What is the purpose of those HUMPS in the bottom of the 2 round intake plenum holes (just behind the throttle body)? I was told they were there to reduce the incoming air from raming to the back of the plenum and leaning out the front two intake runners. I also was under the impression that if they were ground down, it added to the CFM air flow and improved performance. I have never seen a report of a before and after this was done to see if it really works or not.

 

It works

http://www.austinthirdgen.org/index.php?pid=21

 

Any noticeable performance gains?

 

That was part of original question, has anyone done this with before and after 1/4 mile runs? I have to imagine that GM put those HUMPS in there for a reason, but so far nobody has an answer for this.

 

The single thing Ive notice was my car pulls hard to 4800 where it started to fall flat around 4200 rpm with the stock unported

 

Right on. I think I will go ahead and port mine since it's off right now for an injector swap anyway. I will post results when I'm done.

 

I noticed a better throttle reponse when I did mine a long time ago

 

Like anything else, on a stock motor there is probably very little to be gained. On something that's going to breathe a little deeper the details become more important.

My personal belief on why they were put there by the factory is they were trying to keep the carbon and other nasty stuff that's in exhaust gasses from having too direct a path to glue themselves onto the back of the throttle plates. Not that they don't get choked off pretty bad after a while anyway, but that's the kind of stuff that causes warranty headaches for a manufacturer.

 

Anti reversion dams for the EGR ports

 

In layman terms, what the hell it that?

 

You're looking at about a 100cfm increase through the T/B with the EGR wall removed - allowing the t/b to flow near full capability. I saw a flow comparison where the stock t/b with the EGR wall removed flowed more air through the plenum than a 52mm t/b with a stock plenum. This is one of those mods that increases airflow enough that it requires an AFPR or some other means of increasing the fuel for proper air/fuel ratio under WOT. Expect very little gain porting the plenum without adding the fuel. If you do it right you should expect to see around a .3 et drop and close to 2mph increase on a stock combination in good health,, or about three car lengths in the 1/4 mile. More modified or larger engines could be a bigger gain.

 

What Damon said ; walls to stop the EGR gases going forward to the butterflies

 

Okay so I was ready to tear into my plenum but did some last minute searching. I found some older threads where some people claimed that removing the egr walls causes a decrease in torque. I don't understand flow dynamics well enough to understand how this would effect hp and torque numbers. Could somone please explain what effects removing the egr wall would have on hp and torque output. Thanks.

 

I lost throttle response but gained top end. Im sure it can be fixed by tuning. After I added an airfoil I was back to stock throttle response and kept the gain.

 

Any noticeable loss in torque?

 

Off the line, yes. Up top, no. But considering I couldn't hook the car in the first place I didnt really mind a slight loss in TQ. And I mean this was very slight...hardly showed up on the butt dyno.

 

kind of the same loss of low end you get putting to big of headers on a car. I put the 1 3/4 SLP's on my 305..low end went to hell..but up top is a diff story. I believe it all has to do with velocity; which is why he gained it back when he added the airfoil. Remove those walls, the air doesn't fill as aggressively ( my understanding) but feeds more volume which helps the top end.

 

Okay I guess that makes sense. I probably won't do anything too drastic then. I like having a torque monster. Thanks for explaining.