Turbo vehicles use the wastegate to control boost, not the BOV. A BOV simply releases pressure in the system when the throttle is closed.

 

Yes you are right. I was in a hurry this morning..... Thanks for the correction.
Never the less, a BOV is not designed for an SC.

Here is a quick discription of a BOV http://www.streetracersonline.com/ar.../turbo/bov.php

 

My point was that a blow off valve in a supercharged car was analagous to flooring an NA car. The by-pass valve is to allow both sides of the supercharger to be at about the same pressure, so it free-wheels when you don't need boost. And this pressure is usually sub-atmospheric. It spools down automatically when you are off throttle, as it's connected to the crank.

For a turbo, it continues to generate lots of boost even when the motor is slowing due to inertia of the impellor/shaft/turbine assembly. The blow off valve lets out this overboost so the motor doesn't keep going when your foot is off the gas pedal.

But if you open the intake on a supercharged car to atmosphere when the by-pass valve would be open would be like flooring a NA car, in that you'd have close to atmospheric pressure in the intake, and the car would either take off, or the electronic brain would get confused, seeing too much pressure in the manifold, and it gets interpreted as a MASSIVE vacuum leak, and you limp home or run like crap and get lights. Neither of these is the result, smooth, economical low power operation, that is desired.

Really, these two items share NOTHING in function other than they both have the word "valve" in thier name!

Matt

 

Thank you for that explanation. That was the one part I did not know, which is exactly how the bypass operates in a supercharged vehicle. I'm still having a hard hard time picturing everything in my head, but that's just cause i'm not in that mode right now.

Correct me if i'm wrong, but this is what I have concluded now.

Due to the operation of the different valves at vacuum, one being open(bypass) and one being closed(BOV) is the reason why a BOV will not work on our cars?

 

If you have a supercharged car and someone gives you a blow off valve, THROW IT AWAY! There is no place on an supercharged car for one.

To find out why, read Supercharged! by Corky Bell. He also wrote "Maximum Boost!" I think. The first is about supercharged engines and the second is about turbos.

Start with the books, and then you'll save time and $.

Matt

 

So there is no presure at closed throttle.

 

I've got maximum boost already. Haven't actually started reading it though.

 

So what are you saying?
Maximum boost is close to WOT. As you let off the throttle the boost drops, even if the BPV is wired shut.
Are we still in BOV for an SC?

 

is a book.

Matt

 

Thanks....... I needed that.
Started the day waaaayyy too early

 

My MAP readings support Dr O's comments, I believe. The MCS is rarely in boost mode--i.e. the MAP rarely reads over barometric pressure (which for me at altitude is about 12.1 psi). And so if you opened up the intake path to the atmosphere, via some type of valve, you'd be letting way more air into the system causing all kinds of trouble for the ECU and the car in general. Remember if the MCS runs a vacuum most of the time (and by most I mean over 90% of the time) then blowing off over-boost is rarely required, and might cause more problems.
I'm seeing approaches of 8F while cruising, and even under hard acceleration, I might momentarily see an approach of 40-50F. So long as I dont then stop and wait at a light, the approach drops to 20-25F quite quickly. I really don't think the recycled SC air via the BPV is our biggest problem here. Personally I think it's keeping the hot engine and radiator air from our intake components. And to this end, getting more fresh air in, and heated air out, is the solution, not BOVs.

cheers,

 

Except for the quality of the OE BPV there is no problem.
Under hood heat management is the biggest problem not just the IC or CAI but everything. A BOV has no function with an SC.

 

Ah, we are of the same mind! (scary!!) Here is my list of the current activity in that area:
1. M7s Aerogel blanket is being installed on more cars and hopefully some data will become available soon from in-car applications.
2. Joel (JS) is hopefully still working on an exit scoop for the DFIC.
3. Partsman is looking into opening up the shrowd above the radiator for airflow over the intake manifold. I am too.
4. My FAD is clearly producing a wind-chill factor that provides lower than ambient air into the airfilter.
5. Various insulation installations have appeared. I'm currently running insulation on the outside and inside of the airbox, as well as some on the face of the intake manifold next to the radiator hose.
6. Unbolt the radiator hose from the intake manifold, btw!

I'm out.

 

Done.

Did someone tag you out? Otherwise you're not out.

When you open the hood ( on an early car ) there are oblong holes ( the late cars have black plastic plugs ). At 1 time it was thought you should plug these holes to prevent hot air from entering the OE under hood diverter. Since the OE diverter has already been played, try removing the plugs if you have them ( lots more potential air & room to do it with ).

Air flow anyone???? Another thread? Play it again, it's our favorite tune. Might be if it gets played often enough it will be a sticky.........

 

and that was to reduce heat by taking the SC out of the equation. And there is one more step no one here has done, but Mercedes has! They use a clutch on the SC pulley like what AC systems use to really reduce drag. While it's not pumping air agains boost, it is moving a large volume rather violently. I wonder what gains are to be had from that? A few HP? Less heat build up via reduced turbulence and parasitic drag? But that would have to be a friggin tiny clutch to fit our cars....

And if the SC had a clutch, air actually would flow through the by-pass into the engine, as so many believe...

Matt

 

This is the way it was done pre BPV. For the Mini the clutch would need to have the pully cantalevered on the SC side away from the clutch ( this has been done for some pumps ). Lowering the SC temp would be very benificial. You have seen the M45 off the motor & seen the passage for the BPV, if not I'll post 1 that is part of an XB project. And yes your statement has merit & could be done.

 

I've seen one of the pulley/clutch assemblys from one of the SLKs and it just looks too big to fit. But if it did, you could have the same diaphram for the BPV trigger the SC clutch.....

Science project....

Any takers?

Matt

 

There are some pretty small clutches. The room part could be a problem. The space between tne pulley & the frame horn is a little iffy. The BPV could be in it's original location.

 

I don't see a problem with this. Just cap off the throttle body to supercharger pipe (where the BPV connects) and then get an adapter plate for the horn.

However I don't know if you will get engough vaccum or boost pressure to open the valve. If any one is in the NC area I would be more than glad to try it out on your car. That is if you pay for the expenses. I wouldn't charge too much for labor.

 

Why not use a a stepping motor or a solonoid for those that want "Road Warior"?
The pics I posted of the M45 are not for a Mini but to point out the passage. All the bosses are already on the OE unit to relocate the valve as it is in the pic.

 

The problem with disconnecting the S/C pulley via a clutch is that the water-pump is also driven by the S/C. I think this sort of upgrade would wind up causing more heat by disabling the cooling system.
However, if one were to install an electric water-pump (aka M62 kit) possibly the clutch off the S/C in VW's twin-charged 1.5L motor would be small enough?

 

The electric water pump is a must. The VW clutch is a good call, it could work.
This thread could be the begining R&D for the latest Eaton offering.........

 

Sorry, Steve, it's an oblique reference to the Seinfeld episode called "Master of your own Domain" or something like that, or "The Challenge" when Kramer slaps his money on the table after a couple of hours, and says "Im out!" much to the astonishment of Jerry, George and Elaine. It comes into my head just after I've "blown my wad" on a rant, or long post here on NAM!

Again, I'm really still in...
Back on topic--I thought the BPV (such as the DT-BPV replacement) on the MINI was between the IC out horn and the inlet to the SC. The photo you posted has the butterfly inside the SC. Does that mean we have 2?

 

Great episode! Kramer was the only one that got any sleep that night.

 

Nope the charger on the mcs only has one. Not the one pictured. Can't remember if mine had that on the back. Oh well.