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3.4 pulley and only 5 psi boost at full throttle?

B

bfox507

New member
hey guys I'm running into a problem with my boost number i did a gen 3 top swap with xp cam, 3 inch hi flow cat down pipe and new dual exhaust off an 04 impala ss on my 04 impala ls. I changed the pulley to a 3.4 to get at least 8 to 10 psi and I'm not even see in close to that. I'm only getting about 5 and i don't even get into boost unless i got my pedal mashed to the floor and it doesn't even stay in boost for a good amount of time. not sure what the problem is but I'm thinking it may be the bypass valve because i replaced the seloniod and the supercharger is completely rebuilt. I'm join to put this on a dyno and have them tune it because I'm having issues with zzp's basic tune and i really want to get this car dialed in and make it perfect for being my DD. i was wondering if u guys could give me anything you think could be wrong with the boost and ill double and triple check it because at one point i was seein 10 psi and now I'm only getting 5 and when i hit that 10 psi the car felt like a rocketship and i want to get that feeling back and get my car to be at full potential.
 


Yeah could be the bypass valve, but realistically you won't see more than 6-8 on an XP Cam and headers with a 3.4 pulley. could probably run a much smaller pulley with those mods.
 
post some pics of your vac line routing, and make sure the bbv lever moves when you rev the engine. not a tune issue at this point.

carb cleaner sprayed at the vac lines, blower base, tb gasket will let you know if you have a vac leak.
 
Check your boost bypass solenoid,when they fail you will see real low boost numbers.Usually 3 pounds tho, still something to check.
 
Ok lets do this the easy way. Im assuming you know what you boost bypass valve is here. If you dont then google is your friend. Anyways unplug the little line that goes from the boost bypass valve to that little solenoid with a plug on it (Not the one going to the top of the blower... that one will hiss at you so dont unhook it). By unhooking that we are eliminating ALOT of variables. There is a flappy lever thing that the boost bypass valve assembly is hooked to. It should be under a fair amount of spring tension tryping to make the flappy lever push "down" towards the base of the blower. This would be considered the closed posistion where you would make boost. When the little flappy lever thing is pointed almost straight up its open. The flappy lever should point up when your car is idling and should point towards your coil packs when you rev the car. If it isnt flapping like I said then your flapper is broken and you need a new boost bypass valve. To confirm this you can wedge rocks, zip ties, small animals, or your mom into the flappy lever thing to hold it "open" and pointing towards your coil packs. Then go drive it and see if you have boost again. Thank your mother afterwards.....

Or if just unhooking the line from your boost bypass valve to the solinoid fixes the problem then you have some vacuum lines or other stuff messed up.
 
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