The Cal-look Lounge

I was browsing the Jenvey web page when I read this "As peak RPM increased year by year, the required induction system length reduced. At the same time, the ideal butterfly to valve distance increased. Over about 15,000 rpm, the ideal butterfly position falls outside the induction system - clearly useless"

They talk about formula one so the 15000 rpm can be disregarded in our case, but they are pointing to a consideration I have never heard about, and by the way it's written It's not tuned lenghts they are talking about...

It would be nice to know if its better to have the adjustable rubber hoses under or above the butterfly when I make my next manifolds.
Any thoughts?

Regards Jon

At extremely high rpm having the fuel enter the intake tract higher up, or even outside the runner, can deliver a more atomised mixture to the cylinder i.e. more power - assuming the port is well designed.
This why why you'll see injectors mounted above the air horns/velocity stacks on some highly tuned n/a engines, which by their nature tend to have short intake runners.

F1 use roller barrel TBs, therefore 'butterfly' postion isn't an issue when operating at WOT.

Engines operating across a wide rpm range and a range of throttle positions can have the best of both worlds by running two injectors per cylinder - the lower injector takes care of low to mid-range rpm, giving better throttle response than a single top mount injector.
Dyno testing will reveal where in the rpm range switching to the top injector proves to be an advantage.

As an example, Kinsler twin injector setup designed for I4 drag race Honda:
(http://sphotos-h.ak.fbcdn.net/hphotos-ak-snc6/231059_525828414095606_1956735626_n.jpg)

Thanks John, see what you read out of the complete text:

Butterflies, barrels or slides?
20 years ago, carburetors and mechanical fuel injection were the only choice to fuel a racing car engine. Selection of air valve type was simple and apparently carved in stone; carburetors used butterflies and injection used slide throttles. Motor Bikes and their history are a special case but what follows is true for any performance 4-stroke petrol engine.

With the advent of electronic fuel injection and a more adventurous (better funded) approach from the leading engine designers, it was discovered that butterflies, whilst sometimes (but not always) giving slightly less power than slides, inevitably gave better lap times. The explanation was simple; butterflies give more progressive throttle control, improved transient conditions, and aid mixture quality throughout the RPM range.

As a result of these discoveries most (possibly all) of the leading car race engine manufacturers switched to using butterflies. Lap times continued to tumble, but there was a problem brewing for the future. As peak RPM increased year by year, the required induction system length reduced. At the same time, the ideal butterfly to valve distance increased. Over about 15,000 rpm, the ideal butterfly position falls outside the induction system - clearly useless. Enter the barrel.

The barrel has some, but not all of the attributes of a butterfly. Opening is reasonable progressive and, like the butterfly, it is easily packaged. The great advantage is that it can be made as a continuation of the port shape, regardless of profile (slides would overlap), and thus be placed near or even in the cylinder head, allowing for a very short system to suit the 18,000+ RPM which is now common. Any compromises (poor idle control, tendency to stick, poor flow vector control, etc.) were once believed to be offset by the sheer power available at these RPM, although once again most of the leading car race engine manufacturers (e.g. F1) had switched back to using butterflies by 2006. It follows that barrels on a sub 15,000 RPM engine will suffer from the compromises without gaining the possible benefits.

The main advantage of the barrel - maintenance of port profile - can be obtained by using fully profiled butterflies. These are made to precisely fit the port profile and are shaped in cross-section to achieve the required characteristics; minimum drag, controlled turbulence or whatever else best suits the application. This is now the preferred solution for top-end engines used in Formula 1, World Super Bikes and some sports-racing engines. Jenvey Dynamics supply these for specific applications since they must be designed to suit the engine and cylinder head used.

In summary; Butterflies are best wherever they can be used. Jenvey Dynamics have a design and make service for engine specific profiled butterfly bodies. Barrels are suitable only for engines running at over 15,000 RPM and must be designed to suit a particular engine type. Jenvey Dynamics have a design and make service for engine - specific barrel bodies. Slide throttles are best reserved for classics, if the rules prohibit a change.

In a back-to-back comparison, using a Rover K series engine in race trim, Jenvey road going butterfly bodies were found to give significantly more power at all RPM when tested against barrels. Full race butterfly bodies would further increase the margin. Whilst the power improvements are unlikely to be found in all engine types, the performance gains almost certainly will.



http://classicinlines.com/TBI_QA.asp#butterflies (http://classicinlines.com/TBI_QA.asp#butterflies)

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Are they talking about  "butterfly" placement or injector placement, or am I reading it wrong?

Jon

Sounds like butterfly placement to me,and it reads that the throttle plate/barrell needs to be in the cylinder head,not further out,interesting that they recomend butterflies for sub 15.000rpm engines,I think they will work ok for my needs then :)

cheers Richie

i can imagine that the 'aerodynamic wake' or turbulent distortion of a butterfly is key here. Very hard to visualize the dynamic behaviour of air during the intake time-frame and the time between them but
The air has to go around the butterfly, effectively splitting the incoming air stream in 2, those 2 vectors, if you like, converge like the tip of a flame at a given point. I bet it has something to do with the placement
of this 'tip' in regard to the dynamic behaviour of the air in the runner volume, between intake valve opening, effecting nett air mass entering the engine and thus potential power at a given rpm. The distance from butterfly to 'tip of the flame' cant be unlimited since airspeed is limited, so i'm putting my money on the dynamic,  thing between intake valve opening

This might be potential bull***, just spitting my thoughts...


EDIT:

The above...though without the dynamic story, what was i thinking...  ;D...if you keep shortening the runners, the butterflies will come down as well, eventually placing the distorted airflow from the butterfly in the port, messing up engine breathing  ;) . Thats why, for a given length, the butterflies will need to be _outside_ of the runners... tuned length versus aerodynamic misbehaviour  :)

They write about profiling the butterfly...didnt AT Power advertise with their 'profiled butterflies' for like forever ? (their website is under construction a.t.m.)

who knows..   ???  .interesting read though!