Hard or soft spring on BOV

[Kaas]

What will happen if the spring on a dual piston BOV is to soft? And what will happen if it is to hard? Can there be knock if it is to soft?

Thanks!

[nutcase]

I've got the stronger spring on my Bailey dump valve - it was in an attempt to keep the noise level down by opening slower. Didn't work, it's still silly loud! The possibility with a soft spring is the turbo pushes the valve open. The possibility with the strong spring is the vacuum isn't strong enough to open it.

Depends on how much boost you are running really, and how strong the various springs are. The valve manufacturer should be able to advise which to use.

[Kaas]

It is adjustabel with a screw in the top!




Its blowing out loonger and sounds lauder when it soft. And when its hard, the blow is fast and sounds low!

[nutcase]

Ooh, a posh one!

I think probably the most effective in its actual intended purpose will be as soft a spring as possible as then the excess pressure will be released quicker. How much actual difference it will make I don't know.

Thinking about it I doubt you'd get knock as when the valve is operating you have released the throttle so there's no load anyway. However, I'm not an expert

[Saab-Daniel]

You say posh nutcase, but it is actually very cheap! Around £75 incl VAT and so on, am I right Lars?
The bov should NOT cause knock, think about it, if the valve opens a bit at hight load, you will vent already measured air. This will cause the air/fuel-ratio to get richer= less air to same amount of fuel... So no problem there Lars
Daniel.

[Orca]

Nutcase already summed it up exactly ... a soft spring is very loud, but prone to being opened by charge air and can lead to stalling when letting off from high boost. A hard spring has the risk of not opening. Remind me, are you running a T8?

I spoke again to my garage today, following my experiment with the dump valve sited on the elbow of the intercooler to throttle pipe. Again, they said that the dump valve should be located as close to the throttle as possible on a T8. They're right! Simple as that. I like the noise a little more now off the pre-throttle, but the delay in opening when letting off the boost and the lag going into turbo (yes, I popped it back onto my throttle body again today, just to remind myself) is not good. I prefer the valve off the throttle body itself. On a T16, siting the valve too close to the throttle (off a shorter pipe) can lead to metering problems.

I think Daniel has a very good setup - the valve is close to the throttle plate, but benefits from the wider aperture that the throttle body does not provide. If/when I get round to it, I'll get a 25mm spigot set off the throttle body. Best of both worlds

... back to springs ... get an adjustable valve like the one already mentioned and tune it to where you want it. It will be a compromise between performance and noise. As for a double piston with a fixed spring, you should get a "spring tuning kit" as well as the valve and see which one you prefer for your setup. I'm afraid (after some extensive testing on my valve) that's the best I can advise.

[Orca]

Originally Posted by nutcase

I've got the stronger spring on my Bailey dump valve - it was in an attempt to keep the noise level down by opening slower. Didn't work, it's still silly loud! The possibility with a soft spring is the turbo pushes the valve open. The possibility with the strong spring is the vacuum isn't strong enough to open it.

I'm sensing that you're not quite happy with your choice of valve Do you want to swap for a state of the art and very high quality Forge valve for a few months? I'm informed that my valve is a little more suited to the stealthy 99T owner

[nutcase]

Not totally unhappy - and when I fit an intercooler, the lengthened pipe run should hopefully make things a little quieter. And is yours super-stealth black?

Not ruling out a (temporary) swap though

[Saab-Daniel]

Kaas drives a T16...
I have mounted by bov again, this time around with the IC in place, and far away from the TB, almost at the IC, because I have a stud welded on at the bend before the TB, which is going to be fitted with a fifth injector, thus leaving me no other option. The sound from the bov is now way more quite, and the venting-time is shorter than before, so I really liked my old setup... I like having the IC on though, and the 5-injector is a must in search for more power, so there is really nothing you can do... The best option in my opinion is to get a large stud welded on the old tb-outlet and vent from there. This is just not an option on my car, I'm afraid...
Daniel.

[uberfast]

Can you install your 5th injector after the throttle?

[Orca]

We've been reliably informed (by Eric Van Spelde, IIRC) recently on another similar topic that the 5th injector must be before the throttle. The reason is that after the throttle, there is a chance that the fuel will not mix well and "miss" some of the cylinders.

[Alex]

You could always mount a 5th and 6,7,8th injectors after the throttle body. This way you ensure even fuel mixing.

[Saab-Daniel]

My point exactly Alex, and I have placed the fifth injector like the way james from saabworks did on his T8-rallycar, and like he suggested other to do... Once MS is in control of that and ignition, I will look into complete MS fuel-management...

Daniel.

[Kaas]

Originally Posted by Saab-Daniel

You say posh nutcase, but it is actually very cheap! Around £75 incl VAT and so on, am I right Lars?
The bov should NOT cause knock, think about it, if the valve opens a bit at hight load, you will vent already measured air. This will cause the air/fuel-ratio to get richer= less air to same amount of fuel... So no problem there Lars
Daniel.

Yes Daniel, the price is right And the BOV is really cool, adjustabel and all. When I was going to buy a BOV I was thinking force and turbo xs and this one from www.secretpower.dk I talked to the guy some times and decided that I would give this BOV a try, and I really think its a cool BOV, its sounds great!

That you white about the air/fuel mix, is just what I meen, there will be to much fuel in the intake and couse knock or will it? I dont have that thing on the TB to slowly stop til gas, mine has lucas! So I will to mount one of those, and see how it goes!

I am allso up for the MS fuel-management, that could be cool! Controlabel timing, NICE

[Saab-Daniel]

With more fuel to the same air, you will get LESS knock, that is why you threw in the chip from Mats, to get more fuel... Fuel cools the charge and surpresses knock, so you will get LESS knock if the valve opens, you will also get less boost getting into the engine and that way loosing power, but that is a different story...

Daniel.

[Matthew]

Originally Posted by Orca

We've been reliably informed (by Eric Van Spelde, IIRC) recently on another similar topic that the 5th injector must be before the throttle. The reason is that after the throttle, there is a chance that the fuel will not mix well and "miss" some of the cylinders.

I seem to remember a post on here warning about doing that when using an atmospheric dump valve. Throttle snaps shut, valve then vents air and petrol mix into the engine bay.

[Orca]

Matthew - 'Aye I think our man John-W has found that. A picture of his pre-throttle setup is around here somewhere; this thread, or the recent epic about dump valves.