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Well I have my engine out and if I want to port the manifolds, now is the time. Is this something I can trust a good machine shop to do? Or is it something that needs to be done precisely by learning from experience? The machine shop that I have been recomended to mainly work on older "hot rods" and I doubt they have worked on MN12 exhaust manifolds. If not, who do I go to, is there a certain company that works on MN12 exhaust manis?? Would it even be worth it to port the manifold with my mods below?
 

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either have Extrude Hone do it or take a grinding medium to the casting bumps on the ports and clean up the rough surfaces and take down the casting lip on the collector.
 

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I looked closely at the stock manifolds and really I don't think much can be done.

The casting lip on the collector looks to have been put there for anti-reversion IMHO.

The manifolds seemed to be designed to work with the cats very close, and that each cylinder only uses the manifold one at a time to dump each cylinder individually into the cats. The small "collector" seems to support this theory. In actuality there appears to be no collector considering how the manifold and cat relation is and the size of the "collector"

Anyone with dyno before and after manifold modding let me know what you find please. I would think the only viable true gain would be the Kooks where you are extending each cylinders exhaust length significantly. The decent performance of these cars with the stock exhaust seems to bear this out as well.
 

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Your manifolds must be diferent from every set I have seen the lip is huge. On the driver side where the bolt hole is is the only place I saw that I really don't think you can do much about.
Alan
 

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Ask yourself - why did a Ford engineer make that lip into the design, because it wasn't put there by mistake from what I remember. It was placed there for a reason.

I believe its there for anti-reversion from the expansion area in front of the cat honeycomb. Remember these manifolds are designed to connect directly to the cats, there is at most a few inches of pipe between the manifolds and cats, which places the expansion/honeycomb less than 36 inches from each exhaust valve.

Anyway getting back to it, has anyone done any dyno testing with only modding the manifolds? There is a curve before this lip that is the flow "restrictor" if you want to call it that. I don't see how the lip would restrict anymore myself.

Look at these manifolds as being used by only one exhaust port at a time and you will see where I am coming from. This is why shorty headers don't show any significant gains on most cars as well when the dyno is turned on. Its only when the exhaust port length is increased before a "collector" that you see any gains. Its also why the "equal length" shorties show higher gains, they have longer primary pipes because the longer the better up to a certain point (figure 36" max for 6000RPM average for most engines)
 

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or u can put in shorties if u want, since kooks arent smog legal.
 

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I have a set of the shorties for these cars, stick with the manifolds IMHO. The shorties for these cars have smaller tubes than the stock head port and make a nasty step at the head/manifold junction. As such they don't flow any better (and probably much worse). Plus the passenger side is known for cracking from a design flaw that is near impossible to fix.
 

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the thread starter is in california alan. Look next time:D
 

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I would imagine that most states have laws written against any exhaust modifications but most don't enforce them. I know Florida is one of these, the law is written so vague here that any exhaust modification whatsoever could be construed as illegal.
 

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We have a car that is going to be on the road here in a few weeks that is the test mule. I will let you know how it turns out.
Darrin
 

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nickmckinney said:
I would imagine that most states have laws written against any exhaust modifications but most don't enforce them. I know Florida is one of these, the law is written so vague here that any exhaust modification whatsoever could be construed as illegal.
Fortunately i've never heard of a fl cop bothering to write a ticket for an illegal exhaust system and there's no yearly state safety and emissions inspections to deal with. :thumbsup:

my condolences to those living in CA.
 

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Southpaw said:
Fortunately i've never heard of a fl cop bothering to write a ticket for an illegal exhaust system and there's no yearly state safety and emissions inspections to deal with. :thumbsup:

my condolences to those living in CA.
as nick as has heard, my exhaust is loud and annoying...knocketh on wood, PBSO and DOT just cruise by me.
 

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yep living out here sucks when it comes to car mods, and other things, cant wait to move out.
dirtyd0g said:
Someone shake the fault line and fix this problem already
ahah
 

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I am planning to run 2¼" pipes from my manifolds back. Am I right in assuming that it would be pointless to do so without porting the manifolds? With ported manifolds I could run 2¼" duals all the way, right? ($700 is way out of my budget for Kooks.)
Darrin said:
We have a car that is going to be on the road here in a few weeks that is the test mule. I will let you know how it turns out.
Darrin
Any word on this, Darrin?
 
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