# Trumpets inside intake plenum-What do they do?



## Irish GTR (Apr 23, 2007)

Quick question for you guys.

The bellmouths/trumpets that protude out into the plenum itself-what exactly do they do.Is it to do with disturbing the air flow or what?

What are the benifits of them?
Thanks.


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## Boosted (Jun 5, 2008)

Probably to ensure even flow into the head. Without them, it would end up into the first couple of trumpets after the inlet on the plenum, but with them the plenum fills up and equalises the flow for all inlets, so they all get an equal amount. That's what I think anyway, never thought about that until now.

Rob @ RIPS will probably explain it better than I have.


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## R.I.P.S NZ (May 7, 2004)

There's alot of debate about plenim design but TBH in most RB applications its probably not as important as some make out.

I can honestly say that not 1 plenim we have ever made has trumpets like that and we make very good power V boost and extreemly even air distribution so obviously what we do works also.

Possibly if your looking for every last little bit (or if your class of racing had a boost limit) the minute details of plenim design would show benefits but in most cases personally I don't think its that big of a deal.

Rob


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## Irish GTR (Apr 23, 2007)

Ive seen alot of aftermarket Mitsi Evo plenums/intake manifolds with these trumpets inside them aswell.so I just wondered what exactly they do and if they were left out would it make any noticible difference?


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## cokey (Sep 11, 2003)

I think its a tuned length~flow bench thing !
But as rob and others say... not vital in a boosted environment.
Ever played a flute ? 
Try gaffa taping a hairdryer to the mouthpiece !

cokey


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## SteveN (Aug 6, 2002)

stock cosworth inlets and so on are like that.

but like a LOT of things in tuning, theory and reality are wide apart and the real world differences are rather small, and FAR less worth worrying about than other glaring errors in spec people make.


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## freakazoid3 (Jan 19, 2008)

The trumpets are there in order to achieve the theoretical "laminar air flow" That means that the air flowing in the head isn't turbulent thus having a higher density. This is important when tuning NA cars, but when the air is crammed in the engine at 2 bars boost, a lot off the theory is lost :chuckle: 
But I guess when pushing the enveloppe to the last hp out off your setup things like this make the difference on the track


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## GT-R Glenn (Nov 9, 2002)

Ummm
whether you suck or blow into a pipe , the square end will cause a restriction to the air flow in the inlet , which effectivley makes the throat diameter smaller.
Theres a huge amount of opinions about the radius , ie exact size where it starts, but generally speaking it will effectivley even out all the air trying to go into the pipe and assist in openning the airflow up to whatever the max flow rate could be.
Or
It makes it flow more bettera....
Presurized Plenums are a bit different to atmo sidedraughts also, because atmo has other influeneces on the ability to grab or Flow air.

I had a bit to do with venturi design years ago ... shrug


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## Lith (Oct 5, 2006)

You wouldn't believe how much restraint I am showing to not write a huge rant. 

Instead of boring people... I'll summarise by saying that the way I think about it - the net effect they have is effectively increasing the surface area an "intake" can draw air from, and create a smooth and high velocity flow into the valves. I ultimately agree with what others have said, its probably not so crucial with turbocharged cars.


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## GT-R Glenn (Nov 9, 2002)

Lith have you read Helmholtz theory at all?


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## Lith (Oct 5, 2006)

GT-R Glenn said:


> Lith have you read Helmholtz theory at all?


Only basics and there is so much stuff I'd like to get more in depth understanding of but so little time and its just a interest so it doesn't get the highest priority. I guess the main thing that has me ponder is I can't help imagine the resonant effect would be a bit messed with by the fact that the flow of air into the engine under boost is largely dictated by the turbo pumping the air in. 

I'm sure there may be some resonance somewhere but the fact that the intake (and the exhaust for that matter) sides sound so much less raucous I can't help but imagine that the advantages you'd get from exploiting Helmholtz theorum really wouldn't be the same. Surely any returning "wave" would just get pummelled by a flow of air being pushed by a set of blades spinning at 100krpm haha so beyond that I tend to consider the throttles as just being a bigger mouth without hard edges - at least in respect to turbos.

If you are holding onto something further on it, I'm always keen to learn and someone effectively opened the can of worms by asking about them


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## Corsa1 (Sep 8, 2003)

You have to look at off boost performance as well as on boost. rob have you put one off your inlets on the flow bench without ram pipes and then with you would be surprised at the out come.
thanks
[email protected]


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## GT-R Glenn (Nov 9, 2002)

Lith, it was just out of curiosity.
Heres something I designed and biult 20 years ago,
Using his theories to fine tune
YouTube - Pulse Jet


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## Lith (Oct 5, 2006)

That is exceptionally cool!!!!!!! Very nice. And I love the shorts!


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## GarethK (Aug 29, 2004)

Loads of minor breathing improvements are overlooked on turbo cars because you can normally achieve the same effect by just cramming in a bit more boost.

It's a fact that they work better, which you can prove on a flow bench or using CFD.


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## R.I.P.S NZ (May 7, 2004)

GarethK said:


> It's a fact that they work better, which you can prove on a flow bench or using CFD.


I'm sure you are right and its been generally agreed that the internal trumpets are the way to go.

I'm all tooled up to make our style of trumpets and we are getting good results with very good hp V boost so for now I'll stick with what we have been doing for the last few years.

If and when the time comes we are hitting a brick wall with power we'll no dought look into it further.

I might arrange a back to back test on an engine dyno sometime and find out for sure what the improvements are when changing nothing but the plenim.

Rob


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## GarethK (Aug 29, 2004)

R.I.P.S NZ said:


> If and when the time comes we are hitting a brick wall with power we'll no dought look into it further.
> 
> I might arrange a back to back test on an engine dyno sometime and find out for sure what the improvements are when changing nothing but the plenim.
> 
> Rob


It would be good to see the results of that test!

I'm not having a dig though, you are right that the difference will probably be minimal in comparison to the overall improvements from one of your plenums or 1 extra psi of boost! The difference comes when the last extra few % make a difference, like in race engines and more and more often the new breed of high specific power NA cars like Ferraris, BMW Ms etc, which all use trumpeted intakes.


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## GT-R Glenn (Nov 9, 2002)

If you read what Keith Duckworth has to say, nothing has changed.
They started with velocity stacks, with basically a radiused flare on a pipe the evolved into like an O ring on the end of the pipe, theres actually quite a bit off difference in how far round the curve continues,
Cant really explain it without drawing pictures, 
google it 

oops forgot to say, its all whats the saying ,nickles and dimes make dollars or whatever....
Its not done to look cool.


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