1fastrock

Hey everyone

Been reading up on super charger set ups now that I have mine up and running and I'm looking to improve on it now.

I was reading that a blow off valve can up the horse power of a supercharged motor and I'm not sure how reliable that information is. Does anyone know if it is true?

Thanks in advance
1fastrock

fasteddi

iTrader: (2)

Is the supercharger a centifical on or a screw?? If its before the throttle plate then you may need a BOV mainly for a safetly item to protect the charger. If its after the throttle plate then you would not need a BOV. So Screws dont need one if IIRC.




Im not sure howd you gain HP from a BOV. It would just save your compressor wheel if a centrifical or save other items as there would be nowhere for the air to go but backwards when you let off the gas and the throttle body closes. I wouldnt think it would be too much though in a supercharger application.

Im sure someone will chime with some experience on it. As I am no supercharger expert. Ive only delt with turbos.

1fastrock

Thanks for the reply!! It's a centrifical set up with a carb box and demon carb

fasteddi

iTrader: (2)

You running alot of boost? From what I read you can have one but I never hear of gaining Hp from it whatsoever But I will say Ive never seen a BOV on a supercharged car before now that I think of it. I know theres no gain in Hp from having one on a turbo set up except it keep the turbo and my throttle body in one piece.



Heres some general info on the topic.

If you're questioning whether or not to install a blow off valve on a supercharger, in general the simple answer is that your money would be better spent on some other aftermarket upgrade. It isn't necessary and doesn't provide any benefit whatsoever. Blow off valves (BOV) are used only in engines that are turbocharged, and its purpose is to relieve the pressure built up within the air intake system, preventing the backup of pressure into the turbo which slows or can even stall the compression wheel. A true supercharged engine works using forced induction which internally channels the air pressure back into the combustion system and compresses it using a pump. A turbocharger works on the same principle, however uses a turbine and the exhaust from the car's engine to provide the necessary compression in the air system, not a crankshaft driven pump.

Blow off valves are sometimes confused with bypass valves, which in a supercharger, diverts the air back into the engine directly, it doesn't vent out into the atmosphere. If your supercharger is centrifugal, a blow off valve can be used however you should only use them if your supercharger has a blow-through mass-air meter (mass-air flow, or MAS) installed or your vehicle will suffer performance problems. If your supercharger isn't a centrifugal one or utilizes a mass-air meter, a blow off valve is pointless. A supercharger typically is always on, and doesn't need a blow off valve to sense the pressure build up and engage to vent the pressure. Some Roots type superchargers can have a blow off valve installed, but still you would need to have a bypass valve to properly run the supercharger as designed.

The_F_body_kid

sorry to chime in her gents but i have been contemplating a centrifical system my self id be running about 8psi so 1.do i need a bov if so how do i plumb it 2.do i really need a blow-through carb or will my 750 holly double pumper mech secondaries work? either way im going to run an intercooler . thanks

Six_Shooter

iTrader: (2)

No power gain, but a good way to protect the compressor wheel, when the throttle is snapped shut.

fasteddi

iTrader: (2)

Drac0nic

I was under the impression that the bypasses were supposed to be more like a wastegate. By this I mean that it will vent air past a certain level of boost. The reasoning is that you end up with lower boost at lower RPM with a centrifugal, so if you increase the drive speed you can get boost earlier but bypass the excess in order to avoid over boosting at higher RPMs. Probably not more peak HP but more area under the curve at that point.

fasteddi

iTrader: (2)

Info from paxtons site: copy and pasted it.

The bypass valve is a release which vents off pressure in a rapid de-acceleration situation. When the Supercharger is producing boost and you abruptly let off the gas, closing the throttle plates, the boost has nowhere to go (also known as compressor surge) kind of hard on everything. The Bypass helps relieve this and also helps smooth out your idle. It is also helpful in building up boost faster, and as a bonus, it helps to prevent parasitic power loss. Under idle or normal driving (vacuum) the valve is open. When it sees a boost signal it closes.

Six_Shooter

iTrader: (2)

Fasteddi, I wouldn't listen too closely to that (the no need for a valve part), anytime, there is flowing pressurized air inside a pressure vessel (tubing in this case), and the path is abruptly closed, there will be a reversed shockwave, that can cause damage to the compressor wheel, be it super or turbocharger based, and that is the purpose of a BOV.

BOV = Bypass valve, end conversation. To muddy things up many VW guys will swear up and down that the "diverter valve" found on their cars is in now way like a BOV or bypass valve. :facepalm:

Some people like to differentiate saying that one "recirculates the air back into the system". They both serve the same purpose, they both function the same, it's just that one is usually vented to atmosphere.
Now that being said, there is one form of bypass valve that I would not contest and would actually separate into it's own functionality, and that would be as used in some Eaton superchargers (possibly others), that bypass the rotors of the supercharger, providing a shorter path from the throttle body that is placed before the supercharger rotors.

I would use a BOV on any supercharger system that places the super before the throttle plate, to protect the supercharger and the throttle plate. I've seen both damaged from high boost applications that didn't use a BOV.

anesthes

iTrader: (12)

(centrifugal blowers)

1) BOV are needed on anything making moderate flow (i.e, 800+ cfm). when you suddenly close the throttle (between shifts?) the air has to go somewhere. Without a BOV you risk the belt slipping, or jumping, breaking, etc.

2) An electronic controlled BOV (i.e, wastegate) can be used to regulate boost to make a centrifugal blower act more like a roots blower by regulating boost to be constant (full charge low rpm, leak at higher RPM). I actually have a nice article on that that I've been meaning to scan and post.

(here is an old article, not the one I was talking about though)

http://www.camaroz28.com/forums/forc...-boost-554304/

-- Joe

fasteddi

iTrader: (2)

Thats a good artical


The main idea I had in post#2 was that a BOV is for safety so that the comp wheel stays in one piece when the air is suddenly closed off. Same exact throry as a turbo application.

But whats the engeral rule for screw ones? No need for them at all on them?? Saftey wise?

anesthes

iTrader: (12)

I can't see how you would use one in a screw application. It's a good question. When the throttle slams shut on a twin screw blower, does it strain the case, rotors? I've never seen any reference in any of my books to that.. There must be at least some concern because I know a lot of guys with the 17x cid blowers typically make custom tensioners to keep the belts from jumping.

-- Joe

fasteddi

iTrader: (2)

Is there a way that the bypass valve or a set up like that would bleed the air off arround the rotors back into the piping on the intake side of the supercharger when X amount of boost was sencesd?. Just makes me wounder ya know?

Drac0nic

Some people seem to use conventional wastegates on the cold side of a supercharged engine to do this. RPS sells flanges for it anyways. You throw whatever spring you want and/or your boost controller on it and go to town. Wouldn't be surprised to find out some one makes a conventional style bypass/blow off valve that lets you do pretty much the same thing honestly or if you plumbed the Procharger valves in if they would too.

RBob

iTrader: (1)

Being draw-through there is no need to blow off the pressure. I don't believe I've seen many positive displacement setups that where blow through. Although I do know of one that had twin Eatons blowing into a TPI set up.

RBob.

anesthes

iTrader: (12)

On a draw through, what happens when the throttle plates suddenly close?

I guess, probably nothing.

-- Joe

Confuzed1

iTrader: (4)

Absolutely...nothing happpens. When the throttle blades close, you're cutting off the air supply almost completely to the blower also...and a roots or screw is designed to move air...so since there's a greatly reduced suppy of air...nothing happens. Just like any engine, intake vacuum increases and RPM's drop and you go to idle.

It's when you're cruising at 70 mph on the highway at steady part-throttle...that's when a bypass valve is handy. I honestly think of it as a "dump" valve....since the blower is still spinning and compressing air in excess of what you need at part throttle, the "dump" valve dumps the air somewhere outside in the engine bay from below the rotors.

- And in reverse, when you tromp on the throttle, and intake pressure drops...to say 5"...the valve shuts and allows full boost to the engine. The valve allows the blower to operate a lot more economically that way. Boost only when you need it, and one of the main reasons I went with a Magna-charger over a Weiand 142/144....well..that and the rotor design...

hrspwr

iTrader: (3)

Couple years ago I found an article where they added a WG or extra BOV(can't remember which) to a centrifugal system on a fox body Mustang. What they did then was put a smaller pulley to produce higher boost than they wanted. This allowed them to make more boost in lower RPM, but still regulate max boost to something less than what the charger was pushing out. Almost making it act like a turbo system where boost comes in quick then plateau's while engine speed increases, instead of being linear. Very interesting article, will have to see if i can find it again.

Guest

Do post.

anesthes

iTrader: (12)

Post 11...

-- Joe

hrspwr

iTrader: (3)

Dismissed that thread as it was from a Camaro site. But if I had opened it......
Thanks.

Confuzed1

iTrader: (4)

Check out what Procharger has up their sleeve....BOV's for these could be a thing of the past!
http://www.modernmoparmagazine.com/w...ndustry-first/

anesthes

iTrader: (12)

One of my old car books has a similar thing from the 50s. A centrifugal that had a clutch, was wicked weird. I believe it was a factory item on a long since vanished car company.

-- Joe