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Boost question...


Stockpat
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I've had my 2010 for a few weeks now and just pushed over 500 miles on the clock. I've taken it easy on the car out of respect for the new motor and fear of its potential to kill me. The last couple of days I've been more liberal with the throttle and find myself smiling a lot and looking for reasons to run errands.

 

This is my first experience with a supercharger. I've had a bunch of forced induction cars, but it's always been a turbo(Conquest, RX7, STi and most recently a 911). I've searched the site and I'm familiar with the specs of our supercharger. My question pertains to day to day experience. Around town in a turbocharged car, you constantly see boost while pulling away from a stop sign, climbing a hill, passing on the highway, etc. Other than the few times I've really romped the GT500, the boost gauge doesn't even wiggle. I assume it is clutched which would be the equivalent of a wastegate on a turbo. Is there a set point(RPM) when it comes online? Is it based off throttle position? Is it load/vacuum based like a turbocharger?

I apologize if this is a dumb question. I'm not looking for more boost, I'd just like a better understanding of when and why it arrives. I'm afraid the answer is going to be stop driving like a sissy...

 

Thanks in advance,

Stockpat

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This is my first experience with a supercharger. I've had a bunch of forced induction cars, but it's always been a turbo(Conquest, RX7, STi and most recently a 911). I've searched the site and I'm familiar with the specs of our supercharger. My question pertains to day to day experience. Around town in a turbocharged car, you constantly see boost while pulling away from a stop sign, climbing a hill, passing on the highway, etc. Other than the few times I've really romped the GT500, the boost gauge doesn't even wiggle. I assume it is clutched which would be the equivalent of a wastegate on a turbo. Is there a set point(RPM) when it comes online? Is it based off throttle position? Is it load/vacuum based like a turbocharger?

 

 

 

First, let's clarify two terms. Vacuum and Boost.

 

Vacuum is any pressure below atmospheric pressure.

Boost is any pressure above atmospheric pressure.

 

A supercharger is a positive displacement (air) pump. The output is directly proportional to RPM.

EDIT: That means the faster you spin it, the more air it pumps.

 

In order to see boost you must first overcome the vacuum produced by the engine (typically between 17 and 22 inches of Mercury ("Hg)). Once the volume of air being prduced by the supercharger exceeds the volume required by the engine (i.e. "vacuum") under partial throttle conditions, you get boost.

 

That's a *very* simplified description of how it works and if you need more, I'll be happy to try to explain when I have a few minutes to do so. Right now, I gotta run!

 

 

HTH,

Phill Pollard (former EMD Auto Vo-tech instructor and retired Auto Tech)

Edited by 2010KonaBlueGT
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The engine is under vacuum at most throttle and load conditions. Under wide open throttle or high load, it will be in boost. Doesn't matter what RPM, floor it, the gauge will deflect.

 

 

Correct.

 

The supercharger is equipped with a boost solenoid valve which is controlled by vacuum. It then is mechanically connected by a small arm or lever that opens and closes, it looks very similar to small throttle body blade. It is open under normal driving conditions (its venting what would be boost). Your driving Stockpat, J/K....With enough throttle pressure you will create enough vacuum to close the solenoid which closes the valve, which then now the supercharger will now start to create boost. To answer you question it is not related to your RPM. It is very easy to wind up your engine with out creating boost.

 

This is how positive displacement blowers work, that is also how these blower create such a great hp and torque curve at such low RPMs, much different than any other type of forced induction system. I hope this clears up any confusion and answers you questions.

Edited by jsvtcobra
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Correct.

 

The supercharger is equipped with a boost solenoid valve which is controlled by vacuum. It then is mechanically connected by a small arm or lever that opens and closes, it looks very similar to small throttle body blade. It is open under normal driving conditions (its venting what would be boost). Your driving Stockpat, J/K....With enough throttle pressure you will create enough vacuum to close the solenoid which closes the valve, which then now the supercharger will now start to create boost. To answer you question it is not related to your RPM. It is very easy to wind up your engine with out creating boost.

 

This is how positive displacement blowers work, that is also how these blower create such a great hp and torque curve at such low RPMs, much different than any other type of forced induction system. I hope this clears up any confusion and answers you questions.

 

Thanks

Another Ques.Has the whine been quited down on the 2010s

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Thanks

Another Ques.Has the whine been quited down on the 2010s

 

 

yes theres a baffle iinside the tube beetween the SC and air inlet that has almost eliminated the SC whine.Some folks have just taken the baffle out,others like me have bought the JLT intake--looks great and sounds real good too.

On the boost question, if you hit full throttle from the get go, youll see boost --but gradual rpm increase in 1/2 you wont see much.As Justunwoody said, cheange your drivng habits and see boost--but remeber to set your shift alarm,because like me youll staret hitting the rev limiter.The sift alarm is audible and visual, the tach lights up.I had to set mine at 5600 so id shift before it hit 6200

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Thanks for all the replies. As I suspected, the concensus appears to be I drive like a wuss :doh:

 

One follow up question, to prevent compressor surge in a turbocharged car upon abrupt throttle closure(shifting, lifting, etc.) most cars are equipped with either a blow off valve or bypass valve. Do we have something similar(or indentical)?

 

thanks,

Stockpat

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Thanks for all the replies. As I suspected, the concensus appears to be I drive like a wuss :doh:

 

One follow up question, to prevent compressor surge in a turbocharged car upon abrupt throttle closure(shifting, lifting, etc.) most cars are equipped with either a blow off valve or bypass valve. Do we have something similar(or indentical)?

 

thanks,

Stockpat

 

 

Bypass valve.

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Thanks for all the replies. As I suspected, the concensus appears to be I drive like a wuss :doh:

 

One follow up question, to prevent compressor surge in a turbocharged car upon abrupt throttle closure(shifting, lifting, etc.) most cars are equipped with either a blow off valve or bypass valve. Do we have something similar(or indentical)?

 

thanks,

Stockpat

 

 

That little valve in the S/C that I explained earlier does that. As soon as you release the throttle the process works in reverse. The less vacuum actuates the solenoid in the opposite direction which opens the little valve/throttle body looking thing in the S/C which vents air/pressure overboard. This is the simplified explanation. There are a few valves the work together to operate you S/C. The Boost Solenoid valve, boost bypass valve, and EGR valve. There are a few little trick that you can do to milk a few more ponies out of the car. On the Terminators you could swap the vacuum line on the boost bypass valve to get a little bump. On others some do the EGR delete, but remember some of these thing come at a cost. I believe the EGR delete comes at a little cost. I believe it causes the S/C to run a little hotter, but not for sure. I am no expert.

 

On the Terminators when you got out of the boost if you listened carefully you could hear the pressure being released. It sounds like tiny BOV. Its kinda funny. I would think it is the same with these blowers.

 

I would like to know the displacement of these blowers anyone know off the top of there heads???

Edited by jsvtcobra
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jsvtcobra thanks for the detailed responses. It appears the two forms of forced induction are very similar in function if not design. One more elementary question. The pulley on the nose of the supercharger is obviously always spinning. Are the screws always spinning also, or only when boost is required? There is no perceivable lag in the boost, so I assume they spin all the time...but I guess they could spin up very quickly with the direct connection.

 

thanks,

 

Stockpat

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That little valve in the S/C that I explained earlier does that. As soon as you release the throttle the process works in reverse. The less vacuum actuates the solenoid in the opposite direction which opens the little valve/throttle body looking thing in the S/C which vents air/pressure overboard. This is the simplified explanation. There are a few valves the work together to operate you S/C. The Boost Solenoid valve, boost bypass valve, and EGR valve. There are a few little trick that you can do to milk a few more ponies out of the car. On the Terminators you could swap the vacuum line on the boost bypass valve to get a little bump. On others some do the EGR delete, but remember some of these thing come at a cost. I believe the EGR delete comes at a little cost. I believe it causes the S/C to run a little hotter, but not for sure. I am no expert.

 

On the Terminators when you got out of the boost if you listened carefully you could hear the pressure being released. It sounds like tiny BOV. Its kinda funny. I would think it is the same with these blowers.

 

I would like to know the displacement of these blowers anyone know off the top of there heads???

 

 

Here is a pic of a Eaton M112. It is not the S/C on the GT500 but it is a Eaton and they are just about the same. It is the one on the 03/04 Cobras. This is also a ported blower in the first pic and the second pic is a stock port. I am not sure what the little blower is.

 

I posted the pics so you could see the little valve/throttle body looking thing I have been talking about.

 

NewCobraShape.jpg

 

cobra_mag_exit_port.gif

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Stop driving like a sissy...Just Jokin with ya! But seriously, stop driving like a sissy...shift.gif

 

 

+1 on the sissy :). My car has 1000 miles on it and has a pulley, tune etc putting down sae corrected 523rwhp/515rwtq. The silencer is removed and SLP's on the back. She's a beast now and like she should have been from the get go. I estimate just over 600hp at the crank.

 

As for the boost gage, had they installed a vac/boost gage like my other shelby has (Whipple 550 on my GT) you would see the vacuum slowly going away as boost builds when you accelerate. I look at my boost once in a while on the GT500 but mostly the road now because this thing gets moving quite fast now. I don't see wheel hop either, but maybe because she lays rubber so fast not getting traction.

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