So i post this in different areas and got nothing im not sur eif it is only cause people avoid these or what but, As i am running out of factory mods to do, i was jsut woundering if anyone has any experience with the Gm exhast manifold. Is it worth the 400 bucks, does anyone know?!?!?

 

Not worth it. Get a true header.

 

no, no and no...

 

biggest waste of money ever on an ss/sc. i bought one and it didnt do a damn thing. on non-supercharged balts its a moderate gain because the stock manifolds are smaller than the stock 2.0 one.
go with ZZP

 

Actually, the stock manifold is a very well designed piece that maximizes our power band. The stated 7% flow improvement on the GMPP is quite respectable on a part that already works very well. Here's a few points that I noticed after comparing the GMPP manifold design to known exhaust tuning effects.

1. The primaries are actually slightly bigger than the exhaust ports on the head. Getting a header with large (1.75") primaries only slows down the exhaust velocity and causes extra turbulence. Unless your head is ported to take advantage of larger primaries, the GMPP manifold is the perfect size for the stock head.

2. The Tri-Y design provides power accross a wide band due to the 1-3-2-4 firing order. The firing order alternates the exhaust pulses between the two "Y" primaries. Therefore the "small" (as most call them) primaries are not a restriction. They actually help keep exhaust velocity very high.

3. Perfect fit. No leaks, no blown gaskets, and no rattles.

4. Price. CED lists the GMPP manifold for $280, which is competetive with the aftermarket stuff.

 

Yeah, I agree with Sergio. It is a quality piece. Most people on this site just see that its made from GM, so it must be crap. I mean they only spend millions of dollars testing these parts.

Speaking of testing... One of my fellow cobalt ss/sc owners back in AZ tested every header that was out 1.5 years ago. He dyno tested all 5 on the same day. The results were that while the headers made 1-2whp more than the GMPP, they lost 5-10 torque through the middle of the powerband, the GMPP did not.

He finally just made his own tri-y header, and gained 9whp and 7wtq, with a 2wtq loss in the middle.

 

Replace your downpipe first.

Actually read this thread first. Replace your dp second.... Manifold 3rd if you got some extra $$$.

https://www.cobaltss.net/forums/2-0l-lsj-performance-tech-47/flow-calculation-some-lsj-parts-67539/

 

A member by the name of DOC dyno tested his GMPP Manifold and got 4whp and 10wtq, I am pretty sure he had a CAI and Catback on at the time, so 4whp, 10wtq more than he put down after he installed the catback and CAI. So an alright gain, mostly feel it in the midrange.

The GMPP manifold vs header debate will still be raging years from now on this site, IMO.. great piece, proven gains, no leaks, warranty friendly but a bit pricy. A ZZP or Vibrant header will give you higher gains for less money but are also noticably louder and not covered under warranty....it all depends on what is important to you

 

Another thing you might consider is the fact that the GM manifold is quiet. I'm not sure if you'll like that or not. Personally I enjoy creeping up on Civics and screaming at them with my supercharger rather than my exhaust.

 

Maximizes our powerband? What does it maximize with a 1.75" outlet?

 

They are speaking about the performance gm Header....not the stocker...

 

the performance manifold is not any larger than the stock LSJ one. it is only extrude-honed which means they smoothed it out inside. feel the outer surface of the stock manifold. thats how rough they are inside as well.

 

I love this statement. Just goes to show you how clueless you are about exhaust tuning. The collector diameter is not what is important, but rather the collector VOLUME. Since Volume is a function of Diameter X Length, you cannot say the outlet is a restriction whatsoever.

Infact, the GMPP has a very nice stepped/tappered collector that serves to counter reversion and brings a broader powerband.

Nice try, but you should hit the books before you run your mouth on a subject you clearly have no clue about.

 

Correct.

Larger is not always better. you have to keep the exhaust temperature high and the velocity up. If you make the primaries and the collector too large, the extra space will cause the exhaust to cool down, and slow down. What you want to do is match the primary diamater with the exhaust port diameter, so that the flow of gasses does not change once they exit the head. You want the gasses to travel fast until they hit the collector, where the combination of the 4 primaries will converge and the pipe diameter will increase to allow the extra gasses to keep travelling the same velocity. This is true for the entire exhaust system, however you have to account for the fact that the gasses will cool as they make their way to the outlet at the rear of the car, and that's where things get confusing. Resonators, mufflers and pipe bends create points that affect the velocity of the gasses. this is where a properly sized system (not the largest) will give you the best overall gain in the powerband (eg. I would rather have a 250Hp car with a broad powerband, than a 270Hp car with a peaky powerband). Reversion can happen on an exhaust system that is too large, because the gasses will slow down significantly when they suddenly encounter a pipe that has a larger diameter than the port. Volume changes will also affect the temperature of the exhaust as it is now exposed to more of an open space and loses heat faster - it is harder to push a cool, slowly moving gas out of a pipe, than it would be to push a fast moving, hot gas out of a smaller pipe.

It is all about balance - too small and you WILL choke the motor, to large and it will fall flat on its face.

-P

 

There is no such thing as too big. I'd rather be too big then too small

 

And you're talking about what?

Question : Does anybody know what kind of downpipe fits between the GMPP manifold and the GMPP cat-back? Does anybody know the measurements of the openings? I think the exhaust is 2.25'' but I don't know about the manifold..

 

Well..yeah...in the situation you are thinking about, you want your "pipe" to have a large diameter and a good bit of length too :P

 

X2...

 

zzp, cobalt addiction, and some other companies sell direct replacements to your cars stock dp. i have the 2.5in from zzp with high flow cat, its a great piece.

but i also considered the gmpp manifold, then i thought about it and decided it was a waste of money (IMO). Im getting the zzp header/dp combo or the vibrant one.
honestly if you NEED to get the gmpp manifold i would pick up a used stock one for 50 bucks and port it yourself=same thing

 

Good point