dizwiz24

curious.

Thanks!

mzgp5x

97ss 383 D1 with MM6
With PCV system. I got alot of ring blowby. Also, with pulling vac from the blower suction side, it got things dirty/ oily. Oil separator did not work good for me. I had to run the MAF on the suction side. Also, the stock Opti check valve is not designed for by-pass valve Op. Can over pressure Opti vent and blow oil into opti.

Note: I designed my own ball check for the Opti vent.

Without PCV system/ vac pump. No ring pac blowby or very little. Better ring seal. I had to move rad for a crank driven vac pump. Limited space in a 4th gen engine bay. Performance up due to much better ring seal. You can run them on the street but requires oil feedback to lube the pump vanes. It keeps everything on the induction side clean. MAF will not fowl due to NO oil suction thru blower. It requires money, time, Engineering to install.

I like the crank driven vac pump for FI applications.
B.

dizwiz24

Why were you pulling from the suction side of the blower and not the intake manifold( were you running an aftermarket intake w/o pcv provisions?).

My stock pcv valve plugs into the drivers side of the intake manifold..

Kevin Blown 95 TA

When you are under boost, there isn't any vacuum in the intake manifold - it is pressurized. The only vacuum (less pressure) is before the blower inlet. You have to watch that boost doesn't go backwards into the crankcase from the intake manifold, which it can do with only the stock PCV valve to stop it.

dizwiz24

I routed a checkvalve inline w/ the PCV valve to prevent this.
Wouldnt that be easier than routing a hose all the way to the suction side?

My thought (w/ the checkvalve) was during normal cruise, let PCV valve function, during boost... shut it down.

Blowby is a known fact with forced induction, I just assume shut down the PCV system w/ boost. Or was that the goal here, to still 'suck' blowby products in while under boost.

Youd suck in all kinds of nasty (head-fouling) stuff if operating the PCV system while under boost.

My next step is an inline oil catch can w/ the PCV system (and check valve as Ive described) to prevent that nasty blowby stuff from getting sucked in the instant I let off boost (and PCV begins to function normal again).

My new AFR heads are too pretty to let get crapped up.

Kevin Blown 95 TA

I have an extra check valve in the PCV line, too, and that does work for normal driving. But if you don't evacuate or at least vent the crankcase while under boost, you will probably get more pressure and maybe oil leakage.

dizwiz24

Does open valve cover breathers count as venting the crankcase?

Kevin Blown 95 TA

That works but it is unmetered air which then goes back into the intake when the PCV is working, so it has some effect on your maf measurements.

dizwiz24

WOuld it have any effect on a speed density based system (I dont have a MAF)?

Ever since I first swapped heads/ cams (back in '01) to hotcam / ported LT1 heads, I got split 'BLM's'.

I also got rid of factory valve covers / EGR / AIR, etc. and went to valve covers w/ open breathers at that time (to run 1.6:1 roller rockers).

I attributed split 'BLM's' to just the characteristics of the hotcam and assumed there was nothing I could do about it. Though I did try and play around with tuning the cells at idle to balance out the split BLMs (make the diff from 128, on both sides, equal) as best as possible.


If you think my open breathers would have an effect of speed density fueling calculations, then is there a way I could 'rig' the system such that it wouldnt?

Kevin Blown 95 TA

I think you're Ok there if it speed density. Breathers shouldn't matter on your car - I use them even though I have a MAF car and so do a lot of other people - on our cars it probably makes some amount of difference.

As to your other question, split blms can be caused by a few things - you can have exhaust or intake manifold leaks, injectors not matched, - really anything that could be making one side of the car run different than the other -- a valve adjustment problem (not as likely with hydraulics) or a spark/ignition issue.. Way back when this stuff was first being figured out some guys found that they could make it change at idle a little by adjusting their throttle plates a little bit - other guys with aftermarket throttle bodies reworked the idle air circuits to match the stock TB configurations. I guess it depends how much they are off whether or not it is worth losing sleep over. Start with the basics I mentioned and make sure the engine is sealed up tight from before the intake to after the o2 sensors, and if you can't find it, you can try swapping the sensors from side to side and see if it changes.

zmike

good info. I have been chasing a slit BLM, lean condition and never considered possibility of valve cover breathers causing split BLM. If I understood what you said correctly.

dizwiz24

ive already done all that when i relentlessly pursued the issue.

Swapping O2's, checking all fuel injectors for leaks, removed intake / headers and resealed, swap to heated O2's. Tune w/ Alvin (he was there w/ the car)., etc.

Nothing ever made any difference in my split BLM's.

Note the split BLM's was most pronounced at idle and there was also some nasty smell to the car at idle (also didnt have cats, AIR, or EGR). Interestingly the idle smell has improved with the addition of my blower.

Like I was saying, I went into the tune myself and changed VE values to at least equal out the difference in 128 from one side to the other.

I also know of other (vette lt1 guys w/ speed density) guys who had the same issue.