Help On Intake Design

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
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as.racing
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Joined: 04 Feb 2013, 23:16
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Help On Intake Design

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Hi,

Would be grateful if someone can help me with this. I'm making a carbon inlet manifold and set of trumpets for a bike carbs conversion on my 1.9L 4 cylinder, but need to know how best to use the space I've got under the bonnet. My two options are:

1. Have the intake trumpets as long as possible to improve torque and therefore, reduce the length of the intake manifold.

or,

2. Am I better to have the manifold as long as possible to maximise fuel mixing, at the expense of trumpet length resulting in more peak power, but less torque???

I've had a look already, but not having much success. Can anyone point me in the right direction?


Cheers,

Andy
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mep
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Joined: 11 Oct 2003, 15:48
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Re: Help On Intake Design

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I think the best is if you use some simulation software to fine tune that. I don’t know if there is a general answer for that. Like you can’t just say you make the trumpets as long as possible. The length must be fine-tuned with great care. However, in general I would say trumpet length will alter your performance much more than manifold volume. But also take into account that most simulations can’t represent the mixing process of fuel and air.

zonk
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Joined: 17 Jun 2010, 00:56

Re: Help On Intake Design

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The acceleration of air flow into a duct is inherently a highly efficient process and the difference between even the crudest radius inlet, and the most aerodynamic shape possible is slight, amounting to no more than a few percent. The flow coefficient of a perfect entry would be 1.0 while the coefficient for a sharp edged entry would be 0.6 and a re-entrant plain pipe 0.5. In practice these latter types of entry are never used for engine intakes. There is always some attempt to provide some radius at the entry. This means that total engine airflow would not increase by the amount suggested by these figures, which apply only to the entry alone, as the inlet end is never the smallest or most restrictive part of the system. Because the greatest losses to flow occur near the valve seat, actual overall gain from any improvement of the entry flow would be much less.

In the real world, on high-rpm IR IC engine, using a minimum amount of inlet radius gives the best wave strength and a power boost of 2% to 4% over a 3000 to 3500 rpm range. Using a larger radius, like 3/4", broadens out the resonant pressure wave rpm range, but the compression boosting pressure wave is greatly diminished and almost unnoticed by the engine.

source wiki.


autogyro
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Joined: 04 Oct 2009, 15:03

Re: Help On Intake Design

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It will be the make and type of carbs you intend fitting that will make the most difference.
Motorcycle carbs are designed generaly for higher rpm and faster response than carbs for cars.

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as.racing
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Re: Help On Intake Design

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Thanks for the responses so far. I'll be using R1 bike carbs.
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olefud
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Joined: 13 Mar 2011, 00:10
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Re: Help On Intake Design

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I’m not sure there is an issue. Trumpets, I would guess, are primarily to fix the distance from the intake valve to the intake opening for pressure wave tuning. Thus if the manifold runners are longer then you’ll need only shorter trumpets. Of course if your manifold has a plenum rather than individual runners it won’t make any difference since the tuned length will be to the plenum.

If you’re just trying to smoothly feed air relatively short parabolic trumpets should work just fine.

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as.racing
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Re: Help On Intake Design

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olefud wrote:I’m not sure there is an issue. Trumpets, I would guess, are primarily to fix the distance from the intake valve to the intake opening for pressure wave tuning. Thus if the manifold runners are longer then you’ll need only shorter trumpets. Of course if your manifold has a plenum rather than individual runners it won’t make any difference since the tuned length will be to the plenum.

If you’re just trying to smoothly feed air relatively short parabolic trumpets should work just fine.
My thinking is though, that a longer manifold will give the fuel more time to mix, hence the placement of the injectors in this btcc engine:

[youtube]http://www.youtube.com/watch?v=CnmC-j28xOQ[/youtube]
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Brian.G
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Re: Help On Intake Design

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Without sounding like a pr!ck, there is more info on this subject online than there possibly is about the amazon.

It depends on a lot of things, cam profile too, and static/dynamic compression ratios,

There are online calcs too,

Googling 'resonance tuning' should give you 6months of reading,

Brian,
If you think you cant, you wont, If you think you can, you will

olefud
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Joined: 13 Mar 2011, 00:10
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Re: Help On Intake Design

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as.racing wrote:
olefud wrote:I’m not sure there is an issue. Trumpets, I would guess, are primarily to fix the distance from the intake valve to the intake opening for pressure wave tuning. Thus if the manifold runners are longer then you’ll need only shorter trumpets. Of course if your manifold has a plenum rather than individual runners it won’t make any difference since the tuned length will be to the plenum.

If you’re just trying to smoothly feed air relatively short parabolic trumpets should work just fine.
My thinking is though, that a longer manifold will give the fuel more time to mix, hence the placement of the injectors in this btcc engine:

[youtube]http://www.youtube.com/watch?v=CnmC-j28xOQ[/youtube]
You’re getting into fairly involved design considerations. Fuel doesn’t make the port turns as well as air. And it takes up flow volume. Thus port injectors may be aimed at the intake valve to allow “dry” air flow to that point. But if early injection is your aim, you could position your injectors in the trumpets. The old Hilborn injectors were pretty much of such design.
Before starting on your ambitious project you may want to do a bit more study so you have a firm understanding of the actual tradeoffs. Imitating one aspect of a sophisticated design will just get you disappointment.

Tommy Cookers
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Joined: 17 Feb 2012, 16:55

Re: Help On Intake Design

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as.racing wrote:
olefud wrote:I’m not sure there is an issue. Trumpets, I would guess, are primarily to fix the distance from the intake valve to the intake opening for pressure wave tuning. Thus if the manifold runners are longer then you’ll need only shorter trumpets. Of course if your manifold has a plenum rather than individual runners it won’t make any difference since the tuned length will be to the plenum.

If you’re just trying to smoothly feed air relatively short parabolic trumpets should work just fine.
My thinking is though, that a longer manifold will give the fuel more time to mix, hence the placement of the injectors ....
agreed, in principle the aim should be the optimal overall inlet system length for charge(ie length pre-trumpet is tradeable with trumpet length)
but with carbs the reverse airflow inevitable with a sporty cam at lower rpm will be carburetted
unless this air/fuel mix is contained for re-ingestion (ie by use of a suitably long trumpet) consistent carburation is impossible
when British motorcycles (all pushrod valves) went sporty in the late 50s trumpets were introduced for this reason
one had 135 deg of valve overlap and the flow reversion was conspicuous
presumably the Japanese carb mouths and airbox/plenum and ohc have together dealt with this (is this all transferrable ?)
I guess the carbs will have complex mouths unsuited to adding trumpets ?

mixing time is good for economy and emissions, but not necessarily good for the track
ideally for power the cylinder should ingest fuel as tiny droplets (ie not vapourised)
any vapourisation before valve closure displaces some induction air, 'stealing' some of your 1900 cc (this is partly why DI is good)
non-direct injection will often give less max power than good carbs for this reason

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