Hi guys, I thought I would make a thread showing the differences between my GMPP Extrude/Honed Manifold before & after porting. Back in the day, I ran an unmodified GMPP Manifold, and then later switched to a Badmab 4-1 Shorty Header. Well, since my goal is to build my car with mainly GM, GMPP, and GMR parts, I figured I would start searching for a GMPP Manifold. There was no way I was going to spend the $280-$320 for a new one, so I hoped to find a good used one. Well, I made out even better than I would have ever thought. While browsing E-bay, I came across a brand new GM Exhaust Manifold for sale. The part number listed matched the GMPP Manifold's part number, but was not listed as such. I contacted the seller, and later that day, I purchased a brand new genuine GMPP Extrude/Honed Manifold for only $50!!! Since I did not want to go "backwards" in my performance quest (I def. felt a gain going from my old unmodified GMPP Extrude/Honed Manifold to the Badmab Shorty Header), I decided to have the manifold ported. I contacted ItalianJoe1, and asked him if he would port the manifold for me. He agreed, and said he would port it for only $50. I could not let this deal slip by, so I took some "before" measurements, and shipped the manifold down to Florida. Within a week, Joe had the manifold ported, and shipped back to me. The port work looked amazing! Before installing the manifold, I coated it in VHT ceramic header paint (VHT SP998 NU-Cast Iron), and cured it as per the instructions. I then took some "after" porting measurements, and bolted the manifold on. Below are the results.... Enjoy!

Outlet:


Primary:


Unmodified:


Ported:


Unmodified:


Ported:


Unmodified:


Ported:


Photos of the port work:






Installed Photo:


All in all, this was a great mod for my setup. I felt no loss in top end power going from the Badmab Shorty Header to the Ported GMPP manifold, and my car still flows a constant 36.14-37.03 lbs/min of air w/o any knock. I did notice a nice bump in midrange torque while running some tests. This bump in midrange torque, and zero loss in top end was verified with my Gtech Pro RR output graphs (I have it calibrated to read torque perfectly). I will upload the graphs as soon as I purchase a USB-to-Serial (DB9) adapter. My Gtech Pro RR is an earlier edition, and does not have the proper cable for my laptop. Anyways, this thread is not intended to say what header/setup is best. It is merely to show the improvements some porting work can provide to a stock or GMPP manifold. I'm going to leave you with a post from a member by the name of Sergio. He made this post in a thread about the GMPP Manifold back in early 2008:

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 1-3-4-2 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.

^Sergio knew what he was talking about, and understands exhaust flow/exhaust velocity principles.

Special thanks go out to ItalianJoe1 for his amazing port work!! Thanks Joe

 

This thread is now open!

 

Awesome.

 

great work as always Joe and great right up staged.

 

Thanks man

 

I like the fact also that this keeps in tune ( no pun intended lol ) with your build plan of GMP parts.

Good stuff as always man

 

very nice! i like where youre heading with the car.

 

Thanks guys!

One day (when I have extra funds), I will be building my engine to Time Attack specs aka the build book Chapter 6.

Until then, I will continue on the quest of searching for the parts I will need.

 

To my knowledge the Firing Order is 1-3-4-2, so it's not alternating between the 2 -Y's.
Most 4-cylinder performance headers are paired 1+4 and 2+3. Packaging and fabrication for the GM's 1+2 and 3+4 was probably much easier...

 

U are correct.

Good catch.... he may have made a typo (fixed).

Anyways, running a back to back comparrison, I saw no loss in top end power going from a 4-1 shorty header to the ported manifold. I also gained mid range torque/power with it. So, all in all, the ported manifold flows very well.

 

good stuff joe!

 

if the header is bigger then the port then you wont see any turbulance of the header is small then you see turbulance or reversion

 

To a point you are correct, but if the car isn't flowing the air to justify a larger primary, exhaust gases can slow down & create eddies.

Same goes for too small of a primary....

What Sergio was getting at, and what I agree about is the GMPP manifolds primaries are not a restriction on the stock head (for most setups).

 

I'm excited to see the graphs.

 

I still need to pick up the damn cable to upload the graphs

I haven't touched the car much this summer since this install.

When I get the cable, I'll psot the graphs up asap

 

In for graphs and sound vids

nice work, great research, i love that ur going the gm route on everything. very nice.

 

Thanks!

You can you tube me for sound vids.... It didn't change the sound much.

Power delivery is nice though

 

Not to bring a thread back from the dead but just want to give a shout-out to Staged and ItalianJoe !

Joe does great work and im pleased with the way my GMPP Manifold came out.

Here are some pics ...

Before


Ported:










A nice gasket match, comparison: