Intake manifold P/P

[Replica]

So I've been thinking of buying a stock manifold and seeing if I can port it. But is bigger really better? Won't it cause alot of turbulence inside the manifold to port the hell our of it? One of my friends ported his own 351 heads, so I'm thinking I'll use a dremel or whatever he used and see what results I'll get. Anyone done this?

[Gen1GT]

Do you want to port your intake manifold or your head? Big difference. Unless you know what you're doing, port and polish on a head is not DIY. If you want to do work on your manifold, I suggest extrude honing. Not only does it 'bore' out the chamber, it increases flow, as the places that have the most resistance, are the places that get worn away(a good thing) the most. It's rather expensive though, and might cost you $500. VERY EFFECTIVE though.

I myself, am probably going to go with the custom intake manifold.

[Replica]

Yeah, I just want to port the stock intake manifold. I just hope that porting the runners doesn't cause any weird trubulence. Also, how do i port the plenum?

[Mike R]

Cut it open, port and then get it welded back together. Or send it to extrude hone and pay $$$$$$ If you port it wrong it'll get turbulence, or bad flow/speed through the intake. You need to know what you are doing.

[Gen1GT]

Honestly, I wouldn't worry about it. You don't need to do manifold work until you're flowing huge amounts of air already(ie lots of hp). Work on your weakest links first. Exhaust, intake, throttle body, then maybe throw in some cams, and see if the manifold is a liability.

[twilightprotege]

i will be porting my IM in the near future. there is lots to be gained there, but as gen1 said, it's not something that you should do in the early stages of a build up

[Installshield 2]

The FS DOES NOT respond well to extrude honing....a lot of guys did it in the past, especially the probe guys in the late 90's (when it got really popular), and barely any gains at all...and in some conditions it just made the flow worse...

Yeah like mentioned above, a bad port and/or polish will result in more turbulence, which will result in goofy swirl patterns and poor flow, which will result in a LOSS of power...So I would not recommend it as a DIY procedure...Not many people have had it done though, and I don't know much about the overall flow of th mani itself...The head responds pretty well to a minor polish and galley cut, and some oversized intake valves...but I have not heard of many that actually had a professional and accurate job done on the intake manifold...

But again, ripping it off and attacking it with a dremel will not do anything...and it most likely will leave you with less power than before you started...

[akhilleus]

apparently u can gain decently from an IM pnp because the intake manifold openings on the head side are larger than the IM openings.. for example the 626 fs-de manifold is larger to match the head. so if u know how much to pnp to match the head then u could see decent gains... i believe...anyone swap the 626->fs-de IM.... i would think there would be issues with the VICS...anything else?

[Gen1GT]

My Protege has VICS, and it's much more complicated than you would think. There are two pieces, and the upper intake has a few chambers, not just dual length runners. If you were to port and polish the lower part though, you may see some gains.

This is the upper part. You can see the butterfly valves.
http://ib2.toprotege.com/iB_html/uploads/post-18-22695-DSCF0810.JPG

[twilightprotege]

hmmm....so mazda has been using vics for a while??? i didnt know that. but gen1 that's a fair bit different to our setup. behind the butterflys on the vics part - that's just a "chamber" - ie it doesnt connect to anything else but the other vics butterflys???

[Gen1GT]

It's hard to explain by looking at it, but it's not just a chamber. There's the Plenum, which feeds the bottom runners, but there's a separate chamber/plenum that feeds the high RPM plenum/chamber, which is fed by a single runner from the main chamber. Was that intelligable one bit?

It's a great manifold, and I'm going to probably bore out the the secondary runners which attach to the head, but other than that, it should be good for 170hp +