Intake manifold design.

[Kurtisja]

So recently I've been looking very closely into Intake manifold design.
I know basically the effects of changing plenum size/runner length/runner size etc. But there has been one question that has been bugging me.

Obviously a bigger throttle body will allow more air into the plenum , allowing more air flow at high RPM. When using an OEM manifold, obviously you need a throttle body which will attach to it. BUT, if someone was to say, make a custom manifold, instead of sourcing an expensive bored out throttle body from tuners such as Dinan, why not just use 2 smaller, stock throttle bodies??

For the sake of this discussion assume there is an MAP sensor not an MAF sensor (as the MAF is likely to be the major blockage for air flow, not the TB).

But am I missing anything here? and as an extension of this idea, the more throttle bodies there are, the larger the plenum will seem to the engine? and vice verser?

[Rudolph320i]

well for starters, the MAF isnt exactly a restriction, you could likely use two throttle bodies but they would have to be sync'd or your computer would have to deal with two inputs from throttle position sensors.

[slocar]

well for starters, the MAF isnt exactly a restriction, you could likely use two throttle bodies but they would have to be sync'd or your computer would have to deal with two inputs from throttle position sensors.

I'm thinking that as long as they were in sync (in other words driven by maybe some sort of axle type setup), that only one TPS would be fine.

[Rudolph320i]

I'm thinking that as long as they were in sync (in other words driven by maybe some sort of axle type setup), that only one TPS would be fine.

Thats what I was thinking, you would have them connected and locked together. Im just not totally certain what this would do to vacuum. I know ford did something like this back in the 80s and 90s with the 5.0. Truck engines had a split intake track after the MAF into 2 throttle bodies then into the intake manifold.

[BimmerBreaker]

Very interesting idea

Im not really sure the practicality of it though. I guess it depends what the engine is going to have done to it but for a N/A build a single throttle body is usually more than enough. You would also have to start considering things like turbulence inside the manifold from two separate air inlets which may rob high rpm power. Its hard to say for sure without having done it, but if your custom building an intake, you almost may as well try it. I dont see it being worse than stock, but it may not be better than going with a single bored out tb.

If you are really good with it you could basically re-create a DISA valve using two separate throttle bodies if you could tie one to RPMs somehow and build the intake manifold to work with it. That would be really cool.

[slocar]

^ The m42/m44 have a TB setup that has 2 butterflies http://www.ecstuning.com/BMW-E36-318...ntake/ES34130/

The small starts to open first and then as it passes about the half way point, the large one starts to open ... weird setup but it works I guess. BMW literature said something about smoothness at low rpm or whatever .. who knows.

[Rudolph320i]

^ The m42/m44 have a TB setup that has 2 butterflies http://www.ecstuning.com/BMW-E36-318...ntake/ES34130/

The small starts to open first and then as it passes about the half way point, the large one starts to open ... weird setup but it works I guess. BMW literature said something about smoothness at low rpm or whatever .. who knows.

sounds like a pretty similar theory as with 4 barrel carbs. smaller primaries for throttle response in the low end and large secondaries for flow up top.

[BimmerBreaker]

Its a dual runner design like a DISA valve. The longer intake runners are used down low for torque where immediate air is necessary, at higher revs fast airflow is more important so the DISA (or second TB) opens to create a shortened path for the intake air to take. Its not really necessarily about smoothness, but it does a lot to maximize power over the entire rev range.

[Rudolph320i]

Its a dual runner design like a DISA valve. The longer intake runners are used down low for torque where immediate air is necessary, at higher revs fast airflow is more important so the DISA (or second TB) opens to create a shortened path for the intake air to take. Its not really necessarily about smoothness, but it does a lot to maximize power over the entire rev range.

ahh yea, different length intake runners can do wonders, especially for a smaller engine. but back on topic, I honestly think this could be done, im just not sure if there would be any real gains from it