ss1

iTrader: (32)

I just put my car back on the road after seven years. Mostly not driving it due to lack of ambition to work on it, buying a house, and circle track racing. I got motivated this spring and after three months I rebuilt most of the driveline, suspension, etc., everything except for the engine/tranny, Vortech V9 supercharger, & FLP headers.

I replaced all of the silicone couplers, fixed what may been a small boost leak at a pipe fitting, replaced the blower belt, adjusted and realigned the blower tensioner/idler pulley as it was not previously running true. Last time the car was on the road it made about 8lbs of boost.

Old exhaust was FLP headers with 3" collectors, 2.5" cats, X-pipe, 3" true dual exhaust with two Moroso spiral-flow mufflers.

New exhaust is FLP headers with with 3" collectors, 3" hollow cats, TSP Y-pipe (all 3"), Magnaglow catback.

On the highway I brought the car up to 6K RPM and watched the boost go up to 13lbs. This scares me a little since the car still runs great, but I don't have a wideband.

Any ideas if just the exhaust would give me a 5lb gain of boost, or is it possibly the combination of everything?

HCI2000SS

iTrader: (2)

I was under the impression that opening up the exhaust should lower the boost. That's what I've heard, but maybe I'm wrong here

LilJohn

odds are the new belt, and fixing your boost leaks had more to do with it than what you did on the exhaust side.

ss1

iTrader: (32)

HCI, I think by going to the Magnaflow with the single 3" to the dual 2.5" tailpipes it is more restrictive than what I previously had on there. The old exhaust was big and loud, unfortunately too loud to pass inspection and a cop magnet.

Where I'm confused is I've seen threads on here about guys running a Magnaflow and opening a cutout didn't change the power or boost very much.

LilJohn, you're probably right. I'm thinking the belt alignment may have been a majority of the problem. The small leak around the fitting was barely noticeable by a little bit of "soot" around it. I tapped the hole to 3/8 NPT and plugged it off. It was

HCI2000SS

iTrader: (2)

Gotcha! Yes I've read the same thing about the Magnaflow. The difference between your 2 exhaust setups doesn't appear to be huge. At least not big enough to cause what's happening here

stevieturbo

I think you'd almost need to completely block the exhaust to see such a huge increase in boost.

Silver408z

iTrader: (1)

If you increase boost by a more restrictive exhaust, you will lose power.

I-H8-RICE

when my cobalts converter plugged up it would peg the boost gauge almost instantly at wot, you might be making more "pressure" but its making less power as stated above

edit, after cutting out cat peak boost went from 17 psi to 15

ss1

iTrader: (32)

One of the problems I'm running into is I have no back to back comparison of a before & after the exhaust change. Also, with the all new suspension the car hooks really well now, and I switched out the 4.11's for 3.73's as well. I think both of those changes make the car "feel" slower because hooking and not instantly annihilating the tires like it use to. The pull at top end still feels about the same as I remember years ago.

sweet99ss

iTrader: (41)

You know centrifugal superchargers work completely different than turbos right? When you make the exhaust more restrictive on a centrifugal setup the blower will make more boost to make up for the lost power. It sounds weird I know. The more power you make on motor the less boost you will make.

ss1

iTrader: (32)

Yeah, I understand that completely. I'm just surprised at how much it increased and haven't really heard of anyone with the v9 G-Trim making that much boost before.

sweet99ss

iTrader: (41)

Okay gotcha

wolfinsheepsclothing

iTrader: (1)

Was going to post this (verbatim).