Supercharger Blow-off valve? :::

[Badtz]

does superchargers use a blowoff valve? [i don't think they do, since they aren't releasing excess exhaust, but just thought i'd ask]

i love the blow-off noise ;-)

[macncheese]

Quote:

Originally posted by Badtz
does superchargers use a blowoff valve? [i don't think they do, since they aren't releasing excess exhaust, but just thought i'd ask]

i love the blow-off noise ;-)

Yes it does, and I think the noise exits at this vent.

Vent.


--
Cheese

[Root Ginger]

Ha ha. That's a good one.

If only it were true!

[Loui]

Regarding the blow off or dump valve issue on the cooper s` I have a feeling that a while ago when I was thinking of buying a VW G40 Polo which is a 1.3 supercharged Polo coupe that looks like an ordinary Polo coupe except for some descreet badging and a set off BBS wheels I saw a site where somebody had managed to fit a dump valve to one. I can`t remember the site but Dubs sport`s web site maybe worth a look as they are VW nutters and have had a go at some completly ridiculous stuff, e.g a MK1 golf with two 2.0 litre Audi engines and nitorus that produced 400bhp. The only thing is they are based in the UK.

[Loui]

Looked for that web site and cannot find it at all it was a while ago. It wasn`t Dub sport either, sorry.

[noahe]

No dump valve. The supercharger recycles the boosted air back into the intake, so as to minimize parasitic loss.

The Supercharger is a roots-style, twisted vane unit produced by Eaton. Do a search of this site for more info, or use a search engine to check-out the Eaton web site, they have a lot of info.

[karmuze]

Quote:

Originally posted by noahe
No dump valve. The supercharger recycles the boosted air back into the intake, so as to minimize parasitic loss.

What da heck are parasites doin' in the S/C intake? Can't the Oxford factory hire an exterminator to eliminate the problem on the factory floor?

[Bilbo Baggins]

Quote:

Originally posted by macncheese


Yes it does, and I think the noise exits at this vent.

Vent.


--
Cheese

Very good one! Right on!!!!!

[Fifth Gear Racing]

Honestly guys can a BOV be added to the Cooper S. In theory wouldn't this allow the high stock psi's to escape when we take our foot off the pedal instead of having the air slam back into the intake which would over time shorten the lifespan of the supercharger?!

[macncheese]

Its called a bypass valve and its integral to the supercharger.


--
Cheese

[SSj4G60]

i dont know how your S/C is setup but on a G60 if you remove the boost return tube from the bottom of the Throttle body which has a 2nd butterfly on the bottom to "reroute" boost off throttle back around to the S/C some people have been able to remove the tube and attach a BOV to they have noticed practially instant on boost instead of somewhat progressive boost especially one guy who retrofit an Eaton M62 to his G60 hes getting about 18psi at 2krpm ,

[noahe]

Here, check this out. This is not exactly the set-up on the MINI, but it shows you how the Eaton Twisted Vane Roots-Style Supercharger works.

The blow-off valve works on a turbo, because the exhaust gasses blow by one turbine, which in turn spins another. So the exhaust blowing out of the engine, in turn compresses the inlet air.

When you down-shift, the back-pressure between the intake manifold and the turbo, causes resistance, and the turbo slows down.

The brilliant little blow-off valve opens at a pre-determined pressure (say, near max RPM) and lets the boosted air simply escape. But the turbo is still spinning very fast. So when you slam the shifter into the next gear and hit the gas again, the turbo is already up to speed.

A supercharger is physically attached to the engine, so it cannot remain spinning quickly when the engine slows down. So a blow-off valve would be pointless.

Now, even with a supercharger, there are some circumstances when the engine is spinning quickly, and the intake is not drawing much air. Like when engine braking on a downshift. You could simply 'blow-off' this air, but since the Supercharger is a drag on the engine, the by-pass valve opens and dumps the unused charge back into the supercharger's inlet. Since the inlet pressure and the outles pressure are similar, this reduces the drag the supercharger places on the engine. This is preferable to a blow-off or dump valve.

At least that is my understanding of it.

[SSj4G60]

yea its like that on a G60 too , but what we've been thinking is , your blowing HOT air back into the intake and heating up the IC and the intake charge period even more, causing lower efficiency

[DaveNagy]

Quote:

...your blowing HOT air back into the intake and heating up the IC and the intake charge period even more...

If your intercooler is heating up, then the air must have gotten cooler. If you were able to recirculate the air enough times, it'd get downright icy!

(Okay, it'd only be icy when uncompressed. The coolest you could get it in it's compressed state would be "room temperature", but that in itself would be fantastic.)

That intake air is only hot becaused it's been compressed, and if it's already been through the intercooler at least once, it's going to be less hot than if you took "fresh" air and compressed it by the same amount.

This is how air conditioners work. Compress a gas to make it temporarily hot, then cool that hot compressed gas with regular ol' air so it's somewhat less hot, then uncompress the gas and presto, coldness.

-Dave