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Old 03-06-2014, 07:34 PM   #81
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Originally Posted by goingtoscotland View Post
And you have a complete misunderstanding of fluid dynamics and how they come into play in a restriction

That's static air pressure(at sea level), and has nothing to do with velocity or volume. Not sure where you're even going with that? If you take a throttle body and reduce the size of the venturi you will increase pressure(prior to the venturi), lower pressure IN and after the venturi , increase velocity, and decrease the maximum amount of air that venturi is capable of flowing in whatever measurement you decide to use. Should you increase the size of the venturi you will DECREASE PRESSURE(before the venturi) AND VELOCITY, and INCREASE VOLUME. Higher velocities=lower volume. Smaller opening=higher velocities.

So yes. a larger opening will increase volume, but pressure isn't involved in the way you think it is.

A larger TB on an FI car will net you good gains because it produces WAY more suction than an NA motor.

Where does pressure come from?

Again, you're forgetting variables.
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Old 03-06-2014, 07:44 PM   #82
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In this case, pressure has nothing to do with atmospheric pressures. The pressure in this case is suction caused by the vacuum the piston creates on the intake stroke.

I agree with you, yes a larger opening will result in more flow(less air pressure, though), but you don't understand why. That much is clear when you're citing atmospheric pressure as a reason.
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Old 03-06-2014, 07:46 PM   #83
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What does a MAF measure?
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Old 03-06-2014, 07:52 PM   #84
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The density of the intake charge, in the middle of the restriction(whether in a flow tube or on the TB itself(rare)) where pressure is the LOWEST.
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Old 03-06-2014, 07:54 PM   #85
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I give up.
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Old 03-06-2014, 07:57 PM   #86
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Atmospheric pressure is actually a pretty big deal for n/a engines, especially considering the fact that suction doesn't actually exist in the way that most people think does.

The Ti-VCT responds very well to simple bolt-ons and reductions in intake restriction. I would not be surprised to see a gain with the larger TB, though I don't think it will be a decent cost-per-HP gain.
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Old 03-06-2014, 07:59 PM   #87
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If you were trying to get me to say that the MAP measures atmospheric pressure, I won't because it doesn't.
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Old 03-06-2014, 08:11 PM   #88
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Quote:
Originally Posted by goingtoscotland View Post
If you were trying to get me to say that the MAP measures atmospheric pressure, I won't because it doesn't.
The Focus N/A engine uses a mass air flow sensor, which uses a hot wire film to measure the air flow based on a voltage change across it.

However the Focus ST does directly read absolute pressures using a Manifold Absolute Pressure Sensor, well technically three as part of it's speed density system.
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Old 03-06-2014, 08:18 PM   #89
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I have to say that as a former student of fluid dynamics and temperature related sciences this thread is making my head hurt. If you are unsure about what it is you are talking about...please don't.

Actually the map sensor will measure atmospheric pressure, if there is an absence of vacuum and or boost pressures inside the manifold...
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Old 03-06-2014, 08:29 PM   #90
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I read MAP for MAF, my mistake. Anyway, yes, a MAF measures the volume of air and accounts for density to meaure engine load as well

However, basically all you have done so far is use some half assed attempt with a static atmospheric pressure and in general been a douche. So how about you elaborate on your one liners and tell me why you think a larger throttle body will vastly improve performance, even if the stock TB is not a bottleneck. You could put a 150mm TB on it and it wouldn't make a difference, there's only so much air the manifold and valves in the engine can accommodate before you start artificially pressurizing the intake with forced induction.

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Quote:
Originally Posted by dyn085 View Post
Atmospheric pressure is actually a pretty big deal for n/a engines, especially considering the fact that suction doesn't actually exist in the way that most people think does.

The Ti-VCT responds very well to simple bolt-ons and reductions in intake restriction. I would not be surprised to see a gain with the larger TB, though I don't think it will be a decent cost-per-HP gain.
It most certainly does. The denser the ambient air is, the more oxygen enters the engine for a given volume of air. However, it does not matter in the way he thinks it does. He's stating static atmospheric pressure acting on a surface in the vertical somehow directly relates to the flow of a fluid being forced through a restriction. That is not how it works, and regardless of pre-restriction pressure, pressure will always drop in the middle of that restriction. The larger the opening the less the pressure will drop, the smaller the opening, the more the pressure will drop, but only in the middle of that restriction.

And yes, it's not actually SUCKED IN, as higher pressure moves to lower pressure. In a carburetor for instance fuel isn't sucked out of the float bowl by the low pressure in the venturi, it is forced out because the float bowl is at a higher pressure than the venturi is.

Quote:
Originally Posted by GhostTribute View Post
I have to say that as a former student of fluid dynamics and temperature related sciences this thread is making my head hurt. If you are unsure about what it is you are talking about...please don't.

Actually the map sensor will measure atmospheric pressure, if there is an absence of vacuum and or boost pressures inside the manifold...
Indeed it would, but it's all in the application That is why the two sensors for Inlet Air Pressure and Ambient air pressure are usually the same part number on motorcycles. They have a vacuum hose nipple on the sensors, but only the IAP vacuum hose actually attached to anything which leads to the throttle bodies after the throttle valve. The atmospheric sensor vac hose just dangles there.
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