To Bov Or Not To Bov

[No Crust Racing]

Afternoon Gents

I've been doing some "seat of pants" testing with the Silvia (CA18 no BOV from factory) for track style driving, as in flat out - not street style get on boost for a bit in one gear to get some flutter then cruise stuff.

The car seemed to build boost slowly, hold it poorly and fall off boost quickly between shifts.

I put this down to one of two things.

1) The Turbo XS bleed valve it came with.

2) No BOV (my reasoning being that between shifts it was stallin the comp wheel a tad).

So to remedy this I did two things.

1) Fitted a TurboTech boost tap, I've had great experience with these in the past.

2) Fitted an R33 plumb back BOV, plumbed in between the AFM and the turbo inlet.

I noticed afterwards that boost was building about the same rate (noise is slightly different though) and that rebuilding boost between gear shifts seems to be about the same. No bleeding in the top end now and holding boost much more steadily.

I removed the BOV completely, leaving only the new boost tap, and found that (from the seat of the pants) boost came on quicker and seemed to come back on after shifts about the same as with the BOV. I know the BOV does have that small port that bleeds some boost off and I can feel that the car drives smoother between semi boost shifts with it on but it kind of feels worse from a "motorsport" point of view - power delivery just seems a bit flatter.

So, is there any reason for me to persevere with the BOV, perhaps block off the small bleed port? In my head the car should have been better with it on but it seems to vent too much between shifts and takes time to spool again, I wondering if the rate at which I'm shifting when on the track negates any risk of flutter/comp stalling as I've already shifted and opened up again before that becomes a problem.

Lots of rambling I know, lol

Thoughts?

Cheers

[BOZ22N]

How much boost are you running?

I run a v port bov wound in hard for my track car and works great.

I have an r33 on 14 psi.

[No Crust Racing]

14psi on a T25G (SR Turbo)

R33 Factory BOV is not adjustable. Read a few threads where people block the small port.

Have you run without one?

[MBS206]

Dan, where is the pressure source for the wastegate coming from?

I found on my old setup with no BOV, if I ran the pressure source anywhere pre throttle bottle, it lagged a bit coming back on boost. If I ran it post throttle bottle, it came back on boost really hard.

From what I could figure, when shifting, boost stays above the wastegate limit as it "spikes", and this allows what ever exhaust gas is flowing out of the motor, to go around the turbo if the wastegate pressure source was pre throttle body. If I put it post throttle body, because the plenum went into vacuum it would pull the wastegate shut again forcing what ever exhaust gas was flowing through the turbo, so keeping it spooled up a bit more.

Give it a go and see what you find.

[No Crust Racing]

Hmm I was told to have the wastegate source as close to the turbo as possible so it's right on the turbo outlet pipe.

What I'm more interested in is whether or not to stick with the bov, maybe with the small port blocked. I might test that today.

Have others found their power delivery and lag between shifts better or worse?

[sav man]

I thought running the BOV as close as possable to the throttle body was the go

[BOZ22N]

I run my bov very close to the throttle body and I get my boost pressure line from post throttle body.

Maybe the spring in the bov is just not strong enough to snap the valve shut when between gears as the bov was from a car that only ran STD 9 psi or so? Maybe try a rb20 or gtr bov ??? Don't know. What type if bov does an Evo run, they run mega boost STD.

[No Crust Racing]

I've opted to remove it. Did some more testing and the car is better to drive hard without it.

I'll stick it on the shelf for now incase this thread produces some good reasoning for putting it back on.

Cheers

[mad082]

does the ca powered s13 come with a factory side mount intercooler like the sr20 does? if yes then have a look on the side of the intercooler for a BOV (doesn't look so much like a bov like the skyline ones do). my sr powered had a bov there and it was crap (makes a good paperweight though). if you have pulled off the side mount cooler and run a front mount then ignore the above.

as for where to run the boost feed from, i found on my 33 that when i had it from a vaccum line off the plenum i got boost spiking occasionally. off the 'hot' cooler pipe (between turbo and cooler) it held much more stable.

as for bov vs no bov, for track work it won't be that much of an issue. you can simply keep the throttle either partially or wide open as you change gears (still using the clutch) so the bov would only really be opening at the braking points when you lift off, and boost built won't be that much off an issue either as you don't simply floor it coming out of a corner you wind the throttle on, however the sooner you can get boost to come on the better.

[No Crust Racing]

Ca has no bov from factory at all and seems more aggressive without it, just felt a lazy with it on, smoother bit lazy.

I've tried feeding the wategate from the tb and from its current location on the hot pipe, boost is far more stable on the it pipe on this car.