Ok i can get this deal on an 2g ported exhaust manifold. My question is, they have knocked out the divider in the manifold is this a good thing or bad. The reason I ask is because I think I have heard bad thing about doing this.

There is NOTHING wrong with eliminating the center divider. Actually, this is the most restrictive part of the manifold and where you will see the most improvement.

Dan7040 said:

There is NOTHING wrong with eliminating the center divider. Actually, this is the most restrictive part of the manifold and where you will see the most improvement.

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can you prove that

mirkoelek said:

can you prove that

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I would like to see that also

The divider is there to direct the exhaust gasses toward the turbine.
If you want to improve on it, then port it slightly but smooth the ruff casting and keep the nice curved transitions.
I would have to say it's a bad thing. Just my opinion.

VBGSX said:

I would like to see that also

The divider is there to direct the exhaust gasses toward the turbine.
If you want to improve on it, then port it slightly but smooth the ruff casting and keep the nice curved transitions.
I would have to say it's a bad thing. Just my opinion.

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I completely agree. The divider is there to keep the exhaust gasses from slamming straight into each other at the collector. If there were no divider, it would most likely cause excessive exhaust turbulence and kill the exhaust velocity. I highly doubt that the extra "airflow" you would get from taking out the divider would be worth the negative side-effects.

The wonderful success of twin-scroll turbine housings prove this point

mirkoelek said:

can you prove that

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I couldn't find my personal pictures of before/after my manifolds porting, but my personal experience is that the porting IS worth it. I reduced spoolup on my B16g by 2-300 RPMS. I may have been wrong in my wording when I said "elminating" the divider. I did leave some of the divider to direct some exhaust gas flow, but 80% was removed. I think its a compromise of increased flow vs. increased turbulence, but my personal experience has shown me that the performance increase from the former outweighs the effect of the later.

BTW just some pics from SBR's website that clearly shows the increase flow you can get from porting the center divider.

guitarXgeek said:

I completely agree. The divider is there to keep the exhaust gasses from slamming straight into each other at the collector. If there were no divider, it would most likely cause excessive exhaust turbulence and kill the exhaust velocity. I highly doubt that the extra "airflow" you would get from taking out the divider would be worth the negative side-effects.

The wonderful success of twin-scroll turbine housings prove this point

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Just noticed that you listed a ported 2g manifold in your mod list. Was this mod done before you decided that an unported manifold was prefered? Or did you just port the runners? Just tryin to see from your point of view.

Also Twin-scroll designs utilize a lighter rotating assembly in addition to a more efficient turbine scroll. I dont think that they are more efficient because of decreased manifold turbulence, but rather from an increase in overall efficiency.

doesnt vfaq tell you to completely remove that divider??? i see how it makes sense to make it flush with the other perpendicular one, but as far as i know is mild porting is usually filing down the larger step and making it match a 7cm housing (if you have a 7cm housing to match).. thats what im getting done by my boy right now...

Dan7040 said:

Just noticed that you listed a ported 2g manifold in your mod list. Was this mod done before you decided that an unported manifold was prefered? Or did you just port the runners? Just tryin to see from your point of view.

Also Twin-scroll designs utilize a lighter rotating assembly in addition to a more efficient turbine scroll. I dont think that they are more efficient because of decreased manifold turbulence, but rather from an increase in overall efficiency.

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I did not really do any porting to the manifold runners. I did clean up the runners and removed any rough spots or carbon build-up, but I did not do any enlarging of the runners. I did port the manifold collector to match a 7cm gasket but left the divider alone as much as possible. I did smooth the outside edges of the divider down because they seemed a bit sharp, though. With the 14b, that got me down to about ~3150 rpms to reach 17psi.

As for the twin scroll housings/manifolds, the main purpose is to keep the exhaust pulses separated for as long as possible in order to maintain velocity and overall exhaust gas energy. More exhaust gas energy and velocity = more efficient use of the exhaust and therefore better performing hot-side of the turbo (quicker spool-up, etc). The decreased manifold/housing turbulence is where the twin-scroll really shines. This is one of the many reasons the new EvoVIII stock turbos are so badass.

I can understand the benefits of keeping exhaust velocity up and turbulence down, but I also can see the benefits of decreasing airflow restrictions. Like I said before its a give and take situation that I would be more interested in the learning about.

Dan7040 said:

I can understand the benefits of keeping exhaust velocity up and turbulence down, but I also can see the benefits of decreasing airflow restrictions. Like I said before its a give and take situation that I would be more interested in the learning about.

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That's pretty much how I see it. I think finding the happy medium between getting max flow with least amount of turbulence would be the ideal situation. This is usually where the twin-scroll comes into play because it provides a very nice mix of high velocity/low turbulence while keeping airflow high at the same time. However, we DSMers really don't have the option of a twin-scroll setup, so we must work with what we have to achieve that sweet medium