Redneck Truck

While I'm aware of the benefits of a variable intake manifold, I'm curious how the E39 M5 makes such great low-end torque with individual throttle bodies.

Eight 1" throttle bodies have the same gross cross-sectional area as one 70mm throttle body, though the actual proportion might vary due to having 8 times the hardware in the path of the air.

What are the arguments for and against such systems? Also, how about using ball valves instead of butterfly valves? Seems like most of the benefits are in high pressure differential systems.

2.7Lturbo

cross sectional areas are only one aspect to look at, airflow patters are another big aspect as well that factors in. bottom line is that the one TB may have the same cross section as 8 individuals, but that air is forced into an intake manifold that then forces it into smaller inlet ports to the head, leading to flow issues and pressure increases.

Redneck Truck

I have to wonder then how BMW achieves it on the M5. Who's to say the same manifold couldn't exist before 8 throttle bodies rather than after a single one?

2.7Lturbo

does the m5 have the itbs going directly into the head or into a manifold? usually ITBs go directly into the head

Redneck Truck

On the motorcycles I've seen, there was a very small manifold that housed the injector between each throttle body and the head, and a velocity stack on top of each throttle body. Before the throttle bodies, there was an air box and a duct that together acted as a plenum and probably influenced intake resonance and momentum.

As for the M5, I don't know.

rs4-380

Throttle response is much quicker with ITB's, E39 itbs are direct-to-head with a shared plenum. Power delivery can be tuned by the length of the velocity stacks. Shorter stacks will give better top end, longer will give better low end. That is one reason it is hard to fit itb's in a daily/street driven car, because you need relatively long velocity stacks. If you look at an e39 m5 with the plenum cover off you will see how they have snaked the velocity stacks in order to achieve the desired length.

JediJoker7169

Don't forget the M1, E24 M6(35CSi), and E28 and E34 M5s, with the various evolutions of the M88/S38 i6, which had individual throttle bodies and a shared plenum. Same with the E30 M3's S14 i4. Admittedly, they do not make the same kind of low-end torque as the S62, but the M88/S38 comes close.

2.7Lturbo

a shared plenum is not as much of an issue before the throttle as it is after

lastls1

Ahhhhhh......Weber down draft carbs.....A thing of beauty. The racers choice.
Very much like an ITB per cylinder.
Butterflies....YES. History has proved them to be the item of choice.
Ball valves?? Only for plumbing. Too much mass to move quickly.
Plus you has the "sync" problem. All have to flow the same amount of air as they open and close, based on throttle position. Many bikes with a side/downdraft carb per cylinder need to be synced occasionally. See Honda ST1100.

Redneck Truck

Once the throttle is wide open, what difference does it make where in the tract it is located?