Intake Info

[nathan s]

Hey, I am new getting into designing intakes and am having to learn as I go. I have found a lot of info from just looking around, but got confused at the same time. Maybe you guys can answer some of my questions.

Does anyone know of any information about how helmholtz resonators are applied? I know the basic theory behind it, but how is it effected by placement in the intake. By this I mean, when you are tuning it, say the runners are 14 inches and the plenum is about 1 liter, will any extra pipe on the upstream side count in your frequency calculations or will the pressure waves be reflected back to the engine at the plenum.

Are there any basic rules for throttle body sizing? I think it has something to do with the CFMs you are flowing but am not sure.

Also, if any of you know of any good books, websites, papers, etc on intake design, I would greatly appriciate your help.

Thanks for your help.

[nathan s]

Hey, I am new getting into designing intakes and am having to learn as I go. I have found a lot of info from just looking around, but got confused at the same time. Maybe you guys can answer some of my questions.

Does anyone know of any information about how helmholtz resonators are applied? I know the basic theory behind it, but how is it effected by placement in the intake. By this I mean, when you are tuning it, say the runners are 14 inches and the plenum is about 1 liter, will any extra pipe on the upstream side count in your frequency calculations or will the pressure waves be reflected back to the engine at the plenum.

Are there any basic rules for throttle body sizing? I think it has something to do with the CFMs you are flowing but am not sure.

Also, if any of you know of any good books, websites, papers, etc on intake design, I would greatly appriciate your help.

Thanks for your help.

[John Bucknell]

Sorry, there isn't much practical info out there. However I will say that helmholz is almost invisible compared to organ pipe and throttles are for drivability - make sure it isn't a light switch.

Couple of books on this list I like: Reference books (http://fsae.com/eve/forums?a=tpc&s=763607348&f=125607348&m=29410020411&r=37310493611#37310493611)

With the addtions of:
SAE PT-53
Design of Racing and High Performance Engines
Joseph Harralson
ISBN Number: 1-56091-601-X
Date Published: February 1995

SAE R-274
Design Techniques for Engine Manifolds
AUTHOR(S):
Desmond E. Winterbone
Richard J. Pearson
ISBN Number: 0-7680-0482-9
Date Published: October 1999

SAE R-186
Design and Simulation of Four-Stroke Engines
AUTHOR(S): Gordon P. Blair
ISBN Number: 0-7680-0440-3
Date Published: August 1999

And then:
My opinions on flow (http://fsae.com/eve/forums?a=tpc&s=763607348&f=125607348&m=99810976611)

More opinions about development (http://fsae.com/eve/forums?a=tpc&s=763607348&f=125607348&m=62510103511&r=20410331611#20410331611)

[Daves]

According to SAE paper 2000-01-3090, the throttle body should be sized based on (drivability based on) the intake restriction. For example, a 3" throttle body is going to give very poor throttle response with the intake restrictor in place (less than 1"). When the throttle body is only slightly open, the flow through the restrictor will already be maxed out, similar to wide open throttle. Therefore, you want a throttle body that you can actually use.

[Charlie]

John-

Can you explain what you mean by 'organ pipe'? That's a new one for me.

I am a big fan of WInterbourne and Pearson's book you .listed above.

[Ben Inkster]

I think John is referring to the calculation of the harmonic frequencies of an open or closed end pipe (please correct me if I'm wrong). I believe the accuracy of these predictions will be greatly increased if you include your acoustical impedance.

John, i was just reading your opinions on F-SAE engine development and i noticed you discouraged the use of variable runner length, could you please elaborate on this? do you feel the effort could be used better on another part of the engine, or are there no real gains to be made?

[DPH]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by stotera:
According to SAE paper 2000-01-3090, the throttle body should be sized based on (drivability based on) the intake restriction. For example, a 3" throttle body is going to give very poor throttle response with the intake restrictor in place (less than 1"). When the throttle body is only slightly open, the flow through the restrictor will already be maxed out, similar to wide open throttle. Therefore, you want a throttle body that you can actually use. <HR></BLOCKQUOTE>

Stotera,

I have looked at the paper 2000-01-3090 and if I only allow myself to take issue with just the matters at hand I feel I need to ask one question. What if any quantitative evidence did the authors provide to support their conclusion on improvements in "throttle response"?

[John Bucknell]

Charlie,

Ben's right, I was referring to pipe reflections in the runner (helmholz is also technically acoustic). I've met Desmond Winterbone at the SAE Congress, my boss even got him to sign his book.

Ben,

My variable runner comment was more of a time investment comment (ie if you spent 25% of your total resource budget on a variable runner manifold, you've probably shortchanged yourself in other ways that would've made you faster). By all means, if your testing shows that a variable runner manifold is worth the investment - do it. Just be prepared to justify.

[B Lewis @ PE Engine Management]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by John Bucknell:
My variable runner comment was more of a time investment comment (ie if you spent 25% of your total resource budget on a variable runner manifold, you've probably shortchanged yourself in other ways that would've made you faster). By all means, if your testing shows that a variable runner manifold is worth the investment - do it. Just be prepared to justify. <HR></BLOCKQUOTE>

I have to agree with John on this one. In my years of being involved in FSAE I have never seen a variable length runner manifold that provided enough gain to justify the expense (time/energy) to develop it. If you get everything done early for this year, start the design for next year http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Charlie]

Besides the time investment, the three variable intakes I've seen (may have missed one) have never actually functioned at competition. Either there was really no benefit and so they just tuned and left them. or they were just broken.

So make sure you do your homework and know that what you are building is going to be a benefit.

As for throttle sizing yes you want a car with good throttle modulation, which ideally would mean it would have full flow only at 100% throttle. However, you certainly don't want to restrict airflow on these cars, they are bad enough already. If you have to err in one direction, err bigger. If you get full flow at 85%, still better than never getting there at all. And of course you can affect the linearity with linkages, etc. With a linear linkage setup, it is my experience that you can get a very drivable car even if it has a large throttle body, and drivability has much more to do with other parameters such as mapping (accel enrichments, etc). After all the throttle is pretty far removed from the cylinders on our cars.

[nathan s]

John, which of the three books you mentioned would you recommend the most? I looked into them and saw they were a little pricey so I will probably only be able to get one. I am leaning toward Design Techniques for Engine Manifolds, but Design and Simulation of Four-Stroke Engines looks good too.

Thanks for the help guys

[BryanH]

Sorry Charlie but I have diff view on butterfly size. Real world testing on many diverse race engines have shown ideal size for single T.B. is max flow @ redline = 70 to 80% tp. Any smaller than this will reduce output.
My twisted opinion is that organ pipe theory belongs in churches or in engines maxing at &lt;6000rpm. If you want a flat torque curve leave it in the church.
Bryan Hester

[nathan s]

How about SAE Papers? Which ones have you guys found the most helpful?

The budget isn't really allowing for books at the moment http://fsae.com/groupee_common/emoticons/icon_frown.gif. Maybe I will be able to get some after we get money comig in.

[Charlie]

Library!

Or buy your own, that's what I've always done. And I ain't exactly rich. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[nathan s]

Well, I was kinda looking for a little bit of direction as to what I should get. We have access to them through our advisor.

Are there any in particular that helped you a lot? What are your favorites? http://fsae.com/groupee_common/emoticons/icon_smile.gif

[John Bucknell]

Nathan -

When I was in school, I went to the engineering library and requested certain engineering texts be added as reference material - and usually they complied pretty quickly, after all they have a budget to buy books. The papers in the SAE collection I mentioned above (PT-73) are very useful. I like Winterbone's book, but at the same time Gordon Blair's book (if understood) will make you a pressure-wave tuning god.

Halfast -

Everything tunes like an organ pipe, whether you want it to or not. A 19,000 rpm F1 engine has some amount of runner length - only about 150 mm from the intake valve, but it is worth it.

[nathan s]

Ok, thanks for the help. Hopefully I can scrounge up some money to get one of those books.

Thanks again.

[Sam Zimmerman]

Here is my little blurb on intakes, some of which people will take issue with.

For starters, most SAE papers are simply wrong on the subject and often are not even acoustically correct. Do not rely on them.

A Helmholtz resonator is a Coke bottle that makes noise when you blow over the top and an organ pipe is simply a long pipe. I haven't seen anybody in this competition build an intake that looks like either of these yet these acoustical terms and equations are often used when designing intakes without any idea where the equations are coming from. The organ pipe equation was first used in 1931 as a simplification and the Helmholtz equation was first used in the 1950's as a more complex model. These methods were needed before computers but are now antiquated. When using these equations, there is always a very large "fudge factor" involved but, due to the lack of computing power at the time, the assumptions worked when coupled with the "fudge factors."

So, here is the real deal: Get an acoustics textbook and learn the impedance transfer formula (3 equations used repeatedly.) Once you know these equations, you can write a very simple matlab code that does not over-simplify the process. These equations will give the correct results for Helmholtz resonators, organ pipes, and bastard cross-breeds, which is what we are designing.

No matter what method you use to analyze the intake, once you have an analysis complete you can build it out of PVC pipe (simulating a cylinder on the end of one runner and the other 3 runners closed off as though the intake valves are closed) and take it to your local acoustics professor or grad student. They will be able to tell you the real resonant frequency of the intake before you spend the time to build the final product.

Or maybe I am just making all of this up because I am ****ed that we will not be at competition this year. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Hopefully somebody will take issue with all or part of this so I can find out if I am right or not. I wish the intakes were discussed and argued about here as much as suspensions are.

[jack]

sam, i thought i had you converted to a suspension guy http://fsae.com/groupee_common/emoticons/icon_biggrin.gif http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

you should come to WWU, and work on our car...so it gets done http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Ben Inkster]

Sam, great post!

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> No matter what method you use to analyze the intake, once you have an analysis complete you can build it out of PVC pipe (simulating a cylinder on the end of one runner and the other 3 runners closed off as though the intake valves are closed) and take it to your local acoustics professor or grad student. They will be able to tell you the real resonant frequency of the intake before you spend the time to build the final product. <HR></BLOCKQUOTE>

Up until now, i haven't heard of anyone else doing this. I tried it last year whilst investigating methods to produce multiple natural frequencies, and it worked great. I built the model out of PVC pipe and to replicate the restrictor i found that a plastic coke bottle had an exact 20mm restrictor on it! I then used my PC speaker to excite the intake at different frequencies and recorded it on a laptop, I havesome pics of this but i don't know how to post them.

I also agree with you on the acoustical theory. I was using acoustical transmission line theory; equating acoustical impedance between pipe junctions. I found that using a Helmholtz impedance function for the plenum chamber is the most accurate and 1D plane wave impedance for your runners seems to work quite well. However I did eventually move to commercial 1D software.

So, I don't really have any issues to take up with your post...
except maybe the comment about SAE papers, i once found a great paper on the design of unrestricted big block V8's, i think there is a lot to be learnt there http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Cheers

Ben
UWA Motorsport

[B Lewis @ PE Engine Management]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Sam Zimmerman:

Or maybe I am just making all of this up because I am ****ed that we will not be at competition this year. http://fsae.com/groupee_common/emoticons/icon_wink.gif <HR></BLOCKQUOTE>

Sam,

What happened? Why won't you guys make it this year.

[BryanH]

WE HAVE A WINNER!!!! Sam Z you are spot on.
A 6 pack of Pale Ale is yours at detroit 05.

An Aussie Co has written software which designs speaker enclosures in one go, no trial and error testing. The end product is fantastic, especially their big Sub. They discovered (as you have) that it also can acc. predict inlet manifold design.and came up with one that matched the performance of an 03 BMW vari manifold...sorry, can't tell you any details but its all about helmholtz.

[nathan s]

Hmm...Sam, I can somewhat see what you are talking about. Do you have any accoustic book recommendations?

That is a cool idea about using PVC to test the intake. I will have to try that.

Sucks that you guys didn't get in. We almost didn't, cuz out team leader was in a meeting to get permission to go. If it would have lasted 15 minutes longer, we wouldn't be going. http://fsae.com/groupee_common/emoticons/icon_eek.gif

It is amazing how fast it filled up!

[Ben Inkster]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>An Aussie Co has written software which designs speaker enclosures in one go, no trial and error testing. The end product is fantastic, especially their big Sub. They discovered (as you have) that it also can acc. predict inlet manifold design.and came up with one that matched the performance of an 03 BMW vari manifold...sorry, can't tell you any details but its all about helmholtz. <HR></BLOCKQUOTE>

Halfast, are saying this company has a code that can automatically design a manifold based on engine parameters? I hate to sound like a sceptic...

but I am!
especially if it is limited to helmholtz theory. Are you also saying that this magic code designed a static manifold better than BMW's variable? even harder to swallow.

Give us details!

Cheers

Ben

UWA Motorsport

[John Bucknell]

Resonant frequency isn't everything, and strict acoustics isn't going to get you there. Manifolding is THE hardest part of tuning, which is why 1D code was written.

We're starting to stray into subjects where I can't tell you how I do this professionally, because I don't want it regurgitated back to me in the design tent. However, I would like to hear more discussions like this, and I will speak up if you're way out in left field....

[Sam Zimmerman]

Nathan - One of my acoustics books is titled Acoustics. The author is Leo Beranek. This is a 1993 edition published by the Acoustical Society of America. It is good and cheap.

Brian - Our team will not be there because we did not register in time. If I went into the reasons why I might sound bitter, which I am not. http://fsae.com/groupee_common/emoticons/icon_smile.gif I will have to see if Western Washington has a spot open for a team member who lives too far away to attend any meetings or do any real work. I would be the ideal teammate. Living 300 miles away you would have no expectations and I would live up to them. http://fsae.com/groupee_common/emoticons/icon_wink.gif btw, Thanks to James Waltman for calling me to let me know that we were not yet registered and it was filling up fast. I tried to get to a computer but it was too late.

Halfast - Right now I plan on being in Detroit with or without a car. Although I would enjoy the six pack, I only drink beer when I have someone to B.S. with so you will have to help me tip a few. (OK, that was a lie. I have very few constrints on drinking beer, but we could still B.S.)

Now, about the PVC pipe. About 1.5 years ago when I first started working on our engine I sent an email to Charlie Ping. The credit is his for the prototype PVC intake and we ran with it. You can get remarkable results building a PVC intake, "sealing" it with plumber's putty, and running it on the dyno to make the final adjustments on intake geometry before fabricating the final result.

[nathan s]

Thanks guys for the help.

Checked at the library here and put in a request for some books. Hopefully they can find something.

I'll check into the Acoustics book.

I also started learning how to use Ricardo yesterday. Seems pretty interesting, but it is unlike anything I have ever used.

Wish me luck! I am sure you will hear from me again http://fsae.com/groupee_common/emoticons/icon_biggrin.gif