Anyone here w/a blow-off valve?

[BillyGman]

I'm just curious.....do any of your supercharged Marauders here use a "blow-off" valve? And if so, do your Marauders make that same blow-off valve popping sound as the turbocharged Japanese cars make like the Evo I passed lastnight, or the Turbocharged Integra that I saw? :puke:

No offense, but I'm amazed at how some young kids really like that sound. I definately don't. Just my opinion ofcourse. But I was just wondering if any of you guys have that on your Marauders, and if you happen to like that sound.

[Logan]

The Lightning has a Boost-bypass setup that most folks bypass...

Same general purpose. Blowoff valves are critical in a turbocharged setup.

[BillyGman]

The Lightning has a Boost-bypass setup that most folks bypass...

Well I assume that it's just like the bypas valve on our Trilogy supercharger set-ups. But it's my understanding that blow-off valves are different than bypass valves. please correct me if I'm wrong about that. :) BTW, I wasn't aware that some guys bypass the bypass valve. What would be the benefit of that? Wouldn't that kill your gas mileage and potentialy tax your supercharger for street driven vehicles?

[python357]

I'm not the most literate on such things but I don't believe a blow aff valve is used on super chargers as they work off the engines drive pulleys thus engine RPM dependent.

A blow off valve is used on a turbo system to keep the turbo boost down when the gas pedal is released and the cluth is depressed during shifting (drastic change in RPM) with a manual trans, the poping sound is the excess pressure bleading off, you woulden't need to use use one on an automatic trans because RPM's are always up during a shift.

SC's make more power but turbos make power faster......Max boost with less RPM. SC need to get to max RPM for max boost.

Anyone please correct me if i'm wrong.

[BillyGman]

SC need to get to max RPM for max boost.

Anyone please correct me if i'm wrong.Not so with roots and twin screw superchargers. My engine gets maximum boost even at 2,500 RPM's as long as I'm at WOT. As far as the blow-off valves, I've heard that Turbochargers can be fitted with bypass valves or blow-off valves (I'm not sure how true that is though) but I wasn't sure if any superchargers use blow-off valves.

[python357]

Not so with roots and twin screw superchargers. My engine gets maximum boost even at 2,500 RPM's as long as I'm at WOT. As far as the blow-off valves, I've heard that Turbochargers can be fitted with bypass valves or blow-off valves (I'm not sure how true that is though) but I wasn't sure if any superchargers use blow-off valves.

Sorry should refraise that... engine RPM must be at an "optimal" RPM for max boost for a supercharger typically higher than for turbos. Some turbos deliver max boost as low as 1000 RPM it also depends on the amount of boost you can get from your turbo, your exhaust system, your engine size, 4 cylinders operate at high RPM already, and other junk.

[BillyGman]

sorry should refraise that... engine RPM must be at an "optimal" RPM for max boost for a supercharger typically higher than for turbos. Some turbos deliver max boost as low as 1000 RPM .I'm really not intending to debate with you, but I've never heard that before. Which doesn't neccessarily mean that it isn't true, but overlooking the fact that full boost wouldn't do anything below 2,000 RPM's with an automatic transmissioned car because of the typical stall speed on performance set-ups being over 2,000 RPM's (2,300 RPM stall speed even for a stock Marauder) I don't see how a turbo set-up can possibly deliver full boost pressures at 1,000 RPM's or even at 1,500 RPM's when it runs off the exhaust velocity.

[Hotrauder]

:burnout:
Not so with roots and twin screw superchargers. My engine gets maximum boost even at 2,500 RPM's as long as I'm at WOT. As far as the blow-off valves, I've heard that Turbochargers can be fitted with bypass valves or blow-off valves (I'm not sure how true that is though) but I wasn't sure if any superchargers use blow-off valves.
My experience with turbo charging has been only with Porsche Turbos. They were both exhaust driven turbos and equipted with waste gates to relieve boost pressure short of detonating the engines. Boost level controlled by the wastegate could be adjusted by changing the wastegate spring or increasing or decreasing the spring tension. I am not an engineer but didn't need to be to enjoy the rush...and I am looking forward to a SC on my DTR. When the boost exceeds the preset wastegate tension you get the "blow-off" Typically with mine the compression level was quite low compared to a SC or normally aspirated engine-around 8 to 1. Again to get the engine home in one piece. I don't know if Porsche is typical but I think so. Anyway they were a blast to drive fast as stink straight line or crooked. Dennis :burnout:

[BillyGman]

Thanks for eveyone's replies so far. Just so I'm not misunderstood here, I'm not asking what blow-off valves do, nor am I questioning the need for them on turbocharged engines. I'm simply wondering if there are centrifugal supercharger set-ups that have blow-off valves also. Particularly on Marauders. ;)

[python357]

I'm really not intending to debate with you, but I've never heard that before. Which doesn't neccessarily mean that it isn't true, but overlooking the fact that full boost wouldn't do anything below 2,000 RPM's with an automatic transmissioned car because of the typical stall speed on performance set-ups being over 2,000 RPM's (2,300 RPM stall speed even for a stock Marauder) I don't see how a turbo set-up can possibly deliver full boost pressures at 1,000 RPM's or even at 1,500 RPM's when it runs off the exhaust velocity.
I'm not trying to debate with you either but i'm not talking about Marauders, on a Marauder an SC is the ONLY way to go, just talking Turbo in general as it relates to the use of a blowoff valve and why it's their.

[BillyGman]

just talking Turbo in general as it relates to the use of a blowoff valve and why it's their. Fair enough my friend. Again, I don't question the need for blow-off valves for turbocharged vehicles, nor how they work. I'm just wondering if any supercharger set-ups use BLOW-OFF VALVES instead of BYPASS VALVES, and if so, does anyone's supercharged Marauder use one of those.

[Zack]

A Blow off Valve is used ONLY in a Blow-Thru Maf set up.
A By-Pass Valve is used on a suck through and opens when you let off the gas, recirculating the already metered air back into the inlet side of the blower.

[BillyGman]

A Blow off Valve is used ONLY in a Blow-Thru Maf set up.
A By-Pass Valve is used on a suck through and opens when you let off the gas, recirculating the already metered air back into the inlet side of the blower.Are there any advantages or disadvantages to a "blow-thru" MAF set-up? And of so, what are they? I asssume that amongst suercharger set-ups, you would only have the option of using a blow-thru MAF set-up with centrifugal blowers, but please correct me on that if that assumption is wrong.

[SergntMac]

All Kenny Brown Marauder S have a TurboXS blow off valve, model H., except mine. I have a Vortech.

http://www.turboxs.com/shop_prod.php?what_category=2

[FordNut]

Fair enough my friend. Again, I don't question the need for blow-off valves for turbocharged vehicles, nor how they work. I'm just wondering if any supercharger set-ups use BLOW-OFF VALVES instead of BYPASS VALVES, and if so, does anyone's supercharged Marauder use one of those.
I was waiting for Marty to chime in, but yes, his car has blowoff valve(s). Most of the centrifugal blower setups use a draw-thru MAF which should use a bypass valve rather than a blowoff valve. Marty's has a blow-thru MAF so he can use either a blowoff or a bypass valve, the blowoff being easier since it doesn't have to be ducted back into the blower inlet pipe. It does need to be after the blower and before the MAF even in blow-thru applications so the MAF accurately meters air into the engine.

[FordNut]

Are there any advantages or disadvantages to a "blow-thru" MAF set-up? And of so, what are they? I asssume that amongst suercharger set-ups, you would only have the option of using a blow-thru MAF set-up with centrifugal blowers, but please correct me on that if that assumption is wrong.
Most tuners I have talked to claim that the blow-thru is harder to tune for good drivability. Yes, centrifugal blowers are the only practical use of the blow-thru setup. It can be very useful if space limitations are a problem.

[BillyGman]

This is proving to be very educational (atleast for me anyway). Thanks for your replies bruthas....

[RR|Suki]

My car also has blow off. The whistle sound you speak of doesn't happen as a fact of having a blow off. Some actually have the outlet built to make a sound upon opening. Mine is just an opening and only makes a large woosh.

[SergntMac]

Are there any advantages or disadvantages to a "blow-thru" MAF set-up? And of so, what are they? I asssume that amongst suercharger set-ups, you would only have the option of using a blow-thru MAF set-up with centrifugal blowers, but please correct me on that if that assumption is wrong.Having tried both, IMHO, a suck through design is superior to the blow through design. The advantages are subtle, but important.

Blow through means the MAF follows the supercharger, thus it must process turbulent air, recently superheated by the blower and recently supercooled by the intercooler. There's a heape of violence to that air as it passes through the MAF. At lower boost, say 6-8-10 PSI, the MAF function is relatively smooth, and you can program a decent tune, achieve maybe 400-425 RWHP and 380-400 RWTQ. You'll have a spirited ride, but obviously you are leaving power on the table, considerable power.

A Vortech S-Trim can produce up to 625 RWHP with a smaller pulley, a T-Trim can produce 850. However, as you increase boost, a stable tune is more difficult to achieve due to the turbulence inside the induction path. Keep moving up in PSI and tuning, and eventually, all stability will be exhausted, but you will not have exhausted your power potential. This is why a blow-off valve is preferred here, no need (or, way) to recirculate the air charge. All it does is relieve pressure in the induction path. When you suddenly pull out of the throttle and close the throttle body, all that internal pressure has to go somewhere, and it's enough to break some very strong parts. Ask me how I know.

In a suck through, the MAF is before the supercharger, mine is at the very beginning of my air path, just behind the paggenger side fog lamp assembly. The MAF processes the incoming air before it's compressed and cooled, which defines air mass with greater accuracy. The ability to tweak and tune is greatly enhanced, and the air charge is much more stable. You can achieve a flat AFR ratio as flats as________this, and tune that ratio to meet your needs. Now, you want a bypass valve. It functions just like the blow off valve, because it is a blow off valve, just one with a 2" OD flange to mount a recirculation hose. Now your air charge can be relieved of it's pressure, and recirculated back into the air path as metered air.

Before I switched over, I had 478 RWHO/434 RWTQ, a 3.12 pulley and my tune was maxed. If I tried anymore tweaking, the tune would degrade. After the switch over to suck through, I dropped to 464 RWHP/425 RWTQ, but a much better running car, with greater low end acceleration and power. It was an amazing change. The car lost power, and drove twice as good.

What would you expect me to do now? Right, change pulleys again, and see how far I can push this SCT tune. So, changing nothing but the pulley from a 3.12 to a 2.70, I get 502 RWHP, 480 RWTQ, 12.5 AFR through 6400 RPM.

I'd never see this power, or tune performance with a blow-through design, never. Too much turbulence present, even the SCT Big Air 90mm couldn't handle anything over 14 PSI. Again, subtle but very important differences. Hope this helps.

[BillyGman]

My car also has blow off. The whistle sound you speak of doesn't happen as a fact of having a blow off. Some actually have the outlet built to make a sound upon opening. Mine is just an opening and only makes a large woosh.Thanks for your reply. It isn't any whistle sound that I was talking about, but that "woosh" sound followed by a pop or the sound of some type of door or plate slaming shut that I was refering to. nit my cup of tea, but that's okay. We all have our own opinions, and it's still good to be able to talk cars as far as I'm concerned. Different strokes for different folks, ya know? (in the case of your engine set-up, I guess that can be taken literally :D ). And thanks for sharing with us about what you have in your car my friend.:banana2:

[Todd]

Most tuners I have talked to claim that the blow-thru is harder to tune for good drivability. Yes, centrifugal blowers are the only practical use of the blow-thru setup. It can be very useful if space limitations are a problem.
With the right MAF a blow through can be as easy as a draw through to tune. The Pro-M Univer MAFs were very easy. Macs KB marauder is blow through also IIRC.

Dont forget the turbo marauders in the use of blow through mafs... What FordNut was saying was any non-'roots' style blower can use it. Some say it is more accurate once you get it to work....

And lots of guys I know use bypass valves on blower cars. It makes much more sense. Throttle blade shuts, blower is still spinning per motor rpms, pressure has to try to go somewhere so it backs up into the blower. More compressed air means more heat, possibilities off blown off hoses, etc....


EDIT,,,,, whoops, I see Mac posted while I was typing!

[BillyGman]

And lots of guys I know use bypass valves on blower cars. It makes much more sense. !I'm not sure if this was a typo error, but I just want to repeat that I wasn't talking about "BYPASS" valves. The Trilogy/Eaton blowers all have bypass valves which ofcourse includes the one on my Marauder, and that is no mystery to me. it's the "BLOW-OFF" valves that i was asking about.;)

I just don't want this thread topic to be confused. Thanks very much for your post. :)

[MikesMerc]

I'm not sure if this was a typo error, but I just want to repeat that I wasn't talking about "BYPASS" valves. The Trilogy/Eaton blowers all have bypass valves which ofcourse includes the one on my Marauder, and that is no mystery to me. it's the "BLOW-OFF" valves that i was asking about.;)


By-pass valves and blow-off valves do essentially the same thing....they bleed off un-needed boost pressure which lowers compressor temps and reduces back surge.

The only difference between them is that a blow-off valve bleeds air charge into the atmosphere, while the by-pass bleeds off air charge back into the air intake system.

By-pass valves are used to bleed off pressure when the compressor compresses the air charge after the mass air meter, while the blow-off bleeds off pressure when the compressor compresses the air charge before the mass air meter.

Once the air volumes have been measured by the MAF, the air MUST remain in the system for proper engine management. Hence the need for a recirculating by-pass by systems that compress after the MAF.

[BillyGman]

By-pass valves and blow-off valves do essentially the same thing....they bleed off un-needed boost pressure which lowers compressor temps and reduces back surge.

.Yep..... I knew that, but they do it in different ways,(as you've described in your post) and "BYPASS" valves don't make that weird noise that "BLOW-OFF" valves do. Furthermore, since roots type blowers only use bypass valves, I was wondering if atleast some of the centrifugal type superchargers use blow-off valves instead. And that question has been answered by Zack, FordNut, and MAC.

[martyo]

Billy: Are you aware that they actually make these valves that are intentionally louder?

[Joe Walsh]

Billy: Are you aware that they actually make these valves that are intentionally louder?


Yep, Like the dork driving next to my Cobra this weekend in his Dodge SRT-4 Neon......
revving his little turd up then backing out of the throttle quickly to get his aftermarket blow-off valve to whistle and pop.
I just kicked in my clutch, revved the 468 cube FE and parted his hair with my 4 inch side pipes!!!
Then I just looked over and smiled at him... :)
I wasn't even going to waste any 93 octane to prove the obvious... :D

[BillyGman]

Billy: Are you aware that they actually make these valves that are intentionally louder?That's a good point Marty. I've heard that they do, but I really didn't know much about this blow-off valve topic before I started this thread. There are a number of board members here who helped to bring some things to light on this topic for me in this thread. Something tells me that a number of the ricer cars that I've been passing by lately have after market bypass valves installed which makes them loud. They obviously must think that it sounds cool. :rolleyes:

I guess if they like that annoying beehive sound that their engines make when they step on the go pedal, then it shouldn't surprise me that they enjoy the annoying sound of the blow-off valves.

[MikesMerc]

I guess if they like that annoying beehive sound that their engines make when they step on the go pedal, then it shouldn't surprise me that they enjoy the annoying sound of the blow-off valves.

No kidding. Every boy racer in the neighborhood here has gone to loud blow off valves. Man, I find it totally annoying. Between the fart can and loud blow off valve, these guys gained zero performance and a whole lotta noise.

If you think about it, though, that's the point with many of today's kids. They all live for the "gee, look at me" attention thing.

It takes a completely different mentality to appreciate the sleeper that the marauder is.

[RF Overlord]

If you think about it, though, that's the point with many of today's kids. They all live for the "gee, look at me" attention thing.

It takes a completely different mentality to appreciate the sleeper that the marauder is.Exactly. :up:

[DEW34]

Yep, Like the dork driving next to my Cobra this weekend in his Dodge SRT-4 Neon......
revving his little turd up then backing out of the throttle quickly to get his aftermarket blow-off valve to whistle and pop.
I just kicked in my clutch, revved the 468 cube FE and parted his hair with my 4 inch side pipes!!!
Then I just looked over and smiled at him... :)
I wasn't even going to waste any 93 octane to prove the obvious... :D
i know i dont post a whole lot in here but thats funny no matter who you are :lol:
mike

[BillyGman]

If you think about it, though, that's the point with many of today's kids. They all live for the "gee, look at me" attention thing.

It takes a completely different mentality to appreciate the sleeper that the marauder is.Very true Mike. It's like if you've ever used those self-serve car wash bays, and during the time you're washing your car, as well as afterward when you're in the parking lot drying it off, you have to listen to the annoying noise that one of the ricer boy kids call music, as they blast it loud enough for the entire block to hear, as if to say " Look at me everybody...Hooray for me" Meanwhile their pants are hanging down almost to their knees as they're tripping over them and walking like they're limping. These dudes dress like they're orphaned kids. :shake:

....okay, I know this is nothing new, so let me stop.....rant OFF.

[mpearce]

Heather and I refer to that sound as "turbo sneeze". Her Buick will do it right after a hefty burnout, as soon as she lets off the gas. Her turbo is quite large, and moves a lot of air, so when she lets off the gas after a burnout, the blow off sound can be heard quite easily. Sounds like a loud fluttering noise. The sound got louder when she added her cold air intake. The air filter is now located next to the front air dam on the drivers side of the car down low. Now that the filter isn't under the hood anymore...the blow off sound can be heard more easily. But we didn't do this to "intentionally" make that sound louder.

-Mat

[RR|Suki]

Heather and I refer to that sound as "turbo sneeze". Her Buick will do it right after a hefty burnout, as soon as she lets off the gas. Her turbo is quite large, and moves a lot of air, so when she lets off the gas after a burnout, the blow off sound can be heard quite easily. Sounds like a loud fluttering noise. The sound got louder when she added her cold air intake. The air filter is now located next to the front air dam on the drivers side of the car down low. Now that the filter isn't under the hood anymore...the blow off sound can be heard more easily. But we didn't do this to "intentionally" make that sound louder.

-Mat
That fluttering is bad, what that is is the blow off not being able to purge all of the boost effectively and you are hearing the air that is supposed to be released being "chopped" by the turbine as it backs down the tube. Change that Blow off valve to a better more adjustable one. Just my $.02

[juno]

.

SC's make more power but turbos make power faster......Max boost with less RPM. SC need to get to max RPM for max boost.

Anyone please correct me if i'm wrong.
Hijack

The gents using two smaller twins have the right idea. They spool up faster and they just keep making power. Check out turbochargedpower.com I have resorted to begging these guys to make a MM kit. :)

Excellent discussion on blow-off's and bypasses!!!

[SergntMac]

Noting the differences between blow off valves, such as the TurboXS Model H Kenny Brown uses, and the variety of bypass valves used in centrifugal supercharger builds from Vortech and ProCharger, I am unfamiliar with any excessive "pops", "whistles", or, obnoxious noise from their legitimate use.

Most blow off and bypass valves are identical with one exception, a way of attaching a recirculation hose. There may be other valves out there that intend to create disturbing noise, I have seen one advertised as the "loudest", however, that appears to be just one selling point.

Both types of valves I have become familiar with produce a woosh of air when the valve functions properly. If released to the atmosphere, it's a blow off valve and you will hear this woosh. If it's recirculated, it's a bypass valve, and you'll detect that same whoosh, but muted to some degree by the recirculation path. In either case, these valves serve a legitimate purpose, and are part and parcel of a responsible supercharger build.

Perhaps what is being heard at the car wash is a sound recording over a PA system, which is something I would not put past the rebellious ricer crowd as yet another way of flipping off the rest of the non-ricer world. Quite likely if the range and volume expressed in this thread is accurate, and all those other colorful noises occur as well. The legitmate whoosh isn't all that loud, and if you haven't heard it before, it's unlikely you would notice it in the first place. Moreover, someone could have converted a bypass valve into a blow off valve, feeding the air charge into a sound device, like maybe air horns? Who knows? Maybe next time, someone will take a peek under the hood?

If there is supporting power adder hardware under the hood, you have to pay some respect to the owner, despite his obnoxious appearance and behavior. It's as much a challenge to turbo/supercharge a Neon, as it is to likewise power our Marauders. So, a tip of my hat (baseball cap?) goes out to the builder who gets his job done. Personally, I've seen Neons and likewise FWD cars run in the 12s, and you have to respect that mechanical accomplishment for what it is, "sneeze" and all.

[BillyGman]

Both types of valves I have become familiar with produce a woosh of air when the valve functions properly. If released to the atmosphere, it's a blow off valve and you will hear this woosh. If it's recirculated, it's a bypass valve, and you'll detect that same whoosh, but muted to some degree by the recirculation path. That may be true with both types of valves ( ie. "blow-off", and "bypass") when using them with centrifugal superchargers, but you cannot hear the operation of the bypass valves that are used in the Eaton roots superchargers at all. And going by everything I've read published by both Eaton and magnuson (Eaton's main after market distributor) the bypass valves used on their superchargers are only needed for increasing the gas mileage during part throttle operation. Otherwise they're not needed at all with roots superchargers as far as I know. I don't beleive that the huge roots superchargers on the SuperGas, alchohol, and Top fuel dragsters use bypass valves at all.;)

[MikesMerc]

Perhaps what is being heard at the car wash is a sound recording over a PA system, which is something I would not put past the rebellious ricer crowd as yet another way of flipping off the rest of the non-ricer world.

Nope, this isn't what we are referring to at all. There a dozens of companys that make aftermarket blow off valves for the import turbo crowd which do nothing except make a big, loud, woosh noise. Some of these valves do come with better adjustability...but that's not the main focus of these noise making valves. You can buy an aftermarket adjustable blow off valve that is virtually silent (or at least as quiet as the OEM valve).

For example: THIS (http://www.turboxs.com/shop_prod.php?what_category=2) valve is advertised as "the BOV-H-RFL remains true to it's roots - it's still really f'n loud" and " If you need to ask how loud it is, this valve is too loud for you! "

BTW, the Neon SRT comes turbo charged from the factory. There are highly modded SRT Neons that run well into the 11s and deserve and have much repsect. However, the "wanna be" boy racers with stock turbos that make 8-12 psi and run 14 seconds have no performance reason to add these super loud blow off valves. Its nothig but noise without the "go-fast" to back it up. They are about as annoying and worthless as those fart can mufflers they run.

[MikesMerc]

Heather and I refer to that sound as "turbo sneeze". Her Buick will do it right after a hefty burnout, as soon as she lets off the gas. Her turbo is quite large, and moves a lot of air, so when she lets off the gas after a burnout, the blow off sound can be heard quite easily. Sounds like a loud fluttering noise. The sound got louder when she added her cold air intake. The air filter is now located next to the front air dam on the drivers side of the car down low. Now that the filter isn't under the hood anymore...the blow off sound can be heard more easily. But we didn't do this to "intentionally" make that sound louder.

-Mat

Mat-

With big boost comes the need for a big blow off valve! Your blow off flutter is a true sign of the boost your making and a real indication of the power potential heather's car has.

My comments regarding noisy blow off valves for the ricer crowd that have no need for such ridiculous sounding valves was not meant for you or anyone one else running big turbo boost.

By the way...I am sure you are aware already, but the "flutter" is nothing bad at all as someone earlier stated. When you a running big boost with significant cfm a blow off will almost always flutter. Only the real small turbos that push lower cfm levels have a blow off that doesn't flutter. This is because a "single purge" of compressed air on smaller turbos is enough to bleed off the excess boost when the turbo isn't making enough cfm to refill the volute and pipe leading to the valve. Bigger turbos making big CFM need to flutter as they open at a preset pressure when the intake sees vacuum (foot off the gas). As the bigger turbo is still spinning down, enough cfm is produced that requires another purge cycle. This happens over and over until the turbo impeller hits a low enough rpm to produce insignificant boost.

I know you knew that though :)

[RR|Suki]

Mat-

With big boost comes the need for a big blow off valve! Your blow off flutter is a true sign of the boost your making and a real indication of the power potential heather's car has.

My comments regarding noisy blow off valves for the ricer crowd that have no need for such ridiculous sounding valves was not meant for you or anyone one else running big turbo boost.

By the way...I am sure you are aware already, but the "flutter" is nothing bad at all as someone earlier stated. When you a running big boost with significant cfm a blow off will almost always flutter. Only the real small turbos that push lower cfm levels have a blow off that doesn't flutter. This is because a "single purge" of compressed air on smaller turbos is enough to bleed off the excess boost when the turbo isn't making enough cfm to refill the volute and pipe leading to the valve. Bigger turbos making big CFM need to flutter as they open at a preset pressure when the intake sees vacuum (foot off the gas). As the bigger turbo is still spinning down, enough cfm is produced that requires another purge cycle. This happens over and over until the turbo impeller hits a low enough rpm to produce insignificant boost.

I know you knew that though :)
why would you want that to happen? that is kind of ludacris, why would you want only a partial purge and have your turbine and throttle body holding undue strain? and then having to flutter... why not just purge it all at once more efficient, because you purge 1 time and you aren't straining parts with backed up air, there are bov's that will deal with 30psi blowers, why not just use one... that really doesn't seem logical :confused:

[python357]

I seen alot of the ricer blowoff valves and they have "trumpet bells" on the output to get the loud pop, like a cracking of a whip, or a variety of other sounds. But like others have said not much functionality.
:whistle::popcorn:

[MikesMerc]

why would you want that to happen? that is kind of ludacris, why would you want only a partial purge

Its not a partial purge...its a full purge. You're not understanding what's happening.

The blow off valve is set to open at a given pressure when the intake is also under vacuum. It only opens when the intake is under vacuum (throttle plate mostly closed) so that boost is not bled off unintentionally under high boost WOT conditions.

Now, assuming the intake is in vacuum, and the pressure inside the flow tube hits the set pressure point, what happens?....the blow off valve opens. Within miliseconds of the valve opening, pressure drops, and when that happens the blow off valve closes. After it closes, the turbo is still spinning down, so boost is still created....pressure builds and the blow off valve opens again. This cycle of open/close causes the flutter sound and continues until the turbo is spinning slow enough not to cuase enough boost to open the valve.

Because the valve is triggered to open at a set pressure, obviously it closes when the pressure is releived. There really isn't any other way to do it.

The only other option is a valve that is operated soley on whether the intake sees vacuum or boost regardless of the boost pressures it is releiving. In this case, the blow off valve would remain open as long as the intake sees vacuum and there would be no flutter at boost is bled off.

However, this is a problem for turbos that already have lag. So, in order to reduce lag, boost is allowed to build even in vacuum state. In this situation, it takes both a vacuum condition AND a preset pressure to open the valve. This, as explained above leads to flutter as the pressure is releived, builds, releived, builds, etc,etc.

Smaller turbos have less lag so the valves can be run off the intake vacuum with a very low preset pressure to open. In addition, smaller turbos produce less boost pressure during spin down. These characteristics of smaller turbos allow them to be bled off without flutter.

Hope that helps.

[yamahaSHO]

I'm not exactly sure on the SC configuration on the Marauder, but I have a blow-off/bypass valve for my supercharged motor.

Superchargers need some kind of blow off valve to relieve pressure just like a turbocharged engine. Just like stated on the first page, a supercharger is driven off of the engine. When the throttle is closed, the engine does not stop turning. With that said, the blower is still moving air. At idle and regular cruising, the BOV should be venting boost. When road racing, you want to keep the motor spun up to stay in the power band. When I let of at 6k or 7k RPM yet keep it in gear (leaving the motor spinning) to have the power on hand out of a turn, the blower is producing around 10 PSI. You'll want to vent that with the BOV instead of surging the supercharger.

A BOV and a bypass valve share the same function, but a bypass vavle will also limit boost. Both relieve pressure when vacuum is applied to the manifold (IE: throttle is closed). A bypass valve also utilizes a spring and boost both sides (boost/vacuum on one side, only boost on the other) of the diaphragm to limit boost at whetever the spring is set to. Genearlly, you can adjust what boost the spring will "pop-off" by compressing it. For example, if you wanted to gain more low end power on a centrifical blower, but risk over boosting at redline, you can run a small pulley to get the blower spinning faster, but have the spring relieve boost at set RPM (provided the valve can handle the flow).

On either configuration, the BOV/BPV is held shut under boost because boost is applied to the opposite side of the valve equalizing the pressure. I have ligthest spring they make for my application so that the valve reacts immediately (and it would not open under cruise/idle with the stiffer spring)

http://www.hksusa.com/categories/?id=1062

[yamahaSHO]

Most tuners I have talked to claim that the blow-thru is harder to tune for good drivability. Yes, centrifugal blowers are the only practical use of the blow-thru setup. It can be very useful if space limitations are a problem.

Blow-thru is much harder to tune versus a pull-thru configuration. I have also found that the tune is not consistant with a blow-thru with the hot blower creating a vortex.

[SergntMac]

Don'tcha love it when everything gets said 3-4 times over...

[AzMarauder]

Heather and I refer to that sound as "turbo sneeze". Her Buick will do it right after a hefty burnout, as soon as she lets off the gas. Her turbo is quite large, and moves a lot of air, so when she lets off the gas after a burnout, the blow off sound can be heard quite easily. Sounds like a loud fluttering noise. The sound got louder when she added her cold air intake. The air filter is now located next to the front air dam on the drivers side of the car down low. Now that the filter isn't under the hood anymore...the blow off sound can be heard more easily. But we didn't do this to "intentionally" make that sound louder.

-Mat
Does your car have a blow off valve? A lot of turbo applications (specifically American) do not. My Ford Thunderbird Turbocoupe doesn't... and in fact neither does my Mitsubishi Starion Turbo (yet).

[AzMarauder]

Billy....


One of the reasons the Lightning crowd (and Cobra crowd) were bypassing the boost bypass valve was the belief that it dumped TOO much boost when you came off the throttle. So in a 1/4 mile situation, coming off the gas for the shift... they felt the bypass dumped too much boost and it took too long to build it again. (we are talking 100ths of seconds here) I wasn't sure it would make that much difference with the automatic truck... However, that is what the going story was for why one would bypass the boost bypass. I left mine alone in my Cobra! I was quite happy with how mine ran!

:D

[blackf0rk]

Nope, this isn't what we are referring to at all. There a dozens of companys that make aftermarket blow off valves for the import turbo crowd which do nothing except make a big, loud, woosh noise. Some of these valves do come with better adjustability...but that's not the main focus of these noise making valves. You can buy an aftermarket adjustable blow off valve that is virtually silent (or at least as quiet as the OEM valve).

For example: THIS (http://www.turboxs.com/shop_prod.php?what_category=2) valve is advertised as "the BOV-H-RFL remains true to it's roots - it's still really f'n loud" and " If you need to ask how loud it is, this valve is too loud for you! "

BTW, the Neon SRT comes turbo charged from the factory. There are highly modded SRT Neons that run well into the 11s and deserve and have much repsect. However, the "wanna be" boy racers with stock turbos that make 8-12 psi and run 14 seconds have no performance reason to add these super loud blow off valves. Its nothig but noise without the "go-fast" to back it up. They are about as annoying and worthless as those fart can mufflers they run.
I had that TurboXS BOV on my Turbo Impala, it was quite loud. It's all advertising though, I've heard different ones that sounded the same.

[BillyGman]

Billy....


One of the reasons the Lightning crowd (and Cobra crowd) were bypassing the boost bypass valve was the belief that it dumped TOO much boost when you came off the throttle. So in a 1/4 mile situation, coming off the gas for the shift... they felt the bypass dumped too much boost and it took too long to build it again. (we are talking 100ths of seconds here) I wasn't sure it would make that much difference with the automatic truck... However, that is what the going story was for why one would bypass the boost bypass. I left mine alone in my Cobra! I was quite happy with how mine ran!

:DOkay. Thanks ;)