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Discussion Starter #1
causes the engine to lose low-end Torque?
I've been feeling and thinking about it since I put it on.

I mean technically we're only pushing in more cold/condensed air into the combustion chamber, which should allow the engine to burn more efficiently and create more energy, RIGHT?

The only thing I can think of is the distance which the air has to travel thru the pipe to get to the engine, causing a lag effect. Any thoughts?

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01' Base 5-Speed
Stock for now
Parts to be installed-
AEM CAI, Neuspeed Sports & KYB AGX, Neuspeed Front STB, Apex V-AFC
 

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The more flow that the AEM provides is good for top-end power. While at the same time that extra flow is detrimantal to low end torque. This will be true of headers and exhaust also. If you slap on a 4" exhaust, you might gain some top-end, but you will lose a bunch of low-end torque.
 

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Discussion Starter #3
But the headers and exhaust are dealing w/exhaust gases!

what u said about H/E is correct due to higher flow of EG's and therefore changing the backpressure. But how does the CAI have anything to do w/backpressure.
 

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<font face="Verdana, Arial" size="2">Originally posted by EBP Lude:
But the headers and exhaust are dealing w/exhaust gases!

what u said about H/E is correct due to higher flow of EG's and therefore changing the backpressure. But how does the CAI have anything to do w/backpressure.
</font>
It is the same as cylinder head porting. If you make big-ole whopping ports, you will lose low-end torque.
I'm not an expert, but as far as the intake goes, I would guess that there would be insufficient manifold pressure at low rpm.
 

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You're right, but you have to look at it from a point of flow (in and out). Your engine is essentially a big air/fuel processor- the more of it you can move in and out, the faster it runs and hopefully the more power it makes. You can make all the intake and fuel mods you want (or exhaust), but if you improve one while not improving the other you aren't going to realize the full potential of *any* of those mods.

The dynamics of it are explained easily for intake and exhaust; a smaller & longer pipe typically yields improved low-end torque while a larger, shorter pipe yields better high-end power. That's just the simple fact of it.

By improving the intake you're not "pushing" anything more into the engine- the engine is *sucking* through the intake, just like you would through a straw. Doesn't matter how hard you suck, if the straw is the size of a pinhole, it will be restrictive. Likewise if the straw is the size of a sewer pipe but your dog w/no lips is on the other end trying to suck (and can't), you won't move any air (think of that as a big intake and a restrictive exhaust).
 

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<font face="Verdana, Arial" size="2">what u said about H/E is correct due to higher flow of EG's and therefore changing the backpressure. But how does the CAI have anything to do w/backpressure. [/B]</font>
As Billy stated the other day, and I will reiterate, backpressure is not the major detriment to exhaust gas flow. Exhaust gas velocity is the single most important aspect of exhaust gas flow.

Now the reason the AEM supposedly looses low end torque is due to greater airflow at a lower velocity. The valves only stay open for a certain amount of time and if the velocity of the incoming air is less than it was with the stock intake there is not as much air in the chamber to be used for combustion. This leads to a loss of low end torque.

Personally, my low end feels the same as before I put my intake on. I think it's merely a placebo effect. Someone says that they lost low end torque and everyones thinks maybe they lost it too. I also think it may have something to do with the increased power in the rest of the rev range. This makes the low end seem weak due to the minimal gains achieved in the low end.

Gabe

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97 Prelude
see it here:Hondaprelude.com
 

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Discussion Starter #7
Guys thanks for the example and insight.
I was planning to just add the CAI, and not doing the exhaust, just for the sake of not losing low-end tq., believe it or not I'd rather improve tq over hp! But I guess its pretty impossible since it's a HONDA.
 

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<font face="Verdana, Arial" size="2">Originally posted by EBP Lude:
Guys thanks for the example and insight.
I was planning to just add the CAI, and not doing the exhaust, just for the sake of not losing low-end tq., believe it or not I'd rather improve tq over hp! But I guess its pretty impossible since it's a HONDA.
</font>
Get a JRSC.
 

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<font face="Verdana, Arial" size="2">Originally posted by Gabe:
Personally, my low end feels the same as before I put my intake on. I think it's merely a placebo effect. Someone says that they lost low end torque and everyones thinks maybe they lost it too. I also think it may have something to do with the increased power in the rest of the rev range. This makes the low end seem weak due to the minimal gains achieved in the low end.
</font>
My sentiments exactly.

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It all has to do with gas velocities, inertia, and scaveging.

Air does not just flow through the intake or exhaust, it flows in pulses. Inertia of the gasses helps scaveging and cylinder filling.

Here's a quick explanation:

At low rpms, you need high gas velocities so that the gas has a bit of inertia to fill the cylinder better on the intake stroke. You also need high exhaust gas velocities so that the inertia of the gas will help "pull" the gas out, like siphoning (also the pulse will help pull the next pulse out, but this has to do with header design).

At high rpms, gas velocities are already high, so port sizes can be larger. Same principles apply, but since the gas is already traveling so fast, the ports need to be big enough so that there is no pressure drop due to a restriction.

The rule of thumb is that a long, small intake/exhaust tube will boost low end power because the gasses will have a higher velocity (thus, higher inertia). Smaller exhaust ports will also promote better scaveging, thus increasing power at lower rpms. Problem is, trying to run small ports at high rpms. The tubing can't support the flow, so you end up choking the engine at high rpms. Now, short, large intake/exhaust tubing promotes better top end power because the tubing can support the higher flow.

So, there is a compromise to be made...make the tubing for low end power or high end, etc. etc.

Header design also plays a role in exhaust performance.

So, now look at Honda's intake design. When the butterflies are closed at low rpms, the intake is a small, long length intake, which promotes low end power. When the butterflies open, the intake tubing is essentially larger, and it appears shorter to the engine, so it promotes top end power.

Whew...that's about all I can think of right now. I know I made some typos, but I am too lazy to correct my spelling!




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Billy
North Texas Prelude Owners Group
www.ntpog.org
 
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Oh yeah, about the exhaust back pressure thing. If back pressure was the key to low end power, why couldn't you run a super huge exhaust that's free flowing, but with a restrictor plate to give you back pressure??

Back pressure does not give you low end torque, it's as simple as that!



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Billy
North Texas Prelude Owners Group
www.ntpog.org
 

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So if I didn't lose torque, why is my idle a lot rougher? It's not loping, but I can feel the car jiggle now - it didn't used to until I put the AEM on.

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<font face="Verdana, Arial" size="2">Originally posted by spite:
So if I didn't lose torque, why is my idle a lot rougher? It's not loping, but I can feel the car jiggle now - it didn't used to until I put the AEM on.
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Torque has nothing to do with your idle. It's probably due to the fact that the intake is transmitting vibrations from the engine through the rubber mount that bolts to the car or it's rubbing on something.

Gabe

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97 Prelude
see it here:Hondaprelude.com
 

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Discussion Starter #14
OK, what u guys described makes complete sense! Glad I didn't take up engineering or something back in school.

Anyhow, is there anything that I could change to increase tq? No FI is not in my future


BTW- do u hear a lil whining sound when u stand in front of the car at idle? I've been getting this sound since the CAI. Tell me it's the intake pls?
 

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And... that's why OEMs are getting into variable mufflers and air induction systems. These systems adjust to improve torque & efficiency at certain speeds. At low speed, i'm guessin' variable air induction systems will have a smaller opening for improved response and will open larger at higher speeds. As for mufflers, how does it go? small opening for low speeds and larger opening for high speeds? that's right, right?

So if someone concocted some way of having an air box that would open up at high speeds and close at low speeds, that'd be awesome. Or, like everyone said, just get some forced induction action going.

my .5 cents
 

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<font face="Verdana, Arial" size="2">Originally posted by EBP Lude:
OK, what u guys described makes complete sense! Glad I didn't take up engineering or something back in school.</font>
Be glad some of us did


<font face="Verdana, Arial" size="2">
Anyhow, is there anything that I could change to increase tq? No FI is not in my future
</font>
You could try pullies or cam gears. But if you tune the cam gears for low end umph you'll lose some high end.

<font face="Verdana, Arial" size="2">
BTW- do u hear a lil whining sound when u stand in front of the car at idle? I've been getting this sound since the CAI. Tell me it's the intake pls?
</font>
Yep it's normal.

Gabe

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see it here:Hondaprelude.com
 

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<font face="Verdana, Arial" size="2">Originally posted by slickshifter:
And... that's why OEMs are getting into variable mufflers and air induction systems. These systems adjust to improve torque & efficiency at certain speeds. At low speed, i'm guessin' variable air induction systems will have a smaller opening for improved response and will open larger at higher speeds. As for mufflers, how does it go? small opening for low speeds and larger opening for high speeds? that's right, right?

So if someone concocted some way of having an air box that would open up at high speeds and close at low speeds, that'd be awesome. Or, like everyone said, just get some forced induction action going.

my .5 cents
</font>
The prelude already has a sort of variable intake on it. It has a butterfly valve in the resonator that opens up to let more air in at higher rpms. There are also secondary intake runners in the intake manifold that open at higher RPM's too.

As for variable exhaust systems, it's been tried. I'm not sure if any current cars use them but they were used on the mitsu 3000 gt. I think they add more in weight then they make up for in use.

Gabe

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Discussion Starter #18
Quick response Gabe

I would do Cam Gears in a sec if not for the OBDII's self-compensation. I'm not in the mood to reset the ECU every 2 wks.

Billy- I forgot, but what was ur conclusion regarding the pullies after u took apart the engine?
 

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Gabe,

Maybe this has been asked before but, do you know what powers the butterfly valve? is it electronically actuated according to rpm or does it rely on air pressure? I haven't modded my 'lude yet, aem cai to come soon, so i don't know the area around the intake/resonator that well.

variable exhausts: well, nissan has them on the maxima, sentra, and i think the skyline started it????? not sure. i'd rather dump it for an aftermarket exhaust though.
 

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Discussion Starter #20
Slick,
the butterfly valve is controlled bt air pressure. There's a hose attached to it.

Also, I would DEFINITELY recommend taking out the resonator when installing the CAI. it's definitely worth the time and effort.
 
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