Butterfly's On Throttle Bodies

[DRTDVL 4 1 Cars]

Now i'm hoping someone much wiser than me can explain this to me and it's always been a case of why do they do it that way???

 

I'm refering to the butterflys on a lot of quad throttle bodies... (Batfink i hope you don't mind me using your photo - if you want it removed let me know or get a mod/admin to remove it.) - If you look you can see the large square bar with the large screws on top of the bar, all causing turbulence in the throttle body. A while back a few friends of mine and i where talking about it and they decided that they would try something out.

 

In this photo you can see what i'm talking about - the large square bar on the flap of the butterfly. nice and square leading edges...

 

We played around with the mirage mivec throttle bodies and found that just removing the leading face bar improved the throttle response and mid-range pickup considerably. Even more so than boring the throttle body out from 60mm to 63mm. You can also see the rounded bar and counter sunk screws which is factory for the mivecs... even this would be a improvement over the above setup.

 

Can someone tell me why you wouldn't want to do this?

 

Even rounding the bar on the backside of the butterfly to improve wide open throttle again to reduce turbulance in the throttle body, and the disturbed air into the port (Quad setup)... You spend all that money improving the flow into the port only to have turbulant air flowing into the port from the throttle bodies...

[dee205 3]

If the bar was at the back of the butterfly surely it wouldn't be in the direct flow of air and only cause turbulance when on WOT (which is probably 99% of the time tbh!) And also would the slight turbulance not aid air/fuel mix or atomization (if that's the right word)??

[DRTDVL 4 1 Cars]

I couldn't find a shot from the front on batfinks - it was more a general statement.

 

My friends been looking to import a set of bmw e36 throttle bodies and they have the square bar on both sides, as did the factory mivec ones which we removed the front side.

 

unless the leading edge of the butterfly broke the air up (thinking like ducks in a V here) and that this might cause the airflow over the square bar to not really be effected as it's broken messy air anyways. but i'm more thinking that it would be a big cause of turbulence and would effect the core lug of undisturbed air flowing on each side of the butterfly.

 

Wouldn't reducing the profile of the mounting equipment for the butterfly be of benefit, improvements in flow velocity would aid in improving fill rates to the chamber at low to mid lift of your cams...

Edited December 15, 2009 by DRTDVL

[dee205 3]

I think we need some flow tests here! Would be an interesting test as it does seem a little odd when every other part of the tb is about smooth flow.

[dee205 3]

I found this DIY tb smoothing

[tri_longer 25]

These guys have already addressed this problem with a range of spindleless throttle bodies.

 

http://www.atpower.co.uk/main.html

[DRTDVL 4 1 Cars]

nice find man...

 

might have to look at a set for the car later... in the meantime i'll look at tweeking the factory one until i can afford one of those sets.

[Cameron 16]

We've got one of those bad-boys for out formula student car, will be interesting to see if we get any gains.

[Galifrey 1]

About 25 years ago, we used to gasflow the spindles on tillotson carbs for 100cc Karting, then they started selling slide carbs

 

Yes it does make a difference at WOT but very little difference elsewhere, as when the butterfly is at an angle, the airflow is already disrupted.

 

of course, wide open throttle can affect a lot of rpm ranges, it doesnt just mean max rpm.

[Batfink 201]

I believe the stuff like AT powers version allow you to run a smaller throttlebody unit due to the design.

[Rippthrough 98]

I believe the stuff like AT powers version allow you to run a smaller throttlebody unit due to the design.

 

Bingo, the only advantage is being able to run a smaller throttle body, the leading edge of the butterfly creates a shockwave anyway, even at full throttle as the plate isn't at 90*

[tri_longer 25]

The other option is roller barrel throttle bodies, I'd be interested to know if anyone has ever used these,

 

http://www.titan.uk.net/products/3/titan-roller-barrels

[Vili 18]

The other option is roller barrel throttle bodies, I'd be interested to know if anyone has ever used these,

 

http://www.titan.uk.net/products/3/titan-roller-barrels

 

Spotted same kind of throttle bodies at Finnish rally forum couple of year ago. Bodies were self made and quite rude looking as they were only prototype. They were tested at old 2.0 OCH escort. Result was that the engine worked lot better at mid range 3000-6000 and top end power was cut off because rev limiter couldn't be raised any higher. Figures were circa 200hp at wheels/8200 rpm. 48mm bodies tested were too big for the engine and they were supposed to do new smaller ones, but they didn't post any updates.

Based on that barrel bodies really flow a LOT better than conventional bodies of the same size. Basically you should get better power range with barrel bodies because you can use smaller ones.

[Batfink 201]

roller barrel give better flow at a fully open throttle but they are not as nice to drive with at part throttle.

 

Kev

[Sandy 191]

Roller barrels are significantly heavier than butterfly types and don't seal/balance as well. Slide throttles are also hard to balance and unreliable. The traditional butterfly is hard to beat on all fronts and features on most of the best real world engines around.

[sideways danny 0]

I believe the stuff like AT powers version allow you to run a smaller throttlebody unit due to the design.

 

yeah they told us that too. Put them on an engine built to make 225-230bhp and it wouldn't go past 200. Fitted some Jenvey 45s and the power was back.

Also AT trumpets dont taper over a long enough section.

Edited December 18, 2009 by sideways danny

[Cameron 16]

Bingo, the only advantage is being able to run a smaller throttle body, the leading edge of the butterfly creates a shockwave anyway, even at full throttle as the plate isn't at 90*

 

 

That's what makes me think smoothing the spindle might not make any difference.. you're going to have separation starting from the leading edge and probably heading past the spindle and the rest of the butterfly. Anyone done any CFD?

[EdCherry 34 1 Cars]

Read that wrong, thought it said CFM. Too many beers.

Edited December 21, 2009 by EdCherry

[Cameron 16]

Here we go.. someone has tried it with a trapezoidal butterfly with good results. IMO a flat throttle would have similar results with and without the spindle, we'll see I guess!

 

Blue surface represents a 75m/s boundary, i.e. inside <75m/s, outside >75m/s,

[Galifrey 1]

Here we go.. someone has tried it with a trapezoidal butterfly with good results. IMO a flat throttle would have similar results with and without the spindle, we'll see I guess!

 

Blue surface represents a 75m/s boundary, i.e. inside <75m/s, outside >75m/s,

 

I think the issue then becomes the turbulence around the trapezoidal at certain throttle openings.

 

The only way you could get a perfect throttle is with an iris type choke.

 

Everthing is a compromise.

[Cameron 16]

Well, at part throttle you'll get some pretty horrific turbulence but I'm not sure it matters. The point of being at part throttle is to restrict the airflow anyway.

[DRTDVL 4 1 Cars]

Here we go.. someone has tried it with a trapezoidal butterfly with good results. IMO a flat throttle would have similar results with and without the spindle, we'll see I guess!

 

As per: http://www.raetech.com/Engine/Fuel_Injection_Development.php

CFD analysis revealed significant wake turbulence caused by the unstreamlined round throttle shaft and the screws attaching the butterfly. Based on this information, RAETECH redesigned the throttle components using a new trapezoidal section butterfly and carefully designed shaft attachment to provide much less disruption to the airflow in the runner.

 

I'm going to assume that the CFD images where their after design..

 

by looking at their CFD model's it no way represents the original square bar with bolts on top design that i was originally referring as a potential area of improvement.

 

It would be really nice to get a cloud and annimation for flow/turblance as the throttle is openned and closed to see the possible gains over the factory setup...

 

i.e.

pictures care of http://www.exa.com/ (i love their software)

 

again i was initially refering to gains over this butterfly/factory:

 

[Cameron 16]

Well, they've worded that to sell a product so a "significant gain" could mean anything!

 

My point is do you really need to make any flow gains anywhere other than full throttle?

[Galifrey 1]

Well, they've worded that to sell a product so a "significant gain" could mean anything!

 

My point is do you really need to make any flow gains anywhere other than full throttle?

 

And can you achieve that just using a larger choke?

[Sandy 191]

That's the thing. You can oversize the TB no problem, if the tract and port shape and size are optimised for the application well. Back to the same old thing, looking at the detail is healthy, but it's the overall package that counts.