What would be the effect of changing the inlet from a single throttle body, with runners to each cylinder, to a single throttle body with a single plenum chamber feeding all the cylinders?
Possibly a loss of torque lower down the rev range at a guess.
I hope I am not missing the point of the question, but what engine does this relate to?
I guess it will depend on how clever you are with the plenum, build it with internal trumpets, think about air flow in so the rear pair if fed from the front get the same access to air with some internal ducting and you may improve things.
I'm having the same debate with myself, so building both:
This is based on the stock jag xj6 setup
Modded XJ6 Plenum 5
Here's the custom job, which I must say I prefer, and you'll recognise some of the bits
ITB Progress 1
The itbs will be harder to setup and balance, but should be less restrictive at higher rpms, plus, within reason I can vary the trumpet length to
alter the torque curve.
With the plenum, balancing will not be an issue, and hopefully Jaguar got it close, but, there is a company who have proved cutting into the plenum
and lengthening the runners yields a torque improvement - here
The engine is a Jaaaaag AJ30 
I am trying to get it lower to fit under the bonnet.
The standard inlet is this monster
The Duratec V6 inlet will fit, but needs a 30mm thick spacer plate. This is lower but wider.
Something like this is what I was thinking
Once it is in, running and got a few miles under the bonnet, I will consider throttle bodies
Now where did I put those Triumph Triple bodies? 
Nice, but!......... http://beta.atpowerthrottles.com/product_info.php/jaguar-injected-p-179
[Edited on 26-9-14 by 40inches]
quote:
Originally posted by 40inches
Once it is in, running and got a few miles under the bonnet, I will consider throttle bodies
Now where did I put those Triumph Triple bodies?
[Edited on 26-9-14 by 40inches]
quote:
Originally posted by r1_pete
quote:
Originally posted by 40inches
Once it is in, running and got a few miles under the bonnet, I will consider throttle bodies
Now where did I put those Triumph Triple bodies?
[Edited on 26-9-14 by 40inches]
I wonder....
I do have a couple of sets of triumph body mounting rubbers which may be of use if you go triumph bodies, I bought them planning a weber type inlet and then just went with tube and sleeves.
Pop in next time you're in Aston, you can have them if they'll help, I'm sure they fit the bodies with injector points as well as the ones I used.
Longer seems to be better when it comes to runners, so if they're very short you may lose in the midrange as said above.
As I understand it, a plenum per se shouldn't have many adverse effects, providing its volume is large enough.
quote:
Originally posted by 40inches
The engine is a Jaaaaag AJ30
There is a site if you gogle it fitting the mondeo inlet on a jag v6 in a lotus esprit, this may give you some ideas.
I've been investigating this myself this weekend and David Vizard seems to be the go-to guy for plenum and inlet manifold design.
It seems that its not so much the plenum design as the throttle body and duct leading to it that matters. With the right design of that portion
utilising the Helmholtz effect you can get up to 7psi extra pressure in your plenum at certain revs.
Obviously runner lengths and area are also critical and depend on engine displacement, valve timing and rev range that you want to enhance.
There's some info here:
http://books.google.co.za/books?id=OAw1GDB0kN0C&pg=PA36&lpg=PA36&dq=david+vizard+plenum+chamber+size&source=bl&ots=C_cl6Z-vQS&
sig=X2Jw2OZnycWIiZ9gDVTCZoid2iM&hl=en&sa=X&ei=T84nVNjZEovearzfgfgN&ved=0CDQQ6AEwAw#v=onepage&q=david%20vizard%20plenum%20chamber%2
0size&f=false
And also here:
http://www.gmh-torana.com.au/forums/topic/34855-intake-manifold-design/
[Edited on 29/9/14 by Ivan]
quote:
Originally posted by 40inches
What would be the effect of changing the inlet from a single throttle body, with runners to each cylinder, to a single throttle body with a single plenum chamber feeding all the cylinders?
quote:
Originally posted by MikeRJ
quote:
Originally posted by 40inches
What would be the effect of changing the inlet from a single throttle body, with runners to each cylinder, to a single throttle body with a single plenum chamber feeding all the cylinders?
If you are running a single throttle body then there will be a plenum in either case, so not sure that's relevant? Shortening the runners between the port and the plenum will lose torque at lower RPM, and possibly gain you a little power at higher RPM provided the new induction system still flows well (i.e. no runners with sharp 45 degree bends in them).
The Jag induction is still a plenum system, but because the runners themselves have significant volume the plenum volume can be smaller.
Most production cars have the longest possible runners within the given space to enhance low/mid range torque, in fact some of the small VAG engines
have the runners coiled like a snail within the plenum to get the greatest length in the smallest space.