Just How Many Bov Topics Can We Start?!

[skybus]

Hi guys

I have been through almost every BOV topic / post / thread on this and the sylineowners.com forum ad infinitum, but still have not seen any discussion on the below:

Here's a little background info: I have an R33 GTST with...

2835Pro S set to 1.1 Bar

HKS induction

Z32 AFM

Apexi PFC / Boost control kit (and Datalogit on the way)

ARC Frount Mount

HKS SSQV BOV!!

Plus other bits that are not really relevant to this discussion

My tuner has plumbed the boost control kit into pre intercooler piping, basically just off the turbo (boost gauge on PFC commander never shows vacuum!), which I can understand the reasoning - you see actual boost pressure from the turbo, not post Intercooler / throttle body boost). Also, all recirc piping has been removed / blanked off, so I can't really head back down the recirc route.

Because of this new "plumb boost feed directly off turbo" method, I now see massive spikes of 1.9 Bar plus massive flutter on gear change (you wouldn't normally see this when the boost controller is tee'd off the manifold). I'm guessing here that the BOV is not opening enough (it does open a little though).

So, there are two things to note with this issue:

1. HKS SSQV. Now I don't want to go into recirc / atmo discussions (as we've all seen multiple different theories here ) so can anyone tell me if this BOV can discharge the excess boost (1.1 Bar) effeciently? One thing I've noted with this BOV as well, is that the pressure generated by the turbo pushes against the piston, keeping it closed. So in theory, wouldn't manifold vacuum have to be greater than the boost pressure to pull the piston out?

2. 1.9 Bar being measured at the turbo. Surely this is bad?! For the guys that do not run a BOV, when the throttle body is closed, this equates to (I assume that a closed throttle has an area of 25mm / 0.025m (radius) squared times pi = 0.001963m2):

Pressure = Force x Area

1.9 x .98 (to get atmospheres) = Force x 0.001963

1.82 / 0.001963 = 927 N

Force = Mass x Acceleration

927 = Mass x 9.8m/s/s (gravity)

Therefore Mass = approx 100Kg?!

So an instantaneous mass of 100Kg is either being applied to the throttle butterfly / throttle butterfly pin, or the turbo blades?!?! Even if my theory of obtaining a figure for mass is incorrect, there can be no argument that 927N of force is being applied to either / both these parts, instantaneously...

Has anyone else measured boost spikes on the turbo side, or is there something completely wrong with my setup?? Thoughts / input on my force theory would be welcomed, as would an idea on an appropriate atmo BOV to vent the right amount of boost...

Cheers

Steve

P.S. I have now changed into my flame-retardant suite - let the burring commence!

[GeeTR]

-20 points for doing math on NY eve

Edit: I should prolly post something worthwhile.

Those BOV's have been used on cars running more boost then that.

The reversion and boost spike your seeing is clearly due to your BOV not opening properly. Check the vacuum feed your using (between TB and motor yes?) Check the BOV on the bench with a vacuum pump maybe?

The trick for easy 100% workability would be to use a recirc BOV, not an atmo one... but you don’t wanna hear that

Your calcs could be correct, but the way the comp wheel is shaped means pulses can go backwards through it much easier (iv heard) and air ain't that viscous

my 2 cents

Edited December 31, 2007 by GeeTR

[Adriano]

You havnt taken into account that there is vacuum on the other side of the throttle plate, so that force is more like 150kg. I dont think a boost spike like that woiuld be particularly uncommon, its just that people dont usually measure it. Maybe try blocking the BOV altogether, and ill bet it goes to 3bar.

[govich]

Kilograms are not a measure of force guys. All you've calculated is the mass you'd have to apply a force of 927N to in order to accelerate it at 9.8m/s/s in ideal conditions, which has nothing to do with this.

Stick with the 900N force, although in reality i think you'd find the conditions way, WAY more complex and delicate. Some sort of sensors would help

[joeyjoejoejuniorshabadoo]

[Adriano]

Kilograms are not a measure of force guys. All you've calculated is the mass you'd have to apply a force of 927N to in order to accelerate it at 9.8m/s/s in ideal conditions, which has nothing to do with this.

Stick with the 900N force, although in reality i think you'd find the conditions way, WAY more complex and delicate. Some sort of sensors would help

Hmmm, seeing as we are all living on the same planet, fro arguements sake Kg is an effective measurement, as he was simply trying to determine a relative amount in perspective.

[govich]

Kilograms are a measure of mass, nothing to do with different planets.

Edited January 1, 2008 by govich

[skybus]

-20 points for doing math on NY eve

Edit: I should prolly post something worthwhile.

Those BOV's have been used on cars running more boost then that.

The reversion and boost spike your seeing is clearly due to your BOV not opening properly. Check the vacuum feed your using (between TB and motor yes?) Check the BOV on the bench with a vacuum pump maybe?

The trick for easy 100% workability would be to use a recirc BOV, not an atmo one... but you don't wanna hear that

Your calcs could be correct, but the way the comp wheel is shaped means pulses can go backwards through it much easier (iv heard) and air ain't that viscous

my 2 cents

It was still afternoon here in the UK, so the brain was (kinda) functioning I'm not feeling particularly clever today however...

It appears the best route for me to take is get all the bits back for a recirc. Can this be done, even if my engine has been tuned for no recirc?

Oh, and happy new year everyone!

Steve

[r32woohoo]

Arent the ssqv's adjustable to some degree?

Maybe it needs adjusting to open at the right pressure

[Brocaine]

I don't see why you've set the plumbing up that way. With a decent intercooler you shouldn't be seeing massive pressure drops anyway.

As for the massive spike, a blow off valve is basically a piston or valve with a spring on it, and a vacuum/pressure line running to it. While the throttle body is open, the idea is that the pressure inside your inlet piping is equal to what's held inside the chamber in the blow off valve. What I'd make sure is that the vacuum line going to the blow-off valve is coming from somewhere post-throttle body.

[sh@un]

2. 1.9 Bar being measured at the turbo. Surely this is bad?! For the guys that do not run a BOV, when the throttle body is closed, this equates to (I assume that a closed throttle has an area of 25mm / 0.025m (radius) squared times pi = 0.001963m2):

Pressure = Force x Area

1.9 x .98 (to get atmospheres) = Force x 0.001963

1.82 / 0.001963 = 927 N

Force = Mass x Acceleration

927 = Mass x 9.8m/s/s (gravity)

Therefore Mass = approx 100Kg?!

i don't know how you came up with this, but it would have nothing to do with the air-flow dynamics inside the engine

[Simon-S14]

The prob is the boost gauge and PFC boost gauge cannot be taken from the turbo compressor outlet, there is no vacuum in the turbo, and also there is massive pressure fluctuations. If you hook up a mechanical boost gauge, you'll see the needle dance around like crazy, and even worse when you back off, this is where your "spike" is coming from, doesnt mean the engine is acctually seeing 1.9 bar.

Boost gauge needs to be taken from manifold, and EBC needs to be taken from turbo outlet.

[Adriano]

The prob is the boost gauge and PFC boost gauge cannot be taken from the turbo compressor outlet, there is no vacuum in the turbo, and also there is massive pressure fluctuations. If you hook up a mechanical boost gauge, you'll see the needle dance around like crazy, and even worse when you back off, this is where your "spike" is coming from, doesnt mean the engine is acctually seeing 1.9 bar.

Boost gauge needs to be taken from manifold, and EBC needs to be taken from turbo outlet.

Thats what he is saying, the pressure spike inside the IC piping on gearchange is 1.9bar, hence the pressure on the closed throttle plate.

[skybus]

I don't see why you've set the plumbing up that way. With a decent intercooler you shouldn't be seeing massive pressure drops anyway.

As for the massive spike, a blow off valve is basically a piston or valve with a spring on it, and a vacuum/pressure line running to it. While the throttle body is open, the idea is that the pressure inside your inlet piping is equal to what's held inside the chamber in the blow off valve. What I'd make sure is that the vacuum line going to the blow-off valve is coming from somewhere post-throttle body.

I'm not getting a pressure drop, it's the fact I'm getting spiking of .8 bar - that's the problem! I can only put this down to a faulty HKS BOV (I've disassembled for inspection, and everything's in order as far as I can see)

What I question with the HKS BOV is, if you have a look at the way the SSQV works, boost is always in the chamber of the BOV pushing the seat against the seal - it helps keep the valve shut (in theory you could block the vacuum line, and the piston will seal against the seat based on pre throttle body boost). Most BOV's (non-HKS!) I'm aware of use spring tension and boost found on the vacuum line to remain fully closed. When there is vacuum at the manifold, both manifold vacuum AND boost in the pre manifold piping are used to push the valve out / compress the spring, and vent the excess boost. What I don't understand with the HKS is, the vacuum release has to work against spring tension AND residual boost pressure to open!

Well, to answer my own question (under "Product Detail") http://www.racinglab.com/mit3019turhk.html still not sure if I understand fully though...

Also (for Simon-R32), the way the PFC boost controller works is, it comes with a MAP sensor that plugs into the PFC and uses the existing two wires to the stock boost control solenoid. Because the PFC uses this MAP sensor to display boost on the Commander and control boost, the Commander will never display vacuum (due to my MAP sensor being plumbed into turbo piping rather than post throttle body). Is this OK? Does the PFC need to know if there is vacuum? Before I had the work done, tuned etc., I had plumbed the MAP sensor into post throttle body...

Thanks for all your input...

Steve

Edited January 2, 2008 by skybus

[Simon-S14]

yeah your map sensor needs to be on manifold, then it will read vac and correct boost pressure.

im fairly certain your "spiking" issues doesnt exist either, its just air fluctuations from the turbo causing the gauge to go spastic.

i used to have an AVCR which uses the very same map sensor and solenoid as the PFC kit, and i had it hooked up to manifold and then to turbo outlet, and with stock turbo it said it was spiking to 1.5 bar... which is simply;y not true, the figures were fluctuating like crazy, i was only running 10 psi haha

[Adriano]

I wouldnt be surprised at all idf the stock turbo without bov makes 1.5 bar on liftoff/gearchange. The turbo can be flowing 100's cubic feet per minute, at a pressure ratio of 1.7, then the throttle is shut, and the 100's CFM has nowhere to go, the piping/intercooler act like a big pneumatic spring, with the pressure building right up, then the pressure waves bounce back off the throttle body and out through the turbo, then the process repeats itself, hence fully sic flutter

[Simon-S14]

i had the stock BOV

[Shaun]

Kilograms are a measure of mass, nothing to do with different planets.

I thought Kilograms were a measure of weight, and Newtons are a measure of mass. Its been a long time though.

I hate the SSQ BOV's; i found them to be more about noise than anything else. Have a look at the opening and you can see that its not significantly bigger than a stock item; thats why theyre so loud, so they cant really be efficient at venting air between the throttle and turbo at 1.9 bar. I really like the Tial 50mm BOV's.

Shaun.