BOV

[macky17]

Can I ask (having searched to no avail) why people fit just 1 BOV to a noble with 2 turbos? Wouldn't 2 be even better?

Also, does anyone have a valve installed to recirculate? Wondered if that sounds any different to stock (particularly m400)

Thanks

[Hollowpockets]

Because there is only 1 inlet path and both turbos feed it, so no it wouldn't be any better.

Think a couple of cars have re-circulating set ups but again, doesn't make much odds or sound much different.

You don't need a bov for these pressures anyway. Just if you like the noise.

[macky17]

That explains it, thanks. Waste of money other than the noise then? No meaningful increase in life of turbo or improvement to responsiveness after gearchange?

[Hollowpockets]

Yep just something else to break, I had one for a while, liked the noise, then it broke so removed it and now prefer the noise with out it.

No noticeable difference to anything else, and turbos still going strong

[macky17]

Thanks bud

[EW486]

Doesn't any turbo engine with throttle bodies need a BOV. My old turbo'd nissan was factory-equipped with a re-circulating BOV at a boost pressure of 0,6 bar. If there is no BOV fitted the turbo will suffer from compressor surge and therefore have a bigger turbo lag.
Only difference with open BOV's is the noise.

Regards
Ben

[Hollowpockets]

In a word no.

The boost pressures we run don't need a BOV as it wouldn't be enough to stall the turbo or at least cause any real damage, it doesn't affect lag either really as modern turbos spool up so fast anyway, if your in the right gear, there's no such thing as lag in a Noble.

This has been covered on here plenty times by people much more experienced than I, but if it's fine on my race car at 1.4 bar for 2 years with no BOV and no failed turbos, it'll be fine on the road cars.

[sjc]

I have to say, from my experience with two Nobles,and having a Forge BOV fitted after a period of ownership on both, there was a perceptible difference in pick up after gear changes both times.In effect,it didn't feel as lazy, if that makes sense?

[macky17]

I've been reading a few threads on this, including the rossion forums, and I have a theory. The track guys who are constantly at optimum and 9/10 tenths say there's no difference to the responsiveness after a gear change with a BOV. The road drivers all say there is a difference. Might this be because the latter are not always at optimum revs in the optimum gear - probably 'pottering' at 6/7 tenths as I do - and hence are allowing the turbo to fully wind down as the pressure escapes. If a BOV makes the car feel faster at more casual speeds/effort levels then it's probably something I would benefit from. I agree that when you're really going for it, an M400 has no detectable lag at all but you can't and don't want to drive that way all the time.

[EW486]

Hmm ... sounds like there are two opinions. I don't know what boost pressure the Nobles run but I have noticed a faulty (stucked) BOV because of the noise (I could hear the compressor surge) and I could see the boost pressure building up after the gearchange (I had a boost gauge in the car and could feel the lag). And this was at a moderate 0,6 bar, don't know what would have happened when running the modified 1,3 bar. I would guess the Nobles run a fair bit more boost. But it might be the way you shift gears. Maybe the track drivers don't lift the right foot so the pressure can escape through the engine.

Regards
Ben

[Blu3R]

I've always found fitting a BOV on a road car INCREASES lag which I've put down to the pressure being released when the BOV opens whereas without any release there's still some pressure remaining when you put your foot back down and close the actuators again.
Plus without one it sounds like a rally stage reject which does it for me

[andygtt]

a BOV is there to keep the turbo from snapping when the throttle is snapped shut... basically the boost works against the turbo slowing or completely stalling it when you were on boost and throttle shuts... larger turbos running big boost need one to stop failure.

On little turbos you would need to be running 4bar to get enough 'stall' to snap a shaft... so the only reason to fit one is to reduce 'lag'... the issue with you twin turbo boys is that you run low boost that will have little slowing effect on the turbo anyhow and also you have miles of pipework after the turbo before the throttle body that the turbo would have to build boost up again when you open the throttle again.

Basically the science doesn't add up that you will see any positive gains at all....

I run one on my car due to the size of my turbo and volume of air my car consumes and I also have very little plumbing between turbo and throttle body (half the stock twin turbo cars) however I fitted a very stiff spring so it only dumps air on high boost.

[The devil]

I have considered a BOV and having just put the hard pipe kit on I've had a spout put on just in case. On Pro-alloys advise I had the 35 mm spout put on as it seems there is a larger choice of BOV
But, how do you know what to buy, are they different pressures?