Powerworks bypass valve vac line mod!!!

pzev04boy · Oct 23, 2009

Just an fyi. I have found on a pw car that re-routing the line for the powerworks bypass valve is very helpful in a few ways.

I have had a feeling that at times the bypass valve can stick open a bit causing lower boost & this also allows already compressed /heated up air to be recirculated through the blower one more time causing higher IAT's. This may explain why a lot of powerworks owners notice their car will have it's moments where it makes less boost and feels slower.

There is also another Issue I just encountered with a local who has a built motor and a custom 2.5 pulley. He was making only about 14 psi and noticed the boost would not stay consistant. We did the mod I am about to describe and the car picked up 2 psi boost and dropped about 15 degrees of IAT's. He needs to get back on the dyno now.

The solution & my recomendation to all PW owners is to pull the vacuum line off the Bypass valve & plug it, get a tee and tap into where the fuel pressure sensor hose is on the upper plenum and run a new hose from there to the bypass valve. Use zip ties or clamps to hold the hose on.

Now with both a source of boost and vacuum to the valve it will still function as a bypass at idle or cruise, but will also have the boost pressure to hold the valve shut under boost.

I have not tried this on a stock boost car yet, but I see no issues only potential performance gains. This also should help prevent the bypass valve from sticking open like has happend to some.

I feel this is especially important for big boost cars as there is a spring in the bypass valve and it wasn't calibrated to hold much pressure. It's a very light spring in fact.

Try at your own risk, but this should be a worthwhile mod

If you end up with more boost you need to make sure it's safe.

dhardison · Oct 23, 2009

Very interesting! So the thought is the 'default' PWSC vacuum line connection between the bypass valve and lower 'intake tube' doesn't reduce the vacuum enough to fully close the bypass valve, even under boost conditions?

If so, it makes sense.

pzev04boy · Oct 23, 2009

dhardison said:
Very interesting! So the thought is the 'default' PWSC vacuum line connection between the bypass valve and lower 'intake tube' doesn't reduce the vacuum enough to fully close the bypass valve, even under boost conditions?

If so, it makes sense.

No. It doesn't use vacuum to close it. It uses vaccum to open it. But now that you mention it I'll bet there is a little bit of vavcuum in the neck itself when the car is under boost, which would futher support the need for this mod. The inlet to the rotors of the blower are bigger than the throttle body opening so when it is drawing air in it's almost for sure a slight vacuum in there.

Here is the scenario. The vaccum line that goes to the bypass valve goes to the inlet/neck of the PW housing. It never sees boost in the neck, only vacuum. The bypass valve has a spring and a diaphram in it and it gets opened by vacuum at idle & cruise. Then it relys on just a spring inside of it to keep it closed under part throttle & boost.

The re-routing of the hoses to put boost to it will give it a little extra to keep it shut under boost.

gti_uk · Oct 25, 2009

Sounds intresting, where it currently is it only sees about 10psi vac. Moving the pipe to the plennum means it will see vac and boost like you say.

My only question is can the diaphram handle ~15psi of boost pressure?

Trev

pzev04boy · Oct 25, 2009

gti_uk said:
Sounds intresting, where it currently is it only sees about 10psi vac. Moving the pipe to the plennum means it will see vac and boost like you say.

My only question is can the diaphram handle ~15psi of boost pressure?

Trev

I don't see a problem with it. The diaphram is made of a pretty tough material. Seems to be working just fine.

If you did have a diaprham failure it won't blow the engine up as it doesn't control boost. You just would have no bypass valve at idle so the car would have a poor idle.

DigitalGT · Oct 26, 2009

gti_uk said:
Sounds intresting, where it currently is it only sees about 10psi vac. Moving the pipe to the plennum means it will see vac and boost like you say.

My only question is can the diaphram handle ~15psi of boost pressure?

Trev

It should handle 15 psi of boost no problem. It handles 30 in/hg of vacuum no problem which is equal to 15 psi of boost.......just moving the the opposite direction.

SVTADAM · Oct 27, 2009

This is very interesting. I am new to the PW, and the slight fluctuation in boost is something I noticed right away. At times I can have only 7.5 pounds of boost while others hit consistent 9 pounds. I may have to try this out over the weekend.

Terrible1 · Oct 27, 2009

I've done something similar to this. Reason I did it though is because I pulled out all of the vacuum line that came with the kit when I removed the DPFE sensor and other related sensors off of the firewall. I just ran a line from the vacuum "tree" on the lower portion of the blower intake to the bypass valve. Seems to function just fine except I haven't really noticed any performance increase.... just less clutter :dunno:
Although I've never once had any issue with my kit. Mine was one of the first and from the sounds of it I've been pretty lucky having ZERO issues.

pzev04boy · Oct 27, 2009

Terrible1 said:
I've done something similar to this.

I just ran a line from the vacuum "tree" on the lower portion of the blower intake to the bypass valve.

If you are running it from the lower part of the blower you are not getting boost to the bypass valve. Anything from neck of the blower does not see boost.

And just to confirm, we hooked a vacuum gauge to the inlet neck of the blower and it does have some vacuum in the neck at wide open throttle. Almost 5 hg. Probably not an issue with stock boost levels, but you can imagine that it is going to further allow the bypass valve to leak during boost. I'll bet the spring in the bypass valve begins to open around 8-10 hg. Especially with boost helping push the butterfly open from the other side.

Terrible1 · Oct 27, 2009

pzev04boy said:
If you are running it from the lower part of the blower you are not getting boost to the bypass valve. Anything from neck of the blower does not see boost.

So are you saying I've done this incorrectly???

BOWERSdaAZIAN · Oct 27, 2009

subscribed. Im kinda intrigued to see if this will be worthwhile for me to do.

greentengu · Oct 27, 2009

x2 here. Very interesting! Looks like a little Thanksgiving weekend project on the floor of the garage. Anyone post a schematic for this? Just a thought as I'm sitting in my office trying to visualize this, scratching my head.

--Scott

COSDEVSVT · Oct 27, 2009

The reason for the pre-blower location is because it is a clean source of vacuum for the BBV ... not much chance of re-circulated oily air to find its way into the BBV while it always experiences vacuum.

The post blower location will be a dirtier air source. Not saying it won't work, but keep any eye on it so that that you aren't blowing oil (mist will pool) into the BBV and causing other problems.

ZX3TUNING · Oct 27, 2009

:lol:
dammit!
that means another oil catch can for this car? :lol:

pzev04boy · Oct 27, 2009

Terrible1 said:
So are you saying I've done this incorrectly???

You have it pretty much how powerworks has you hook it up.

pzev04boy · Oct 27, 2009

COSDEVSVT said:
The reason for the pre-blower location is because it is a clean source of vacuum for the BBV ... not much chance of re-circulated oily air to find its way into the BBV while it always experiences vacuum.

The post blower location will be a dirtier air source. Not saying it won't work, but keep any eye on it so that that you aren't blowing oil (mist will pool) into the BBV and causing other problems.

Good point. I know some blow of valves come with filters and it may be something to add on to this. Although I doubt oil is going to make it into the bypass valve seeing as the teflon line to the boost gauge is see thru and I have never seen any oil in it. I'm guessing that under boost if there is any oil in the system it will go with the air flow and since air doesn't flow through the bypass valve it shouldn't get any oil in it.

TXFO · Oct 28, 2009

bypass valves Vs. supercharged cars. the oldest boost battle ever. :lol:

DigitalGT · Oct 28, 2009

I think that if I were going to try this hose reroute that I would simply tee off the boost gauge port next to the IAC valve and run the bypass valve hose to that. Positive boost pressure at WOT along with manifold vacuum at low load/closed throttle. Just seems simpler to me than teeing the fuel pulse damper hose......which if I'm not mistaken, comes from the three way vacuum distribution hose connected to the intake neck of the blower assembly doesn't it?......which means it does not see boost pressure...... Hmmm.

I also just don't see the point of doing it in the first place. It's very hard to blow open a butterfly style valve that seals properly.....even one held shut with light spring pressure. Glad it worked for the OP. I can only assume that it wasn't sealing perfectly if the hose reroute caused a boost increase.

pzev04boy · Oct 28, 2009

DigitalGT;7134460 which if I'm not mistaken said:
No. There are 2 nipples on the upper part of the blower. 1 comes capped from powerworks and is for use with a boost gauge. The other goes to the fuel pressure sensor. You could tee into either of those actually.

It's a known issue on 03/04 cobras so they have been doing this for a long time and getting gains from it.

DigitalGT · Oct 28, 2009

Ahhh yes yes yes. I was wrong. I thought you were talking about the pulse damper in the middle of the fuel rail not the pressure sender on the end of it. Went back and re read your post and see that's actually what you said. My brain saw otherwise. You were correct at the onset.....though my previous post, from a "seen" vacuum/pressure point of view is just as accurate as yours.

Carry on maestro.

Powerworks bypass valve vac line mod!!!

pzev04boy

dhardison

pzev04boy

gti_uk

pzev04boy

DigitalGT

SVTADAM

Terrible1

pzev04boy

Terrible1

BOWERSdaAZIAN

greentengu

COSDEVSVT

ZX3TUNING

pzev04boy

pzev04boy

TXFO

DigitalGT

pzev04boy

DigitalGT

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