Aos

[The Radium King]

an interesting note regarding aos. i was reading an online diy install of a tpc turbo kit on a boxster. one of the issues with forced induction is that the high pressure on the intake doesn't allow the aos to vent to the intake plenum. what does tpc do? they plumb the aos to underneath the car and put a little breather filter on the end of the hose. no catch tank. on an application designed for the street. no hydrolock or blue smoke with a setup like that.

anyone run a tpc kit, tracked behind someone with a tpc kit, or has a similar 'vent to ground' approach on their aos? any james bond oil slicks on the track?

[JFP in PA]

What they have done is come up with a cheap and crappy way to slap a 1955 vintage Band-Aid on a problem they cause. I also know of no sanctioning body that is going to allow that nonsense on their track, it is a recipe for an oil slick.

The M96/97 engines are all low ring tension design; without and AOS to provide crankcase vacuum/evacuation, ring seal will be poor and oil consumption will soar, as will fuel dilution of the oil. This is a bad idea…………..

[The Radium King]

here's the page (about halfway down):

TPC Racing ATP:2 turbo kit DIY Install - Page 2 - 6speedonline.com Forums

does the aos need vacuum or just a lower pressure than in the crankcase (ie, ambient, but vented to a catch can)? i thought connection to the intake plenum was not for vacuum but to recycle any 'oily discharge' for emmissions reasons.

[The Radium King]

been doing some more searching on tpc installs. i note that, whenever tpc posts a build log, they always fail to say anything about the aos component. it's only when a private guy logs his install that it shows up. and the aos thing that i note in my previous post isn't a hack, as tpc provides a specially formed silicone hose for the purpose; this is how they designed it.

6speed is a bit of a sleazy site, and tpc is better than the soviets at propoganda and image control; i bet the pictures get removed asap.

[JFP in PA]

Originally Posted by The Radium King

here's the page (about halfway down):

TPC Racing ATP:2 turbo kit DIY Install - Page 2 - 6speedonline.com Forums

does the aos need vacuum or just a lower pressure than in the crankcase (ie, ambient, but vented to a catch can)? i thought connection to the intake plenum was not for vacuum but to recycle any 'oily discharge' for emmissions reasons.

The manifold provides vacuum to lower the crankcase pressure, which it does via the AOS unit.

[The Radium King]

i understand. what i am wondering is is whether the crankcase needs vacuum or atmospheric pressure.

the pistons are slapping around, fluids are heating, pressure increases in the crankcase above atmospheric pressure. as a result, air leaks past rings, pistons have to work to compress the air in the crankcase, etc. etc.

the 1955 solution is to vent the crankcase to atmosphere so that pressure doesn't build. this venting, however, lets bad gasses out into the environment. to address this, in modern cars the gasses are now vented back into the intake to combust and eventually get scoured by the cats instead (via an aos to remove as much liquid from the gas as possible).

so, you can vent the aos into the intake before the throttle body or after. if you vent after (as per the boxster) you will get vacuum. i see the benefit to vacuum as it will provide some scouring of the system; vent to before the throttle body and you'd get all kinds of deposition of crud.

given that, the requirement for vacuum is not of any benefit to the crank and engine longevity/efficiency. but rather to facilitate introduction of crankcase gasses into the intake. if that is the case, then redirecting the output of the aos to a catchcan at atmospheric pressure is a valid thing to do for engine health (not environmental health, however). dumping it to ground as per TPC isn't, as there is risk that liquid oil can get past the aos and make a big mess.

[JFP in PA]

Originally Posted by The Radium King

i understand. what i am wondering is is whether the crankcase needs vacuum or atmospheric pressure.

the pistons are slapping around, fluids are heating, pressure increases in the crankcase above atmospheric pressure. as a result, air leaks past rings, pistons have to work to compress the air in the crankcase, etc. etc.

the 1955 solution is to vent the crankcase to atmosphere so that pressure doesn't build. this venting, however, lets bad gasses out into the environment. to address this, in modern cars the gasses are now vented back into the intake to combust and eventually get scoured by the cats instead (via an aos to remove as much liquid from the gas as possible).

so, you can vent the aos into the intake before the throttle body or after. if you vent after (as per the boxster) you will get vacuum. i see the benefit to vacuum as it will provide some scouring of the system; vent to before the throttle body and you'd get all kinds of deposition of crud.

given that, the requirement for vacuum is not of any benefit to the crank and engine longevity/efficiency. but rather to facilitate introduction of crankcase gasses into the intake. if that is the case, then redirecting the output of the aos to a catchcan at atmospheric pressure is a valid thing to do for engine health (not environmental health, however). dumping it to ground as per TPC isn't, as there is risk that liquid oil can get past the aos and make a big mess.

Actually, the slight vacuum in the crankcase is critical to the low ring tension design rings creating a seal to the cylinder walls. Eliminate the vacuum below the rings and ring seal deteriorates significantly, blow by becomes rampant, ring “flutter” starts scoring the cylinder walls, and you loose significant HP, not to mention engine longevity. Do not run one of these engines without some level of crankcase evacuation, even if it comes from a supplementary source such as a belt driven vacuum pump, common on high output race engines. On a street engine, it also aids in pollution control, but it cannot be removed without consequences………

[Dale_K]

I had a 6.7L Cummins diesel in a Dodge pickup truck and it came with an air/oil separator. The owner's manual called for it's replacement at 67k miles. Interestingly, the ECU monitored crankcase pressure and would display a message if the AOS failed.

Cummins used an AOS because it provided better oil control (less oil burned). On recent diesel pickups the entire exhaust gas stream is run through a particulate filter, which is periodically burned off at high temperatures in a process called regeneration. The filter is quite expensive and must be warrantied for EPA emission system compliance. The main culprit in clogging up the filter is not carbon soot because that can be burned off. The problem comes from non-combustible ash and a big element (no pun) is zinc anti wear ingredients in the motor oil. The AOS contributes to the particulate filter life by reducing the amount of motor oil consumed. The motor oil itself was also reformulated to use less zinc (ashless oil).

[Pat]

Yeah, he dumped oil a while, then they suggested he run a catch can and less oil. IIRC this was on his stage II kit.