Ok i just installed a boost guage and when it idles its at 15 vacume and under short burst to the throttle it goes to boost 10 psi and hard throttle to red line its around 12 psi...i checked the bypass and checked for vacume leaks...it has a 17 % alta pulley...the question is does that vacume psi sound right? and if you hold the throttle at 4000 rpm is it normal for the boost to drop back down while still holding the rpm?
thankyou

 

Yup, it's right. It only reads boost when you get on it. I read about 24 hg when idling and when I'm
Just doing some normal driving I hit about 13 psi of boost. At WOT, I'm hitting 17 psi.

 

Yes, at least on mine, the boost is proportional to how hard the engine is working. So if it's floored at 4000 RPM, the boost will be high, but if it's just cruising, it won't be. On the highway at about 75 MPH, it's at about 3000 RPM and it's a negative boost (about -10 mmhg vacuum).

BUT....that boost sounds pretty low for a 17%. Mine peaks at about 14psi with a 15% pulley. You may have a boost leak or a poorly adjusted bypass valve.

 

i checked my bypass i pressure tested it and it held and closes...i am stumped...maybe its not a 17% pulley...anybody in the east toronto area that can look at these cars beside the dealer?

 

Yeah, you might have just a 15%. I have a 15% s/c pulley and a 2% oversized crank pulley and I hit 17 psi at WOT. I would think with a 17% you'd at least get 15 psi. So you notice any other aftermarket parts under the hood?

 

mini madness filter but it had the snorkle missing from the airbox to the front of the car..cooler plugs and a aftermarket vacume line split from the fuel regulater to the in sid of the car (boost Guage) from old owner....should i steal the vacume from somewhere else besides from the fpr???
so i assume that the old owner had more mods but then removed them b4 he sold....so who knows what else

 

Yes, that's where you run the boost gauge line from, however, check the vacuum connector for the boost gauge line. Mine was dry rotted all to Hell and when I put a new one on, my car ran better and showed the correct amount of boost on the gauge.

 

well i changed the bypass with a brand new one....what a waste of money. now i am really stumped...awell i guess its a weak sc...heads up people the sc wear out at 132,000 km

 

Ok just checked your other thread. As mentioned there boost on a SC car depends on a few things if you have head work it will be lower or a free flowing exhaust it will be lower. Might have missed it but have you changed your belt?

 

yes new belt napa 535