# Greddy Type S BOV



## asleepz (Feb 24, 2004)

Alright I'm getting a BOV... Pretty soon at least. Alright I need to know if I install one do I have to recirculate it back into the intake?

If so why?

If so would it be any quieter of a psh sound? I am getting ready to do a lot of things.

Intercooler
BOV
Boost Controller 

(not in specific order)


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## myoung (Apr 15, 2002)

yes to run properly it needs to recirculate. If not, your venting air that has been metered by the MAF. This can cause numerous problems ,, basically the ECU makes the calculations. Then adjusts accordingly... changing things after the calculations are made throws everything out of wack..

This is a common mistake that many turbo owners make that have maf'd cars, simply for a "cool sound". 

Our ECU's are smart.. that gives us an advantage.. don't waste it.


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## Teknokid (Jun 1, 2002)

Yup even my VW 1.8t need to be recirculated. Im currently running the TurboXS Diverter Valve which works better than my crappy stock unit. I think you will be pleased with it on your car. You can buy Blow off valves but you should also get a recirculation kit.


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## asleepz (Feb 24, 2004)

does Greddy make a recirculation kit for the Z31? If not are there any other kits that would fit?


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## Marc Z31 (Jul 25, 2004)

you DO NOT need to recirculate. None of us recirculate ours. DSM's VW's and pretty much everyone exept nissan and toyota have big problems when not recirculated, but you really DO NOT need to. I ran open to atmosphere for a year, the car pulled like hell and there was NO lag or sputter when shifting gears. BTW I have a type S, looking for a second one.

I had an idea a few days ago. I will need more than one type S when I run race gas, and I don't like the sound of a type R. I was going to run one normally, and have like 8 feet or more of vacuum line going to the other one (neatly tucked away of course) so that one opens, and then the second one opens just slightly after the first. It's like a custom SSQV, and it'll sound really neat. Under big boost, they will open almost simeltaneously, getting the air evacuation I need.


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## asleepz (Feb 24, 2004)

So you say I don't and , and myyoung and Teknokid say I do. I am going to take your advice and not I've seen pics of BOV's on Z's and they weren't. So I will give it a try.


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## Marc Z31 (Jul 25, 2004)

I have four friends that run open to atmosphere on Z31's
All of my DSM friends have to run recirculated, but none of the nissan guys do


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## Zen31ZR (Mar 24, 2004)

Big difference between the DSMs and our cars as to length of intake piping , though. We have 1/2 to 3/4 less piping then they do. Gotta figure they have about 7 feet of pipe going to the IC and then to the TB. We have what , 3? When they vent to air , they consequently run a lot richer , due to a lot more air being missing. You can probably get away with venting to air on a non-intercooled Z , sure. But for all intents and purposes , it's best if you recirculate , especially if you have an IC.


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## Zen31ZR (Mar 24, 2004)

And besides , something you guys are forgetting , the recirculated air inlet is pointing at the turbo , and keeps it spooled up for that 1/2 second while you are shifting.


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## myoung (Apr 15, 2002)

SKD_Tech said:


> So you say I don't and , and myyoung and Teknokid say I do. I am going to take your advice and not I've seen pics of BOV's on Z's and they weren't. So I will give it a try.



You're venting metered air on a MAF'd car.... should be common sense.

_To quote Mike Kojima:__



The bypass valve is plumbed back into the intake tract just before the throttle plate so when the throttle is closed, boost pressure can be re-circulated through the compressor and back around and around until the throttle is opened again. This keeps the turbo spinning fast even when the throttle is closed, reducing lag when the throttle is opened again. By re-circulating the air instead of dumping it overboard, air metered by the Mass Air Flow meter, or MAF, is retained in the system instead of being dumped outside the induction system like the typical blow-off valve. This prevents the engine from running too rich on overrun with a possible loss of driveabilty, a typical problem of the conventional blow off valve.

Click to expand...

_


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## Zen31ZR (Mar 24, 2004)

myoung said:


> You're venting metered air on a MAF'd car.... should be common sense.
> 
> _To quote Mike Kojima:_


See my last 2 posts , I basically said the same thing.


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## myoung (Apr 15, 2002)

[email protected] said:


> See my last 2 posts , I basically said the same thing.


yep.....

This is one of those things you just can't seem to get across to some.. I would think the whole idea is to get the best performance possible.. not to sacrifice performance simply for a "cool" whooshh sound.. but to each his own.


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## asleepz (Feb 24, 2004)

Is that why on supras when they run hard then hit the clutch that mofo smokes like crazy


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## JakeMonkey (Feb 3, 2004)

well, i run a Greddy Type-S into open atmosphere on my 87t, and while it runs the slightest bit rich, i have never ran into any real problems with it. no crazy puffs of black smoke between shifts, no bogging between gears, nothing at all. The only thing that i have noticed is that sometimes when i'm taking it easy and driving normally, it backfires between shifts sometimes, but it's really not much of a deal at all. I sounds kind of cool actually.


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## asleepz (Feb 24, 2004)

JakeMonkey said:


> The only thing that i have noticed is that sometimes when i'm taking it easy and driving normally, it backfires between shifts sometimes, but it's really not much of a deal at all. I sounds kind of cool actually.


Sounds pretty fun.


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## Marc Z31 (Jul 25, 2004)

I had the same setup with the previous engine. greddy type S on a non intercooled Z31. I never had any problems at all. There are two other intercooled Z31's with a fair amount of piping, and they have no trouble running open atmosphere BOV. It makes sense to recirculate, but in our cars, I guess the ECU compensates and there are no problems, save the occasional puff of flame out of the tailpipe.


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## asleepz (Feb 24, 2004)

Puff of flame is cool with me. I am getting a new front airdam then boost controller then BOV


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## morepower2 (Apr 19, 2002)

Marc Z31 said:


> I have four friends that run open to atmosphere on Z31's
> All of my DSM friends have to run recirculated, but none of the nissan guys do


You should run recirculated. I have seen so many driveabitly problems on MAF equpped cars that I traced to open BOV's. Run open on speed density equipped cars only.


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## Zen31ZR (Mar 24, 2004)

Marc Z31 said:


> I had the same setup with the previous engine. greddy type S on a non intercooled Z31. I never had any problems at all. There are two other intercooled Z31's with a fair amount of piping, and they have no trouble running open atmosphere BOV. It makes sense to recirculate, but in our cars, I guess the ECU compensates and there are no problems, _*save the occasional puff of flame out of the tailpipe*_.


 That right there should tell you you're running rich during shifting. As rich as an RX7 , and those run hella rich. Rich is slow.  It takes a few seconds to clear all that extra fuel out of the cylinders.


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## 0341TODD (Nov 15, 2003)

People are going to do what they are going to do. The right way to run it is to recirculate it. Unless youre a label whore like me and you have to have an Apex Integration BOV. Its stupid to argue though- when someone whos an actual engineer and studies this stuff everyday tells you that a recirculitory Bov should be used rather then an atmospheric Bov, then its sometimes wise to listen


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## Marc Z31 (Jul 25, 2004)

you will probably run a tenth fastr in the 1/4, but If you are making a street machine, it really doesn't matter WITH THE Z31. Mitsu's and VW can't do it, but the Z tends to work fine without being recirculated. I'm not saying it is better, I'm just saying it doesn't hinder the Z nearly as much as all the other cars I have dealt with.


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## Engloid (Jul 7, 2002)

Don't bother recirculating it...it's wasted time. Fact is that when you shift and your throttle plate shuts, the ecu reads this via the TPS and any metered or unmetered air will make little difference...as the ecu will be trying to run a bit lean anyway by DEFAULT. This is for emissions...the manufacturers know the cars are tested at idle so they make them run a bit leaner at idle. 

As for spooling the turbo....you'll never notice the difference. 

I've put about 6 bov's on z31's, and have never had a problem with them venting to atmosphere. If it were such a common problem when doing it, the manufacturers wouldn't make the venting type, they'd only make them recirculate.

I've done several like this below. I modded the pov to hold more pressure and moved it to the intake pipe. This keeps the bov from venting out all the pressure, reducing lag. Yes, it works. This is the aluminum intake pipe used on the 88-89 models with the t25 turbo.









Below is the TurboXS-RFL, mounted on another z31 intake pipe. The pipe is the one used on t3 equipped models from 84-87.


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## Zen31ZR (Mar 24, 2004)

Tested at idle? Ours run the treadmill here. Only 81 and older is exempt.  And most turbo ECUs run rich by default , it's the manufacturers way of protecting warranties. If venting to air is not a problem , why do _ALL_ manufacturers recirculate?  And if venting to air is not a problem , why do DSMs have such a hard time with it. Most cars smaller than 3 liters do , in fact.


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## Engloid (Jul 7, 2002)

[email protected] said:


> Tested at idle? Ours run the treadmill here. Only 81 and older is exempt.  And most turbo ECUs run rich by default , it's the manufacturers way of protecting warranties. If venting to air is not a problem , why do _ALL_ manufacturers recirculate?  And if venting to air is not a problem , why do DSMs have such a hard time with it. Most cars smaller than 3 liters do , in fact.


They run rich OFF idle. Not only that, but if you've ever had an air fuel ratio guage, you've likely seen that it will go nuts between shifts, with or without a bov of any kind. Why do they recirculate? Well, I guess it's like asking why they want to run rich off idle...horsepower isn't their main goal, and far from the only objective they have. It could even be an emissions thing...so that the air from the air from the egr goes back through the engine...and it keeps down noise. There could be many reasons they recirculate and I can't really tell you what exactly they are.

Why do DSM's have a hard time venting? I don't know. Maybe the ecu's are even sorrier than on the z31, and they don't compensate as well or as quickly. Either way, it doesn't matter if they have problems or not...it doesn't cause problems on a z31.


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## 0341TODD (Nov 15, 2003)

kinda like on the spec-v's. If removing the friggin balance shafts to get 15 or so horsepower is such a good idea then why didnt Nissan do it from the factory


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## 0341TODD (Nov 15, 2003)

hey engloid- those are some very nice installs by the way- they look really nice!


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## myoung (Apr 15, 2002)

0341TODD said:


> Its stupid to argue though- when someone whos an actual engineer and studies this stuff everyday tells you that a recirculitory Bov should be used rather then an atmospheric Bov, then its sometimes wise to listen


Then say hello to an _actual_ Automotive Engineer...who has written the book on it...literally.

Listen and learn

*


morepower2 said:



You should run recirculated. I have seen so many driveabitly problems on MAF equpped cars that I traced to open BOV's. Run open on speed density equipped cars only.

Click to expand...

*


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## myoung (Apr 15, 2002)

0341TODD said:


> kinda like on the spec-v's. If removing the friggin balance shafts to get 15 or so horsepower is such a good idea then why didnt Nissan do it from the factory


If you have to ask then it's not worth the time to explain it, obviously you didn't use much common sense thinking that one through...

..not to mention it's so far off topic it's not funny..

ether post on topic or move on.


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> kinda like on the spec-v's. If removing the friggin balance shafts to get 15 or so horsepower is such a good idea then why didnt Nissan do it from the factory


 Because most people like their cars quiet and peaceful and don't like to be disturbed by such things as vibration , engine noise , or even turbo whine. Yeah , most of the world is gay , get used to it.  Nissan builds 99.9% of it's cars for the mass populous , as do most other manufacturers , at most 1% to 5% of cars get modified like ours do. So , if you want to sell cars , you build them how people want them. Quiet , peaceful , boring , even stodgy. This includes Corvettes and even Skylines. Cars are dumbed down so far below their true potential for the general publics consumption , it's not even funny. It's up to us to unlock the true potential , so we end up removing a lot of otherwise useless (to us) pieces parts.


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## Zen31ZR (Mar 24, 2004)

myoung said:


> If you have to ask then it's not worth the time to explain it, obviously you didn't use much common sense thinking that one through...
> 
> ..not to mention it's so far off topic it's not funny..
> 
> ether post on topic or move on.


 I don't mind explaining , it's quite simple really , see above ^^


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## myoung (Apr 15, 2002)

[email protected] said:


> I don't mind explaining , it's quite simple really , see above ^^


I guess I should have said explain it again... lol

We've explained this so many times it's not funny... not to mention 2 articles explaining it in NPM.


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## Zen31ZR (Mar 24, 2004)

myoung said:


> I guess I should have said explain it again... lol
> 
> We've explained this so many times it's not funny... not to mention 2 articles explaining it in NPM.


 We all know Todd does a lot of research here........  I've explained a few things several times here , it's actually not so bad as other places I've been. I guess Nissan people are a bit smarter.......


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## morepower2 (Apr 19, 2002)

JakeMonkey said:


> well, i run a Greddy Type-S into open atmosphere on my 87t, and while it runs the slightest bit rich, i have never ran into any real problems with it. no crazy puffs of black smoke between shifts, no bogging between gears, nothing at all. The only thing that i have noticed is that sometimes when i'm taking it easy and driving normally, it backfires between shifts sometimes, but it's really not much of a deal at all. I sounds kind of cool actually.


If your BOV is adjusted to be really working well when the throttle shuts at high boost, it is open during periods of high manifold vacume as well, like during idle and part throttle causing a huge unmetered air leak. Don't tell me this gives good driveability.


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## Engloid (Jul 7, 2002)

0341TODD said:


> kinda like on the spec-v's. If removing the friggin balance shafts to get 15 or so horsepower is such a good idea then why didnt Nissan do it from the factory


I really have no idea about this specific situation you are talking about, but I would definitely consider that it's possible that Nissan was able to achieve the HP they wanted without removing it, and they wanted it there for another reason. I'll agree with the other points mentioned above on this.

So to suggest a similar rhetorical question, I'll ask: If an RB26DETT is their best engine, why do they make so many others? I'm sure we can all figure this one out.

And thanks for the compliments on my bov work.


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## Zen31ZR (Mar 24, 2004)

morepower2 said:


> If your BOV is adjusted to be really working well when the throttle shuts at high boost, it is open during periods of high manifold vacume as well, like during idle and part throttle causing a huge unmetered air leak. Don't tell me this gives good driveability.


 I thought the BOV spring was engineeered to open only during periods of extremely high manifold vacuum spikes , such as the 20+ hg when the throttle is slammed shut at mid-high rpms when you lift off to shift. And not to be open at idle , when vacuum is around 14-16 hg. I could be wrong , but I thought BOVs only responded to high spikes in vacuum.


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## Marc Z31 (Jul 25, 2004)

morepower2 said:


> If your BOV is adjusted to be really working well when the throttle shuts at high boost, it is open during periods of high manifold vacume as well, like during idle and part throttle causing a huge unmetered air leak. Don't tell me this gives good driveability.


The type S only opens when there is a large difference in pressure. at idle, there is vacuum in the charge pipes and the manifold. Your BOV was designed a little better than that. If it does open at idle (which would be hard to do), it is set very poorly, not for performance, but for sound. It would have to be set VERY soft, which subtracts from your performance. You want to vent the extra pressure to prevent compressor stall, not dump all the boost.


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## morepower2 (Apr 19, 2002)

[email protected] said:


> I thought the BOV spring was engineeered to open only during periods of extremely high manifold vacuum spikes , such as the 20+ hg when the throttle is slammed shut at mid-high rpms when you lift off to shift. And not to be open at idle , when vacuum is around 14-16 hg. I could be wrong , but I thought BOVs only responded to high spikes in vacuum.


Nope, not all of them.


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## morepower2 (Apr 19, 2002)

Engloid said:


> Don't bother recirculating it...it's wasted time. Fact is that when you shift and your throttle plate shuts, the ecu reads this via the TPS and any metered or unmetered air will make little difference...as the ecu will be trying to run a bit lean anyway by DEFAULT. This is for emissions...the manufacturers know the cars are tested at idle so they make them run a bit leaner at idle.
> 
> As for spooling the turbo....you'll never notice the difference.
> 
> ...


Wow you are one of the best Z31 tuners in the country and its an honer to have you here.

Let me ask you Z31 guys who run unrecirculated. What sort of MAF do you guys run, flapper or hot wire, I forget which is stock on a Z31?

My only experiance is with hot wire equiped cars. If the TPS is adjusted correctly, the ECU goes momentarily into fuel cut when the throttle is shut so it should not spike rich when the throttle is shut.

With an open BOV, if you rev the engine, on recovery from overun the engine will stall or try to stall. It may aslo do this when coming up to a light. The engine will blubber if you do slow shifts but still apply WOT. This is what I have seen with hot wire or Karmen MAF cars with open BOV's. The exception is what some guys are now doing, puttung the MAF after the turbo and the BOV in front of the MAF. This can create different problems with swirl in the MAF though.

I mean you can train your foot so it won't do any of this but that is still what I call flawed driveabitly.

Why even run a POV? I'd just plug it with the NA plug.


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## morepower2 (Apr 19, 2002)

Marc Z31 said:


> The type S only opens when there is a large difference in pressure. at idle, there is vacuum in the charge pipes and the manifold. Your BOV was designed a little better than that. If it does open at idle (which would be hard to do), it is set very poorly, not for performance, but for sound. It would have to be set VERY soft, which subtracts from your performance. You want to vent the extra pressure to prevent compressor stall, not dump all the boost.


Boost holds the BOV closed, in most BOV's, the diaphram is bigger the the size of the valve so it will stay closed or at least it should, more boost will only hold it close tighter. On problem stalling MAF cars, I set the BOV to open at 14 in of hg. This usualy cures it

The reason why you would want the BOV to open at idle is to avoid MAF backflow and stalling on overun. If the MAF opens at idle and the placment of the MAF is not ideal due to packaging reasons, opening the BOV can make all the difference in the world in preventing stalling when like coming to a stop and pushing the clutch in, reving, etc. Iealy the MAF should be at least 18" awy from the turbo but you can't always do this. Open BOV's really help if the MAF is closer.


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## morepower2 (Apr 19, 2002)

Engloid said:


> And thanks for the compliments on my bov work.


And your manifold work!


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## morepower2 (Apr 19, 2002)

0341TODD said:


> kinda like on the spec-v's. If removing the friggin balance shafts to get 15 or so horsepower is such a good idea then why didnt Nissan do it from the factory


Removing the balance shafts is a good idea for racing. The RTR car has no balance shafts as do many SE-R's that are raced for real, pounded on road coruses and in pro-rally with no engine failures associated with the removal. 

The balance shafts were there to make the engine smoother for sedan use. i-4's shake up and down and the shafts counteract this. Funny thing is that removing them harldy makes any more vibration.

Using JWT's removal kit gets you 1 quart more oil capacity, a slosh baffle and a windage scraper. These probably help durabilty if anything.

Of course any mod except Nismo S-Tue will void your powertrain warranty.


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