In a boosted engine, the crankcase is vented to the intake ductwork before the air is compressed and therefore the percentage of crankcase gasses to outside air entering the intake remains the same. 15% or more in most cases.

This causes your 70F intakes air to be increased to a temperature of about 88F when miced with 200F crancase gasses. Obviously these are all dependent on crankcase temos, size of crankcase vent and size of smallest inlet diameter before compression.


So, unless you believe that intake temperature increases of 18F do not effect performance, then there IS a sizable power increase.

 

I think it is quite normal for 996 Turbos to burn a quart every 1-2k miles. I am no pro, but think it is just the inherent design of porsche turbos to do this. Now why would a catch can help to burn less oil?
I had an 02 M3 without any real mods(ie: turbo) that burned a quart of Castrol TWS ($10 a quart) every 5k miles. I think for the M it was the iron (someone told me that) engine block that was burning oil.

Last thing I want to say about my cars is that when I am referring to burning oil, I mean it is not pouring out smoke from the tail pipes and polluting the air while I drive down the road.

 

I'm sorry...where do you come up with this 15% (or more) figure you keep stating?

I actually wrote a patent last week for a new technology aimed in part at positively evacuating PCV gases in FI engines, oddly enough. I don't have any of the data handy from it here, but 15% is a phenomenal amount. All of these gases are coming from blowby past the rings. Given the dynamic Vmax of a 3.6L FI motor, 15% is a HUGE figure...I hope my rings don't leak that much.

I can't think of any benifit to using a catchcan unless you have really big oil problems, in which case the can isn't going to solve them, its a bandaid for a larger problem. We use them on our racecars because the rule makes make us for safety reasons - ie keeping fluids off the tracks. If I had an old V8 with a poorly designed PCV system I'd consider it... there are better ways to address the problem. With flat 6 motors much of the oil that gets past the rings seeps by while parked, hence the large amounts of smoke at startup. keeping the oil at the 50% mark on the guage seems to lessen this issue a lot. also a lot of oil seems to accumulate in the intake when the system gets clogged or overfilled and oil gets all backed up through out... there are tons of posts on here about it.

-dw

 

Take the smallest diameter opening in the intake system before the compressor and add the diameter of the crackcase outlet. Then devide that total by the diameter of the crankcase outlet. You now have what percentage is crankcase gasses.

EXAMPLE. If the smallest diameter on the intake before compressor is 3 inches and the crankcase outlet is 1/2 inch, then the calculation would be as follows:

3 + .5 = 3/5
3.5 / .5 = 14.29%

So, from there, you can calculate how much the crankcase gasses increase overall intake temps once you know the temps of both.

Although the gasses do decrease performance a small amount, it is the temperature of the gasses that do the most damage. It has no relationship to burning oil, just the temperature of the gasses, whether they contain oil or not.

 

Unacceptable IMO.

M3 motors are very high-strung and I've heard they eat oil. I've also heard that they knock like crazy after a few hot laps.

I get ZER0 oil consumption on 2 of my LS1'S every 5K miles and it only takes 5 1/2 quarts; one of them is modified to over 600 rwhp.

I'm gonna have to do some more research on the Turbo 996 motors since I'm about to purchase . . . I had no idea that oil consumption at the levels of which you speak were normal

 

you assume an open and freeflowing system. its not. the pcv valve has a spring loaded pintle in it that restricts flow at various loads, and the crankcase is a closed system, you can only suck so much out of it before odd things start to happen. the actual volume is quite small...please believe me. if 15% of your intake charge = ring blow by, you would consume more oil than fuel (assuming you had any compression). i would be far more concerned about the egr system increasing the temp of my intake charge than the pcv...

by the way, the technology I've been working on in this regard actually does use positive suction to help draw the piston from the backside and hence increase efficiency...its pretty cool.

also keep in mind that your ecu maps are written with the PCV system and the fuel it contains factored in. Simply removing it w/o remapping will yeild a rich condition...

dw

 

I have one on my EVO8

 

So, I assume your engine is prone to imploding since you are sucking out more crankcase air than is available? So, at WOT, you have crankcase vacuum? I suggest you put an airflow meter on your return line and you'll be surprised as to how much airflow is coming from the crankcase at WOT (when crankcase gases are at there highest).

Or, simply disconnect the return line, plug the intake connection and watch how much your O2 sensors have to adjust for the non return of the metered air.

 

No the engine does not implode it is designed to work with the positive suction drawing on the pistons and therfore reducing volume proportionate to vacuum.... we are not a bunch of kids in a garage (anymore) and are working closely with the worlds largest automobile manufactures on this design....even some german ones.

Yes there is a good amount of "Positive Crankcase Ventilation" pressure at WOT. But there is also an inverse relationship between available engine vacuume and power output. There is the most vacuum at Idle (or more so during engine breaking with throttle plate shut) and the least at WOT...hence the need for a pintleated PCV valve that opens wider when there is less vacuum available and closes at idle to lower the flow rate.

I agree with you on all points, just not the 15% value....

think of it this way...the crankcase has a constant volume, (more or less depending on engine design and cylinder number and configuration, and more so for a flat 6). The only change in pressure within that volume results from compressed gasses that leak past the rings (and some insignificant minor fluctuations caused by the oil pump). Otherwise all things remain equal.
So use your formula to calculate total intake air flow rate at WOT and multiply by 15%...do you really believe the result ='s the volume of gas that is getting past your rings?? That would be 15% of your combustion charge mathmatically, which is a very large leak down value and I would say you need a ring job... especially considering that a 15% dynamic leak down ='s a far larger static (and dry) leak down value....

-dw

 

This is a DIY in-line crank case course filter type routed back to intake on my SC system for my 996. I choose the course filter gl*** see through type instead of a catch can because it fit nicley and can be easily monitored and cleaned periodically, this goes along way in keeping my IC cleaner longer. If you wish to see DIY or maybe will give some ideas of your own go here.

http://www.webbspot.com/porsche/html/crank_vent.html