I have a GMPP manifold id like ported

 

Stock header is fine, Roots blower equipped cars don't give a **** about the exhaust lol.

 

With a dremel you will be in there for a while

I use an angle grinder with an assortment of carbide cutters and finish with grinding stones, there's a LOT of material to remove in key areas. I spend several hours on them normally and i've got it down to a process now. For me buying $200 in tools at the beginning wasn't a big deal because i'm a tech anyway but unless you do it all the time, porting isn't a very profitable line of work

 

LMK, i'm still happy to do them for people.

 

The design is solid, I wish there was a bit more equal-length to the 1-2 and 3-4 runner pairs, but it's still gotta be simple to produce and fit nicely behind the engine so what we get works.

Yes, on a blower car, scavenging is a moot point, so it's mainly removing restriction that matters. Which is why any header works. As does removing the casting flaws and some design "mistakes" in the stock piece. They also retain the durability of a cast iron piece with no welds to crack or flanges to warp, etc.

I did crack mine, but it was from the extensive nitrous use and running it lean to the point of glowing red over and over again
It still didn't crack really until I removed it anyway

 

The stock header's a champ!

I have the stock header, ZZP 2.5" downpipe with metallic spun cat, a CAR CHEMISTRY 3 DISC SILENCER in the end of the downpipe (Lmao!), stock catback, and stock muffler. Beat a brand new Mercedes E Class from a dig last night on snow tires, haha. I love the Cobalt SS S/C.

 

Here is a shot of Joes work:



Sorry Infraredline, no more thread jacks, I promise

 

Dang.. Lol

You might hve a pm coming your way then in the future when i get around to taking it off

 

I used to love my ported gmpp, but the hole that ended up in it was disturbing. 1/4 inch wide by 4 inches long. Sold it for my badmab and got good gains so thats where ive recided.

Op piece looks good ! Always wondered is it better to have a 3 inch downpipe or 2.5 ?

 

No worries guys, get Joe some business lol.

Metallic. It depends on the application and how much power you are trying to make and what you have for airflow. On a stock car I doubt a 3" dp is going to have any gains. On my TVS setup I'm sure there were noticeable gains with the 3". This car has a 3" collector that goes into a 2.5" downpipe...then to a stock catback lol

On a side note. The car runs! Gonna take it out for its mayden voyage tonight.

 

im on a tvs setup as well. think a 3 inch downpipe will provide an increase over my 2.5?

on a side note I was just talking about your ion with someone on a facebook group last night

 

What size pulley do you run? I can't remember. Also what size catback?

Lol oh boy, my cars getting talked about The red one has no motor or TVS or anything now lol...she will be back soon though.

 

I have a 3" downpipe on my car Kev.

Didnt notice a huge change over my old 2.5" downpipe.

Do u still run that catless downpipe smg made u? Looks to be crush bent.

A 2.5" mandrel bent pipe might help u out, or even a nice 3" zzp downpipe.

 

DarkmanX dynoed back to back from the GMPP exhaust to a 3" on a heavily modded TVS car and gained 2whp. Catback doesn't matter under 400whp unless you are turbo, any of them will flow fine. Header and DP is where it counts, once the exhaust gets that far back it's cooled and condensed enough to easily pass through a 2.25" system that isn't poorly constructed.

 

im all about the sound could give a fxck about the flow haha

 

Did Joe smooth out the porting on the head side? That's what disappointed me some with the production GMMP honed manifold, most of the honing was done where the downpipe meets

 

Yep, he sure did.

All of the runners were honed nicely from GM in my manifold. Joe cleaned up some of the inlet, but focused a lot on the outlet.

He removed a good amount of material. I have a thread with the measurements. Search for it.

 

Im running a 2.8 pullied tvs. Currently installed is a crush bent catless 2.5 setup. Thinking about high flow catted 2.5.
Catback is 2.5.

3 inch bangs on rear beam with my setup.

 

A nice 2.5" or 3" mandrel bent downpipe will do ya well buddy.

 

I linked the comparison thread with measurements.

Extrude honing pushes an abrasive-filled clay like material through the item, so it only really smooths out the high points. In the case of a stock header, there is a pretty good neck down in the collector that gets almost polished because it's far smaller than any other area of the merge. On the inlets, there are those little bumps for clearance of the mounting screws, they get the lead-in surface smoothed but the extrusion media doesn't really do much on the rest of them.

I remove those completely btw

 

 

We were talking about downpipe sizing. That is good information to know though. When Bluelightning and I had identical TVS setups I had a 3" catback and he had 2.5 and neither car was faster in the multiple times we raced.

Started driving the car last night and drove it to work today The exhaust is so nice and quiet!

 

I ran my ported manifold to a 3" catless DP to the GMPP cat-back forever. When I switched to the header combo I stayed with the GMPP system. I've always been a believer of at least a 2.5" catless DP to wake these cars up, the 3" is probably overkill for most people but with me and the nitrous use, the exhaust volumes I was seeing were far greater than the average blower car.

 

got to be a nice difference from the other redline!

So even on a 300+ TVS balt I could run the GMPP 2.25 and be no different than the 2.5 corsa I have on there now?

 

Stick with a full 2.5" system Kev.