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Unread 11-12-2009, 10:00 AM   #151
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Originally Posted by unlimited4x4 View Post
Will pulling outside 90 degree air result in better throttle response vs pulling from the hot engine compartment?
if you remember back to page 2 and 3 those of us with ScanGuageII's reported some IAT sensor results under varying conditions. Regardless of what kind of intake box you have, if its under the hood its pulling in hotter air.

Either way, if you drive long enough distance, the intake tube will eventually reach an average temp based heat transfer from the engine and outside air.

You're best bet is a cowl or snorkel CAI, and wrap the plastic tube with some heat-resistant insulation, like header wrap.

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Unread 11-12-2009, 10:36 AM   #152
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If I do this it will definitley be something similar to the hummer set up or MCAI setup. Here's another question, Most of us know what throttle response is and can describe it,but what is the "mechanism" behind it? Is it due to more efficient combustion due to denser air (more air) being introduced into the cyclinder?
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Unread 11-12-2009, 11:42 AM   #153
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Originally Posted by unlimited4x4 View Post
If I do this it will definitley be something similar to the hummer set up or MCAI setup. Here's another question, Most of us know what throttle response is and can describe it,but what is the "mechanism" behind it? Is it due to more efficient combustion due to denser air (more air) being introduced into the cyclinder?
On our Jeep's, throttle response has more to do with the efficiency and flow of the manifold & throttle body.

Introduction:
Throttle response - Wikipedia, the free encyclopedia

the technical stuff is covered on page 8:
http://www.jeepforum.com/forum/f9/fa...ml#post7833663

Basically imagine if you have no manifold at all - the engine wants to turn at max rpm constantly because it is sucking in as much air as it can use. A prime example is when people don't get their intake manifold seated on the gasket properly when removing the intake and exhaust manifolds. The manifold is basically wide open - there is no restriction, the engine instantly revs full throttle.

To modulate this, we have an intake manifold and a valve that limits the amount of air that enters the engine. This valve can be a throttle body or a carb, they function in the same manner we're talking about here - strictly air modulation on an air pump. When you open the valve wide open, the engine goes to max RPM. The time it takes it to do that is throttle response. Whenever you put your foot on the pedal, you're modulating the amount of air entering your engine. The restriction of the air pump creates vacuum - a suction. The vacuum is what powers your brakes for example.

A bigger valve and bigger manifold allows more air to enter the engine - in other words - you are more closely approximating no manifold. This means the vacuum decreases. Decreased vacuum = less pressure difference across the manifold = increased throttle response. Well, sorta...a bad explaination for the race techies in the crowd, but its an OK way to think of it.

This doesn't automatically mean you make more horsepower or torque - it just means you're more closely approximating no intake manifold in less time.

On engines that don't have a particularly restrictive intake manifold, like the 4.0L, there will be minimal power gains. Any power gains, if any, will be at RPMs where air flow is the limiting factor to approximating that no manifold thing - high RPMs. However, throttle response will be improved because you are now allowing more air past the valve for every increment you open it. This is shown in the math by the very slight difference in pressure between a 58mm and 62mm throttle body.

And that throttle response/pressure difference is slight on the stock 4.0L. Not worth $300 to me, but it was worth ~$80-90 for an Ebay throttle body. It depends on your preference. But there are always better things to spend your money on.

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Unread 11-12-2009, 12:18 PM   #154
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Thanks for the explanation Unlimited04. So, bringing temperature into the discussion again. The reason I feel the increased throttle response is due to the cooler air being denser, thus bringing in more air, simulating the "no manifiold condition". Is this correct?
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Unread 11-12-2009, 01:27 PM   #155
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sometimes when I put my jeep into park and let off the gas it decides to idle around 2500 rpm which is high for it being in park. it doesnt happen often, but could this be a problem with the intake manifold that you were talking about and the rev problem?
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Unread 11-12-2009, 05:18 PM   #156
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Thanks for the explanation Unlimited04. So, bringing temperature into the discussion again. The reason I feel the increased throttle response is due to the cooler air being denser, thus bringing in more air, simulating the "no manifiold condition". Is this correct?
sort of...theres two things at play there. while there is less pressure drop with colder dense air, you have to account for the A/F ratio and adding more fuel to compensate for the denser air.

Using the calculator described on page 7 -
Throttle Body Sizing Calculator | REVTRONIX

Test the extremes:
20* F = 0.24 psi, 320 CFM
175*F = 0.18 psi, 320 CFM

So on a 155* F temperature swing there is a 0.06psi difference due to air density. Theres also a difference in fuel delivered, which I have no idea how to measure or speculate on, especially considering the PCM's propensity for rich-lean A/F behavior depending what RPM & loop we're talking about. Obviously more fuel + more dense air = more power. If you're drag racing it makes a world of difference, but in the context of the 4.0L, who cares.

Thats pretty much the idea - who cares - the 4.0L isn't a wicked performance engine - its a tractor motor. Put paper filters in it for $5-10 each and be happy knowing you're keeping junk out of the engine. End of story!

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sometimes when I put my jeep into park and let off the gas it decides to idle around 2500 rpm which is high for it being in park. it doesnt happen often, but could this be a problem with the intake manifold that you were talking about and the rev problem?
no thats and electrical/computer problem. Most likely your IAC or TPS.
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Unread 11-12-2009, 05:35 PM   #157
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No doubt, very knowledgeable. Bad thing about stroker is mpg is bad enough already ..it's only going to be worse.
That statement is debatable...I only have about 3000 miles on my Stroker so it's really not broken-in. However, my mileage is probably no worse than a stock 4.0L.
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Unread 11-15-2009, 10:22 PM   #158
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That statement is debatable...I only have about 3000 miles on my Stroker so it's really not broken-in. However, my mileage is probably no worse than a stock 4.0L.
Maybe you don't need to rev as high and/or throttle it as much as before? Would be nice to think a stroker (or the awesome 4.7 crate motor discussed) could get approx the same MPG.
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Unread 11-21-2009, 09:39 PM   #159
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Cold air warm air whatever. Bottom line where the air intake is sucks water. A paper filter is junk after it gets wet. I plan on moving my air filter under cowl as suggested by unscathed DIY project. http://articles.jeepforum.com/Tj_Cowl_Induction_Snorkle. A regular filter won't fit. I am going to leave the old filter box where it is plugging the holes and using it as a tool box. Have a nice day.
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Unread 11-22-2009, 06:39 AM   #160
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Cold air warm air whatever. Bottom line where the air intake is sucks water. A paper filter is junk after it gets wet. I plan on moving my air filter under cowl as suggested by unscathed DIY project. http://articles.jeepforum.com/Tj_Cowl_Induction_Snorkle. A regular filter won't fit. I am going to leave the old filter box where it is plugging the holes and using it as a tool box. Have a nice day.
Cowl is the way to go, BUT rather then putting the filter in the cowl research the Buick or Windstar Airbox Cowl intake.
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Unread 11-30-2009, 04:13 PM   #161
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I've started this thread so the info can be added to the FAQ or stickied in some way.

The question is frequently asked: "Do cold air intakes make a difference?", whether this be improving gas mileage or improving performance.

the simple answer is NO. If you're interested why, read further.


Performance Gains:

JP Magazine's Intake Shootout on a TJ: Jeep TJ Wrangler - Intake Shootout - Jp Magazine

Notice they showed a gain of 6 hp and 4 lb-ft of torque at around 4500rpm.
Just a note:

The newer JP link you cite shows stock HP/TQ at 142.3/188 and gains ranging to 154/200.9. That's a potential gain of 11.7/12.9 (or ~double your cited 6/4).

It's quite possible those are high-RPM gains, but that article doesn't seem to include any charts or numbers to verify.
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Unread 11-30-2009, 04:59 PM   #162
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Just a note:

The newer JP link you cite shows stock HP/TQ at 142.3/188 and gains ranging to 154/200.9. That's a potential gain of 11.7/12.9 (or ~double your cited 6/4).

It's quite possible those are high-RPM gains, but that article doesn't seem to include any charts or numbers to verify.
Those stock HP and TQ numbers are very generous. Mine was 122RWHP and 153RWTQ when the motor was stock. My rig sits on 35" tires, 4:56 gears and the 3 speed auto. The dyno was a DynoJet.
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Unread 11-30-2009, 08:28 PM   #163
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Just a note:

The newer JP link you cite shows stock HP/TQ at 142.3/188 and gains ranging to 154/200.9. That's a potential gain of 11.7/12.9 (or ~double your cited 6/4).

It's quite possible those are high-RPM gains, but that article doesn't seem to include any charts or numbers to verify.
I looked at that article, they call it a cold air shootout, but they didn't have one single cold air set-up! WTH! Everyone of them sucked the same old air from under the hood the stock set-up does. I don't get it.
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Unread 11-30-2009, 10:44 PM   #164
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Unread 12-01-2009, 06:44 AM   #165
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If you look real close you will see that they are shielded somewhat from the engine compartment and when you close the hood it finishes the shield. Some are done a lot better than others. With the shield moved all the way forward up against the back of the headlight they draw some cool air from around the headlight. Talk to SavageSun on the Rubicon Owners Forum. He built a homemade intake out of plastic he cut from a plastic bucket and did essentially the same thing for the intake to his super charger. It cooled the air enough that it stopped the detonation he was getting and was able to run 87-octane gas. He claims it made a BIG difference.
The shield serves as a good target for junk flung into it by the engine fan. The pain fell off in a matter of weeks, and the rust began soon after. The shield also served as a nice pool to collect mud, leaves, dirt, sticks and other debris. I tried all sorts of gymnastics with rubber sheet and zip ties to keep the junk out of mine, but nothing helped. 3-4k of junk collecting on the filter and the engine wouldn't idle worth a damn - idled at 1200rpm.
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