MINI Cooper Forum banner

1 - 20 of 31 Posts

·
Registered
Joined
·
42 Posts
Discussion Starter #1
Hello fellow mini lovers,

I was just wondering whether or not a supercharged engine can have a blow off (pop off) valve installed similar to a turbocharged engine?


Cheers,

Rob
 

·
Mini Mod
Joined
·
9,227 Posts
AMUSE COOPER S said:
Hello fellow mini lovers,

I was just wondering whether or not a supercharged engine can have a blow off (pop off) valve installed similar to a turbocharged engine?


Cheers,

Rob
No.
Stop thinking about it or I'll have to whack you :rolleyes: ;)
 

·
Its not small its Mini
Joined
·
163 Posts
No you get a different noise from a supercharger as its sucking in extra air all the time. Turbos suck air in based on the vacume from the exhaust or something hence the initial lag and then the whose when u release pressure.

www.howstuffworks.com has some stuff on the differece between a turbo and a supercharger
 

·
www.totalmini*****
Joined
·
15,256 Posts
Don't do it dude!!!!! :D:D:D

Get yerself a fruity induction kit and make your air filter woosh like a rocket and make your supercharger scream louder!!!
 

·
UberGeek
Joined
·
850 Posts
Why? Because it sounds good? ;)

A dump valve is designed to release excess pressure from the turbo, so that when you change gear, the airflow doesn't slow down the turbo, rather, it's left spinning so that when you put your boot down again, you're back up to full boost very quickly indeed.

Your S is supercharged, which means the compression is driven from the crank (engine) rather than by recirculating exhaust gases.

-Lee
 

·
The Hartge Experience
Joined
·
1,032 Posts
punkeyfunky said:
Why? Because it sounds good? ;)

A dump valve is designed to release excess pressure from the turbo, so that when you change gear, the airflow doesn't slow down the turbo, rather, it's left spinning so that when you put your boot down again, you're back up to full boost very quickly indeed.

Your S is supercharged, which means the compression is driven from the crank (engine) rather than by recirculating exhaust gases.

-Lee
Spot on.
 

·
Registered
Joined
·
39 Posts
Pop-Off valves are designed to stop turbos from over spinning, as the compressor is driven by a turbine moved by the exhaust gases. The more gas, the more exhaust thus the more compressed air is pumped to the cylinders, to a point that the engine cannot take it anymore, and the pop-off release pressure. Without a pop-off valve, it would be an endless and unsustainable exhaust/compression cycle for turbos

SC in the other hand are moved by the engine itself, not by the exhaust gases, which makes the use of a pop-off valve unnecessary

Also, pop-off valves are sometimes used to limit the real power a turbo engine can deliver by lowering the air compression pressure. This was used on Formula One circa 1987, to close the power gap between normally aspirated engines and turbo engines (nevertheless, turbo still kicked asses)

Going back to your point, the explanation above makes the use of a pop-off valve on a SC engine unnecessary, unless you want to severely limit the compression to reduce power. Why would you like to do that?
 

·
Registered
Joined
·
1,313 Posts
Another difference between a turbocharged engine and the Roots-type supercharged MCS is the location of the throttle body. In a turbo (or a centrifugally supercharged engine), the compressor forces air through the throttle into the intake manifold. When the throttle is closed suddenly, a pressure wave can build up against the throttle and bounce back to the compressor causing at best an unpleasant sensation and at worst serious damage. In the MCS, the throttle is UPSTREAM of the supercharger, so it never sees compressed air. Slamming shut the throttle by lifting off the gas does nothing more than reduce the pressure on both sides of the supercharger. The bypass valve in the MCS goes one step further in allowing intake air to pass through the supercharger without significant compression.

So, the moral of the story is, a BOV is neither necessary nor a good idea for the MCS.
 

·
Registered
Joined
·
39 Posts
Another difference between a turbocharged engine and the Roots-type supercharged MCS is the location of the throttle body. In a turbo (or a centrifugally supercharged engine), the compressor forces air through the throttle into the intake manifold. When the throttle is closed suddenly, a pressure wave can build up against the throttle and bounce back to the compressor causing at best an unpleasant sensation and at worst serious damage. In the MCS, the throttle is UPSTREAM of the supercharger, so it never sees compressed air. Slamming shut the throttle by lifting off the gas does nothing more than reduce the pressure on both sides of the supercharger. The bypass valve in the MCS goes one step further in allowing intake air to pass through the supercharger without significant compression.

So, the moral of the story is, a BOV is neither necessary nor a good idea for the MCS.

Andy,

Great and very interesting explanation. I’m curious why the throttle body on turbos is located after the compressor and not before as on SC engines. It is because the compressor is moved by the engine and not by a turbine? What would prevent a turbo engine to have the throttle body before the compressor?
 

·
Registered
Joined
·
429 Posts
The SC in the MINI has a bypass (not blow-off valve). It's used when just cruising or when off throttle at higher rpm's when the engine doesn't need all that air because it's not injecting much (or no) gas. You can't hear it. A way to notice when it's engauged is when driving in 2nd gear, slowly bring the throttle up to around 4k (you won't hear the SC whine) and then floor it and instantaneously, you'll hear the whine we all know and love. The bypass is used to increase efficiency when off-boost. I believe it just recirculates the air through the intercooler but I'm not exactly sure.
 

·
Registered
Joined
·
507 Posts
kapps said:
The SC in the MINI has a bypass (not blow-off valve). I believe it just recirculates the air through the intercooler but I'm not exactly sure.
There is an image showing that circulation design in the MTZ article , unfortunately the link to the document doesnt exist anymore. However, the diagram shows that the air is recirculated through the intercooler AND the supercharger itsself, making sure, that pressure boost is available when it´s needed again.

Klaus
 

·
Canyon Mini
Joined
·
310 Posts
A dump or blow off valve is there....

punkeyfunky said:
Why? Because it sounds good? ;)

A dump valve is designed to release excess pressure from the turbo, so that when you change gear, the airflow doesn't slow down the turbo, rather, it's left spinning so that when you put your boot down again, you're back up to full boost very quickly indeed.

Your S is supercharged, which means the compression is driven from the crank (engine) rather than by recirculating exhaust gases.

-Lee
:redblack: because it takes a little time for the turbo to slow down. You wouldn't want the turbo still producing boost when you let off the throttle. Street turbos don't produce usasble boost untill they are spinning somewhere around 150,000 rpms, racing turbos spin a lot faster and it takes a little time for anything spinning that fast to slow down. On the flip side lag is caused because it takes a little time for the turbo to spin fast enough to produce usable boost. I don't like turbos because anything getting that hot and spinning that fast isn't going to last vrery long and they are expensive to replace. :redblack:
 

·
Registered
Joined
·
24 Posts
I don't believe the statement that turbo chargers are less reliable due to the heat produced and the RPM's of the turbochargers. All diesel 53' 18-wheelers are turbocharged, and probably put more km/miles on in a day then we do in a month. They've been proven to go for long distances and have little problems. Sure, turbos do require more preventative maintence though.

It's also misleading to say turbochargers take a while to spool up to usable boost. If that were the issue, the tuner either mated too big of a turbo [without getting into specifics] or has suited his turbo for a higher rpm power band. You can almost eliminate turbo lag by using a smaller turbo for your given application, or fitting the proper sized turbo.

What most people don't realize though, is that a lot of torque at low rpm on a fwd application, makes it really hard to launch, control and use. I say, if you want quick 1/4 mile times or something to rip the track up with, you need more usable power higher in the power band, cue turboing. I'm a little biased on turbo charging if you haven't noticed :)
You'll have less problems getting traction on the fwd, higher trap speeds, and on the track more power in your powerband. turbo's can push more psi, more cfm and as a result, more power. :D

In response to Charlie Brown's post (how the throttle body being after the compressor on a turbo setup) You can't put a throttle body pre-compressor just because the way turbochargers are setup. Turbo's require the exhuast gases from the engine to spin the impellers which in-turn spins the compressor. Putting a throttle body pre-turbo yet after the engine would mean you would have no control of air entering the engine. Unfortunately you have to have the trottle body post turbo and before the engine.

ps: You also need bov's for Centrifugal superchargers under high psi ;)

I'm not saying turbos are better then superchargers or vice versa, I'm a little turbo biased myself. I just wanted to clear up some misinformation regarding turbochargers.

Peter.
 
1 - 20 of 31 Posts
About this Discussion
30 Replies
21 Participants
chiptuning
MINI Cooper Forum
Join our Mini Cooper Forums to talk about your new Mini. From reviews, mods, accessories, reliability concerns and more, this Mini Owners Club is full of info!
Full Forum Listing
Top