Bypass valve "Stop Screw" adjustment

[jrcalvin]

Okay, I have another general question regarding the Saleen SC By Pass Valve. I have also sent this question to Saleen Techs for a definitive answer.

The Saleen SC installations instruction note that NO adjustment should be made to the By Pass Valve stop screw. This stop screw position was precision adjusted at the Saleen factory when new and being manufactured. "Do Not Adjust Stop Screw".

The adjustment stop screw stops the internal butterfly in the closed position, thus directing incoming air to the SC twin screws when no vacuum is present when the throttle is fully opened under load in 3rd-4th gear.

One of the reasons for the precision adjustment of the By Pass Valve stop screw when the butterfly is closed is to prevent the butterfly from potentially "sticking" in the closed position. This "sticking " occurs when the internal By Pass valve spring does not overcome the "stuck closed position".

I have noted this "sticking" situation when manually moving the butterfly to the closed position with the stop screw totally removed. So it is "possible".

So..... My question for today is; Is it possible for the internal butterfly to move to a position...... beyond the "closed position".....so that a portion of the the incoming air slips by the butterfly and is not directed to the SC twin screws for boost.

I have attached a photo I found on the web (mustangworld.com) of the Saleen Series VI SC cross-section which shows the position of the internal butterfly. This photo may be of interest to those curious about the Saleen SC internal design.

jc

[OneQwkStang]

Looks like a maze..so how does the air travel in that thing?

[Werecow]

I don't believe it can go past the position to reopen again. I believe there is a physical stop there, but I am not 100% sure. By the description you wrote, it seems to say that as well.

[wiggywigton]

Hey guys, so I m working through some boost issue and I think I along with Jason have narrowed it down to the bypass actuator.
Here is the issue, on 3rd gear pulls about 5600 rpms the boost drops off. Seem to be getting worse the more I look into it. I went to Test in tune the other night thinking that I fixed the I've last week with a Loose fitting but the problem seems to have gotten worse.

So if I understand this bypass correctly the idle creates enough vacuum to close the bypass preventing compressed ir from entering the combustion chamber. Under acceleration vacuum pressure drop offs which open he bypass allowing the SC to boost.

So I have checked the actuator with a Vacuum tester and it holds pressure fine at 15 psi. So my theory is tht the actuator is closing somehow under boost. The only thing Is if vacuum is the only thing that is able to close the bypass and how would the SC create vacuum, close the bypass, all the sudden at high rpm and boost?
Could the arm be sticking a bit nd just the massive amounts of air be forcing it to close? What else could be the problem? Could the set screw be set too high considering the amount of boost I am running now as compared to stock?

Think of taking the lid off just to check things out. Any suggestions would be helpful.

[seelye76]

You sure that your belt isn't slipping? What size pulley are you using? Do you have a mosaleen or thumpr system? If you check the boost bypass valve and it holds vacuum then it doesn't seem to be the culprit. Any chance you have a vacuum leak when the bypass connects? Also I think the vacuum actually opens the butterfly inside the supercharger so the air does not have go through the screws and get compressed. When it loses vacuum, it closes and the air must go through the screws.

[jrcalvin]

I tend to agree with "seeley76" that your belt may be slipping.

One of the things I like about the Saleen SC "boost control" system is that it is so simple. The boost bypass valve normal normal position when the engine is off is closed due to the boost valve's internal spring. Intake vacuum at idle is around -15psi and that vacuum working against the boost valve diaphram opens the SC butterfly so air bypasses the SC screws.

Any vacuum leaks are most noticable at idle rpms. High rpms under load reduce the intake vacuum to zero and the boost valve internal spring closes the SC butterfly allowing intake air to flow to the SC screw and be compressed.

I will say the the SC "precision" boost valve adjustment screw setting by the factory, which they say should NOT be adjusted, confuses me. I say that because I have two Series VI SC and the boost valve screw adjustment differs by 1/8" - 3/16".

A replacement boost valve is not much money but your test seems to idicate that all is well with your boost valve.

By the way, you can temporaily disconnect the vacuum line to the boost valve, plug the vacuum line, and make a short drive to check boost under load when the boost valve is normally closed by the spring. Vacuum to the boost valve is then out of the equation.

Again, as "seeley76" said, check for belt slippage.

jc

[seethrough]

Originally Posted by wiggywigton

Hey guys, so I m working through some boost issue and I think I along with Jason have narrowed it down to the bypass actuator.
Here is the issue, on 3rd gear pulls about 5600 rpms the boost drops off. Seem to be getting worse the more I look into it. I went to Test in tune the other night thinking that I fixed the I've last week with a Loose fitting but the problem seems to have gotten worse.

So if I understand this bypass correctly the idle creates enough vacuum to close the bypass preventing compressed ir from entering the combustion chamber. Under acceleration vacuum pressure drop offs which open he bypass allowing the SC to boost.

So I have checked the actuator with a Vacuum tester and it holds pressure fine at 15 psi. So my theory is tht the actuator is closing somehow under boost. The only thing Is if vacuum is the only thing that is able to close the bypass and how would the SC create vacuum, close the bypass, all the sudden at high rpm and boost?
Could the arm be sticking a bit nd just the massive amounts of air be forcing it to close? What else could be the problem? Could the set screw be set too high considering the amount of boost I am running now as compared to stock?

Think of taking the lid off just to check things out. Any suggestions would be helpful.

You have this backwards - at idle the engine has vacuum and pulls the bypass OPEN. Bypass OPEN equals no pressure between inlet/outlet of the SC and 0 boost. When you stomp on the GO pedal vacuum drops and the bypass valve shuts on it's own under spring pressure. Once closed there is no path between the outlet and inlet of the SC and you have a sealed (somewhat) outlet that builds boost. If you want to see this watch the valve as a someone starts the engine - you will see it move as soon as the engine starts. If you rev the engine quickly you can sometimes see the valve close.
How are you seeing boost drop? Is it off the stock gauges or is the dyno tech running a boost gauge. Is the motor stumbling or are you losing HP on the dyno graph at this point?

I think the others are steering you correctly and you are experiencing belt slippage but it could be other things that are happening that would cause the engine to stumble and boost to drop.

[wiggywigton]

I have the thumper idler. I would think that if i have belt slip i would see belt dust? How else could i tell if the belt is slipping? Would after slipping cause the bypass to open and block the boost? When the "event" happens it is like i am letting off the throttle, power is gone and rpms drop.

i am sure there are no vacuum leaks. Triple checked and even put hose clamps on the vacuum lines just in case.
pulled the lid...all looks good.

[jrcalvin]

You describe the event as "letting off the throttle, boost is dropping/gone and rpms drop" even though you still have your foot on the gas pedal.

I would guess....yeah just guessing....that the drop in boost AND corresponding drop in RPMs may suggest that fuel delivery has dropped BELOW that which is needed by the motor to maintain power at that corresponding boost level.

Perhaps a drop in required fuel delivery rate produces the same result as letting off the throttle wherein boost pressure drops back to negative vacuum as usually seen at normal cruising speeds and steady throttle openings.

jc

[seethrough]

I am on the same page as jrcalvin. If you are tuning this the dyno tech should be able to get your hand held to display long term and short term fuel trims or maybe even fuel pump dwell % to see if it is a fuel issue. Do you have an A/F gauge in the car? What are your mods?

[wiggywigton]

Tuner is saying that the fuel pumps are working fine. AFR shows 11.7 even during the event.
It is not on a dyno though. Being tund via email.

[seethrough]

I overused your car specs in your signature and don't see any improvements to the stock fuel pump. Am I missing it because a 3.0 pulley on a striker motor with 39lb injectors seems or much motor for a stock pump w/o boost-a-pump or upgraded pump. Are you logging your data and sending it to the tuner? Can you record long and short fuel trims. Can you record engine vacuum through the stock MA?

[seethrough]

Spellcheck stinks - overused should be perused.

[wiggywigton]

Originally Posted by seethrough

I overused your car specs in your signature and don't see any improvements to the stock fuel pump. Am I missing it because a 3.0 pulley on a striker motor with 39lb injectors seems or much motor for a stock pump w/o boost-a-pump or upgraded pump. Are you logging your data and sending it to the tuner? Can you record long and short fuel trims. Can you record engine vacuum through the stock MA?

I am running upgraded gt500 fuel system, 2 walbro ford gt fuel pumps.

[seethrough]

I would try what JRCALVIN recommended above and disconnect/plug the vacuum line from the bypass valve and run your test again. This will keep the bypass valve closed and the engine will always be under boost so I wouldn't do any heavy pulls from low RPM - instead get it up above 3k RPM and then jump in it and record your boost, AF ratio and see if the problem persists. Best to try to rule out issues one at a time to determine where the real issue is.

For short runs with the belt slipping I don't think you would even see much belt dust at all. You probably won't even hear belt sqweal since it happens so fast.

What data can you log when you run your tests?

[wiggywigton]

Originally Posted by seethrough

For short runs with the belt slipping I don't think you would even see much belt dust at all. You probably won't even hear belt sqweal since it happens so fast.

What data can you log when you run your tests?

So I think belt slippage is the issue. I took the intake tube off to clean the throttle body and noticed some what I thought was dirt on the SC input shaft housing. I used some carb cleaner on the TB to clean it and some on the SC pulley to clean it as well. Got a little on the belt. Took the car out for a spin and low and behold of the 4 times I did a wot pull I couldn't replicate the event. I also hit it once in first and then let off and I swear I heard a belt squeal.

Going to give it a couple of days. Probably need to save up for a Mosleen idler set up...

Thanks all for your help and advice. This forum proves to be very helpful without a reputable shop in the immediate area...

[wiggywigton]

Update. And a question.
So still having issues.
I decided to take the IC off to see if there was something wrong with the bypass.
I found the butterfly valve is getting stuck open just enough to let some air past and I am sure under heavy boost it is opening.
I see on the valve there is an "F" but it is in the back. Would it be in backwards? And the "f" is supposed to be facing forward?

[wiggywigton]

Figured out my issue is the butterfly valve rubbing against the bypass wall and sticking partially open under WOT pulls. The valve edge was rough and scratched the wall. Must have happened when I blew the motor. I polished the cylinder wall and deburred the butterfly valve and that seems to have fixed the issue.

[Iceberg120203]

I am also having boost issues, stage 3 setup, and it is not the vacuum line or belt slippage. I have done everything from re-tuning, new belt, adjusting boost a pump, etc. Nothing works and my issue may be the same as yours. I was wondering how you got the bypass valve off with limited space and not damage the plastic enclosure. Is there a way to check if it is getting stuck without taking it completely off? Next option is to adjust the stop screw. Thanks

[jrcalvin]

Wow! This a reply/comment on a 3 year old topic and is probably of no interest anymore to anyone?


1. To verify the "factory precision" adjustment of the bypass valve stop screw, just take the time to remove the SC lid as well as the IC and visually verify that the internal butterfly bypass is in the optimum/correct position for maximum boost.



2. Under boost and also with engine stopped, the vacuum operated bypass valve spring closes the internal butterfly bypass. So with the IC removed, you can visually check/verify that your particular stop screw adjustment setting actually positions the internal butterfly bypass in the optimum position to direct all incoming air to the twin screws with no/minimum leakage to sides of the internal butterfly bypass.


3. If the butterfly is not in the optimum position, adjust stop screw as needed.


4. I have done a simple vacuum test (about 15 psi) on my vacuum bypass valve several times previously, and it checked out good and immediately and easily overcame the internal spring. Bypass valve is "good" Right...? Not really....! The bypass valve with vacuum immediately overcame the internal spring but as I kept the vacuum on the bypass valve longer, after about 15 seconds the 15 psi vacuum slowly started to bleed off and the spring started to open the internal butterfly valve. Thus boost would drop off.


5. I post this mainly as a reminder to myself to always more thoroughly test the vacuum bypass valve for vacuum leaks. Especially if boost seems to ever drop off.



jrc