Perry Gehenna

As i mentioned b4, my mechanic (who has a stable of 400+rwKW rotaries to his credit) detests the things, and says he has never used one in any of his cars.

How many people here run without a BOV?

in his own words
So now I am considering obviating the BOV altogether, especially if it is going to improve the performance of my car for no real negative effect.

Again, just thought you guys would be interested, since BOV's are always such a popular topic of discussion, it amuses me that, after all the noise, they might not even be necessary.
thoughts?

Perry Gehenna

Node

iTrader: (1)

wow, good point.


he's never used a BOV himself? Then he must be pretty biased

isn't that bad. Your intake system should have air travelling in one direction only. But I don't know if a little bit of "backwash" would affect anything.

But a good point none the less, I wonder what the turbo experts will have to say

Perry Gehenna

i suppose that he's never used one himself b/c experience has taught him they are unnecessary, not thru any particular bias.
i think BOV's are a universally popular accessory, and i will be sad to see mine go. But if the BOV is causing the lag I am experiencing, then it has to go, regardless of how much i like it, how nice it looks, and how kool it sounds.
I'm not inflicting lag upon *my* beloved performance machine for no reason!

As you say, I am interested to hear what the resident turbo experts here have to say on the issue.

later,
Perry Gehenna

No7Yet

NOT. This guy is full of crap, high-powered rotaries or not. I bet whenever he toasts a turbo he blames it on "excessive exhaust temps" or some other B.S.

The purpose of a BOV is to prevent compressor surge. The "cool reverberating sound" he talks about is just that. In fact, the BOV helps MAINTAIN boost between shifts, not "waste" it.

How? Okay, at redline in 3rd gear, your turbo is spinning at full tilt (what, 120,000RPM or so). Let's consider each case:

1 - w/ BOV: You release the throttle, closing the throttle plates. The BOV opens from the vacuum after the TB, and vents the pressurised air (between the compressor and TB) to either the intake (pre-turbo) or to atmosphere. The exhaust side of your turbo is being spun with much less force due to less air coming out of the exhaust ports, but won't slow down much due to inertia. You complete your shift and get back on the throttle. You turbo spins back up to 120k RPM from the 90k or so it slowed down to, and you're back in the game.

2 - w/o BOV: You release the throttle, closing the throttle plates. Pressurised air (with momentum in the direction of the TB) bounces off the throttle plates and "surges" back toward the compressor wheel. When this air hits the compressor wheel it slows the compressor down DRAMATICALLY in the space of MILLISECONDS, causing SERIOUS wear. What exhaust flow there still is forces the turbo to respool a bit, which forces air back down the intake, which bounces off the throttle butterfly, and the cycle repeats, ad nauseum. You complete your shift, open the throttle back up, and your turbo has got to respin itself back up from almost nothing to the full 120k RPM at which it makes full boost - hence, MORE turbo lag, not to mention GROSS amounts of wear to the turbocharger.

In a nutshell, your friend is full of sh*t. I've seen firsthand what bad compressor surge can to do a turbo, and it's not pretty - a guy I know was (hell, still is) boosting to 12 PSI in his Dodge Lancer Shelby Turbo with no BOV. Ask him why his turbo dumps a quart of oil/month into his intake stream.

Brandon
98 Camry V6
89 RX-7 TII

turboren

Two books you should look at (and your friend could use to as well), before you decide to ditch your BOV:

http://www.amazon.com/exec/obidos/AS...894948-6767855

Written by Corky Bell, who just might know a thing or two about turbos.

http://www.amazon.com/exec/obidos/AS...894948-6767855

Written by Hugh MacInness. Unlike Corky, this guy has nothing to sell, except his beek. He's a mamber of both the Society of Automotive Engineers, and the Army Corps of Engineers. As I recall, this book was written in the late 70's or early 80's (don't have it here right now), long before turbos gained their immense popularity in passenger vehicles.

Ren

Node

iTrader: (1)

I have Maximum Boost ;-)
I need to force my *** to finish that book, I got about 2/3 finished on account of being so bored at In House detention at school (naughty naughty benny, i should get some cute girls to spank me or i can spank them )

But anyways its a good book. I need to get some RX-7 books soon. And oh yeah, need to get an RX-7 soon *swears uncontrollably*

No7Yet

Hahahaha! Oh, Node, that's - hahahaha - funny, man!!! Hahahaha! Node with an - hahahahaaa! - RX-7... Ah, man you need to tell that one at a party! Hahahaha!!!

No, seriously - heh - don't get discouraged. (*mmmff*) It may take a (hehe) while, but you'll (*chuckle*) get one eventually...

Brandon
98 Camry V6
89 RX-7 TII

Node

iTrader: (1)

YOU MOCK ME
btw wtf is up with your name, says in your sig you got a T2?

Brian_TII

This guy is an idiot, plain and simple. If the blow off valve was not needed then why did Mazda put a factory by pass valve there? Obviously Mazda thought it was needed. No7Yet is correct on all the points he makes, so I won't review those again.

Gimpdiggity

I've always been told that BOVs are necessary in ALL turbo cars if you want the turbo to last any decent amount of time. The BOV is what helps the turbo not get damaged by having the pressurized air just slammed back into it in the opposite direction...

Running without a BOV on anything that is for more than drag racing, is just stupid.


Jeff

Brian_TII

Actually... even in drag racing you want one. You ever seen those guys on TV that run 9's and 10's? Notice under their hood they usually have AT LEAST one BOV? Some even have 2...

Gimpdiggity

Yah, you're right, but I guess what I meant was that if you weren't going to run a BOV, you'd probably ONLY want to do it on a drag car, because it would fry the turbo pretty quick, and I can't imagine anyone other than a professional drag team would want to replace a turbo after EVERY run...


Jeff

B430

automatic turbo cars (eg GNs) don't have BOVs but that only because they only come with automatic transmissions so the throttle isn't closed on every shift.

Node

iTrader: (1)

Maybe his mechanic can't drive a stick?

Perry Gehenna

Oh no, the mechanic I go to produces some of the most powerful rotaries in Australia. They have a couple of reliable daily-driven 400rwKW RX's. This guy DOES know his stuff, he just says he has come to the conclusion that compressor surge is not the bogey man it has been cracked up to be. I seriously think he hasn't had a problem running w/o BOV's in his, and his customer's, cars.
I would normally dismiss so unconventional a theory out of hand as it contradicts given theory so totally, but given this guy's proven expertise and experience with MONSTER rotaries, i am thrown a little.
They have more one 9 second car at their workshop I am pretty sure.

Tho, as you all say, it is not worth the risk finding out though. I can't afford to blithely shrug my shoulders and simply pluck another turbo off the rack if mine gets crunched by compressor surge, so it looks like the BOV is staying put for now.

btw, I s'pose Santa didn't bring you an RX7 for Christmas Node?
What you should've done was tasered him unconscious once he came down the chimney, then tickled him with an oxy-acetalyne torch until he procured an FC for you. Maybe next year 'eh?

RETed

You can listen to whoever you want, but this is the bottom line.

That guy is plain stupid.&nbsp Maybe you should remind him that your car is a street car and not a race car.

That boost has to go somewhere when you lift off.&nbsp If you have no relief (i.e. BOV), it's going to go back into the compressor section of your turbo.&nbsp It'll make this neat chirping sound - this is called compressor surge.&nbsp Compressor surge your turbo long enough, and it'll eat 1) the thrust plate, and 2) eventually it'll eat the compressor blades and the turbo bearings.&nbsp Remember, the turbo is spinning close to 100,000RPM - you're trying to make it stop on a dime from those speeds.

For a race car, this might be something that's looked over, since runs are very short, and you're looking for every advantage (i.e. no loss of power/boost) even if it means blowing things up.&nbsp This is NOT the case on the street.&nbsp If you like replacing your turbo every few months, sure, delete the BOV.&nbsp If you want to keep your turbo alive for more then a couple months, INSTALL ONE.




-Ted

Perry Gehenna

Firstly, for the record i *am* keeping the BOV. Thanks for the advice & replies people!

just taking this a little further, tho on a different tangent-
the old turbo from my car was a stock S4 turbo.
when removed, the edges of the compressor wheel were bent over, twisted, and mangled looking (even tho it was still boosting fine. You would not have noticed there was anything wrong going by feel)
The guy who owned the car b4 me said that was a classic sign of the compressor fins being heat damaged, tho it looked to me like a stone or bit of grit had gone through the turbo, damaging the fins in the process.

Could the damage actually have been caused by excess boost surging back into the turbo b/c the tiny stock S4 wastegate was not adequate enough to vent the 15psi running through the system?

i have since installed a S5 turbo & wastegate, both being markedly superior IAT.

RETed

It really has nothing to do with the wastegate.
If the fins are bent drastically without any sharp edges, it's been most likely dropped with the fins exposed.&nbsp If there are sharp edged or "tears", then somebody wasn't running an air filter.




-Ted

HWO

just for the record - Rice Racing aint running a BOV on his 590HP yellow 1st gen either. but i think that has more to do with him not wanting to work out some plumbing to dumb the air with water and methanol in the blend well outta harms way so it cant go kaboomie on him.

Turtle's TII

no7yet, Your buddies chrysler turbo is a draw through turbo so the throttle body is before the turbo. So it is not an issue with a draw through turbo. Just thought you should know.

No7Yet

Are you sure about that? When he shifts, one hears the very distinctive sound of compressor surge quite well. Or is that perhaps an artifact of such an intake setup?

Jerk_Racer

Perry: this is the same car that the previous owner removed the rear stabiliser bar, right? Who knows what other crazy stuff this guy did before he decided to sell it. I think Ted is correct (so what's new?) that there might have been a time that you car was run without a filter. That way something could have reached the turbo and hit the fins.

jerk_racer@hotmail.com

Perry Gehenna

hmm, upon consideration, you're prolly right.
who knows what he ******* did with that car!
when we were putting on the new S5 turbo, he completely snapped off a bolt flush with the engine, and tried to deny it. It took 4 hours with apair of vice grips to slowly work it out.
this is the same guy that when summoned to court for assault charges, walked thru the metal detectors at the doors with his knife in one pocket, and brass knuckles in the other
is also the same guy that, "just for fun" decided to remove the boost control solenoid and see how fast he could drive his efini b4 the engine blew up
he got pulled over for speeding, and literally came to blows with the copper over how fast he was alledgedly going (tho he miraculously got off that one. I think the copper respected someone who stood up 4 themselves or something gay like that)
i could go on, but he is a 120kg mass of huge muscle, so who's gonna say anything to him?

So something as banal as running without a filter i would *not* put beyond him at all.
Well, it is out of his hands now, so it is safe. Perhaps.

Perry Gehenna

No7Yet

Um, it sounds like this guy has more ***** and money than sense.

Gimpdiggity

Wow, I hate to bring this back to the top of the board, but I just had to let everyone know...


I was talking to a guy today that runs a twin turbo setup on a 96 or 97 Ford Mustang V8, and he doesn't use BOVs either. He says that he WANTS to get some, but the company that makes the TT kit for his car says that they aren't necessary at low boost levels like 8-10 PSI.

Just thought I'd share!!


Jeff