OhioLariat

The '99 PI intake is aluminum. Is this the only reason for it's "holy grail" status? Was it no longer considered "better" when Ford upgraded the plastic intakes?

Did the plenum underneath (which is missing from the '03 intake) actually give the motor more low-end grunt? Wondering, since the HP and torque specs are the same for '99 and '03 trucks. And when/why did it disappear?

Speaking of that plenum, some trucks apparently got a PCM-controlled, variable-position damper. My '99's intake lacks this. Again, when and why wonderment.

Also plenum-related: Was the plastic insulation "cover" underneath it for noise or heat abatement?

Just trying to learn a bit more about this subject, and thought others might want to do the same.

Thanks.

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Jbrew

The 03 is better as far as performance. That's because they are internally smoother than the 99. The 99's are HD but there's A LOT of very ruff casting imperfections internally which creates turbulence. 99's are more of a bullet proof intake. They don't crack.

OhioLariat

Thanks, brew. That sounds good for top end, but what about down low where most of these trucks live? It seems like that higher-volume plenum extension would help. On the other hand, I'm not an engine expert, so....

Lx545

I recently did the swap because my plastic one was leaking. I will say I feel like mine lost a good 25-35 lb feet of torque from idle to 2k rpm. Runs equal above 2k rpm but an absolute dog under 2k rpms. Fuel mileage is equal and fuel trims are perfect. I hate to spend 300+ dollars on a plastic one but its looking pretty good when I hook my boat up and struggle to pull it.

mbb

Theres shops that specialize in working that kind of thing. Honed, polished, flow balanced. No idea whats out there,For this, but worth a look.

white89gt

These guys do awesome work!

http://www.extrudehoneafm.com/

OhioLariat

That's pretty surprising! I'd think it would be just the opposite with the larger plenum volume, and the fact that smoother runners wouldn't have much effect at lower RPM. I wonder if a polished metal one would be "best of both worlds," or if the shape/design of the newer ones is just that much better all around.

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Lx545

If in fact the 99 has a larger plenum volume I could see losing throttle response and torque. The smaller plenum and longer runners would increase velocity. My theory any way. I didnt even pay attention to that detail really. One thing I notice is my engine seems to run 5-10 degrees warmer with the 99 intake.

Jbrew

99-03 specs are identical on paper as far as complete set ups. So there shouldn't be any difference overall. For these engines anyway. You can totally change that with a bad exhaust set up though. Mine is ported, polished, port matched and knifed along with the TB. Mine is a 98 Aluminum set though (nonPI). None of that increased low end noticeable or towing.

It wasn't until the addition of LT headers that I could use those mods. Factory "Exhaust" manifolds are the bottleneck that discourages more or improved air flow. Mike Troyer (a well known tuner back then) was assisting with the improvements to the truck while I was doing this.... I had a lot to learn at the time. I pulled a car hauler and was seriously lacking in low end. All said and done and still running the factory tune this,noticeable woke the low end. So much so, the truck was actually 6 seconds faster 0-80. Just for giggles, -before and vids were recorded.

The 5fours have low end bottle neck at the exhaust manifolds. The 5fours also have a mid-range flat spot due to this bottleneck. Long tube headers had a bad rep for hurting low end at one time. This was probably one of the largest mis representations from users on forums abroad. This was due to improper set-ups AFTER the headers and no more while running factory original tunes. Just a big dumb rumor is all. It's what you do after the headers that makes all the difference. With this, keeping the factory original set up is key to generating more torque down low in order to take advantage of this set up.

With a factory engine, proper know-how and the ability to do the work yourself, this is a very cheap way to noticeably improve the low end with factory original builds. It's been proven and it sticks, without any adverse affects for the life of the vehicle.