99+ Intake Whyd they start using it

Why did they start using the newer better flowing intake? Why is it good for 20+ horse on the older trucks, when they all use a similar head?

summitlt said:

Why did they start using the newer better flowing intake? Why is it good for 20+ horse on the older trucks, when they all use a similar head?

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Because the head it's usually parked on (#0331) has the exhaust ports reduced slightly "to improve catalyst light-off" (by keeping the flow of gas quick, it gets there hotter. Problem is, that reduces the flow volume. Damn EPA - why can't we have an electrically-heated catalyst? We've got electrically-heated HEGO sensors, and the heat gets cut off after about two minutes...)

The earlier heads breathe better, both in and out, which also helps to explain the power increase. Using a less restrictive intake on a less restrictive head means more power. A good head (like the #7120, for us) can be crippled by a restrictive intake.

OK, im getting conflicting info. So the older heads flowed better than my (99) head? This is why they went to the better intake right? All HO 4.0s had the same output.

So why couldnt i get the older head, and run it on my 99 with the better intake to get the 20 or so horse. Then port it to get a little more? Am I right?

summitlt said:

So why couldnt i get the older intake, and run it on my 99 with the better intake to get the 20 or so horse. Then port it to get a little more? Am I right?

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Do you mean the older head with the newer intake? I'm confused by the above statement 'cause you say "intake" twice.
I'd like to check out the newer intake on my 98.

edited up above, my bad

summitlt said:

OK, im getting conflicting info. So the older heads flowed better than my (99) head? This is why they went to the better intake right? All HO 4.0s had the same output.

So why couldnt i get the older intake, and run it on my 99 with the better intake to get the 20 or so horse. Then port it to get a little more? Am I right?

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The older heads flowed better, but were restricted by the intakes (apparently.) The later intakes flow better, but that advantage is lost at the cylinder head (most likely the exhaust ports.)

Performance is all about finding the best of all years, and bringing them all into one place. Then, looking for ways to improve that even farther. Same thing that builders of performance AMC V8s do - there isn't a lot of aftermarket parts available, so you look for the best from the factory (which can be pretty damn good...)

Of course, with SBChevvy, SBFord, and SBMopar (and those damn ricer engines,) the aftermarket support is greater.

So would it be worthwhile getting the older head? And redoing it and porting it? Or just porting my stock head?

It was designed to get back power that was lost elsewhere.

I like the 99+ intake, it looks like someone put thought into designing it for good flow.

The older manifolds just look like a "back of the envelope" design that was thrown together at the last minute to meet minimum requirements.

In the 99 model year there were new, more strict emissions laws in place.
Mopar had to meet new standards which cost them some horsepower in the low-mid range up to 2500 RPM or so. They had to make it up somehow - apparently, changing the shape of the intake runners and volume of the intake plenum made up for it.
If you run the older emissions + the newer, better-flowing-at-2500-and-therabout head style, you run a gain in horsepower. You'll lose a little bit of top-end power but for an offroader it should work well.
Gojeep has a writeup on this. www.go.jeep-xj.info
Should get you some power and economy in the regular running phase, might lose you some top end. Go for it.