OnyxCLK

Hi there,
I have a clk 200 komp, and I was wondering if there is somekind of a blow-off valve for kompressor engines??? I heard several rumors about cutting the air pipe and installing bov around there (pretty much that's how they told me) and they said it would work... I just would like to have some opinions on it, has anyone tried it here? or are there any specific kits for this thing?

Hightower

i dont think so never heard of one the only reason they are fitted to turboed cars is to keep it spinning when u let off the gas to prevent turbo lag and to release the pressure preventing the unwanted compressed air going back through the impellor and stressing it.

levelr123g

yes a BOV will work with a supercharged car. Basically you would need to remove the blade that is currently in place that redirects air back into the engine, and then install a BOV in the intake tract on the positive side of the SC. In reality you will not gain anything other than that psssstttt sound that most blowoff valves make when releasing boost. Not worth the money / time in my opinion on these cars.

Hightower, a BOV valve is used to protect the throttle body plate from being bent, and also causing compressor surge. Basically think of it this way. If you are under WOT on a blown car (supercharged or turbocharged) and the unit is forcing positve pressure (boost) into the engine and you all of a sudden release the throttle and the plate in the throttle body is shut, all the boost that was already made and on its way up to the engine is all of a sudden slammed into a fixed object, the result is a bent throttle body plate, and compressor surge. It would be like you runnig down a hallway and all of a sudden somebody shuts a door in front of you and you slam into it. Not only does this pressure place alot of force on the plate, but it also then backs up and tries to stop the rotors (sc) or the impeler(turbo). All this force is very hard on parts, so to eliminate this, the designer installs a gate (i.e. wastegate/BOV) into the charge side of the intake. Typically these are vacumm controlled so when you shut the throttle the engine goes to vacumm, the BOV/Wastegate opens. Now a wategate and BOV are similar and pretty much do the same functions. The wastegate/bov opens when a predetermined pressure is reached or exceded, or the engine goes to vacumm. Typically these pressures can be adjusted by means of a spring inside the BOV/wastegate that pushes on a diaphram. Hope this helps.

Holmes5518

Hi,

I am somewhat new here, I have been a lurker for a while since I have been in the market for an SL.

The debate of the BOV and wastegate...Theyre not the same. They have two different funtions. Most of your assesment is correct, however:

I have had highly modified turbo cars for years and can tell you without a doubt that you will never bend a throttle plate without a BOV. The BOV is to prevent compressor stall in the turbo which in turn lets the turbo continue to spin down while off boost. The BOV is simply placed in line before the throttle plate to vent the excess air pressure that would otherwise travel back to the turbo when the throttle is closed.

The wastegate simply opens by exhaust gas flow allowing the exhaust gas flow to bypass the turbine wheel preventing the turbine wheel from spinning the compressor wheel faster causing boost spike.

And a BOV is useless in a supercharged engine, unless you just need the sound.

Mrdredd

I can confirm that Holmes5518 is correct.
The wastegate and BOV serve differant purposes.

The wastegate is used to relieve the pressure once the turbo reachs its pre-determined PSI amount and vents the air out to prevent damage.

There really is no use for a BOV even on a turbo car.

Turbo36

You guys are partly right, but mostly wrong. A BOV relieves pressure in the inlet tube of a blower or turbo engine, to protect the impeller blade of the blower/turbo, not the throttle blade. All that air has to go somewhere when the throttle slams shut, having the air reverse directions and trying to stop the impeller, while spinning 60,000 to 200,000 rpms, is not a good thing, a BOV plays a very important role in any forced induction engine, the more boost, the more critical it is to have one.
A BOV does not control boost, a wastegate does. Since a turbo spins according to exhaust flow, not directly corresponding to engine RPM, as in a belt driven blower, without a wastegate, the turbo would produce maximum boost at all times, thus destroying your engine.
If there is no need to run a BOV on forced induction engines, at least above 5psi, why does every single blower/turbo company include them in their kits? It's surely not just to provide that 'cool' whoooosh sound the kids like. OEM vehicles use internal style BOV's that re-circulate the air from the BOV back into the inlet, to quiet the sound and so all 'metered' air is accounted for.
It wouldn't hurt to pick up a magazine or do some research before making a statement that may lead to someone blowing up their turbo or blower.

Cylinder Head

iTrader: (1)

Wow some of you guys are amazingly uninformed with regards to the intricacies of forced induction sorcery. There is NO NEED for a BOV on a supercharged engine, superchargers only run relatively low boost and do not spin because of air flow (unless we're talking centrifugal, but that's a different story), mercedes blowers are all belt driven, so there's no "lag" to speak of, even though "lag" is not the reason for the use of a BOV in a turbo application. Closing the throttle plate on a supercharged car will not cause any backpressure or surge because there is no exhaust side to a supercharger, it only runs off the intake. Turbo cars work best with recirculating valves that dump pressure back into the intake stream, BOV's are only for noise and effect, but do serve a purpose of relieving backpressure, but not in an economical fashion and they actually create lag on larger turbo applications between shifts when compared to recirc. valves. Whoever said wastegates are the same or even similar to BOV's is crazy. Wastegates are boost controllers, they stop your turbo from building up 50+lbs of boost and detonating your engine. They work when your throttle is open, not closed, the complete opposite of a BOV.

Please guys, save the for the ers.

levelr123g

hmmmmm,
I guess we are doing something wrong then at 7.70 and 180+ mph.

www.roncoxracing.com

I guess im just a dumb a$$! You mean you cant regulate boost by using a BOV? I guess ive got it all wrong
As for the BOV and the wastegate being the same thing, technically they are. They both reduce/releive pressure in the intake during boost at a predetermined level!

And YES you can bend a throttle plate with excessive surge in pressure, among other things!

4npower

1st off, yeah, i guess in a dumb-a$$ kinda way you can regulate boost by using a BOV. the problem is that your turbo will spin to infinity and probably not last very much longer. so again, if your using a BOV to regulate boost pressure, then you are a complete dumb-a$$. also a BOV and a wastegate are not "technically" the same thing. one(BOV) relieves pressure from the intake track basically protecting the turbocharger from being damaged from surge and the other (wastegate) "redirectes" exhaust flow away from the turbine side of the turbocharger to REGULATE BOOST.
a BOV on a automatic, supercharged car is pointless. you could use one on a automatic turbo car but that would be to relieve the pressure when you let off the gas. after all there is no throttle lift in between shifts.
also, please forward any pics or even stories of bent throttle plates.
feel free to read this book so that in the future you don't sound like a dumb-a$$ http://btobsearch.barnesandnoble.com...601&z=y&btob=Y

4npower

BTW, to come to your defense, in your very rare set-up on the mustang, yes you would use a bov to regulate boost. with a cog belt set-up there is no belt slip so the blower will create a whole lot of boost that i'm guessing the engine can't handle. there are other ways for you guys to regulate boost but the easiest would be to install a BOV that releases pressure at your predetermined setting. the blower won't over spin because it is belt drivin so there would be no damage to the blower. obviously on your set-up, there is no where to put a wastegate so regulating boost with that wouldn't work.
but also know, that the set-up you are using would not be used on normal supercharged or turbo'd cars.
all supercharger belts slip to some degree, but with a cog set-up, there is no slip.