Hi everybody. I have a couple questions about dropping my pulley size from a 3.4 to a 3.2 or lower. I have a 02 Monte Carlo SS with about 130K miles. I did a top end swap from a 99 GTP with about 75K . I also have 1.9:1 modded rockers, a Wizaired CAI, a 180* thermostat, lower temp plugs (Autolight 104 equivalents), 42.5 lb injectors, Pacesetter headers with a 1.75" primary and a 3" collector, a ZZP highflow Cat, no U-bend or resonator, and flowmaster 40's. I also have a custom tune and no KR. I'm running 190 whp, which if you figure a 20% to 25% drop in power across drivetrain equates to somewhere between about 235 and 255 HP. I'm is also hitting only about 3.5 lbs of boost. Now unless I'm wrong I should be getting about 300-325 HP and 7-8 lbs of boost. The only thing I can figure is the oversized headers are lowering the boost and resulting in less power. What I'm wondering is if anyone can tell me why my boost is so low and if I can drop the pulley without any extra mods. What I'm worried about is overheating without an intercooler. For normal driving the temp is fine and sticks right at 180*. The other day I found a real long, lonely stretch of road and just pegged it for about a minute or two. I hit 137 mph and noticed my tach was at 6K when I redline at 5.7K, and my temp had gone to about 215*. Any help will be appreciated. Thanks.

 

I just remembered another question I had. Would wrapping my headers do anything for power? I assume it would lower engine bay temps, but since my intake is boxed would it really make that much of a difference? Thanks.

 

The headers wont make you lose boost. I would check to make sure you dont have a leak somewhere that is letting the pressure out. That would be my best guess. Like you said, you should have alot more boost and be making alot more horsepower than you are. Something is definately wrong.

 

Headers can drop boost levels- but not that much. The better flowing your exhaust is, the less pressure your cylinders maintain- resulting in less pressure in your lower intake manifold (which is boost on roots blowers cars).

Back on topic- OP, your boost bypass valve solenoid is probably broken- when it goes it defaults to 3.5/4 PSI only. You can test it by removing the vacuum line that runs from your boost bypass valve to the solenoid (believe it's the lower line on the driver side on the boost bypass valve). Remove this line and take it out for a rip- I bet you see closer to 11 PSI and a giant increase in power. Report back and let us know how it goes.

BTW, you'll probably make more power pulleying up to a 3.6 and adding a bunch of timing- our L36 compression bottom ends seem to favor big timing over more boost.

 

I wrapped my crossover pipe to help keep it from heat soaking the throttle body- seems to maybe have helped a bit. I didn't want to wrap my front header because it looks pretty "bling" in shiny stainless right now.

 

I was going to say, let's suspect your tune.

Do you know how the car was tuned, how much timing and everything was pushed?? Or was timing pulled and fuel dumped at it to keep the KR down??

A 3.2 pulley on a top-swapped engine is very small. I would think you would need to get into intercooler and cams to get to that safely.

 

I'm pretty sure it's not his tune limiting him to 3.5 PSI. I suppose you could tune it to limit boost via the supercharger timer/traction control tables, but I've never seen or heard of anyone doing it and I don't even know if it'd work.

I'll bet $5 right now it's BBV related.

 

After your post I do agree with what you are saying.

I still think it's a small pulley regardless

 

As far as the tune is concerned all he did is lean it out. I had gotten a canned tune from ZZP and the air/fuel ratio was less than 10.0. He leaned it out to 11.8 and that was it. At one point he tried advancing it 2* and got a couple degrees KR so he pulled it back. It hadn't hardly affected power anyway. 03SS, I know what you are talking about with the shiny headers. that is a good idea to wrap the crossover. You hardly see it anyway and that would lower the temps in the throttle body. Could you explain how dropping the pulley and advancing would help? I'm still learning. And if possible could I get a pic of what tube I'm going to take off? I don't want to brake anything. Thanks everybody.

 

For right now, let's forget about your tune and about changing pulley sizes. Let's focus on your potential BBV (boost bypass valve issue). We can come back to tune/pulley size questions later.

Do you know what the BBV looks like? If not, here's a picture:


And here it is installed on a 3800:


OK, now go out to your car and locate your BBV. There are two vacuum lines connected to it. One connects the BBV to a vacuum port on top of your supercharger. The other runs to an electric thingy- this is your BBV solenoid. Disconnect the vacuum line that runs to the electric thingy and take the car out for a rip and let us know what happens.

When you disconnect the BBV from the control solenoid, you allow it to run off of vacuum manifold only and it will achieve full boost, if the solenoid is broken.

Let us know what happens- I bet you see 11 PSI.