turbocharged inlet manifolds

In your scenario the pressurized air would be closer to the valve than one where the throttle is in front of the plenum. This would seeem better for transitions.
However if the throttle is round and the head's intake port is oval you have the issue of rapid aspect ratio change in the runner which is not good.
So, has anyone done this?

Hi,

Ive been considering this, Im in the process of turbocharging a 20v 4AGE toyota, which come stock with individual throttles as you describe. My thoughts are that individual throttles give better response, and the only reason i have abandoned them is because you can get a better MAP signal from having a single TB.

Nick

the MAP sensor was one of my concerns actually. what the usual procedure with multi throttles? do you take a vacume/presure feed from behind each into a common chamber and feed your MAP sensor from this to get an average?

The only option with multi throttles is an Airflow Meter setup.

On most aspirated cars they can get away with it by tuning the engine off throttle position instead of MAP or Airflow meter.

This is exactly why you will see a lot of GTR skylines fitted with aftermarket Airflow meters or even twin airlfow meters when they have been seriously modified. GTR skyline engine have a one throttle per cylinder setup as factory fitment.

G-Reddy actually make a single throttle body replacement manifold for the GTR which allows the use of a MAP sensor.

ok.

you said you see a lot of skylines fitted with airflow meters, do you mean by this they are not fitted as standard. what do they use as std?

sounds like a plenum/MAP set up is the best method then when turboing.

I guess it all depends on the final application of the engine, and what is most important to you. multiple throttle bodies are going to give crisper throttle response, and so should a MAP sensor. However an airflow meter is going to give far better control of mixtures at very light throttle opening, such as on a road car.

A map sensed car is also going to be very sensitive to engine tune. It assumes a certain airflow at a certain inlet manifold pressure, but if there is any small change to valve timing or exhaust back pressure, you are going to have to go back and re map it. On the other hand going rapidly on, and off full throttle, a map sensor is going to respond faster than an airflow meter mounted a long way upstream of where the action is. This can be a problem with massive intercoolers and long induction pipework.

An airflow meter corrects for changes in engine tune to a certain extent, more/less airflow adds more/less fuel, so if you expect it to stay in tune over long periods, an airflow meter might be a better choice, if you do not have your own dyno.

Both setups have pros and cons I personally like the single TB due to less turbulance in each runner/port then with a TB in the runner(less turbulance = more flow). The single TB has this problem also but is away from the area I regard as more important(the runner/port area). The multi TB setup gives better throttle response due to the considerably smaller volume the air needs to fill until it reaches the valves.