ok guys ive got a bit of a problem ive almost finished my conversion and ive hooked up a boost guage and it reads 5psi on idle but when i rev it the boost goes up and reached 20psi at around 3 grand im confused any one have any clue what the problem is. thanks in advance

sure you calculated your pully sizing corectly, sounds like you might be spinning the sc to fast. where are you reading boost pressure from? only other thing i can think of is there is a restriction btween the sc and somewhere after where your boost guage line is, but if the boost line is in the plenum that really can't be the case. hmm.

It sounds like your supercharger bypass valve (assuming you have fitted one) is not opening, and the supercharger is blowing against a closed throttle. Do a search, and start reading, there has been heaps of information written about supercharger bypass systems.

but how come the boost goes up i thought sc stayed at one boost the whole time. i have the guage plumbed into the piping just before the tb. thanks

Quote: Originally Posted by nishmix if you see the pics mine is acually a different charger than matts and i have no intension of trading down to a used one. Who told you that the CRS chargers are new? I run one on my VR V6, I brought from a mate 18 months ago for $900 straight bolt on. I run 3psi, I wouldn't even try 9-11psi as the thing would melt. I think your doing a awesome job, but your wasting money with the prices you've quoted. Would have been better off with a turbo set up, as that will piss on a S/C any day. But good luck..

Quote: Originally Posted by vlwagz but how come the boost goes up i thought sc stayed at one boost the whole time. i have the guage plumbed into the piping just before the tb. thanks Superchargers make boost by spinning.. As turbos do, more RPM = more boost.. More RPM = more boost your motor will take also. But it isnt a perfect 1:1. so boost will go up and down over the revrange. "PSI" reading on superchargers is usless to compair with other turbos and SC people.. its simply a reading for that car, anymore and something is wrong, Any less and somthing is wrong.. boost in SC can be changed by so many factors that compairing it to other cars is usless.. As with the stock pully on an SC14 and a 160mm crank pully will get you 5PSI on a 3L RB motor, put a full exhuast on and it will be 3 PSI but make alot more power. headwork will down the boost again but up the power. Its not about the reading.. its about is the reading normal for that car at that time.

Quote: Originally Posted by [T]Matty Superchargers make boost by spinning.. As turbos do, more RPM = more boost.. More RPM = more boost your motor will take also. But it isnt a perfect 1:1. so boost will go up and down over the revrange. not exactly, more rpm will equal more boost for a bit, at low rpm internal leakage has more of an effect, causeing your low readong. but as your revs get toward redline you could start to lose boost if the volumetric effeiciency of your sc falls at a faster rate that that of your engine. so how did your pully sizing work out? you wouldn't just be getting a high reading because air pressure is building up between your sc and throttle plate at at idle, doesn't explain the 20psi at 3000rpm though, unless you this was just free revving the engine on the spot with a fairly close throttle? maybe move the boost line to the plenum and try and drive it? still that doesn't fix the problem of all that pressure in there at idle, you done a re-curculating system?

Quote: Originally Posted by VLT_RB30 Would have been better off with a turbo set up, as that will piss on a S/C any day. that just sums up the whole idea.

yeah that was just free revving it i was a bit sketchy about drining it if it was going to be running 20 pound of boost. we tried putting the boost guage behind the plenum but it just read 15 vacume and wouldnt move when i switch the charger on. so are you saying matty that 10 psi in my car might only be 5 on your car. im confused. also does having the wastegate just make it better to drive? thanks guys

look, i'm only going to say this once more. fit a bypass valve, or it will be impossible to drive normally. even after all the time tony and i have spent helping you guys out, you still can't get the message. i give up.

i was always going to fit one but just wanted to get it running first. so atleast i could drive it with the charger off.

PLEASE HELP. well i found a fairly big boost leak at the outlet pipe because we swapped the original pipes the inlet became the outlet and the outlet became the inlet it lined up but couldnt put a bolt through the middle at the top bacause the pipe is the way you should be able to see what i mean in my pics. so im guessing that is why my boost goes down when i accelerate but im still confused why the boost goes way up when i take my foot of the accelerater. here is a few pics of it so far not very pretty but im not planning on driving around with my bonnet open anyway. also a little vid of my boost guage when im stalling it up. any help would be very much appreciated i hope all this help. not a very good vid but might help. Some original photos have not been recovered yet.

when you take your foot off the accelerator the tb will snap shut creating heaps more pressure in your piping, this would be why your gauge reads more when you take your foot off,correct me if im wrong, but it makes sence also your gauge would be just showing all the pressure in the pipes,not what is actually goin in the engine. ive fitted my gauge to the plenum and it works a treat. i would guess that with the bypass valve it would eliminate this. howcome you have a breather on the back hole of the rocker cover? i just put a rubber 'cap' over mine to block it off. also can any of you please put up a pic of your bypass valves and how they are fitted. thanks

well i was told it was a breather so i thought putting a little filter over it and still leeting it breathe would be better that just blocking it and not letting it breather??? but i read that the charger self destructs after 10psi or somethin i read it in i think streetmachine the one with that twin sc gemini. if that is the case and that huge boost reading is on then all i have to is fix that boost leak. i hope. thanks nishmix anyone else got any ideas.

im not exactly sure what you have done, but i would belive that the gauge is reading completely wrong.no way would your charger be boosting that much, and if it was i wouldnt be to worried about your supercharger as much as your engine. it may have something to do with were it is hooked up to.

Quote: Originally Posted by StockyMcStock look, i'm only going to say this once more. fit a bypass valve, or it will be impossible to drive normally. even after all the time tony and i have spent helping you guys out, you still can't get the message. i give up. Only one idea. FIT A PROPER SUPERCHARGER BYPASS SYSTEM TO IT. Every production supercharged car has a bypass system. But then of course, the professional automotive design engineers at Jaguar, Mercedes Benz, General Motors, Toyota and Nissan are all complete fools and morons, and know nothing at all about supercharging. I give up too. You guys just don't listen.

i was actually referring to how they were mounted, because i actually want to do this, i was just after a bit of information so i could get it done. so i actually was listening, just trying to find out a bit more information.

move your boost guage also.. put it on the intake.. Just hurry up and blow your motor, Get a turbo and bedone with it.

my boost guage is in piping just before the plenum would that cause the crazy reading. ill put it where you said matty. i am going to put a wastegate on my setup and as i have said before i want to get it running ok first then ill get one. so i am listening i wouldnt have been able to do it without everyones help. and i appreciate it.

o and please dont blow your motor Some original photos have not been recovered yet.