Do ITB's really make more power

[Massimo]

So I have been wondering for sometime now do ITB's actually give you any advantage other then quicker response.

You see posts all the time when someone goes from a stock intake to ITB's they always see increases, but I believe this is due to the change in runner lengths and plenum design.

If you had to setups exactly the same runner length and size, and the exact same plenum chamber, the only difference is one has ITB's while the other has a single throttle body before the plenum. Would the peak power and torque be the same?

I believe they would be and can not see any reason why they would not be the same.

[SkiFree]

Would the peak power and torque be the same?

I believe they would be and can not see any reason why they would not be the same.

Whole lot of supposition here. Hopes and beliefs are one thing, going out there and testing it in the real world is another. We can debate all day here and it still wouldn't solve anything.

Have enjoyed watching this unfold.

http://www.e30tech.com/forum/showthread.php?t=118357

[Massimo]

^

Yeh that is what I would of thought as well shorly someone has tested this though

[SkiFree]

^

Yeh that is what I would of thought as well shorly someone has tested this though

True, would be interesting.

[reelizmpro]

Maybe someone with a Dbilas M20 setup can chime in.

[Raxe]

They do make more power, but only if you build it correctly and tune/modify accordingly. Like any induction modification they need to be specially suited for the application if you want to see positive results. You can see a fairly significant increase in volumetric efficiency if the plenum shape and sizing is done right, but that's not something you'll usually get from just bolting on an off-the-shelf application.

Most people just do it for the sound and the cool factor.

[Mr_Tripp]

Just shooting of the top off the dome but how about the M30 vs. S38 can all that power come from one more cam that may support your itb theory? Idk if I'm just really off or not

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[totheredline]

Honestly, the sound alone is reason enough to justify an ITB setup. Bike throttle bodies can be had for relatively cheap and then from there a bit of fabricating. Perfromance gains are just a bonus :)

Read through this thread, some good info.
http://www.e30tech.com/forum/showthread.php?t=118357

[reelizmpro]

High flow engines that need to breathe benefit the most. 4 valve per cylinder high output m engines certainly need them if not turbocharged. Itbs on an eta would probably rob power. Itbs if not open trumpets typically have large volume intake plenums as a buffer of sorts. The s14 on alpha n is a different beast with no flapper door afm choking it. The afm is one of the most overlooked differences between say s14 and s50.

[BlackbirdM3]

High flow engines that need to breathe benefit the most. 4 valve per cylinder high output m engines certainly need them if not turbocharged. Itbs on an eta would probably rob power. Itbs if not open trumpets typically have large volume intake plenums as a buffer of sorts. The s14 on alpha n is a different beast with no flapper door afm choking it.

On the same note, an S38 with a carbon air box and Alpha N would be pretty awesome.

Will

[Massimo]

Seems we are getting a bit lost here lets not consider the engine just the intake if is all exactly the same and the only difference is that one has a single throttle body over the ITB's I seem them making the same peak power.

The way I see it is that they would both supply the same volume of air at the same speed despite where the throttle body is.

[Raxe]

Seems we are getting a bit lost here lets not consider the engine just the intake if is all exactly the same and the only difference is that one has a single throttle body over the ITB's I seem them making the same peak power.

The way I see it is that they would both supply the same volume of air at the same speed despite where the throttle body is.

6 smaller throttle bodies with trumpets can fill the cylinders more effectively than 1 large throttle body. More air being crammed in the engine at high RPM = more power.

Edit: reading your first post that scenario makes no sense, you wouldn't have the exact same runners/plenum for two different throttle setups. Each type has different requirements. :???:

[BlackbirdM3]

Lets look at it this way. Take for example a stock Datsun 510 (or 1600 in the land down under). It came with a single barrel carb from the factory here in the states, and was a dog. The upgrade was to get a pair of SU carbs from the non US spec cars and it was an instant power gain, and then if you make the step to a set of dual Mikunis or Webers with two barrels per carb (effectively individual throttle bodies) even more power is found. Also, with a super long runner for the intake, you lose velocity, and any turns it makes slows things down even more. With a good set of ITBs, the airflow makes one turn, where it enters the cylinder through the valves. More airflow, faster airflow with the least amount of turbulence makes all the difference in the world.

Will

[///schwartzman]

That's pretty much it. Not to over simplify, rather than have one large flap on a single throttle-body and large plenum with many twists and turns, the individual throttle bodies have independent length runners which can be "tuned," long for higher rpm breathing or shorter for a lower flatter torque curve. The key being the laminar flow of the air introduced and individual supply not interrupted (reversion) or competing for the same air as in a manifold plenum. The "trumpet" generally has a velocity stack that guides the flow to each cylinder which should've been pulse tuned if a factory part for a specific motor. You'd have to do 3-D modeling to find the most effective lengths etc. but in general a 4-8hp can be had per cylinder.

[ELVA164]

That's pretty much it. Not to over simplify, rather than have one large flap on a single throttle-body and large plenum with many twists and turns, the individual throttle bodies have independent length runners which can be "tuned," long for higher rpm breathing or shorter for a lower flatter torque curve. The key being the laminar flow of the air introduced and individual supply not interrupted (reversion) or competing for the same air as in a manifold plenum. The "trumpet" generally has a velocity stack that guides the flow to each cylinder which should've been pulse tuned if a factory part for a specific motor. You'd have to do 3-D modeling to find the most effective lengths etc. but in general a 4-8hp can be had per cylinder.

I was under the assumption that longer intake trumpets increase torque and shorter ones increase high-end horsepower. My only good evidence off the top of my head is the intakes for the can-am chaparral race cars were lengthened to increase and flatten torque.