yea it would be cool, someone do it

 

My understanding of ITB's is that they have quicker throttle response and allows for better idle/power with agressive cams. The reason for the quicker throttle response is due to the distance between the butterfly's and the intake valves. With a single throttle body there is a much greater distance between it and the intake valves. This requires a small amount of time for the incoming air to fill the vacuum in the intake.

The better idle is best explained by David Vizard from the book (How to Build Horspower, Volume 2)
"With an IR system, the vacuum created in the runner, largely exists only when the piston starts it's downward stroke. Prior to this, there is, compared to a plenum type intake, almost no vacuum existing in the intake port during the overlap period. As a result, reduced exhaust pollution of the intake charge occurs from this source. This means that the idle mixture used, can be much leaner as the fresh charge is more easily ignited. Also, the ill effects a big cam (ed - read a lot of overlap) can have on part throttle operation at low RPM, are substatially reduced. It is not uncommon to achieve a smooth 600 rpm idle on a V8 equipped with a moderate race cam. "

Now the book was for v8's but still applies. As far as making more power goes this is due to the cylinders being insulated from each other. When you have a standard plenum design with with a single throttle body the engine will pull a small amount of air from other cylinders during the overlap of the valves. Overlap occurs with larger cams when for a short amount of time both the intake and exhaust valves are open at the same time. The overlap creates a low pressue area which helps pull in the intake charge (aka scavenging). The intake charge is the Air or Air/fuel combination depending on your application. I should note that the other part of scavenging is from your exhaust pulses creating low pressure areas which help pull the next exhaust pulse out of the cylinder, but this is a whole other topic in itself. Pulling air from other cylinders creates an imbalence due to different cylinders running richer or leaner. This condition makes the engine work harder because you are not getting optimal combustion in every cylinder. Now as stated before this mainly happens with much larger agressive cams, for instance when vtec kicks in. Also due to the stock vtec cam design you will not really notice a difference in idle due to the smaller cam profiles.

The downside of having ITB's is obviously tuning them. To put it one way it is like tuning 4 engines instead of one, but not only that you have to get them to run the exact same. If for example there is too much play in the linkages connecting the butterfly valves then you could be off setting all the advantage of running ITB's and balencing the power production of the motor (ie one cylinder's butterfly being out of sync with the others making it not quite kick in at the same time). A ITB system is also a bit more finicky due to it needing a little more adjustment over time compared to a single throttle body.

Due take all of this with a grain of salt as it is just from what I remember reading and not from first hand tuning experience.

 

Good luck Fred! The whole thing about ITBs is that they just look so cool. Build a plexi plenum for bling! Hahaha.

 

And guess why all medium to big HP Skylines run a single TB set-up. And the difference between me and you is I see 20 skylines a day

 

I found these pictures here on the boards...so sorry you can't be the first


https://www.s2ki.com/forums/index.php?act=m...d=si&img=357602

 

wow thats insane

 

Well, I guess I'll be the second or third or whatever. In any case, this is the route I'm taking.

Does anyone have any info on that setup? That thing looks like it belongs in a F1 car. I would love to get some information on the plenum.

 

I'm not sure that there is much power to be gained by going this route. The smaller throttled volume will certainly have some effect on throttle response but unless the manifold/throttle body assembly is a better flowing design, I can't see much gains to be had.

I think a single larger throttle body and a manifold designed for FI (ie. one that sacrifices scavenging/resonance supercharging for all out flow) would be a better option. Cheaper, easier to tune, less restriction in the flow path

 

Only the dyno will tell, but I'll bet on a small top end gain and a large midrange gain. I'll also expect a better idle and throttle response.

 

If power is to be made, it won't be because of the location of the throttle bodies, but rather the design and performance of the manifold or a change in size or geometry of the intake runners.

But yes, only the dyno will tell.