Another OHV M90 build

[rocket 5979]

Isnt there allways vac between the tb and sc? If so wouldnt it keep the valve open all the time? Also you only explained how it works when at idle,not wile cruising.

In a reply to Don I just mentioned how the valve works at cruise.

Cliffnotes:

-Engine turned off = vacuum bypass valve pulled closed by return spring tension
-Engine idling = vacuum bypass valve pulled open by engine vacuum acting on the bypass actuator diaphragm that has now overcome the return spring tension
-Engine part throttle = vacuum bypass valve is now transitioning from full open to closed because with TB blade open the engine has less vacuum to hold the valve open against return spring tension. If the throttle position is held constant at some point just above idle then valve will stop somewhere between full closed and full open. If you press the gas pedal further then at some point a split moment before boost occurs the valve will fully close since vac will have disappeared since the lower intake manifold has now reached equilibrium with atmospheric pressure.
-Engine WOT = vacuum is now non-existant and return spring has fulled closed the vacuum bypass valve to allow boost pressure to occur in lower post-blower intake manifold. Boost is now also acting on the bypass actuator diaphragm which now acts in cohesion with the return spring to ensure valve does not open while in boost

While the TB is closed there will be vacuum between the TB and the SC. This vacuum will be a little higher than the vacuum that you will see if you measured vacuum levels post-blower at the same time. This is because the turning rotors are assisting in air movement even at idle and part throttle. However, since the TB blade is still closed the entire system, both pre and post blower is still in vacuum while at idle. If the blower was able to build pressure beyond 0vacuum/0pressure while the engine was idle then the vacuum bypass valve would never be able to be sucked open by vacuum if its little vacuum line were plumbed into the lower manifold. But since the vacuum bypass valve with its little vac line plumbed into the lower post-blower manifold does open while the engine is at idle, and the only way to pull that valve open is by vacuum, one can then conclude that the lower post-blower manifold is indeed in a vacuum state and not a pressure state.

 

[jd4242]

In a reply to Don I just mentioned how the valve works at cruise.

While the TB is closed there will be vacuum between the TB and the SC. This vacuum will be a little higher than the vacuum that you will see if you measured vacuum levels post-blower at the same time. This is because the turning rotors are assisting in air movement even at idle and part throttle. However, since the TB blade is still closed the entire system, both pre and post blower is still in vacuum while at idle. If the blower was able to build pressure beyond 0vacuum/0pressure while the engine was idle then the vacuum bypass valve would never be able to be sucked open by vacuum if its little vacuum line were plumbed into the lower manifold. But since the vacuum bypass valve with its little vac line plumbed into the lower post-blower manifold does open while the engine is at idle, and the only way to pull that valve open is by vacuum, one can then conclude that the lower post-blower manifold is indeed in a vacuum state and not a pressure state.

that doesnt explain how it opens when cruising and the tb blades is open.maybe we are just talking about two different type of things.mine has two lines on it,one is plumed into the pipe witch is between the tb and sc and one that goes to a solenoid then to the lower manifold.its held open by vac till the solenoid opens allowing boost to close the bbv.it will open wile cruising allowing boost to get recycled.so maybe ford uses a vacuum bypass and gm uses a boost bypass

 

[rocket 5979]

that doesnt explain how it opens when cruising and the tb blades is open.maybe we are just talking about two different type of things.mine has two lines on it,one is plumed into the pipe witch is between the tb and sc and one that goes to a solenoid then to the lower manifold.its held open by vac till the solenoid opens allowing boost to close the bbv.it will open wile cruising allowing boost to get recycled.so maybe ford uses a vacuum bypass and gm uses a boost bypass

Look at my above post. I even made cliffnotes just for you. Adding a solenoid into the mix, whose purpose is to modify the vacuum/boost signal making it to the bypass valve actuator diaphragm, turns things into a different ballgame in some ways; and will open a whole new can of worms of how the vacuum bypass valve can be controlled. The Cobalt SS/SC's use this and some other modern factory FI cars do too but the solenoid is not necessary for proper operation of the bypass valve. Most aftermarket vacuum bypass valves only have the single vacuum port on their diaphragm, which is located on the "far" side of the diaphragm on the opposite side of the actuator rod going to the bypass blade.

 

[jd4242]

Look at my above post. I even made cliffnotes just for you.

what you are not understanding is that mine has two lines,not just one to the lower manifold.with it setup that way the ford one will not open at higher cruising speeds or when your not making vacuum at the lower mount.thus only being a vacuum bypass.mine will open and allow boost to bypass when not needed

 

[Dono]

JD, the way mine works is that if there is vacuum after the M90, the valve opens. If there is no vacuum (M90 is pushing air close to as fast, or faster than the motor is requiring) the valve closes as its getting enough air from the M90.

I think that about sums up the bypass valve on my setup. In laymans terms, that is about it.

Thanks for the long explanations. It helps me wrap my head around the valve. I didn't understand it before.

It doesn't help my idle issue though.

 

[Dono]

So, I checked my two wires to the idle valve. Pretty tough to mess it up. Both wires were fine. I logged some of the idle pids and sent them to James. He may not even bother looking at it, but it just might help. I don't know what else to do. I'm stuck.

 

[jd4242]

So, I checked my two wires to the idle valve. Pretty tough to mess it up. Both wires were fine. I logged some of the idle pids and sent them to James. He may not even bother looking at it, but it just might help. I don't know what else to do. I'm stuck.

you said you unplugged it and nothing happened right?maybe its bad or did you log movement?

 

[Dono]

I tried 2 valves. I had picked one up from the graveyard and had pre-installed it on my new tb. Today, I installed my original tb that I know works. Same issue.
Now, when logging, the duty cycle changed on the pid. I don't know what that really translates to though. The idle rpm's never changed.

 

[rocket 5979]

what you are not understanding is that mine has two lines,not just one to the lower manifold.with it setup that way the ford one will not open at higher cruising speeds or when your not making vacuum at the lower mount.thus only being a vacuum bypass.mine will open and allow boost to bypass when not needed

I get what you are saying. Yes, just like how the Cobalt SS/SC's do with their control solenoid. However most positive displacement supercharger systems don't use that valve in that manner and only use it for vacuum bypassing at or near idle. That is the original reason why that type of valve was engineered and included in the Eaton setups as well as other positive displacement supercharger systems such as Whipple, Maggie, and Kenne Bell to name but a few. Since then some people have gone above and beyond in modifying the signal that the vacuum bypass valve sees so that WOT boost can be affected too. This is where your two port vacuum bypass comes in. While its main purpose is to bypass vacuum at idle, it also can be controlled by the solenoid via a computer so that it can control boost too. That is a far secondary use which is not really commonplace or the original intended use. The exact same thing can be said for a turbo wastegate being plumbed into the intake tract of a centrifugally supercharged vehicle to control boost by dumping excess compressed air during WOT to achieve a controlled lower pressure than the pulley combo would have given. While it can be used this way, the primary use is that it be used in the exhaust stream to bypass exhaust gasses around the turbine in the turbocharger which is why we still call it a wastegate and not a boost control valve. Ok I will stop talking about how the bypass valves, turbo wastegates, and etc work, because while interesting conversation fodder, they don't directly apply to troubleshooting Dons issues. It was nice to discuss this with you in a fairly civil manner JD.

 

[Dono]

Wow, I liked that explanation.
I think you said it in a way that I understand both systems now.
On that note, tomorrows a new day. No ones hurt, and everyones hopefully healthy. Lifes good.

Gnight guys!

 

[rocket 5979]

I tried 2 valves. I had picked one up from the graveyard and had pre-installed it on my new tb. Today, I installed my original tb that I know works. Same issue.
Now, when logging, the duty cycle changed on the pid. I don't know what that really translates to though. The idle rpm's never changed.

When the IAC is working properly it will cycle the duty cycle ever so slightly to achieve a solid state idle. So while the engine RPM remains virtually constant the IAC duty cycle will vary a little bit to keep the engine at this corrected idle RPM. Think of it in the same way that you use small corrections to keep the truck straight on the highway. Even though the truck is more or less staying in the middle of your lane, you are still making small corrections to the steering wheel angle to keep it that way.

But if your engine idles at the same RPM regardless of the IAC valve being plugged in or not then something is causing it to not have an affect on incoming airflow bypassing around the TB. Intermittent issues like the one you are having can be a pain sometimes.

 

[jd4242]

I get what you are saying. Yes, just like how the Cobalt SS/SC's do with their control solenoid. However most positive displacement supercharger systems don't use that valve in that manner and only use it for vacuum bypassing at or near idle. That is the original reason why that type of valve was engineered and included in the Eaton setups as well as other positive displacement supercharger systems such as Whipple, Maggie, and Kenne Bell to name but a few. Since then some people have gone above and beyond in modifying the signal that the vacuum bypass valve sees so that WOT boost can be affected too. This is where your two port vacuum bypass comes in. While its main purpose is to bypass vacuum at idle, it also can be controlled by the solenoid via a computer so that it can control boost too. That is a far secondary use which is not really commonplace or the original intended use. The exact same thing can be said for a turbo wastegate being plumbed into the intake tract of a centrifugally supercharged vehicle to control boost by dumping excess compressed air during WOT to achieve a controlled lower pressure than the pulley combo would have given. While it can be used this way, the primary use is that it be used in the exhaust stream to bypass exhaust gasses around the turbine in the turbocharger which is why we still call it a wastegate and not a boost control valve. Ok I will stop talking about how the bypass valves, turbo wastegates, and etc work, because while interesting conversation fodder, they don't directly apply to troubleshooting Dons issues. It was nice to discuss this with you in a fairly civil manner JD.

agreed so yes i was wrong in calling the ford one a boost bypass but at that point i was going off that it used the same as mine because don said he thought thats what it looked like.im hooking my line from the lower mount up to a spare purge valve from the gas tank vent line.that way i can turn it off and it will open the bypass valve at highway speeds when full boost isnt needed.never was trying to turn it into a pissing contest,just trying to learn and discuss all options

 

[rocket 5979]

agreed so yes i was wrong in calling the ford one a boost bypass but at that point i was going off that it used the same as mine because don said he thought thats what it looked like.im hooking my line from the lower mount up to a spare purge valve from the gas tank vent line.that way i can turn it off and it will open the valve at highway speeds when full boost isnt needed.never was trying to turn it into a pissing contest,just trying to learn and discuss all options

When you are talking about being at highway speeds do you mean cruise or WOT accelleration?

Good night guys.

 

[jd4242]

When you are talking about being at highway speeds do you mean cruise or WOT accelleration?

Good night guys.

cruise.but i dont totally understand how or why people are doing that tho.but now we are totally of subject and cluttering up this thread.if you would like to discuss this more tomorrow in my thread i would love the help or bounce some ideas off you.

but gnight yall and don keep us informed what you find out as i may run into it also

 

[Dono]

OK, more tune files from James.
I installed the next tune, and started. Idle was high, but after a bit of driving it settled down to where its supposed to be. I was logging this time, so James will see I'm not crazy. Once again, the idle was fine until I re-started the motor.

I then installed the Next tune, locking the transmission in high gear and did my pull. Pull was quite a bit stronger than the last one. Again, idle settled down quickly. I thought for sure James had done something. I loggged my pull.

I pulled off the highway and re-installed the non transmission locked tune James sent me today. This time, the idle would not go down to where it should be. I logged while I was in park, and cut the Idle control valve wire (I cant get at the connector without pulling the throttle body). No change in idle, and its logged and sent to James.

Whats going on with this idle thing? The fact that when the idle works fine when it does actually start working has me puzzled. Why, with the same tune, when I re-start the motor does the idle go high and stay there again. Software or hardware??

And to add to it, I was pulled over for speeding as I was feeling how the downshits were working. The policeman was very nice. He only gave me a ticket for failure to produce registration. He saw the laptop ang gauges. I explained what I was doing when he clocked me, and he was amazingly nice. Drove away with a $100.00 ticket and no points, rather than a $500.00 and points. Today was my lucky day. Nothing like a good warning like that to remind yourself to be careful.

 

[jd4242]

OK, more tune files from James.
I installed the next tune, and started. Idle was high, but after a bit of driving it settled down to where its supposed to be. I was logging this time, so James will see I'm not crazy. Once again, the idle was fine until I re-started the motor.

I then installed the Next tune, locking the transmission in high gear and did my pull. Pull was quite a bit stronger than the last one. Again, idle settled down quickly. I thought for sure James had done something. I loggged my pull.

I pulled off the highway and re-installed the non transmission locked tune James sent me today. This time, the idle would not go down to where it should be. I logged while I was in park, and cut the Idle control valve wire (I cant get at the connector without pulling the throttle body). No change in idle, and its logged and sent to James.

Whats going on with this idle thing? The fact that when the idle works fine when it does actually start working has me puzzled. Why, with the same tune, when I re-start the motor does the idle go high and stay there again. Software or hardware??

And to add to it, I was pulled over for speeding as I was feeling how the downshits were working. The policeman was very nice. He only gave me a ticket for failure to produce registration. He saw the laptop ang gauges. I explained what I was doing when he clocked me, and he was amazingly nice. Drove away with a $100.00 ticket and no points, rather than a $500.00 and points. Today was my lucky day. Nothing like a good warning like that to remind yourself to be careful.

Haha thats what i like to hear,getting pulled before you even got it all done lol.so how much boost uave you been seeing? What size pulley do you have again?

 

[Dono]

I have factory pulley. I think its 3 or 3.1 inch.
Im seeing 5lbs boost.

In the mirror, I was him writing away, and figured this was really going to hurt. This was an RCMP, which is like a State Policeman there. They are usually much nicer when your nice to them and they see your not exactly a menace to society. I won't be pushing my luck though.

 

[jd4242]

I have factory pulley. I think its 3 or 3.1 inch.
Im seeing 5lbs boost.

In the mirror, I was him writing away, and figured this was really going to hurt. This was an RCMP, which is like a State Policeman there. They are usually much nicer when your nice to them and they see your not exactly a menace to society. I won't be pushing my luck though.

Nice looks to be a 3".from the math it should be boosting more than that.so my 3.25 is probably going to be alot less than i thought, witch is fine as thats my dd pulley.i have the 2.7 witch we thought would give me like 9.9lbs so that may be little less.probably around 8-9.should uave asked him if he wanted to race!!haha

 

[Dono]

I found what they call a 10% pulley on sscoa I purchased. Was $75.00 shipped. I don't have it yet. Not really sure if I will be installing it. I do know I need to get my truck running properly before I even think about it.

How big is the 10% pulley? No idea. I have no idea why they call it that. 10% smaller than what? Different years of supercoup's came out with different sized pulley's. If the 10% is based on 3 inches, that would make it a 2.7 pulley. Thats the smallest that I could go to without machining the snout.

On your motor, I'd expect you to actually see far less boost, as your motor flows quite a bit better than mine. The boost that its getting, it should process and spit out without wasting its time as back pressure.

 

[jd4242]

I found what they call a 10% pulley on sscoa I purchased. Was $75.00 shipped. I don't have it yet. Not really sure if I will be installing it. I do know I need to get my truck running properly before I even think about it.

How big is the 10% pulley? No idea. I have no idea why they call it that. 10% smaller than what? Different years of supercoup's came out with different sized pulley's. If the 10% is based on 3 inches, that would make it a 2.7 pulley. Thats the smallest that I could go to without machining the snout.

On your motor, I'd expect you to actually see far less boost, as your motor flows quite a bit better than mine. The boost that its getting, it should process and spit out without wasting its time as back pressure.

Pulley boys sell all kinds of pulleys for yours.2.8 is the smallest without machining,2.7 and smaller need machining from what ive read.the boost calculations are based on no restrictions. The 2.7 should give you the same boost around 10lbs,i havent done the math for a 3.0 pulley but think it should be around 7-8ish.i dont really wanna push it so if i get around 8lbs off my 2.7 ill be happy,i would be careful pushing your that high without a IC