Hey guys, I am planning on installing a catch can in the near future after my rebuild is done. Just wondering whether it's a good idea to drill the AOS now in preparation for the catch can? Are there any drawbacks of having a drilled AOS on a stock crankcase ventilation system?

 

Drilling the AOS only works if you then use the catchcan. You are effectively replacing the AOS with the catchcan, and turning the AOS into a sort of "pre-catch can" that mostly serves to fill the holes in the side of the block.

The AOS is a type of "cyclonic separator".
Enlarging the orifice at the top makes the AOS less efficient than it was designed to be.

 

If the AOS is off the motor, now is the time to drill it I'd say. If you keep it plumbed like stock you may end up with more oil in the intake than you otherwise would, but that's better than drilling it on the car and potentially getting debris in the oil pan I'd think (or taking it all apart again in the near future when you decide to drill it). Why wouldn't you just set up the catch can now and do it all at once?

 

I would not drill it but add a closed loop catch can similar to what I did...

 

Also interested in this as the OP.

I am using a saikou michi can routed back like stock before the turbo. Would it be best to drill the AOS when using maf and bigger turbo or will that just aid the turbo to suck oil from the AOS?

 

Unless there is a really good baffle\filter system in the catchcan it will not be an improvement by drilling the AOS . I run with out a catchcan and inserted a restrictor in the hose to reduce blowby oil but it should only be needed on a worn engine i have been told. On high boost my sytem would pull out allot of oil.
Curious to see if new rings and a fresh head will make a difference .

 

I can't install the catch can now because I don't have one yet and need to get some cash together first. Right now I'm just focused on finishing the engine and getting it in the car so I can finally drive again. Drilling the AOS now would just be much easier and I won't run the risk of getting **** into my AOS if I drill it later on in the car.

So, I'm thinking I will drill it now, and put a restrictor in the hose, that way when the time comes to install the catch can, I can just remove the restrictor and not mess around with any drilling in the car or taking the AOS off again.

 

You can literally use a beer can as a catch can until you find one you like. Just drill the AOS, and run hose from it to the can and let it vent to atmosphere (smog laws permitting of course). You will get a little smell and lose any crankcase vacuum, but most MAF cars generate virtually none anyway... If you find you are getting very little oil (like most) then you can just plumb it back to the J-boot until until you get a good (closed) catch can.