quiklt1

hello i wanted to know if anyone could help me out with this one i wanted to know where to route the opti vent hoses on a boosted setup the one that goes to the intake ducting do i install that the same way it was on the stock setup? also how about the vent line of the 2 that goes to the intake manifold i am afraid that when the car boosts then it will blow pressure crankcase pressure into the optispark itself or am i wrong?


and on the BOV vaccum line where do i put this to i am running a twin turbo setup do i run it to one of the turbo compressor housings or directly to the intake, any help with this would be glady apprecaited.

thanks.

MikeGyver

For the opti vent you'll probably just have to run unmetered (by the MAF) air. Use a flow restrictor so the vacuum leak is small, and a reversed check so boost doesnt come out the manifold and into the opti.

The BOV hose needs to be after the throttle blades. Run the hose to the manifold. When you chop the throttle the manifold goes under high vacuum. This AND the boost pressure on the valve are what overcome the BOV spring and open it.

boosted-lt1

Or you can run one side of the opti-vent to the pre-comp side of the turbo and the other side open (or filtered). This can be done pre MAF.

MikeGyver

I don't understand, just leave the other side venting to atmosphere (instead of to the manifold)?

boosted-lt1

That's the idea. Use the turbo inlet as the vacuum source and pull in from atm.

MikeGyver

There's really no vacuum there, maybe 1/2". The way you get vacuum is if air is being drawn out at a faster rate than atmosphere can supply it; which doesnt happen unless you have a huge intake restriction like a clogged air filter.
With a properly set up venturi you may be able to generate a couple or few inches when under boost.

boosted-lt1

How much differential is required to pull a little fresh air through an opti?

MikeGyver

Well the more the better. The stock setup gets about 15" of manifold vac at idle and around 10" when cruising. The problem with a intake venturi is you'll literally get nothing until you really get on the throttle and get some airflow into the motor.

boosted-lt1

Point well taken. I don't know how much depression we have at low speed. It's safe to assume it is always less than atmospheric while the engine's running so there will be some flow generation. Let a feather go in front of the intake pipe and it's going in, not out. I also don't know what type of flow through the opti is required to meet GM durability requirements. They obviously thought about enough to pull manifold vacuum through it - which is the easiest and most effective way to get it in most every case.

Our problem with a compressor and MAF post comp (like you mentioned) is that you end up pulling un-metered air. So what is the trade off here?

To the OP - if you run a MAF, and you run it on the intake side of the compressor, you can pull engine vacuum just like stock, while it is all 'metered' air, so no leak so long as you pull between the comp & MAF.


EDIT - question - Can you use engine vacuum to evac the opti with MAF on the pressure side? I'm thinking you can...

Scott

MikeGyver

You can, I think the GN's had the MAF on the pressure side of the turbo, but then you have issues with the BOV dumping huge amounts of metered air and such lol.

There is a one way check valve and a flow restrictor on one of the opti vent lines. The inside orifice of the flow restrictor is tiny, so you may be alright just allowing it to suck in unmetered air (i.e. causing a tiny vacuum leak), the fuel trims should adjust for it.

xBaDaSs97z

I actually have the same question myself... I am going to be plumbing one end of the opti on the suck side of the turbo to suck ambient air.... I'm just not sure which one of the two opti hoses I connect to the suck side.... I blueberry the one that originally went to the intake manifold gets plumbed to the turbo and the other one pulls ambient aire correct?

MikeGyver

You want to draw air in the distributor housing and out of the cap. Shoebox has a pic on his site somewhere.