Ivan
|
| posted on 24/6/08 at 08:15 PM |
|
|
Throttle bodies - dumb question - or not?
Can anybody explain to me why on a EFI motor individual throttle bodies are better than straight individual manifolds with individual air trumpets
sucking from a well designed plenum fed by a large enough single throttle body - or even two.
To my way of thinking each smaller throttle plate is just an additional restriction causing unneeded turbulence at all throttle settings which means
you have to have bigger tubes - giving slower air flow and poorer low down torque. The only advantage I can think of is that it might give slightly
better response to throttle movement - but then you have the hastle of getting them all moving equally and the additional expense of buying each one.
|
|
|
|
|
blakep82
|
| posted on 24/6/08 at 08:20 PM |
|
|
i'm thinking the 'surface area' of each individual butterfly added together is bigger than the one on the plenum?
i've never really looked tbh.
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
|
|
|
Jenko
|
| posted on 24/6/08 at 09:00 PM |
|
|
With ITB's you get better control over the flow of each cylinder............The total inlet area is also typically higher than just one
butterfly.
|
|
|
martyn_16v
|
| posted on 24/6/08 at 09:31 PM |
|
|
Define 'better' 
A well designed plenum system probably should be fairly close to the performance of individual throttles in all areas bar throttle response (due to
the much greater volume of air between throttle plates and cylinder in a plenum setup). The trouble is there aren't very many well designed
plenum setups around, mostly due to packaging reasons. They're usually a collection of horrible bends, a too small plenum and too short runners
between plenum and head, just to fit them into the available space.
|
|
|
Ivan
|
| posted on 25/6/08 at 07:15 AM |
|
|
The only down side that I can see so far is that the plenum would have to be strong enough to withstand engine vacuum.
I agree regarding plenum design - has anyone seen literature re this subject. Of course this applies in both the above cases.
I also don't think throttle reaction would be that noticeable given that at 2000 RPM it would take a 2l motor roughly 0.15 seconds to completely
empty a 5 litre plenum which is almost undetectable.
[Edited on 25/6/08 by Ivan]
|
|
|
Jenko
|
| posted on 25/6/08 at 03:25 PM |
|
|
Problem is with a plenum, is you are trying to get exactly the same feed down each inlet, and inlet flow is very sensetive.
In a perfect world the flow down each inlet would be identical...ITB's at least suck the air in from free air (apart from the air filter
restriction) rather than a combined space where one inlet can massively effect the other. I'm guessing any heat around the plenum would warm it
up also, and therefore warm the air. again a disadvantage.
If you can get the plenum big enough, then my guess is it would limit slightly the adverse effect of having the inlets effectively joind together (as
there would be enough mass of air in the plenum to cope).
So, the Fact is, yes the improvement is not massive, but there is an improvement on pick up, and possibly breathing at peak HP....
Thus ITB's are 'better' for performance engines.
Dissadvantages are noise as the induction is not insulated by a metal or plastic housing.
|
|
|
