I recently bought a z28 with a vortech 9# supercharger on it, it has a crane digital ignition, boost retard, t-rex fuel pump, your standard sc stuff on it.... I havent really punched down the gas yet until today i hit 5k rpms, but the boost gauge read 0 psi.... it never passed 0, at 4k rpms it read around -5 psi. little confused here :-(

 

Have you checked for vaccum leaks? Also have you made sure your blower belt is tight? DO you mean your car is at 5 inches of vaccum at idle and then when you get on it goes to 0 ??

 

Definitely sounds like a vaccuum problem. By 4,000rpm, you should be seeing some boost.

 

At idle i see around -20 to -25 psi, as i drive i see between -20 - -10 in normal driving and when i punch it down i see up to 0 but havent seen above it even at 5 k The car pulls strong, but just not seeing the advertised boost.... If it is a vacuum leak, where should i begin looking for it? i looked along the hoses, but all looks alright there....

Thanks guys

 

FYI anything below 0 is considered vaccum and is measured in inches. Anything above 0 is considered boost and is read in psi.

Basically, I would back track all the vaccum lines you installed when you did the blower. Another thing to look for is kinked lines. Also make sure that the hoses to your blower kit are properly tight. Are you running an aftercooler or intercooler with your setup? What does your gauge read when the car is off?

 

I did exactly that, traced all the hoses and no leaks, everything is very tight....
No aftercooler/intercooler with the unit, I didint install it, the guy I bought the car from did, he claimed it makes 9# and the car runs 11s with stock heads and a ZZ4 cam and slp cat back in addition to the sc.

The gauge reads 0 when the car is off, but never seen it read above 0 :-(

 

Has the supercharger after made boost after you bought it? Also it the blower making any abnormal noises. Hopefully, you did not sell it to you with a bad blower.

 

When I bought the car I didn't get to "try it out" much, i never really paid attention to the boost level as i never really punched it down until i learned to drive stick ;-) there was one time i punched it down a little to around 3.5 k rpm and it hit 0 at that point, but i've never seen anything higher while i owned the car.... could it be something with the gauge maybe? The blower itself sounds fine, i installed a powerdyne kit on my old car when i had it and it sounded very similar just quieter so all seems alright in that area.... kind of bothers me knowing i have this thing on but not really seeing the results on the gauge....
Does the car have to be under a certain load? do i have to floor the car to see boost? when i ran it last night and hit 5k rpms i didnt quite floor it, but i punched it down pretty good....

Thanks again!

 

Well since you posted in the LT1tech forum that your fuel pump was making funny noises. I would not be punching anything. You need to get that fixed before you start getting into boost.

 

If you were seeing 5 inHg of vacuum at 4K rpm you weren't flooring it! Yes plant it to the floor and you will see boost, especially at 4K!

Bill

 

Ahh! well as soon as i get my fuel pump problem sorted out I'll give her a good run ;-)

Thanks everyone!

 

You won't see boost without the throttle all the way open. If the throttle blades are still shut a little, it allows just enough air to get past to take you out of vacuum, but, probably not enough to get into boost. Floor it and see if you get it.. after your fuel pump gets fixed though..

--Sean