Roots vs centrifugal

matteo

Registered User
So I thought all superchargers went after the throttle body, but I recently found out I was wrong. Does that mean that centrifugals have blow off valves? What about a waist gate?
 
matteo said:
So I thought all superchargers went after the throttle body, but I recently found out I was wrong. Does that mean that centrifugals have blow off valves? What about a waist gate?

The simple anwsers;

1. Yes. You can run a blowoff valve with a centrifugal, there are bypass's availiable that do about the same job as ours bypass valves.

2. No. These do not you wastegates. Unlike turbos that use exhaust gasses to create boost, and require a wastegate to help regulate boost pressure, the centrifugals use a belt and the boost is regulated by the pully sizes.

Now, I'm sure you all will, if I stated anything incorrect, please feel to correct it.
 
ok thanks. so if you had a centrifugal what would be better to use, a blow off or a bypass valve?


by the way, im not one of those ricer wannabes trying to get a blow off sound on my SC. i'm just trying to learn about the different setups.
 
vortech kits use a bosch type "BOV" , but it is routed back into the intake track. If you put a BOV on a car that is equiped with a mass air meter (such as an sc), you will be asking for problems. The blow off valve will be "blowing off" air that has already been metered by the mass airflow meter, and you will have big idle and driveability issues.
 
I guess you could use a BOV if you were running a "blow through" air meter. They are really more suited for a turbo car with a manual trans. On a turbo car, when you lift your foot off the throttle to shift gears, the throttle body is closed. The turbo is still spinning and trying to build boost. With the throttle body closed, the turbo keeps spinning and will build enough pressure to slow down or stop itself. The BOV relieves this pressure when the throttle body is closed, which lets the turbo "freewheel". So, when you grab your next gear, it doesnt take as long to spool up, because the turbo is already spinning. A BOV saves alot of wear and tear on a turbocharger also.
 
You still need a Bypass or blow off valve for a cent.

When you lift off the gas at high RPM the bost that is built up will bounce off of the TB blade and surge the compressor and can damage it. This wave will travel back and forth between the 2 until it's energy is dissipated It's the same thing as the water hammer effect.

Basically a blowoff vents when pressure rises above a certian setpoint. It can go back into the intake after the MAF and not effect the computer.

A bypass valve is operated by vacuum and gets it's signal after the TB it can be vented to atmosphere or after the MAF so as to not mess with the computer.

Jeff
 
I don't want to argue with anyone but..a BOV is operated off of vaccum. When a vaccum is pulled, the valve opens and relieves boost pressure. A wastegate relieves exhaust pressure to control the amount of boost, by means of a wastegate actuator (if equipped with an internal wastegate, which most factory turbo cars are), When boost pressure reaches a certain point, the pressure is great enought to overcome the spring inside of the actuator, which bleeds exhaust off to control boost. Thats all a "boost contoller" does, allows you to control the amount of pressure that is sent to the actuator.
 
yeah really..........I would like to see one turbo charged........I know the 03 04 cobras REALLY benifit with a turbo swap. I've read the posts on here from the guys that are actually doing it. Can't wait to hear results.
 
Funny I guess the SC is equiped with a blow off valve.? There are different types and different methods of actuation.

Jeff
 
I think the one on the SC would actually be classified as a bypass valve. It is pretty much is used to "bypass" the blower.
 
It operates by way of vacuum, and you said that is what a BOV does.

It is a bypass valve.

Most all turbo cars are equipped with a bypass valve it serves the same purpose. Look at Saab 900/9000's, Ford Probe/Mazda MX6, Mitsu Eclipse. All are equiped with bypass valves.

Jeff
 
i'm sorry.....i should have stated that both a BOV and a Bypass valve usually are operated by vaccum. A blow off valve does just that.....it blows off pressure. A bypass valve does just what it's name suggests.....it bypasses. But on the SC, the bypass valve pretty much bypasses the blower all together when activated. When the SC is at idle....the butterfly in the bypass valve is open, which allows most of the air to bypass the blower and come strait from the throttle body. As vaccum is decreased, the butterfly closes, forcing all of the incoming air to be routed to the blower.
 
i was just tying to answer matteos question....not looking to argue. Hey matteo, you should give Precision Turbo and Engine, in Hebron IN. a call. They could explain all this better than anybody here. I worked there porting turbochargers a while back, that is where I learned what I know about turbos (lol....at least I thought I knew). It has been years, but when I was there, I saw everything from a twin turbo viper to a vorteched suburban. They know their stuff (anybody who reads MMFF or 5.0 mag. can tell you), and they are good people.
 
speedfreak said:
i was just tying to answer matteos question....not looking to argue. Hey matteo, you should give Precision Turbo and Engine, in Hebron IN. a call. They could explain all this better than anybody here. I worked there porting turbochargers a while back, that is where I learned what I know about turbos (lol....at least I thought I knew). It has been years, but when I was there, I saw everything from a twin turbo viper to a vorteched suburban. They know their stuff (anybody who reads MMFF or 5.0 mag. can tell you), and they are good people.
thanks for the info guys.
 
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