K I've been working on a 03 G with a auto for the past year. It has a basic vortech kit, 1/2" spacer and stillen exhaust. It was making 5 1/2psi at first. Then we had a custom aluminum MAF housing made which bumped the boost to 6 and the car definately pulled harder.

Well last night we install a set of test pipes and the boost DROPPED to 4. If the SC was a roots style I could understand from the loss of back pressure. But we're confused since the vortech is a centrifical. We were expecting a 1/2-1 psi gain not a 2 psi loss. I'll be installing a smaller pulley, injectors and having it tuned this weekend which should take care of everything. But any ideas why we lost boost. Thanks

 

Why are you running such low boost? you should be at 7 or 8psi with vortech. Something seriously doesnt sound right about your setup dude give more info...

 

any time you change anything on your F/I set up you should have it retuned/recalibrated. IDK what you're running with it, but you should be running an AVCR or something of the sort to monitor those things since your set up is so variable.

 

Why would would it matter if the SC is roots or centrifugal? The reduction in back pressure probably helped with scavenging of the cylinders and thus the reduction in boost at the manifold but in actuality the same amount (if not more) A/F is taken in.

 

Same thing happened to my dad's pro-charged C6 when he put headers, hi flow cats and a hi flow exhaust on. SC's aren't like turbos in that a huge diameter exhaust may not necessarily help. I remember Randy's_G discovered that a few years back with his car. (I think? Maybe I'm going senile in my young age.) My dad's solution was to get it tuned (again) and change the pully to a higher boost one. I think he's got it back to the "stock" boost, or still slightly less. In either case, I think he's got enough streetable HP/TQ now.

-drew

p.s. sorry for the pseudo-hijack!

 

what you did is completely normal

unlike turbos which have wastegates that blow out lots of excess boost pressure, SC's including the vortech don't work that way because they don't have wastegates and excess boost availble

If you want more boost you have to change the pulley. Otherwise you're working with a finite amount of boost and if you put some big pipes on the exhaust the pressure/speed of the exhaust gases won't be as high

a turbo will maintain the same psi though because it'll vent out less excess boost pressure and instead blow some of that extra power into the engine to maintain the boost pressure set by the wastegate

 

Yeah I think this is normal. I believe he had Kinetix cats and Injen exhaust so boost loss wasn't as bad as test pipes. He had it retuned in the Texas heat before he sold it to BeerViper. I think boost was ~5-6psi, but it was still putting down ~360 rwhp/300 ft-lbs.

 

Yes this is normal either way. With test pipes your engine now has less back pressure to build boost. Add a smaller pulley and re-tune and you'll be in good shape.

 

I have the stock Vortech with test pipes and full single exhaust and I am hitting 8.5psi at redline.

 

We figured it was normal so no worries there. Just thought I would check. I'm installing the 2.87" pulley, injectors and possibly a meth. kit tomorrow. Then we're having it tuned saturday. So we'll be in good shape then. Thanks for the comments everyone.