mods:
KnN intake
pacesetter header(1.75"primaries)
catless LSP dp
2.5" catback exhaust, megan racing resonator, obx muffler, magnaflow tip
3" pulley
sgII injectors


im gettign 12psi, 13max...im not sure if thats right as i though the 3" would give it a good 14-15psi?

 

is it 3'' pullley or the stage 2 pulley. cause sometimes people call the 3'' pulley stage 2 pulley when really the stage 2 pulley is closer to 3.1 than 3.0

 

mine=3.0"
stgII=3.065"

i got mine directly from nate and it clearly stated 3" on the back

 

did you take and put a new stgII belt on it or a differnt tensonier. because if not your belt could be slipping a little causing you no not make full boost. but that is just my 2 cents.

 

Sounds dead on

On my ZZP 3" pulley I boost 14.1 @ 7000rpm @ 50' elevation

A lsj w/ just GM stg2 on it usually boost roughly 15.5 PSI

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Mods to contribute to my set boost level

LS4 tb
Ported Intake Manifold (.4 drop in psi)
Custom 3" DP w/ high flow cat (1 psi drop)
STOCK LSJ EXHAUST MANIFOLD / 3" resonator / 2.5 piping to a stock LSJ MUFFLER

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The header you have in combo w/ a catless DP easily drops 2.0-3 PSI

 

the header and dp would have nothing to do with a drop of pressure from the sc. they are a completely differnt system.

 

So what your saying is...

It's completely useless to open up the exhaust piping after the exhaust ports on the head.

BECAUSE..... It does absolutely nothing.



Please read the post below

 

Hmmm, I'll answer this simply.
If our motors (or any motors in general) are one giant vacuum pump. Whats to happen if you improve upon a restriction?
Better airflow and less restriction. Hence dropping boost.
As the exhaust side of the vehicle is no longer working hard to extract exhaust gases, making it much easier for boost to pass thru the motor, causing less pressure build up in the cylinders.

To the OP, your boost seems fine.

 

no the exhaust does increase flow. therefore more horsepower. but it will not affect the amount of boost you are making. unless lets say you were turboed. either that or i am failing to comprehend what you are trying to get at.

yes i understand that but that just dont seem right losing 2-3 pounds of boost

 

Think of it this way

Boost is Cyl. pressure

remove the cyl pressure

and there you have it, less boost

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As for the 2-3 psi drop

Your typical midlength or shorty header w/ 1.75" primaries to a 3" collector usually drop on avg. at least 2 psi

A catless dp; and this is including the stock lsj dp w/ it's wonderful crimp. I've also personally seen it drop a full PSI

a catback makes a minor difference; but if your looking for even more flow. a 3" to a straight thru muffler would possibly drop .5-1 psi

 

yes i understand that but what im saying is. the stock pulley and tune reaches 12-13 pounds of boost. there is no reason why he would be losing that much boost to where he is running basically stock boost numbers.

 

Stop thinking before you hurt yourself.

Boost is a measurement of restriction. Take away some restriction, boost pressure drops. It still flows the same or more, with less restriction.

 

Jn2 is a 2.2 cobalt. His head flows differently than ours and their boost readings are gonna be different on the pulleys.

Jn2, you need to post in the 2.2 section, not the 2.0 section.

 

That still sounds right.

HUNTERKILLER boosted roughly 12 psi on similar bolt ons w/ his 2.2 S/C with the 3" pulley.

But def. posting in the 2.2 section would of cleared this up ages ago.

 

2.2 section doesnt have many people that would help, all those who can post in here aswell, and stock i was seeing 10psi which is what the lsj gets isnt it? i understand that having a better flowing exhaust will drop boost, was just asking if it would be the cause of a 2psi drop...im ok with loosing psi as long as it still makes more power...and the boost gauges reads boost @the manifold, so if the engine is taking in more air, than theres less left in the manifold to be read, which like i said, im just seeing if that # looked aboutright