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Discussion Starter #1
Hello everyone. I have a quick question regarding plenum porting. Is it worth it to do? I just recently purchased a 70mm throttle body from a member here and was going to open up the plenum to match the diameter of the throttle body upon install. However, if the plenum is already that diameter and/or there is nothing to really gain, I will save my time and better use it elsewhere. Also, has anyone used a plenum spacer before? If so what were the results? Thanks in advance!

Side note: Yes I did search! :D
 

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Discussion Starter #3
None that I saw with a clear answer. Some people say yes do it, some say don't bother because the restrictions are further down in the intake manifold and heads. Some say the diameter is 67mm....and none that I have seen on an plenum spacer between the manifold and plenum.
 

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Some people say yes do it, some say don't bother because the restrictions are further down in the intake manifold and heads.
...and there is your answer. You answered you own question. You will get the same exact two responses today.
 

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Discussion Starter #5
That being said, I do plan to at LEAST find a set of PI cams and an intake in the near future. Would it then be worth it to port the oem plenum? Or should I just get a C&L unit or something comparable? And what of the plenum spacer still?
 

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You're lucky. As in, now a days you actually have the option of a mass-produced, decent priced, performance intake manifold available for your car, unlike the usually rare and pricey SVO & Bullitt intakes of Ford's yonder years. Why you bother with this mickey mouse stuff is beyond me. If you have the cash to be modding your car, go for something that will be significantly better than what you have now. If you don't know what [intake manifold] I'm talking about, then you're confining yourself and your knowledge unnecessarily.
 

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Discussion Starter #7
I'm assuming the PI manifold from later year mustangs? The fact that I am doing my best to search and ask should lend something to me NOT attempting to confine my knowledge, but rather expand it.
 

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I have. Funny that the first thing that pops up on the search engine aside from the google shopping link is summit racing. First manifold listed under summit is the PI manifold. I get it, there are aftermarket manifolds out there that probably offer more.
 

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I have. Funny that the first thing that pops up on the search engine aside from the google shopping link is summit racing. First manifold listed under summit is the PI manifold. I get it, there are aftermarket manifolds out there that probably offer more.
Yup. With the stuff out there now (not saying there's million choices), everything else makes little to no sense. People are always complaining (not saying you are) about the lack of performance stuff, well here it is. BTW, I'm mainly referring to the TFS stuff.
 

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Discussion Starter #11
No I get it. You were only making a point. Fact is, this is a daily driver. I don't need it to go fast, I need it to last. I like the idea of gaining extra power using OEM parts because that's just it, they're OEM and the quality is hard to beat. If I find a deal on something aftermarket, sure I'll get it and use it. If I wanted to be the fastest guy out there I would have chosen a different platform to start with than an MN12. I do however enjoy turning wrenches and making my daily more enjoyable to drive.
 

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the intake manifold is a non-moving part---there is nothing to wear out, so the "OEM quality" argument is null and void. It's not like I'm asking you to install race-only parts in your car, lol.

All I'm saying is that given the option (as you purportedly have), you'd be wasting your money in the sense that a good intake manifold (beyond a whimpy PI) is light-years above any other mickey mouse intake mod. This coming from actual experience, having had a C&L intake plenum with a 75mm Accufab Tb on a PI intake. Soon as I dumped the PI intake and got a much better one, WHOA! Huge night and day difference. I even datalogged it and the logs confirmed that by butt-dyno was accurate in detecting a hell of a difference. I thought to myself "man, if only I would have looked for one of these 4 years ago!!!" Nothing to worry about either---it was my daily driver and it wasn't some one-off race-only part like some exotic piston or rods or anything like that, so the "oem quality" doesn't even come into question.
 

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Discussion Starter #13
Which intake manifold, may I ask, did you end up switching to?
 

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Keep in mind, this was in 2006 or 2007. Nothing else was really available (aside from the nearly identical Bullitt intake). By today's standards, that SVO intake manifold is c-r-a-p-p-y. But compared to a PI, it tramples all over it, guaranteed. I have no doubt what so ever that the new TFS street intake would flat out murder it [the SVO]. Ask RobertP (the guy with the fastest 4.6 Tbird in the world) what he thinks about TFS intakes and if he had any trouble with his. You'll be pleasantly surprised.

The TFS is not cheap, BUT when you consider that you will likely be spending hundreds of dollars already on mickey-mouse things like plenums, spacers, etc, and you won't even get 1/20th the performance increase that a good intake will give you, it ends up looking pretty cheap. Again, I'm speaking from direct experience.
 

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Ah, I see they even have one that fits non-PI heads. But holy price tag batman!!! :(
 

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You can look for my old posts on the SVO intake in this forum. I posted up the graphs where I datalogged the acceleration of the car with the PI + C&L plenum+Accufab 75mm TB VS. that SVO intake. My car with the SVO out-accelerated the PI + C&L plenum+Accufab 75mm TB combo at pretty much ALL RPMs. With the better runner construction of the TFS street burner, I wouldn't doubt it flows even better.

You're looking at the price tag wrong!!!! The stuff you had in mind won't add up to anywhere near what that intake would give you, YET your proposed mods would cost a very high percentage of that price tag(!). Doesn't make sense, does it? I know it's impossible but I wish you'd be able to drive a car with your "mods" keeping the total cost in mind, then driving one with a real intake on it. I guarantee you, you'd change your mind and be like "no way I'm buying this crappy stuff if it's gonna cost 60% of what a TFS intake will run!"

Oh and you read wrong also---there isn't one that fits NPI heads. Read Carefully.

This is the data I had gathered. PI intake + C&L plenum + 75mm TB vs SVO intake manifold.

look at how the airflow just keeps rising with the SVO, and how the PI intake even with the extra stuff, just gives up eventually.


This is engine load, which you can think of as torque production, which in turn is pretty much looking at the acceleration of a vehicle. The results speak for themselves. PI intake with mickey-mouse stuff didn't even have a chance against a crappy ol' SVO intake that was cast in the 90s, lol.
 

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Out of curiosity GM, was that chart created on two runs (one each with PI and SVO manifolds) or was it several of each with data averaged for the sample points?
 
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