Catchcan setup with GM MAF

[talonDSMerr]

I understand the proper way to set up the oil catchcan off the valve cover breather hose is with a sealed catchcan with one line going to the valve cover and the other to the intake to route back metered air.

BUT, if you have a GM maf in blowthru setup, routing that air back to the intake pipe makes it have to be re-metered. So far, I haven't seen or heard of anybody with blowthru routing the catchcan behind the gm maf, replicating stock config.

So my question is, is it theoretically OK to use a vented catchcan with one line going to the valve cover breather? It would be the same as having it routed back to the intake pipe, would it not?

I'm not really looking for people running it this way, I'm wondering if it is technically "right."

 

[snowborder714]

This might help.
http://www.dsmtuners.com/forums/bolt-tech/285430-guys-blow-through-setup-catch-cans.html

 

[talonDSMerr]

Yes, thanks. I discussed a little in that thread also. It seems like you won't have issues venting the breather hose to the atmosphere. As long as there is a catchcan inline and a filter for when there is vacuum. I always thought catchcans with the filter were a big NO, but doesn't seem that way with a GM maf.


Also, I have another noob question that I never really thought about until now. Why is it OK to vent the bov with a blowthru setup? I was under the impression that the air vented from the bov was metered by the ecu, so wouldn't venting the bov be releasing metered air regardless of the maf positioning? Wouldn't the "Proper" way to run a blowthru be to recirculate the bov after the gm maf? I guess I don't see why the positioning of the maf makes a difference.

 

[Atuca]

The BOV is supposed to be mounted on the intake pipe before the gm maf. Any air that gets passed the gm maf is metered, the air before it is not.

That means all the air leaks before the gm maf, wether it be at the intake filter, turbo, intercooler pipes, or even a leaky BOV, NONE OF IT MATTERS because only the air that gets passed the GM Maf is metered, so the air that actually gets through it to the engine is accounted for. If the BOV opens, it is letting compressed air between the BOV and the turbo to release. Air doesn't release "backwards" as the engine is still sucking some air in to idle/not die when you shift.

Now when I said it "doesn't matter" it sitll matters because those leaks are just lost power your turbo is generating, but as far as metered air is concenred, that lost air is not being missed by the engine calculated AFR.

Hope that helps.

 

[talonDSMerr]

Sorry, I should have worded it a little bit better. I meant the ecu accounting for the air released by the bov. Since the bov is recirculated after the stock maf, the ecu accounts for the air that is let out by the bov by adding more fuel, right? Well, if that's the case, moving the maf into blowthru shouldn't make a difference, venting would still be putting air out of the system that the ecu accounted for.

Am I missing something here??

 

[Atuca]

When you are recirculating the air goes back into the intake after the stock maf, so the air is still in the intake pipes, the same metered air hasn't "escaped". It is just going from the begining again, going through the turbo, intercooler, and back up the intake track.

When the BOV is in a recirculated setup and air is being reintroduced into the intake pipe (stock setup) new air from the air filter in front of the stock MAF will not enter the car, compresed air will be occupying the space from the return tube.

Now if you had a boost leak in a stock setup you could loose metered air and that would cause your car to run rich, but not because the ECU is running it more rich because it knows your BOV went off.

 

[talonDSMerr]

new air from the air filter in front of the stock MAF will not enter the car, compresed air will be occupying the space from the return tube.

That explains it. Thanks. It wasn't making sense to me, but this clarifies it up.

 

[jbark]

i did the maft set up on my 2g and ran a filter off the valve cover. that got all full of oil and i switched to a catch can and i have it venting from the other side and i have had no issues. works good and looks clean. good luck tho, jeremy