruction manual for max power)
73.4 ci x 6200 divided by 3456 (I got that from some course notes) x 0.80 (volumetric efficiencey of a NA petrol engine (Diesels are a bit better!) and I get 105CFM or about 3000 liters per minute.

Does that sound right to you ?

If I'm "banging on", let me know...

If you want to talk about scavanging, look at a Detroit two stroke diesel

Cheers,
Mick.

I am struggling a bit here cos when you gave Albert a hard time suggesting he used WAVE, I assumed you knew a bit about inlet and exhaust design.


Not sure what you are trying to say here.


You may measure flow in CFM, but how much of that flow is trapped when the valves close? It is this air that does the work. Any air that goes straight through on the valve overlap period is wasted.


Yeah, but it IS forced induction. You are using pressure waves to increase and decrease pressure at the inlet and exhaust valves to get more air into the cylinder. A well designed system will get you 110% or more...


I am not sure what you are trying to do here.


Tell us about it mate.

There are loads of good books to read on the subject, this one is a good starting point, even though it is a little old, the physics hasn't changed. This one defines methods that are used in the majority of modern simulations. This one and this one will give you a more practical understanding using rule of thumb principles...

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08 Specialized Langster

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08 Specialized Langster

Blimey! that's a lot of quotes!

I wasn't giving Albert a hard time, I mentioned WAVE becuase the program will calculate db. I was wondering if he'd seen it before.
Sorry if it seemed that way.

A Buell isn't forced induction, it's naturaly Aspirated.
By forced induction I meant Turbo or supercharged, (or both with a jimmy)
You will not get 100% efficiency with a naturally aspirated engine.
What's sucked in will be pretty much ambient, untill it's squeezed of course.

Airspeed... Large venturi low airspeed, small venturi faster airspeed. So at low rpm, a large throttle body will not be very efficient. Hence race cars running rough at low RPM, and having a high idle speed.

The sums where for required airflow at max power RPM.

Volumetric efficiency is badly named, therefore e.g. Blair uses deliver ratio, which is more or less the same term as used in German (Liefergrad). A 2 liter engine will always suck in 2 liters of air/mixture. The question is: at which pressure/density? So if you manage to pre-charge/pressurize the mixture using pressure waves, the mass of the mixture trapped after the inlet valve closes is larger than the mass according to the displacement volume at outside pressure/density.

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"It is often said that before you die your life passes before your eyes. It is in fact true. It's called living."
Terry Pratchett

oops. forgot link: http://www.profblairandassociates.com/p ... basics.pdf

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"It is often said that before you die your life passes before your eyes. It is in fact true. It's called living."
Terry Pratchett

So, my fault for not defining a parameter which has a misleading name...

Volumetric efficiency = Mass of air trapped / (swept volume * density)

And interestingly, if you do a search on the internet, you don't find a clear definition (and I don't think Gordon Blair is that clear on it either by using DR - but then again he is a trailblazer), however it is clear in industry standard texts such as the Bosch Automotive Handbook and Internal Combustion Engine Fundamentals...

But, Mickrick had shown an understanding of the concept and that it was mass weighted when he said:



But to come back to this point, a well designed intake system will ensure that as the inlet valve is closing, the pressure at the in the port will be as high as 1.5bar when ambient is 1bar. This is a a result of the reflection of a negative pressure wave created by the exhaust during the valve overlap period...

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08 Specialized Langster

Unfortunately I don't have a degree in mathematics, so that's intersting article Gunter, Thank You
I see he mentions my 0.80 number, although he puts it at 90%.

Pash you mention the exhaust scavanging, as you know it all has to work together doesn't it.
That's another reason I mentioned WAVE, the tuning of the exhuast length to help scavange the cylinder, my simple laymans understanding of it, is the exhuast header has to equal the swept volume of the cylinder, so with equal length headers the exhaust stroke of one cylinder will help scavange the other.

Going back to intake, I haven't seen a Buell pro-race filter, but do you think the bend on the Forcewinder filter helps matters?
I would have thought that would restrict airflow, or does it help speed it up ? and that's why your graph shows better bottom end performance with the Forcewinder.

I wonder if a straight intake pipe, with a K&N (capable of 105CFM or more ) would work better? And what effect would the length of that pipe make?

Sorry again if my mention of the software gave you the wrong impression of my knowlage.
I've seen the space shuttle on TV, but that doesn't make me a rocket scientist

Mick, the clue is in the name of the WAVE software. Optimum exhaust lengths are not defined in terms of cylinder volume but on the time taken for the reflection of the blowdown pulse to return. I really suggest you read up on this stuff in one of the links I gave you. Long headers work better at slower engine speeds, short ones at higher speeds.

As for the bend in the Forcewinder, this will give you a pressure loss increasing with flow. The diameter is bigger (50mm) than the diameter of the carb (42mm) so the air will be moving slower. The Forcewinder has a longer pipe than the Buell Pro Race filter, so the fact that it works better at lower engine speeds should not be a surprise.

Explain your understanding of the relevance of CFM for filter selection. If you selected one for your engine based on the CFM you calculate, does that mean there is no pressure loss? An acceptable pressure loss? If so, what is acceptable? What happens if you fit a bigger one? A smaller one? Remove it all together?

I think you secretly know all this stuff inside out through your Caterham engine tuning contacts...

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08 Specialized Langster

Perhaps the forcewinder could be improved in an Edd style way by smoothing the transition from the large pipe to the smaller carb? Also would a change in the filter help perhaps to a foam one or one like they use on turbo nutter bastard cars http://upgradecar.blogspot.co.uk/2007/12/eagle-talon-420a-turbo-air-filter-with.html

Could your model handle these proposed changes?

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Buell S1
Buell S3 (Topless for now)
Buell XB12S
Piaggio X8 400ie
Yamaha XTZ750 Super Tenere (x2)
Suzuki GSXR750WR
BSA B441VS
FJR1300

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Buell Ulysses XB12X 06/08

Yes it could. One thing you would also want to sort out is the rubbish airbox adaptor on the HSR42, but these changes will be small compared to the effects of wave timing. As for the filter, this is measured as a pressure loss, so if you have this data, you can model it...

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08 Specialized Langster

So a home made flowbench like the Dave Walker one he had in Fast Car could give you that information re the filter differences.

So your model could handle adjusting the forcewinder length and what differences that made. It might be that the force winder length is not the optimal one as isn't the stock one quite a bit longer(the one in the breadbox)?

_________________
Buell S1
Buell S3 (Topless for now)
Buell XB12S
Piaggio X8 400ie
Yamaha XTZ750 Super Tenere (x2)
Suzuki GSXR750WR
BSA B441VS
FJR1300

Some good reading recomendations there! Thanks Fella's. Some of it a bit over my head though, I suspect.

Here's a snippet from the K&N site regarding airflow testing thier filters.
http://www.knfilters.com/testmethod.htm

Barney, the graph for the two stroke expansion chamber brings back memories of my Yoof, and my RD250LC

Pash an aside, as we're reccomending books, have you read Sir Stanley Hooker's autobiography, "Not much of an engineer" ? What a Guy!

Dave Walker rings a bell... Emerald? Well known in Caterham circles, a bit of a mapping Wizard.

Yes it can handle any design that you would want to throw at it, it all comes down to areas, lengths and losses.

In answer shorter Forcewinder elbow would be optimised for higher revs, the time taken to reflect the wave is shorter and hence this works better with a shorter period between IVO and IVC.

It takes around an hour to do a run, so it is not a quick job to look at the effects of a lot of changes. The model is not a perfect representation of the S1 engine for a number of reasons, hence BHP is not presented, however it is perfectly adequate to look at small changes.

I have learned a lot over the past couple of weeks, suffice to say that had I played with this model prior to my headers being made by Albert, I would have been looking for another design...

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08 Specialized Langster