I have seen cars with 2 valves installed. The question this raises is if it is better.

Since most aftermarket valves prevent the valve from opening at idle, under vacuum. That is not an issue in this discussion.
This leaves us with the closed throttle blow-off/recirc operation.

Ideally it would seem that this set-up would be ideal. Given the piping size of the IC pipes and the size of inlet and outlets of the valve, the valve can olny bleed off so much pressure from the IC pipe. Any pressure on the IC side is going to create some backpressure to the turbo spool or at least affect the speed of the turbo.

With two valves open, the IC pipe pressure would bleed off much faster and allow the turbo to spin as fast as possible given the current velocity of the exhaust gas, etc.

Therefore when the throttle opens and the valve closes the turbo, in theory, is still spinning as fast as it could be.

Of course the only difficulty is getting the two valves install because you will need the additional port on the IC pipe and the intake pipe.

As far as the recir operation, it really shouldn't matter much. The air is reintroduced before the intake side of the turbine and simply recycled back through. It has been said though that this aids in keeping the turbine spinnng. In that case it would be more advantageous to have two valves also.

Post your questions, comments. Let's try to keep this technical and not a discussion on "who has the best BOV"

~Thanks

 

Wow, everybody looky nobody commenty.

 

Anyone, Bueller?

 

I can see where your coming from with the ability to release air faster with 2 valves, but if this was the case why doesn't a manufacturer make a valve with twice the surface area to release the air technically as fast, although there would possibly be a disadvantage to this seeing as the much larger valve would technically take more time to open and close. In that case the 2 smaller would release the charge faster.

kinda reminds of our friend the turbo. Twins are cool cause they spool like a bat outa hell if done right, and big a&% singles are sweet becasue they can give a hell of a punch once they get goin.

Just trying to give your post some attention because I think it is a very good idea.

If I can make it to the machine shop at work I can see if maybe I can modify the IC pipe to accept a second BOV.

Anyhow its a good idea, but from what I understand BOV's really don't make all that much of a difference besides the ear candy At least in my case because im not so heavily modded that I need to worry about these things yet


Jeff

 

Check this valve out it might be what you are looking for.

https://www.evolutionm.net/forums/sh...threadid=28073

 

Manufacturers don't want to spend the extra $$ to do this, obviously they make it out of plastic
I agree completely that a larger valve is to no advantage due to slow response. Two valves could do the same job more efficiently.
The valve tubing is 1 5/8" and the current IC tube is something like 2.25 (I think). There for the cummulative dump would be around 3". Of course it will help to account for the volume of air in the IC and that is just as, if not more important.
There is no performance gain here, but the less possible surge the turbo sees the better. This would go even further to reduce it. Ideally we want to keep that turbo healthy as best we can, that is really the intention. If it helps keep it spooled better that is just a plus really.

To actually do it, you'd really need a hard inlet pipe so it can setup with dual diverter hoses and you'd of course need to modify the IC pipe.
A whole other prospect to this is a slightly softer spring in one to get it open asap without leakage and the normal spring in the other, which will open a fraction of a second later. I am thinking this with the forge valve, adjustable valves would be easier to work here.

Thanks for responding, at least someone had the *****.
I thought I'd get all sorts of comments on this one.

 

As you requested, here are my thoughts regarding your post:

I don’t see any race or high end (Porsche, Ferrari, etc) cars with huge and/or dual BOV's, not to say that alone makes it a bad idea.
I think it might be that if you vent too much air from the intake system and pressure drops in the tubing/intercooler to fast, while the turbo might be able to maintain a slightly higher speed, this could be more than offset by having to re-pressurize the entire intake system. IMO besides closing faster this is another reason why you want to run the highest spring tension possible in your BOV, (that does not cause surging). You want the valve to open far enough so that you don't get surging but not so far that it starts to dump too much air pressure in the intake system.
I think this is why most of the after market/race BOV's come with very heavy spring tensions. They are more concerned with keeping the pressure up by not letting the valve open to far and getting the valve to close faster under throttle application. A small amount of surging doesn’t seem to really hurt the turbo and the throttle response/overall performance does seem to improve. If it is a speed density system or you have the ability to correct the fuel maps then minor pressure surging and venting to the atmosphere will not cause drivability issues. Unfortunately one of the down sides to a mass airflow type system (like in the EVO) is that any surging can adversely affect drivability, as many have already experienced.
As I mentioned in my BOV post, this is one of the benefit of an aftermarket valve. By changing springs and then fine-tuning the compression with the adjustment bolt, you can get the optimum spring tension for your application.
I could be wrong, and two valves may actually work better than one, but how much better could it really be? Enough to actually justify the additional expense and complexity? If you guy’s still decide to do it, I look forward to reading about it. At the very least, it will be a learning experience.

Kind regards,

Eric

 

 

Here's a thought. If in fact one of us was to try and run 2 BOV's do you think it would be wise to adjust the spring pressure differently according to which BOV was closest to the turbo? Got me thinking.

Jeff

 

I agree with you about the excess loss on the IC side with 2 BOVs. It's kind of a double edge sword. Ideally with a sleeve bearing turbo you would think it would be a plus since it can't handle the impeller resonations and surges as well as a BB Turbo. The other point here is that in the applications in which I have previously seen it, it was probably also a large turbo that could use the extra relief due to the volume of air the turbo is capable of moving. The real question I guess is whether the remaining pressure in the IC when the DV is open, slows the turbine and to what extent. Obviuosly the exhaust gas velocity has slowed because there is no air entering the engine. So does the residual pressure in the IC futher slow the turbine because it is in effect back pressure.

Sport Compact Car magazine did a test a while back on BOV/DV valves in which they datalogged a 2G for a 1-2 shift and recorded the pressure in the IC pipe to show the surge of each valve but it also shows the pressure drop of rate of the valves. Naturally the shift time is short so none of the valves actuall dropped off to 0 and I can't say two would still make it down to zero. But it would be interesting to see this theory applied on a dyno and compare the differences. It would also be interesting to see the IC pressure after a shift with 1 or 2 DVs and what the pressure is at immediately after the throttle is opened. And the affect it would have on the engine as far as a lag or hesitation. All that is really needed for testing is an IC pipe with 2 hose outlets. For testing purposes I could get away with a DV and a BOV since I don't also what to go through the trouble of the Inlet Pipe fitting.
If I could get my hands on a IC pipe with out having to get it all done up, I would. I would also add a barb for a boost gauge on the IC pipe so you can see the real pressure in the pipe with one and two, etc.

btw... Thanks for the response. Maybe I need to find HKS or someone and pose this question to them directly. I don't know any enigineers or anything so I can't exactly as around.