Interesting question for those inclined..
 

Is the placement of the throttle body important before or after the plenum??

The reason why i ask this question is from a conversation from someone today...

If the TB is before the plenum and runners then when this opens the plenum is flushed full of air which enters the heads. I.e the air is pushed into the heads..

However if the TB is after the plenum and runners i.e in the TGVs then does this defeat the purpose of a plenum, as the plenum and runners arent able to push the air but infact suck air into the heads??


So would this mean that it would be better to have just a plenum with the shortest amount of runner length??

I hope i explained it properly??

your intercooler and pipework practically become your 'plenum' prior to your throttle body (while your throttle is open).

under load, these are under pressure, and a 'plenum' provides no advantage for 'charged applications.

If my TBs are much further down the line does this mean my runners now also become my plenum??

If you put the TB in the exhaust tip, your exhaust then becomes your plenum.

Yeah i get that..

However, normally when you open the TB the air rushes into the plenum and runners. But now that ive got the TB in the TGVs the plenum will already have air in it, and all a very small section of the TGV will be forced with air..

Is this a disadvantage?? Or does it matter??

under manifold positive pressure it makes next to no difference.

By having a very short intake runner/plenum ie. at the TGV's it makes the drivability and idle a little more erratic. The intake pulses will be very noticeable and may cause a few challenges for your tuner, only at low rpm were the throttle blade is partially open. The air velocity will not be constant and scavenging of the cylinders will be compromised. At idle boost is pretty neglible and the engine will rely on its abililty to scavenge the cylinders to run 'smooth'
Just out of curiosity my TAFE lecturer designed an intake manifold that was about 20ft in total. The idle on it was so smooth and the drivability was very good. Totally impractical but he was a bit weird... Just wanted to prove that the longer the runner after the throttle blade the smoother the engine actually ran...
My 2c...

^^^^

Thats an interesting question you pose.. I was trying to get better driveability with a quad TB setup as i thought using smaller butterflies 4x i.e 50 mm in the TGV instead of a large 80mm at the begining of the plenum would make the car more driveable..

But what your saying that this may not be the case now as it may be harder to scavenge with a shorter path?? i.e there is only around 50-100 mm of runner to the heads after the TB...

You can fine tune a quad TB set-up a lot better with a lot of time and effort.
This is only going to smooth out the idle if the length of each runner prior to the TB (after the intake valve) has a larger volume than the cylinder it is filling.
I don't claim to be guru swami about this but it is definitely true on the NA engines that I have dealt with, and I would have to say that the same principle would apply at idle.

My opinion:
having quads closer to each intake port simply decreases the time air takes to get from the throttle body when opened, into the heads. very popular in the NA world when you get instant response, but as mentioned above, you constantly have air pushing on the throttle body so it doesn't make as much of a difference. i genuinely don't think you will notice any difference between some fandangled custom manifold and a stock one if it sits in a workshop for months on end. I know mine feels almost as fast as it did 6 months ago :P