Throttle Types

[Mandic 0]

Hi,

 

Lets talk about throttles a bit;

 

Which throttle control is best? Butterflies or slide throttles? And how much do butterflies disturb flow if they are positioned right at the inlet port (direct to head)?

 

Is it better to position butterflies further up the runner and benefit from blades cutting fuel drops (if running 8 injector setup, or having injectors further up) and also butterfly and spindle are not disturbing air path at the narrowset part of the runner.

 

What about flow control at part throttle?

 

Why are slide throttles inferior according to jenvey, here . Surely this is way better than if there were spindle and butterfly in the middle.

 

But then again, what happes when You have pressurised induction and when having a gap on the left side of the throttle, does this represent a restriction.

 

 

 

Thanks in advance!

 

Ziga

[Faz85 0]

In my opinion, a butterfly throttle valve is used primarily for its ease of manufacture and to improve driveability. Im sure it would give greater contol at part throttle than a slide valve. Although with that said, a slide valve at WOT eliminates all the restriction to the airflow, unlike a butterfly, so i would expect a slide valve to give greater performance at WOT.

 

TBH, reading that Jenvey info, im surprised they found that butterflies gave greater power over barrel throttles! (but im certainly not one to contradict the experts)

 

Faz

Edited January 11, 2007 by Faz85

[Sam 4]

But then fitting a larger butterfly would overcome any flow issues at WOT would it not?

[Faz85 0]

But then fitting a larger butterfly would overcome any flow issues at WOT would it not?

 

Yes possibly, but considering any one size, then IMO a slide throttle would surely be the better option if reducing the flow restriction is the primary concern. Besides, a larger butterfly may improve the volumetric flow, but wouldnt other effects such as flow separation still be a problem with a larger throttle?

[Sandy 189]

I think Sam's point is even more valid than is obvious. The drag in the air stream of a slightly oversize butterfly would be minuscule, with little or no discernible loss of throttle response or resolution.

The information on Jenvey's site is comprehensive, but not definitive. IMO it's much like any other "technical section" of a commercial company's website, there's a degree of substance, an element of generalising and a certain amount of opinion. Some elements such as their guide to bore sizing and tract length, is helpful and has a sound basis, but doesn't correspond with all cases. The development work I've been fortunate enough to have access to and that I've done myself, does not always support generally accepted views on this matter.

 

I got into a discussion a while back about the comparison of flow against throttle angle, of butterfly versus barrel, and I was surprised to be shown test results that showed a smoother transition of flow and greater peak flow for barrels. What they also give you is a smoother tract at full throttle, not just in terms of obstructions in the air stream, but because the bore and section are consistent, you don't get pressure, gas speed and acoustic changes as you do with a butterfly body. The exact effects are difficult to model or quantify, but never the less, shouldn't be discounted. The most trivial differences can manifest in a big way where inlet design is concerned.

Edited January 12, 2007 by sandy309

[Mandic 0]

Any other inputs on this?

 

Sandy, I agree Jenvey is a commercial company it's interpretation and needs to be take with care.

 

But what about butterfly type throttle right at the inlet port, how restrictive they really are? if any (considering well designed plate and spindle)?

 

What about slide throttles and turbo? disadvantages/advantages?

 

Cheers

 

Ziga

[Sandy 189]

With slide throttles on a Turbo engine i'd be concerned about potential sticking with the heat involved.

[Rippthrough 98]

With slide throttles on a Turbo engine i'd be concerned about potential sticking with the heat involved.

 

 

Not just the heat the increase in the pressure difference wouldn't help either.

[Faz85 0]

Surely heat and pressure effects would be just as detrimental to a butterfly...besides, some F1 cars use slide throttles without any problems.

 

As for butterfly throttles at the inlet port... IMO would be a reasonably good idea, as the flow would be unrestricted up until the inlet at which point the spindle and plate would encourage flow separation, causing turbulence. I think this would be advantageous since it would promote better mixing of the intake charge as it enters the cylinder, which would lead to better combustion.

 

Faz

Edited January 13, 2007 by Faz85

[Sandy 189]

I don't think expansion or distortion would affect a butterfly as much as a slide throttle, likewise the pressure drop.

 

I aim to mount the throttle butterflies as far upstream as possible. This is a subject of much debate and it probably varies with each engine design and certainly with injector position.

[Mandic 0]

I'm planning on using 8 injectors, one set right at the inlet port and one a bit further (not decided where yet).

 

So for a Mi engine with such injector setup, what do You think, direct to head tb ok or not?

 

Cheers

 

Ziga

[Sandy 189]

It depends what your priority is and might take some experimentation, if it's feasible.

[Faz85 0]

Concurrent with what Jenvey are saying, I reckon if you can get the injector as close as possible to the butterfly, then you can make more use of the turbulent flow. As for mounting the throttle butterflies, I would be inclined to get them as close to the head as poss, to improve throttle response time, but like Sandy is saying, it is quite an opinionated topic open to much debate.

 

I agree with Sandy, that an experimental approach would be the best solution if possible...perhaps if you have access to a CFD software package (like CosmosFlow), you would be able to model the effects to some degree. I've never tried to model a throttle/inlet myself, but im certain it would be easy enough to model the drag effects of each throttle type and position, But im not sure it would be possible to model all the flow effects such as mixing and turbulence...I guess thats where a practical approach would be needed, with a certain element of "trial and error".

Edited January 13, 2007 by Faz85

[Mandic 0]

Well I am using Floworks for some time now, but primary goal was to design a plenum.

 

I have modeled TBs as well and wanted to do CFD test, but had no time, will try to do it today.

 

But like You said, to model mixing is going to be pain in the ar*e.

 

Cheers

 

Ziga