angryhillbilly

i apologize if this has been covered but i cant find it anywhere.

i have a JRSC on my B16 with a gsr head. LHT intercooled

the bypass valve would stay open and the engine wouldnt see any boost and then randomly slap closed when it wants to and then boost. so to get the engine tuned we zip tied the valve shut.

i have read that it is completely fine to leave it this way at the expense of your MPG. BUT im having a hard time believing this and would like somone to explain it to me.
maby im just the type of person who needs a little more than a "a post on d series.org said it was fine" so i believe it.

if the valve is always closed, this means you press the gass to any extent and your boost flys up (i like this). then you let go of the gas and the left over boost in the manifold does not escape through the bypass. where does it go? what are the effects of this big bubble of pressure? could it push the manifold and the charger to separate and result in a vacuum leak? go back through the charger and push on the throttle plate? push through the engine and cause problems or premature wear?

wantboost

iTrader: (2)

In a nutshell...

With the bypass closed air doesn't bypass the rotors. This means all of the air the motor ingests has to pass through the rotors. Superchargers require power to turn them, aka parasitic loss, so when you can't reduce the load on the supercharger it causes a higher parasitic loss.. not to mention a loss in part cruise power since the supercharger is absorbing what little power is being made.

If you were having those issues with your bypass valve then it has failed. Replace it.

We defeated the bypass valve on one of our shop SVT Cobras for ***** and giggles.

Motor never ever went into vacuum at light throttle cruise, there was always some sort of positive pressure being made. Car got complete **** for fuel economy and there was a lot of part throttle surge due to the constant change in boost pressure, thus a higher rate of parasitic drag from the supercharger. Also sometimes the ecu would throw a cel and go into limp mode... This was mainly from the supercharger producing boost pressures and high airflow levels at rpms and load points the ecu was never meant to see nor was it tuned for. The ecu interpreted this data as a failure of some engine component/control system and put the car in reduced power mode to prevent what it thought was any further failure. This was mostly noticeable at long periods of higher throttle input cruise. The ecu saw a rapid rise in boost pressure for too long of a period of time it shouldn't have been seeing.

It sucked to drive...

Long story short, replace the bypass valve like you should and allow the system to operate properly

wantboost

iTrader: (2)

And in regards to what happens after you let off....

Positive displacement superchargers are located after the throttle body. After air passes through the throttle body it's a one way street, air cab only go through the motor. There isn't a high enough amount of pressure to cause anything to separate, actually it's physically impossible. If that were even true you'd break a valve head off before anything else.

Positive displacement superchargers make pressure after the rotors, not inside the supercharger, it all works off of the restrictions after the rotors.

The only thing that would (and should) happen is after you let off the throttle you might notice a delay in the rpms dropping off. It should basically feel like surge with the possibility of a little bucking since the ecu sees something that shouldn't be happening, has no idea what's going on, and freaks out a bit.

Again, replace the failed bypass and call it a day.

angryhillbilly

Thank you for that reply and the help. I appreciate it. I am def interested in fixing my bypass valve. Both for the fuel economy and the sake of things operating the way they should.

I definitely experience the bucking, and it's what ever on the street, but once I get on track this just will not due. Down shifting onto a corner and the car bucks and throws weight distribution from the back to the front to the back again will really mess up corner entry grip.

As far as replacing the bypass. Does anyone know how to diagnosis exactly what could be broken based off my symptoms? Also is there a way to test it or inspect it to see what's wrong without taking it off? I have heard that the replacement is like 200 and somthing dollars and well... I'm in college lmao.
And lastly, does anyone know if I can replace this piece without removing the charger from the manifold? Cuz that is such a pain in the *** in a parking lot with a bag of tools lol.

wantboost

iTrader: (2)

It's just a diaphragm like a wastegate or bov with a small spring to keep it closed when vacuum isn't being applied.

Typically the diaphragm will rip or tear resulting in failure. I've only see the spring break a few times, rarely.

If you apply vacuum or pressure to the bypass and it doesn't move, doesn't hold position, or sticks then it needs to be replaced.

I don't think Jackson makes them anymore but a bypass valve for an Eaton supercharger should be the same. Check eBay.

Black R

I have then opposite problem - mine stays open a tiny bit when it should be closed.

I'm not too worried about it bc it's not losing a lot of boost, but still that's annoying.

angryhillbilly

Thanks for the help guys. I am going to attempt to dig into it this weekend. I need to seal up the gap between the manifold and the charger. Hopefully I can do this without taking off the charger and replacing the gasket. Once I kill my vacuum problem I will start fiddling with my bypass. I'll keep this thread updated.

angryhillbilly

Anyone have a link to replacement Bypass valve I can buy?
(got it to work kinda for 2 years but im ready to fix it for real now)

Schister66

Part Number 999-050 for $69.99 looks to be what you need.

MossPerformance.com High Performance Parts & Accessories

angryhillbilly

Thanks man. not too bad of a price actually considering how many years its been since this kit was made lol

porofek

iTrader: (1)

In only a couple of months and the price is now $124.99 at Moss. That's just insane!