Cute little throttle body

[zps2004]

So last night I was working on the 2 and I got a good look at the throttle body. It is so tiny. I doubt that it is a restriction for the intake given how our cars flow so well up top. It is just one of the smallest I have seen in the US. It is in the range of 1.5"-1.75". Given how it is so small I wouldn't be surprised if there was a larger option which would bolt in. Again I don't think there would really be any gains there, but I figure I might just look into it to see. Anyone knows what one of the Mazda 3 throttle bodies look like?

 

[BRIAN_MP5T]

Probably comparable to the 60mm that is on the Protege if not a bit larger due to the 2.3L Displacement.

I find it unlikely that you will find a "Bolt On" that will let you run the stock ECU. You will need to find a "Fly By Wire" TB and I cant see that the Mazda 3 and Mazda 2 TB would operate identically.

 

[magnumP5]

A larger throttle body would be unadviseable unless you're increasing the amount of air entering the intake. For best power you want the highest possible intake air velocity and by increasing the TB diameter you'd be reducing the velocity unless you increase the mass of the entering air. This can be accomplished through forced induction (turbo/supercharging), increasing displacement, or even improving exhaust flow (although to a much lesser extent).

 

[zps2004]

Smaller TB size to get a higher velocity to get more power is way oversimplifying what is going on. Smaller will give you a higher velocity through the TB, but if that restricts the top end, then it isn't really going to help with more power it helps with low or midrange torque. Look any any non LS current GM vehicle intake manifold. Plus you want the velocity going into the cylinder to be higher to get more air in there. There is a long distance between the TB and the head for velocity to change. I am sure that the intake manifold is sized to hit a certain resonance between the back of the valves and the TB as well

As I said the engine flows well on the top end so I really don't think it would make a difference. Especially for the power output of the car it shouldn't be. I just figure it would be something to try once we have the tuning to make the idle play nice.

 

[magnumP5]

Smaller TB size to get a higher velocity to get more power is way oversimplifying what is going on. Smaller will give you a higher velocity through the TB, but if that restricts the top end, then it isn't really going to help with more power it helps with low or midrange torque. Look any any non LS current GM vehicle intake manifold. Plus you want the velocity going into the cylinder to be higher to get more air in there. There is a long distance between the TB and the head for velocity to change. I am sure that the intake manifold is sized to hit a certain resonance between the back of the valves and the TB as well

As I said the engine flows well on the top end so I really don't think it would make a difference. Especially for the power output of the car it shouldn't be. I just figure it would be something to try once we have the tuning to make the idle play nice.

It was an oversimplification but I never stated it as being that simple in the first place. Without looking at the actual design I'm sure the diameter was sized to produce the opitmum power/torque curve for city driving. As you said there are also a lot of other things to take into consideration like intake manifold runner length for resonance tuning but the simple fact is the engine can take in no more air than the TB allows. That being said, if you slow the intake air velocity to a crawl with an overly-large TB no amount of resonance tuning will help. You said it yourself these cars don't appear to suffer from top end starvation so why bother with a larger TB that won't provide any top-end benefit while hurting the bottom end? Of course this argument goes out the window if you're considering other engine modifications.

 

[PGTBrow]

A bigger TB would be nice, but as stated above, needs to be complimented with other mods. I know when I put the 67mm TB and ported out JSPEC IM on my Probe it opened it waaaayy up.

 

[CRG Racer24]

If you wanna do something to your throttle body, and getting a bigger one isn't an option, or you just don't have/don't want to put the money in, you can just optimize the stock throttle body... i.e. Knife-edge the butterfly valve, shave down the counter-shaft (I think that's what it's called lol), countersunk screws, etc. Stock throttle body, with better flow properties.

That was a big thing to do in the CDW-27/Contour world when I owned one before. Definitely made a difference in response

 

[Wall Of Death]

keep in mind porting or swapping throttle bodies will also require port matching the manifold.

 

[CRG Racer24]

No need for portmatching an intake manifold with what I'm talking about:


IMG01601-20130221-2025 by Alexander D.24, on Flickr

 

[Mazda2sp]

The correct size of the throttle body is 2.25 inches and it is more than enough , i'm currently turbocharging my 2 not cosidering any mod to the TB unless installing an aluminuim inlet manifold , which is not feesable at the moment

 

[AN7]

The ID of the TB is around 38mm, sadly I don't remember it exactly.

 

[zps2004]

AN7 beat me to it. The OD is 2.25", but the ID is much smaller. From what I remember the screws are countersunk.

 

[xyrth]

Sizing a TB is like sizing injectors. you want it big enough to support the engine, but small enough so you keep resolution. air velocity has next to nothing to do with it, there is an intake manifold and head after the TB that handles that.

You'd be surprised how little effect tuning up a TB for ideal flow has on flow through it. It's turbulent as hell, having some random smooth edges in there does next to nothing.

 

[magnumP5]

Sizing a TB is like sizing injectors. you want it big enough to support the engine, but small enough so you keep resolution. air velocity has next to nothing to do with it, there is an intake manifold and head after the TB that handles that.

You'd be surprised how little effect tuning up a TB for ideal flow has on flow through it. It's turbulent as hell, having some random smooth edges in there does next to nothing.

You can't completely separate intake velocity from TB size. Where does the air in the intake manifold and head come from? What enters the engine has to go through the throttle body. For the type of flow we're dealing with (sub-sonic, essentially incompressible) velocity is inversely proportional to area. So if the TB area is very large the inlet velocity will be very low. Too low and no amount of intake manifold runner length/diameter tuning or head work will make up. If the area is very small velocity is up but you limit the amount of air into the engine and no amount of head work or intake manifold tuning can increase the mass of the air entering the engine.

 

[AN7]

You can't completely separate intake velocity from TB size. Where does the air in the intake manifold and head come from? What enters the engine has to go through the throttle body. For the type of flow we're dealing with (sub-sonic, essentially incompressible) velocity is inversely proportional to area. So if the TB area is very large the inlet velocity will be very low. Too low and no amount of intake manifold runner length/diameter tuning or head work will make up. If the area is very small velocity is up but you limit the amount of air into the engine and no amount of head work or intake manifold tuning can increase the mass of the air entering the engine.

+1000

 

[xyrth]

You can't completely separate intake velocity from TB size. Where does the air in the intake manifold and head come from? What enters the engine has to go through the throttle body. For the type of flow we're dealing with (sub-sonic, essentially incompressible) velocity is inversely proportional to area. So if the TB area is very large the inlet velocity will be very low. Too low and no amount of intake manifold runner length/diameter tuning or head work will make up. If the area is very small velocity is up but you limit the amount of air into the engine and no amount of head work or intake manifold tuning can increase the mass of the air entering the engine.

so, what you're saying is that with a 3", or hell, 4" TB on a small engine like ours you think it would lose power?

 

[Wall Of Death]

so, what you're saying is that with a 3", or hell, 4" TB on a small engine like ours you think it would lose power?

I think you are missing the point. At a certain point your reach the law of diminishing returns, and you will simply not may any additional power by going larger. Intake air velocity is just as important as exhaust velocity, which is why it is not uncommon to see the venturi effect utilized in intake and exhaust designs. In the case of most throttle bodies a tapered primary port increases intake velocity.

 

[magnumP5]

so, what you're saying is that with a 3", or hell, 4" TB on a small engine like ours you think it would lose power?

Overall? No, not likely unless you get to very large TB diameters. What will happen is you'll start to lose low-end power and torque, unless you add some means of compensating for the reduction in velocity (e.g. forced induction). Think of it the same way you think of exhaust diameter. Eventually you can get to a point where you've moved the peak power and/or torque points outside of the engine operational range.