Plazmaman Plenum On Rb25Det Neo

[GTSBoy]

My fabricator put the bov near the ffp and it vents to atmosphere ( I have a G4 Link with a MAP sensor). I hate the sound. I plan to relocate it to the other side (hot side) of the intercooler so I can plumb it in. I will need a long vacuum line so may make up a hard line.

No nearer the T/B is not better. Garrett actually say as close as possible to the turbo. I am sure there will be a fluid dynamic engineer or suchlike who can correct me but my take is that bovs are not about flow but about pressure relief and so it doesn't matter where it is. Some manufacturers put them on the intercooler itself.

Actually, there is logic to putting them on the pipe close to the TB. When you are on boost the air is flowing towards the TB. The air is at high pressure (obviously). So when you close the throttle, the air does in fact flow from whereever it is in the pipework towards the BOV. Let's say there is 1 bar of boost. There's twice as much mass of air in the pipework as if there was no boost. Assuming that all of the extra has to come out, then you have one complete volume of your pipework that will flow towards the BOV.

Now, if the BOV is near the TB, then the air will keep travelling in the same direction that it was before, except for a small volume of pipework between the location of the BOV and the TB that will flow backwards.

If on the other hand you put it near the compressor, then the extra air volume will need to come out in the opposite direction to what it was flowing before. There is simply no way to think about that air flowing out the BOV without it having to come from further up the pipework, against the original flow direction.

From a fluid dynamics point of view, the velocity pressure of the air flowing towards the TB is added to the static pressure in the pipework when you put the BOV near the TB, meaning that you will vent more air from the same sized BOV (bigger driving force). I'm not entirely sure if that's actually worthwhile, but it still true. If you locate the BOV near the compressor, then the velocity pressure is subtractive, meaning you will flow less through the same size BOV...up until the flow stagnates against the closed TB and sends a reflected pressure pulse back through the pipework to the location of the BOV. But the pipework is long and full of bends (and an intercooler) so expect that pressure pulse to me muddy and messed up.

I would say the "responsiveness" of the BOV system (ie how fast the extra pressure vents) would be better with the BOV near the TB. All in all, I would vote for the location near the TB.

[KiwiRS4T]

My understanding of the purpose of the bov is to relieve stress on the turbo. When you shut the throttle the turbo is still spinning at thousands of rpm and pushing air into a pipe the far end of which has been closed. I would guess that is why Garrett promote putting the bov as close as possible to the turbo.

[GTSBoy]

I don't know why Garrett make that recommendation unless the person who came up with it doesn't understand how fluids flow. Maybe there's some impression that the intercooler core will slow down the venting (from the turbo's perspective) if the BOV is at the other end of the pipe. Which is pretty silly.

Now, Garrett make turbos, so maybe their recommendation is selfish. Nissan make engines, and they put the BOV near the TB.

[34GeeTeeTee]

Well i dont make bugger all, but mine is under the airbox with the return line plumbed into the intake pipe

I wanted it IN the airbox but apparently the clowns thought it was all too hard

[Hanaldo]

Actually, there is logic to putting them on the pipe close to the TB. When you are on boost the air is flowing towards the TB. The air is at high pressure (obviously). So when you close the throttle, the air does in fact flow from whereever it is in the pipework towards the BOV. Let's say there is 1 bar of boost. There's twice as much mass of air in the pipework as if there was no boost. Assuming that all of the extra has to come out, then you have one complete volume of your pipework that will flow towards the BOV.

Now, if the BOV is near the TB, then the air will keep travelling in the same direction that it was before, except for a small volume of pipework between the location of the BOV and the TB that will flow backwards.

If on the other hand you put it near the compressor, then the extra air volume will need to come out in the opposite direction to what it was flowing before. There is simply no way to think about that air flowing out the BOV without it having to come from further up the pipework, against the original flow direction.

From a fluid dynamics point of view, the velocity pressure of the air flowing towards the TB is added to the static pressure in the pipework when you put the BOV near the TB, meaning that you will vent more air from the same sized BOV (bigger driving force). I'm not entirely sure if that's actually worthwhile, but it still true. If you locate the BOV near the compressor, then the velocity pressure is subtractive, meaning you will flow less through the same size BOV...up until the flow stagnates against the closed TB and sends a reflected pressure pulse back through the pipework to the location of the BOV. But the pipework is long and full of bends (and an intercooler) so expect that pressure pulse to me muddy and messed up.

I would say the "responsiveness" of the BOV system (ie how fast the extra pressure vents) would be better with the BOV near the TB. All in all, I would vote for the location near the TB.

This is how I understood it as well, perhaps in a bit less detail though Thanks mate.

Does anyone know where I could get a flange from for the bov? I'm not too keen on just welding the bov to the intake pipe, makes it a hell of a job if I need to remove or replace the damn thing later. A search only provides me with results for adapter flanges for aftermarket bov's like the HKS SSQV.

[34GeeTeeTee]

Should be easy enough to have a shop make one if you cant find one... Its what they were originally going to do with mine until i changed style as the other valve wasn't going to handle higher boost pressures..... Ghey

[Hanaldo]

Yeh I'll give it a go if need be, just thought there may be something off the shelf.

Speaking of bov's and high boost pressures, my GTR bov is fluttering a fair bit with the G3 turbo. It's ok under lightish load, but full boost flutters quite a lot. Have I maxed it's flow capabilities? I do still have the other bov, would it be worthwhile installing the twin setup or no?

[34GeeTeeTee]

Yeh I'll give it a go if need be, just thought there may be something off the shelf.

Speaking of bov's and high boost pressures, my GTR bov is fluttering a fair bit with the G3 turbo. It's ok under lightish load, but full boost flutters quite a lot. Have I maxed it's flow capabilities? I do still have the other bov, would it be worthwhile installing the twin setup or no?

Where is DORI 34, we just had this same convo the other day... It sounds like he had an army of pidgeons under the bonnet

[dori34]

army of pidgeons indeed.

is your BOV vented to atm or plumbed up hanaldo?

i rekon majority of the flutter comes from my intake pipe, its got minimal bends and a pod filter.

on my old setup, it had the same thing, and i rang a stock BOV plumbed up and it still fluttered heaps.

does your flutter sound like this hanaldo?

[Hanaldo]

No, dammit that's the sound I was hoping for when I bought them! Lol. Bov is plumbed up, just sounds like normal flutter though not like that ^

[dori34]

hows your intake pipe setup?

it might sound good for a few days then you get sick of it.

[Bond]

I'm not sure what the big deal is about changing plugs? 5 of them will take the same time and for the 6th it takes an extra 15 seconds when you attach the uni joint to your socket!

[34GeeTeeTee]

I'm not sure what the big deal is about changing plugs? 5 of them will take the same time and for the 6th it takes an extra 15 seconds when you attach the uni joint to your socket!

Last time i did it it was a pain in the ass, i think it was the allen key tops on the cover... But it was not a quick and easy task with the factory setup... You sure you are talking about the same engine?

[34GeeTeeTee]

hows your intake pipe setup?

it might sound good for a few days then you get sick of it.

Not a bird lover eh?

[Bond]

Cover stays off so I just unplug the loom to the coils, Unbolt the rails that the coils are on, pull them out and then just undo the spark plugs. I'm not seeing the hard side. The cross over pipe is only on top of one plug and for that one i use a $2 uni joint on my ratchet.

[copycutter]

I can only speak from my own experience with the plazmaman intake manifolds.

I had a 180sx with an rb25 and one of these intake plenums on it a few years back. I put this manifold on when I got the engine put in the car so I had it for a while with a stock turbo, then with stock turbo + PFC, then also with a bigger turbo + microtech. I always found it to come on boost very quick compared to a few of my friends cars, especially compared to the behavior of other rb25's with similar mods. IIRC with the stock 21U turbo I remember seeing that I could get it up to 14psi by just under 2000rpm which I thought was a laugh. I think we measured a few other friend's r33s at the time and his was in the 2's which is what my current skyline is like.

Now I have a relatively stock r33 myself like my friend used to in the day, and my opinion on it is I couldn't justify the cost of it against the whole car's worth. Cons wise; it always made the intake plenum ancillaries (IAC, AAC etc) difficult to get to except TB, and made the oil filter a real pain to get at, which I always thought offset the spark plug benefit since you do the former at least as regularly as the latter. Plus, the thing always needed metal polishing to keep halfway respectable. As for fuel system I had stock rail which was perfectly fine, but I did have Sard FPR & 550cc injectors. I was never forced to change the FPR, I just got it at the time with the injectors, but no workshop physically forced me to get it, so couldn't say if you can get away with stock FPR.

So these days I just cbf with it. But I always thought it was good at the time, got plenty of compliments on it when I had it, and never thought it was hindering performance. If anything I thought it made the response much more lively.

Hope that helps.

Edited February 21, 2012 by copycutter

[Hanaldo]

It isn't a BIG deal, I mean it's not a deal breaker. It's just a happy benefit that comes with going forward facing. But I've got nicely powdercoated rocker covers and carbon fibre valley cover that gets covered up by this hideous crossover pipe and I'm paranoid about scratching them when I have to do spark plugs etc. It's not all about performance for me

[Bond]

Do you drive with your bonnet open?

[Hanaldo]

What bonnet?

Lol of course not, but I go to Powercruise every year where I enter the show and shine. What can I say, I'm a show pony

[Hanaldo]

Right, so I just wanted to double check before I make a poor decision... Upper plenum gasket.

What should I do here? Plazmaman only offer one for the R33; so I was trying to track down an OEM one, but Nissan wanted $160 and I haven't found any other manufacturers. There's some on eBay but they don't say much so not sure how good they are. A mate of mine who is also on here (Stealth-X) said I should be fine just stenciling one out of gasket paper and then applying silicon, however I'm not going to have a chance to test things before it goes on the dyno due to changing fuel rail, injectors, regulator at the same time. So if it does give out then it's going to cost me a lot of money and time.

Recommendations? Will the gasket paper and silicon do the job?