Losing Boost With Ported Heads?

[Three50won]

Hey guys. Quick question here. I am running a 3.60 pulley with a Vortech S-Trim on my 03 GT. Last year it was making about 8 psi boost. That was with PP intake manifold/upper plenum/75mm TB, stock heads, stock cams, stock exhaust manifolds, HF cats and cat-back. Now the only thing different is that I have ported stage 2 Patriot heads. Everything else is the same. Is it possible to lose a small amount of boost going from stock heads to ported stage 2s? My gut says yes for obvious reasons. I seem to be down from 8 to abut 5-6. What do you think?

 

[Noobz347]

LOL That's terrible!


Oh wait... I mean. Hmmmm.... That's terrible.


I wish I had your problems.



In a nutshell... You've not lost anything. Your motor is capable of moving a lot more air than it used to be because of those heads.
Boost pressure is a side effect from air being contained in a space with nowhere to go. You changed your heads and opened up a bay window.

Very nice... Want to see where that air went? Go get a new dyno or time slip.

Funny things happen when motors get more air.

 

[mogs01gt]

That is exactly how it should happen. PSI is showing resistance, you now have more flow(CFM) going through your heads. Your PSI will be lower but your power will be higher.

 

[Three50won]

I kinda figured that but I didn't think I would lose that much boost with ported heads tho. I thought it would take headers and cams before I lost that much.

 

[Noobz347]

I kinda figured that but I didn't think I would lose that much boost with ported heads tho. I thought it would take headers and cams before I lost that much.

Headers have almost no effect on intake flow at all. Correctly tuned headers, help out quite a bit in the exhaust scavenging department though.

A good set of cams recommended by someone who knows cams would be a great idea. I'm not sure what associated mods go along with that on your model year. Someone will come along that is sure... I'm sure.

You, definitely have a good problem. Now you know how anemic those heads used to be. You've removed a pretty good restriction.

Depending on where you are in the country, you may yet see one or two lbs more boost by doing nothing other than waiting for cold weather.

 

[Three50won]

Out here in NJ Noobz! Yea those stock heads must flow like oak logs or something. Thanks for the info. I think Imma pulley it down to a 3.48 or a 3.33.

 

[Noobz347]

Out here in NJ Noobz! Yea those stock heads must flow like oak logs or something. Thanks for the info. I think Imma pulley it down to a 3.48 or a 3.33.

Just make sure you don't run out of injector. If you're using an FMU and stock injectors, you may want to reconsider. You should have a way to read air/fuel ratio and a "right seater" to monitor.

 

[Three50won]

I got 40 pounders which should be plenty for the limits of a stock block. And if it ain't enough I also got a set of 42s.

 

[Noobz347]