i have a 3 inch magnaflow catback with no resonator and a injen cai would it be wise if i put a 2.8 inch pulley on?

 

It can't hurt. Your intake and exhaust system have nothing to do with your pulley...if you're looking for a significant power gain, than go for it.

Is that the Stage 2 upgrade?

 

do you think all push more boost or just boost quicker?

 

Both.

Remember, the supercharger is connected to the pulley via belt. The smaller the diameter, the less rotation and the less weight it will be just because of it's size. Now because of the smaller diameter, the pulley is able to spin faster which will make the supercharger's blades spin faster...hence...build more boost and make it reach max boost faster as well.

 

i thought the stock ecu wont let you boost more though

 

If it didn't, GM wouldn't offer kits. The kits include:

Smaller Pulley, Bigger Injectors and reflash.

Your TMAP sensor is a 2.5 bar sensor, so it can read plenty of boost. Your computer, if it's not reflashed will not be ready for the bigger injectors and will not be able to comphensate fuel for the more air that you're supplying inside the motor (keeping your a/f ratio rich enough not to detonate) and also it will not be ready to idle better with bigger injectors (it adjusts the duty cycle on the injectors to idle properly).

 

so it will work only if i dont have the bigger injectors? that dont sound right

 

The computer has no type of control over your supercharger...it's all physically and mechanically done. Your computer can't stop your supercharger from spinning faster in result of a smaller pulley.

What I'm saying is that if you were to get a pulley on, you're going to be pushing more PSI of boost into your motor than before. Your computer right now is set to make your motor so rich of fuel at wide open throttle according to the amount of air that SHOULD be in your motor. So if your computer right now is set to send X amount of fuel for 11 PSI stock, changing your pulley to now send say...14 PSI...your motor will lean out some because your injectors might not be able to flow properly for that amount of boost without straining them and your computers perameters aren't set to comphensate more fuel for the extra 3 PSI of boost that you're running. Your motor needs to have a good air/fuel mixture so it doesn't lean out. If it leans out too much, detonation can occur, which COULD mean "boom bye bye motor" or just cause lots of wear on your internals.

FYI: The 14 PSI was just an example...I'm honestly not sure what the 2.8 Pulley will bring you to.

 

our engines run rich as it is though. i wonder if it will lean the fuel too much? only way to know is to try. thanks for your patience and help

 

It runs rich because it's made for certain sized injectors, a certain duty cycle and a certain fuel curve. When you add more significant air like boost...even by 3 PSI, that's going to throw things off it's design.

If GM is offering a new pulley with injectors and a reflash, they are doing it for a reason.

Also, they probably change your ignition timing as well so you don't need some type of really high fuel octane the higher the kit you go.

You're welcome and it's no problem.

 

You need to check out the dyno of the guy who had a 3" pulley and no injectors. He went WAY lean at redline, 13.7 I believe. You need some kind of fuel upgrade if you are going to run a 2.8 and you need some kind of tuning to run the injectors.

 

That was me. DUDE DON"T DO IT! 2.8 with intake and exhaust = KABOOM! Crap, after a while my 3 inch with intake and exhaust = kaboom. You need fuel injectors and a tune. Trust me on this one. I would suggest either getting Intense Stage 3 or GM stage 1.

 

You are correct in saying that the blower will spin faster. However, the Boost Bypass Valve will bleed off any bost over 12.5 PSI while using the stock ECU.

 

there is always the boost bypass mod. but i understand what you are all saying thanks you just saved me an engine!

 

Good luck.

 

Good info to know. Thanks.

 

Yeah. At 6000 it bleeds the boost down to 12.5. You can boost 18 if you have a small enough pulley, but if you don't have the boost bypass mod done, at 6000 rpm, it will go back down to 12.5.

 

What would be the best size pulley (2.7, 2.8, 2.9) with stage 1. I want to run just a little rich to be safe...

 

The best pulley to get is the pulley that comes with a stage 1.

 

u mean stage 2, stage one dosnt come with a pulley, unless we are talkin about the one already on there.