Ok, here's the story. I bought the "GMPP extrude honed manifold" on e-Bay for a helluva deal. Got it via Fed-Ex yesterday, and investigated it. I wrote down the part number listed on it. I then searched a few sites, and the part number coming up is for the stock SS/SC manifold. I e-mailed the seller and told him we had a problem and explained the reasoning. He replied that's what he originally thought when he had bought it, but that GM just took their SS manifolds and did their work. So, is this true? Did they not make another set of manifolds with a new part number to use only for the extrude honing process? How does one tell the difference between a stock vs. extrude honed manifold if they have the same part number listed on the actual manifold? Thanks for all the help in advance.....I hope I'm not getting screwed here.

 

the 2.0 manifold is superior to the other models, but the description under the gmpp manifold said something about taking the ss/sc manifold and making it push 7% more airflow

let me check on that real quick

EDIT: Here we go:

19131972 Cobalt Extruded Honed Exhaust Manifold
We've taken the production LSJ exhaust manifold and had it Extrude Honed. The result - larger, smoother paths and a 7% airflow improvement for more power. Combine it with the Cat-Back Exhaust (sold separately) to provide the ultimate performance exhaust for your vehicle.

 

So the extrude honed manifold will still have the original stock SS manifold's part number?

 

They both have the same part numbers. I put a GMP manifold on mine and the only differance was in the inside of the manifold.

 

it is possible.. post up pics of the tube size.. that will tell you..

 

GM used the same stock castings (including part number), then did the work and Boxed them with a diffrent part number.

I've personally seen a GMPP manifold and it had the same casting number, and the guy that bought it said what everyone else on here has said.

"Damn should got a stock one and cleaned it out myself."

Witch we've done on two other cars.


My 07 2.2 has the same manifold also (runner inlet and flange outlet) ((pisssed me off))... that was one of the revisions, except its a diffrent casting number because the 02 sensor on the flange is not drilled and tapped.

 

I'm at work right now, and I don't have a camera here. I'll take measurements real quick and post them. I'll be right back.....

Ok, the collector is 2 1/4", and the inlets that bolt to the head are 1 5/8".

 

i think you have the better header.. not sure tho have been able to get any pics of the primary's where it bolts to the head..

 

http://www.crateenginedepot.com/stor...P1381C146.aspx

The stock inlets are big enough, they're accually bigger than the outlet of the head. And the gasket is almost matched to it. So any larger isn't going to make a diffrence.

The Flange is fine as well, the Downpipe after the flex joint is the choking point.

 

Yeah, I have an SS downpipe on the way as well. If this is really the extrude honed manifold, I got it for cheap. It's new and I got it for $112 shipped.

 

Is there any way you can get pics of this, or anyone car? I have a local guy who insists that the GMPP manifold that I know was on his car was a stock one, based solely on the part #. I know for a fact that it wasn't the stocker off that car, because I took that one and ported it for use on my car, and I think he threw out a GMPP manifold as a result of his assumptions.

I wish that I would have measured the ported ones I did, im sure I got them to a good 2 1/2 inch inside the collector. There is plenty of material there and that is the only real restriction in the stock manifold, otherwise it is a very good 4-2-1 design, which is exactly why I would never buy a shorty header for this car.

 

I'll be installing the header on Saturday. I will take comparison pics of my 2.2 manifold and this header. My buddy with an SS/SC is installing his header the same day, so I'll try to take comparison pics with his too.

 

They are EXACTLY the same, the stock and the GMPP... WITH THE EXCEPTION, that the GMPP has been "Ported"... it'll be a very shiny silver on the inside. Trust me... I changed my own.

 

The inside almost looks exactly like the outside on mine.

 

That's bad. This is what it should look like. It should be really really smooth. You should be able to rub your finger around... and it feel like sex... uh , I mean smooth.

 

We need a pic of the inside of the outlet flange to tell you if its ported or not.

 

Do you mean shiny inside the collector and such, or on the end (like that flat surface showing closest to the camera in that pic)?

Edit: Ok, I'll take some pics tonight.

 

The inside (where the exhaust flows) should be shiny... like it's been ported.

 

From a members gallery
https://www.cobaltss.net/gallery/bro...imageuser=4923

GMPP Manifold



Another Members Gallery
https://www.cobaltss.net/gallery/bro...mageuser=15466

05-06 2.2l Mani vs. Stock SS/SC Manifold

 

Damn, mine looks like the 2nd mani in the 2nd pic. I think I got ripped off. Anyone know the measurements on the stock SS mani?

 

Theres no measurement diffrence, its just deburred and smoothed out, the stock one has rough casting materal inside, the "honed" one should be nice and smooth, not glass smooth but not rough like the outside, smoother than the outside.

Regardless an upgrade, and you can get a dremel and work on it some more. Even the GMPP has room for imporvement.

 

Odds are you got the right manifold. I honestly found it very difficult to tell the dif. between the stock SS/SC manifold and the GMPP one. The GMPP one is just smoothed out on the inside. It's only a 7% gain over the SS/SC... can you tell what 7% looks like?

But yes... they do have the same part number as the GMPP manifolds are actually production SS/SC parts that have been worked on. Don't worry yourself about it.

 

Well, it's just as rough inside as it is outside. I'm just worrying about it because I could've got an SS manifold cheaper than what I paid for this ****.....which seems to be the exact same thing.

 

Well you've got your answer and theres no definitave way to tell by the manifold alone, so either chalk it up to ebay and drive on, or get your money back.

Dealer cost on that is $275 , i'd say theres a reason you got it so cheap. Lets see the link to the auction.

 

http://cgi.ebay.com/ebaymotors/ws/eB...156814283&rd=1