Dump valves, what am I missing.

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Dump valves, what am I missing.

Postby Spec BSC » Wed Apr 26, 2017 7:42 am

Ok I’m trying to sort out a few things prior to my car going onto the dyno very soon. One of which is trying to understand the operation of the dump valve.

Please correct me or tell me why it operates in the way does.

I totally understand that when you lift off the throttle the pressure in the inlet tract is released thereby preventing the turbine from stalling and adding shock loading back onto the shaft.

What I don’t understand is why the dump valve is open when the inlet tract is under negative pressure and it only closes when there is a positive pressure in the system?

Especially from a supercharger perspective where boost is being added continually as the revs rise, surely it is better to maintain this pressure until the throttle is released?
Under the very limited testing I can do at present due to keeping the revs sensible when I set the dump valve to open at idle the engine makes 2.5psi less at my imposed rev limit than it does when I set the valve to be closed at idle!

Maybe these type of dump valves are good for turbo installs rather than supercharged but even the supplier of the sc suggested using a Forge Motorsports supersize dump valve, and as far as I can ascertain that also works in the sameway?

Please enlighten me.
The first engine died after eating to much CAT
The second engine died of a broken piston
The third engine is in the car
The fourth engine is in the machine shop

So far: Rotrex Supercharger (16 psi) with WTA intercooler,DW300c fuel pump,565cc Pink injectors
Producing 431bhp and 350 lb/ft torque on the Rotrex SC not finished yet
Raptor headers, 75mm Milltek exhaust with Quad tips,
Custom made 4032 forged pistons by JE Pistons, forged conrods, Exedy Clutch
K sport 8 pot front, 4 pot rears all on 330mm discs, Hel brake lines
Meister R coil overs, Whiteline 21mm rear ARB, Perrin end links and strengthening brackets
Complete Whiteline kit for the front suspension including steering rack
One off Carbon effect Front grill, Carbon lip spoiler, Exterior De-chromed, LED interior light conversion.
Recaro Leather front seats with all functionality.
Waist spoiler, Smoked rear lights,, LED sill plates, LED sidelights
Prodrive PFF7's 18x8, in Bronze shod with 235/40/18 Goodyears.
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Re: Dump valves, what am I missing.

Postby Surge » Wed Apr 26, 2017 11:54 am

The BOV should only open briefly after you let off the throttle.

The wastegate would operate as required to maintain a boost level.

Not sure why yours is acting strange.

Mcmtv2 has good videos about this . Search for "go fast Brett on youtube".
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Re: Dump valves, what am I missing.

Postby Spec BSC » Wed Apr 26, 2017 7:00 pm

Thanks only covers turbocharged application.
The first engine died after eating to much CAT
The second engine died of a broken piston
The third engine is in the car
The fourth engine is in the machine shop

So far: Rotrex Supercharger (16 psi) with WTA intercooler,DW300c fuel pump,565cc Pink injectors
Producing 431bhp and 350 lb/ft torque on the Rotrex SC not finished yet
Raptor headers, 75mm Milltek exhaust with Quad tips,
Custom made 4032 forged pistons by JE Pistons, forged conrods, Exedy Clutch
K sport 8 pot front, 4 pot rears all on 330mm discs, Hel brake lines
Meister R coil overs, Whiteline 21mm rear ARB, Perrin end links and strengthening brackets
Complete Whiteline kit for the front suspension including steering rack
One off Carbon effect Front grill, Carbon lip spoiler, Exterior De-chromed, LED interior light conversion.
Recaro Leather front seats with all functionality.
Waist spoiler, Smoked rear lights,, LED sill plates, LED sidelights
Prodrive PFF7's 18x8, in Bronze shod with 235/40/18 Goodyears.
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Spec BSC
 
Posts: 272
Joined: Sun Apr 06, 2014 8:53 am
Location: West Sussex, UK
Car: Spec B supercharged, forged engine
Real name: Richard
Profile URL: viewtopic.php?t=25835

Re: Dump valves, what am I missing.

Postby dr20t » Wed Apr 26, 2017 8:53 pm

A bov or dump valve doesn't serve the same purpose on a supercharged car as it does on a turbo car.

In a supercharged car, a dump valve is used to regulate boost on idle generally. Ie, when your engine is idling its still spinning the charger which is creating boost against a closed throttle plate. If this has no where to go, you can see how it will be a problem.

Thus you will see it mostly open, and since it should be recirculated to your intake pre supercharger, should not create a boost or vacuum leak / or shouldmt have a negative effect on the supercharger system, even when on boost

Hope this makes sense

Mick
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Re: Dump valves, what am I missing.

Postby Spec BSC » Thu Apr 27, 2017 2:42 am

dr20t wrote:A bov or dump valve doesn't serve the same purpose on a supercharged car as it does on a turbo car.

In a supercharged car, a dump valve is used to regulate boost on idle generally. Ie, when your engine is idling its still spinning the charger which is creating boost against a closed throttle plate. If this has no where to go, you can see how it will be a problem.

Thus you will see it mostly open, and since it should be recirculated to your intake pre supercharger, should not create a boost or vacuum leak / or shouldmt have a negative effect on the supercharger system, even when on boost

Hope this makes sense

Mick


Thanks Mick it does make sense, my only observation about this is that unless on WOT there is still only a couple of psi at most in the inlet tract. I will be checking the functionality of my bov as I'm not 100% it works in the way it's meant to. Otherwise I wouldn't have been able to observe such a pressure difference between 2 settings.

On one of the GFB videos they talk about the Bob being closed and only opening when you lift of the throttle.

Thanks again.
The first engine died after eating to much CAT
The second engine died of a broken piston
The third engine is in the car
The fourth engine is in the machine shop

So far: Rotrex Supercharger (16 psi) with WTA intercooler,DW300c fuel pump,565cc Pink injectors
Producing 431bhp and 350 lb/ft torque on the Rotrex SC not finished yet
Raptor headers, 75mm Milltek exhaust with Quad tips,
Custom made 4032 forged pistons by JE Pistons, forged conrods, Exedy Clutch
K sport 8 pot front, 4 pot rears all on 330mm discs, Hel brake lines
Meister R coil overs, Whiteline 21mm rear ARB, Perrin end links and strengthening brackets
Complete Whiteline kit for the front suspension including steering rack
One off Carbon effect Front grill, Carbon lip spoiler, Exterior De-chromed, LED interior light conversion.
Recaro Leather front seats with all functionality.
Waist spoiler, Smoked rear lights,, LED sill plates, LED sidelights
Prodrive PFF7's 18x8, in Bronze shod with 235/40/18 Goodyears.
User avatar
Spec BSC
 
Posts: 272
Joined: Sun Apr 06, 2014 8:53 am
Location: West Sussex, UK
Car: Spec B supercharged, forged engine
Real name: Richard
Profile URL: viewtopic.php?t=25835

Re: Dump valves, what am I missing.

Postby Spec BSC » Thu Apr 27, 2017 4:47 am

Right i have checked out the BOV and it works as Mick described, the only thing I am unable to test is what psi it can with stand before being opened by the rising pressure in the inlet tract .
The first engine died after eating to much CAT
The second engine died of a broken piston
The third engine is in the car
The fourth engine is in the machine shop

So far: Rotrex Supercharger (16 psi) with WTA intercooler,DW300c fuel pump,565cc Pink injectors
Producing 431bhp and 350 lb/ft torque on the Rotrex SC not finished yet
Raptor headers, 75mm Milltek exhaust with Quad tips,
Custom made 4032 forged pistons by JE Pistons, forged conrods, Exedy Clutch
K sport 8 pot front, 4 pot rears all on 330mm discs, Hel brake lines
Meister R coil overs, Whiteline 21mm rear ARB, Perrin end links and strengthening brackets
Complete Whiteline kit for the front suspension including steering rack
One off Carbon effect Front grill, Carbon lip spoiler, Exterior De-chromed, LED interior light conversion.
Recaro Leather front seats with all functionality.
Waist spoiler, Smoked rear lights,, LED sill plates, LED sidelights
Prodrive PFF7's 18x8, in Bronze shod with 235/40/18 Goodyears.
User avatar
Spec BSC
 
Posts: 272
Joined: Sun Apr 06, 2014 8:53 am
Location: West Sussex, UK
Car: Spec B supercharged, forged engine
Real name: Richard
Profile URL: viewtopic.php?t=25835


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