SC Question

DocHolidaySLI

Registered User
Im a bit of a SC newbie, so just a small question...

The vaccum actuator that sits behind the supercharger, is it supposed to move with manifold vaccum or ??, mine just sits against the stop set screw no matter if you snap the throttle or w/e, i pulled the line off, it has vaccum on it.

And what exactly does it do, the car runs fine, has decent power, it misses very light around ~6psi boost, but it's a light miss and you have to be looking for it to even feel it, it's strong past ~6psi, but since i havent really pressure tested any of the gaskets yet, i attribute the misfire to a boost leak somewhere due to the fact the car wasnt driven till i bought it 3 weeks ago and the lines look pretty cracked and old

Thanks in advance any advice is helpful
 
By-Pass Valve

Valve actuator is called the bypass valve on the return plenum and moves to open as boost goes up.So its suppose to move/open!!!

Your miss could be plugs/or plug wires,hope this helps you out.

Tom
 
The bypass valve could be pooched, which happened to mine.

If its closed all the time, the blower will get super hot at idle if the TB is closed as the rotors are cavitating. This means very high ACT's in a very short time.

Frit
 
Actually....the bypass closes with increasing boost. When you lift the throttle and vac. goes "up" the valve opens to prevent the supercharger from cavitating.
 
HHHmmmm

Actually....the bypass closes with increasing boost. When you lift the throttle and vac. goes "up" the valve opens to prevent the supercharger from cavitating.

Mine was doing the oppossite, then again I haven't been able to keep it running when I had the 42's in there.

Thanks for the heads up Duffy:D

Tom
 
Cavitation

I don't think 'cavitation' (cavity) means what you think it means. By definition, cavitation requires a liquid.

cavitation |ˌkavəˈtā sh ən|
noun Physics
The process by which bubbles in a liquid form and collapse close to a solid surface.
• When air gets sucked into a propeller or when a partial vacuum forms around the blades, the effect is for the propeller to lose its grip on solid water and to race ineffectively.


See [ http://www.answers.com/topic/cavitation ] for details...

Our engines utilize a 'bypass' valve that works to prohibit the generation of unwanted vacuum within the intake tract.

Without a bypass valve, what could happen is exaggerated vacuum being generated between the pivoting plate in the throttle body and the inlet side of a supercharger when the throttle plate is closed. A persistent vacuum on the supercharger inlet would result in drag on the impellers and what is known as 'parasitic' loss of power as the belt driven assembly fights against the drag. Since cavitation is the occurrence or incursion of air/gas into a liquid, the term has no reference in our case. We are simply working with only air at various levels of heat, pressure and vacuum which could cause impeller drag, and resulting power loss, if not dealt with accordingly.

The vacuum operated bypass valve, installed between the supercharger intercooler outlet (see image below) and the supercharger inlet (after the throttle body), promotes supercharger efficiency in terms of economy and parasitic power loss. As an example, our M90 superchargers use less than 1 HP at 60 MPH cruising/light throttle.

The bypass is operated by a vacuum actuated control unit that is normally closed (engine off). High vacuum during idle/cruising causes the actuator to open the bypass valve, equalizing vacuum across the system. When boost is generated (accelerating), vacuum decreases and the bypass valve instantly closes, causing cylinder pressure to increase. An appropriately equalized vacuum condition virtually eliminates otherwise normal forced-induction system 'parasitic power loss'.

As Duffy stated...
- open...no boost - vacuum present at the control unit... air off the intercooler is allowed to recirculate back through the supercharger and therefore bypass the cylinders.
- closed...boost present - no vacuum at the control unit, no boosted air is recirculated..all of it goes to the engine.
 

Attachments

  • bypass.jpg
    bypass.jpg
    116.3 KB · Views: 71
The term "Cavitating" is what is used in the Ford Shop Manual to describe the functioning of the bypass valve. From the 94 manual........

"At partial throttle opeing or when vacuum is present in the intake suystem, a vacuum-controlled bypass valve routes some of the discharged air from the supercharger back through the inlet plenum. This prevents the supercharger from cavitating, causing:

Reduced performence
Increased temperatures
Poor economy"
 
Guess I must be a real stupiud idiot then :rolleyes:........


I don't think 'cavitation' (cavity) means what you think it means. By definition, cavitation requires a liquid.

cavitation |ˌkavəˈtā sh ən|
noun Physics
The process by which bubbles in a liquid form and collapse close to a solid surface.
• When air gets sucked into a propeller or when a partial vacuum forms around the blades, the effect is for the propeller to lose its grip on solid water and to race ineffectively.


See [ http://www.answers.com/topic/cavitation ] for details...

Our engines utilize a 'bypass' valve that works to prohibit the generation of unwanted vacuum within the intake tract.

Without a bypass valve, what could happen is exaggerated vacuum being generated between the pivoting plate in the throttle body and the inlet side of a supercharger when the throttle plate is closed. A persistent vacuum on the supercharger inlet would result in drag on the impellers and what is known as 'parasitic' loss of power as the belt driven assembly fights against the drag. Since cavitation is the occurrence or incursion of air/gas into a liquid, the term has no reference in our case. We are simply working with only air at various levels of heat, pressure and vacuum which could cause impeller drag, and resulting power loss, if not dealt with accordingly.

The vacuum operated bypass valve, installed between the supercharger intercooler outlet (see image below) and the supercharger inlet (after the throttle body), promotes supercharger efficiency in terms of economy and parasitic power loss. As an example, our M90 superchargers use less than 1 HP at 60 MPH cruising/light throttle.

The bypass is operated by a vacuum actuated control unit that is normally closed (engine off). High vacuum during idle/cruising causes the actuator to open the bypass valve, equalizing vacuum across the system. When boost is generated (accelerating), vacuum decreases and the bypass valve instantly closes, causing cylinder pressure to increase. An appropriately equalized vacuum condition virtually eliminates otherwise normal forced-induction system 'parasitic power loss'.

As Duffy stated...
- open...no boost - vacuum present at the control unit... air off the intercooler is allowed to recirculate back through the supercharger and therefore bypass the cylinders.
- closed...boost present - no vacuum at the control unit, no boosted air is recirculated..all of it goes to the engine.
 
You are NOT an idiot!!!!!!

Just because you don't understand how things work at that level does NOT make you an idiot!!!!
You just have never taken a class on 'Fluid Dynamics'!!
Liquids and gases flow the same way when in a pipe. The pipe needs to be s-m-o-o-t-h and have nice gradual bends in order to flow the best. 'Cavitation' is what happens when there is blockage in the pipe. (Like suddenly closing the throttle....) The easiest way to see this is to look in a stream or river or creek or whatever, when the water flows around an obstacle, it sort of 'backflows' on the 'downwind' side of that obstacle, this is a 'cavity' formed by the disruption of flow. When you drop a dam in the flow, it causes a backup of the flow, so now that 'cavity' is formed upstream at the next blockage. (In this case, the supercharger.)
Cavitation puts a lot of pressure against the object it occurs around and if the pressure is high enough it can do some damage. Sort of momentarily stopping the rotation of the supercharger, which is probably NOT good for the supercharger over the long run. I mean it is designed to turn in only one direction, so sudden stops are a little tough on the bearings.
So, as I said before, YOU are NOT an idiot!!! You just never had to take the class!!
Lance
 
Thank you for a very precise and acurate description of our SC system....:cool:

I have experienced cavitation on various boats and the definition fits.....

When I get an SC in, I check the vacuum canister to verify that it will hold a vacuum....

Pull the vacuum hose of and move the plunger in as far as it will go,,,,,

Put your finger over the nipple where the vacuum hose goes and release the plunger.....

If the plunger stays in place, the vacuum canister is OK....

If the plunger goes back toward the TB, then the canister is bad and should be replaced.....
 
the-big-e> If the plunger stays in place, the vacuum canister is OK....

If the plunger goes back toward the TB, then the canister is bad and should be replaced.....


That's a good tip, thanks. ;)

I found one that wasn't operating at all...the plate was wedged/stuck closed and the canister, although fine, wasn't able to pull it open.
 
Just because you don't understand how things work at that level does NOT make you an idiot!!!!
You just have never taken a class on 'Fluid Dynamics'!!
Liquids and gases flow the same way when in a pipe. The pipe needs to be s-m-o-o-t-h and have nice gradual bends in order to flow the best. 'Cavitation' is what happens when there is blockage in the pipe. (Like suddenly closing the throttle....) The easiest way to see this is to look in a stream or river or creek or whatever, when the water flows around an obstacle, it sort of 'backflows' on the 'downwind' side of that obstacle, this is a 'cavity' formed by the disruption of flow. When you drop a dam in the flow, it causes a backup of the flow, so now that 'cavity' is formed upstream at the next blockage. (In this case, the supercharger.)
Cavitation puts a lot of pressure against the object it occurs around and if the pressure is high enough it can do some damage. Sort of momentarily stopping the rotation of the supercharger, which is probably NOT good for the supercharger over the long run. I mean it is designed to turn in only one direction, so sudden stops are a little tough on the bearings.
So, as I said before, YOU are NOT an idiot!!! You just never had to take the class!!
Lance

Lighten up dude!!! I was being sarcastic. I studied fluid dynamics and so on with a retired Nasa Engineer and other engineers for 6 years while we decoded the flight dynamics engine within flight simulator :rolleyes:. Fluid dynamics are a HUGE part in aerodynamics.

Frit
 
cavitation is used as a correct term because "air " is fluid

whats in water?
how much of this h2o is in "air" ya see air flows as water does and under extreme rpm levels and closed system air can cavitate at rotors inlet more so on early model m90's
due to the inlet pocket which is filled in on mpiii blowers and newer model m90's

the bypass opens the passage between boost and vacume areas thus saving horse power needed to drive blower and removing the pressure from outlet side and feeding the inlet with slightly pressurized air leting void air pocket with enough pressurized air to let rotors grb the air and eliminate the void

read that vacume bubble I didnt understand this cavitation thing until i worked on my pool pump and had to deal with cavitation
no matter what you do you cant make it pump water intil the bubble or void of water is filled in with water same goes for the blowers this void or cavitation happens in boats and in propeler driven planes
what we call fluid is just denser molicules air if compressed enough will become a liquid its just expanded fluid and still flows as a liquid
just my input take it for what its worth i have no PHD
but i do have a BS in english language lol i
n fact Im full of it ask anyone
I don't think 'cavitation' (cavity) means what you think it means. By definition, cavitation requires a liquid.

cavitation |ˌkavəˈtā sh ən|
noun Physics
The process by which bubbles in a liquid form and collapse close to a solid surface.
• When air gets sucked into a propeller or when a partial vacuum forms around the blades, the effect is for the propeller to lose its grip on solid water and to race ineffectively.


See [ http://www.answers.com/topic/cavitation ] for details...

Our engines utilize a 'bypass' valve that works to prohibit the generation of unwanted vacuum within the intake tract.

Without a bypass valve, what could happen is exaggerated vacuum being generated between the pivoting plate in the throttle body and the inlet side of a supercharger when the throttle plate is closed. A persistent vacuum on the supercharger inlet would result in drag on the impellers and what is known as 'parasitic' loss of power as the belt driven assembly fights against the drag. Since cavitation is the occurrence or incursion of air/gas into a liquid, the term has no reference in our case. We are simply working with only air at various levels of heat, pressure and vacuum which could cause impeller drag, and resulting power loss, if not dealt with accordingly.

The vacuum operated bypass valve, installed between the supercharger intercooler outlet (see image below) and the supercharger inlet (after the throttle body), promotes supercharger efficiency in terms of economy and parasitic power loss. As an example, our M90 superchargers use less than 1 HP at 60 MPH cruising/light throttle.

The bypass is operated by a vacuum actuated control unit that is normally closed (engine off). High vacuum during idle/cruising causes the actuator to open the bypass valve, equalizing vacuum across the system. When boost is generated (accelerating), vacuum decreases and the bypass valve instantly closes, causing cylinder pressure to increase. An appropriately equalized vacuum condition virtually eliminates otherwise normal forced-induction system 'parasitic power loss'.

As Duffy stated...
- open...no boost - vacuum present at the control unit... air off the intercooler is allowed to recirculate back through the supercharger and therefore bypass the cylinders.
- closed...boost present - no vacuum at the control unit, no boosted air is recirculated..all of it goes to the engine.
 
Back
Top