throotle body modification or switch - PeachParts Mercedes-Benz Forum

RBYCC · #1 01-23-2012, 11:43 PM

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Originally Posted by MAG58

lolwut? I'm in for an explanation of how increasing the plentum volume post throttle valve increases air quantity.

Why explain something so basic......

If you increase "plentum" ( your spelling ) volume then by definition it increases air quantity or amount.
So let's define the words....isn't volume the amount of space occupied by a three dimensional object such as a plenum ? And doesn't "amount equate to "quantity" ?
You may be confused with air flow or CFM which isn't altered and I didn't mention.

TB spacer increases the plenum volume of the intake manifold.
This gives the engine a larger plenum to draw its air from at each firing cycle, so velocity in the intake manifold is increased, because it no longer has to rely as heavily on the throttle body for air at each given firing cycle.

What do I know, unlike you I'm new at this, so don't believe me, just read a few SAE papers on the subject.

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Except in a carb there's fuel flowing past the throttle valve. That's kind of a big difference.

Once again you're correct, forgive me for being simplistic in a world that is so complex...

MAG58 · #2 01-24-2012, 02:12 AM

Quote:

Originally Posted by RBYCC

Why explain something so basic......

If you increase "plentum" ( your spelling ) volume then by definition it increases air quantity or amount.

Never seen someone get so unprofessionally defensive so quickly, especially someone who so sarcastically attempts to be as old, seasoned, and well adjusted as yourself.

First, I did not dispute that it increased plenum volume; I also didn't say that it had any positive or negative effects on power (though it's discussed later).

To start, you said that a spacer increases:

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amount of air that the throttle body flows to the intake.

Which in the purest sense, it does not. A throttle body that has X diameter, will only flow a certain amount of air at a certain velocity, increasing until the air goes supersonic, and then a whole set of rules applies. You already knew this. If an engine requires 100Mol of air, a spacer after the throttle body isn't going to make that same throttle body now pass 105Mol of ambient air through it. The only thing it will do is reduce the % of the plenum that is reduced at each individual intake event. That just means that there is more time per intake stroke to replenish the lost air. Given that during one revolution of an engine, the amount of volume removed from a plenum stays constant independent of plenum volume. This also means that the amount of air the throttle body has to flow is also independent of plenum volume.

Since you were very quick to tell me to go look in peer reviewed journals, but were so slow to post one yourself, here:
http://muhserv.atauni.edu.tr/makine/akifceviz/pdf_files/A/e.pdf

Now if you'll investigate Figure 8, you'll find that this manifests itself as a decrease in pressure drop as the plenum volume increases.

You said:

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so velocity in the intake manifold is increased

Now given that the published paper states that the engine has a higher manifold pressure (less pressure drop), Bernoulli's principle states (from wiki):

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In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

Now that means that an increased plenum volume will actually decrease velocity of the air flow. Either that, or a whole bunch of airplanes have been flying on voodoo and prayers for a century now.

This means that it does nothing to increase the flow of the throttle body. What it does mean is that given a lower intake velocity, there is more time to replenish the air in the plenum. It still has to flow the exact same amount of air. Call it Mol, Kg, lbs, what ever else floats your boat.

Let's recap:

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This gives the engine a larger plenum to draw its air from at each firing cycle

Correct

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so velocity in the intake manifold is increased

Incorrect

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because it no longer has to rely as heavily on the throttle body for air at each given firing cycle.

Not sure what you mean by this one. It still relies on the throttle body, but the rate changes. I'll go halfsies?

Edit: let's even do some maths:
On your example, an LS2, the throttle body is 90mm in diameter. Given that the spacers appears to be 1" in length, you've achieved a 161.59 cm^3 increase in plenum volume, or approximately 2.7% of total swept volume.

To achieve results, the test engine was a FSAE 600cc engine (see sources 11,12) and they used either a 90cc or 180cc (cm^3) increase in plenum volume which equates to either 15% or 30% of the swept volume, respectively. How much effectiveness would you see on a spacer that is between 5 and 10 times smaller? Now this does not take into account the overall change in volume of the plenum as a percent of the original. Though on page 3 (963) he does state that:

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There was a reverse effect on engine performance
after attaching additional volume from this point.

Which means, past a certain point, increasing plenum size is detrimental to performance. Bigger =/= better.

As far as the carb comment, you said:

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The TB on an injected car functions no differently then the throttle assembly in a carb.

In reference to using a throttle body spacer. I'm sure you're well aware of the fact that carb spacers are just as much to do with getting equal mixture distribution as it is plenum size (no really, I'm sure you do now that). So if you're saying that the throttle body and the throttle plate on carbs function similarly, than yes. However if you're saying that the spacers serve equal function, the point I thought it sounded like you were attempting to make, than no.

RBYCC · #3 01-24-2012, 08:08 AM

When you grow up and stop being so juvenile then perhaps we can discuss whatever you want....LOL

Google and Wiki seem to be your sources and we "adults" know how accurate Wiki is.....

Those who melt pistons and trash motors while doing finite calculations know much more then I do....and in the end you still have a vehicle that has no value and only appeals to other juveniles !!

A dyno pull on my LS2 proved the TB spacer install gained 7HP and 11Torque...but why use anything other then the SOTP dyno that you're familiar with..
So as I laugh out loud, I'll leave all the expertise on this thread to you..

I need not to prove myself as you desperately seem to do... so the thread is all yours !!!

MAG58 · #4 01-24-2012, 11:10 AM

Quote:

Originally Posted by RBYCC

Google and Wiki seem to be your sources and we "adults" know how accurate Wiki is.....

It's a peer reviewed journal, and wiki quoted a pair of text books. What's wrong with those sources? The paper sourced many different peer reviewed journals, some even published in SAE that I don't have access too, since SAE requires 15 bucks every time you read one of their publications

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Those who melt pistons and trash motors while doing finite calculations know much more then I do

I've never melted a piston.

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A dyno pull on my LS2 proved the TB spacer install gained 7HP and 11Torque...but why use anything other then the SOTP dyno that you're familiar with..

Congrats. You've yet to do anything but believe I'm just supposed to accept what you say as fact. I've never said anything was to be taken as fact on my car unless I have dyno numbers to prove it.

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I need not to prove myself as you desperately seem to do... so the thread is all yours !!!

For someone who doesn't need to prove themselves you did take a good bit of time reminding me why you're better than I am. Anything else I do that really annoys you? Might as well get it out. Have an actual source other than you getting angry? I'll be glad to concede that I'm wrong.