I read that the C5-R has this mutiple throttles and so are the BMW's M's.....

What are the advantages of this setup over a single throttle butterflies like a C5 or C6?

 

Nobody knows nothing about this topic?

Hard to believe!!!!!

 

Yes the C5-R uses a throttle setup similar to the old Hilborn ijection. Pretty much all of your high end F1 engines, IRL, Cart engines will use a multiple throttle setup. These are just another way to tune an engine. changing runner length and throttle size will move you power curves around. The main difference between this type of setup and say a single 4 bbl is that the throttle plates tend to be much larger than what you would believe to be correct. On a typical small block you might use 8 - 2 to 2.125" throttle blades on a hilborn style intake, where as the 750 holley only has 4 - 1.75"(not sure of stock 750 blade size this is just a guess) throttle blades.

Hot Rod did a tech write up on a hilborn injection system sometime ago, you might be able to find the article. They played with the stacks to see what would happen to the engines power. Also check out Hilborns website and Ingleese. Both of those companies make multi throttle/carb setups.

 

In answer to your original question of why racers use individual throttle bodies... Production engines use a shared plenum with single throttle body, where all the cylinders can influence the others. The engine becomes very sensitive to the amount of overlap the camshaft has. When the throttle is closed you have a high vacuum situation where at least one cylinder is drawing on the intake and another cylinder is in overlap. The engine will literally suck exhaust back into the plenum (reversion), which does two very bad things. It heats the intake charge and it displaces air/fuel charge with non-combustable gas. This reduces volumetric efficiency and increases the engines sensitivity to detonation. It's exactly the same thing as Exhaust Gas Recirculation (EGR) under cruise conditions, decreases emissions and improves fuel economy, because there is less air/fuel charge to burn.

Independent Runners (IR or individual throttle bodies) prevent this by isolating each cylinder from the common plenum. The result is dramatically reduced reversion and an engine that is much more tolerant of extended valve overlap and increased compression without degrading low speed operation. Okay, so much for the general overview.

So what's it worth? For that I'm going to point you to an SAE paper (960580) by R.L Duckworth and L. Baker of Cosworth Engineering. In it they worked with two 2 liter engines. One had variable valve timing (VVT) and EGR, the other had IR with barrel throttle bodies, a long overlap cam, and no EGR (except for what occured during overlap - Internal EGR or IEGR). The result was pretty close to the same torque curve and emissions with greater top-end horsepower for the IR engine. There were some dips in the torque curve that they attributed to harmonic pulsing that they believed could be overcome by further tuning the intake tract length. Obviously, this was a pitch to engine manufacturers with older engine designs that can't accomodate VVT, (like our common int/exh camshaft engines), to have Cosworth develop an IR intake package.

You can get an idea of what effect this would have on your Corvette engine if you have Desktop Dyno and use an IR intake, (Be sure to jack the CFM of the throttle body way up - it's usually 330-400 cfn per TB or 2650 CFM total.)

The final benefit of IR is directly dependent on how close the throttle body is to the intake valve. One of the reasons that intake volume is critical to throttle response on shared plenum designs is that the intake tract is very long. With an IR you can make the intake volume in the head much larger w/o sacrificing throttle response. So you get the benefits of greater flow for top-end and the engine can quickly accelerate. Something that is very important when trying to pass another car coming out of a corner.