Maxthe7man

Caught this tip in Car craft magazine , apparently the v-8 turbo gurus run a ford air pump, plumbed to evacuate the crankcase, when running high boost, any blowby into the crankcase tends to push oil past the rings, the oil then in turn, having a tendency to lower octane, causes pre ignition(detonation) and also carbons up the piston tops which can also produce detonation through hot carbon spotting and reducing of the chamber CC's..
I wonder how much of this is applicable to the rotary, and if it would be a good idea when running big psi..
Anyone??
Max

Turbo 3

iTrader: (3)

Guess I'll start... how exactly do you think it would be applicable to a rotary at all? No crankcase, head, valve cover, etc...

There is really nothing applicable in your question to the rotary regardless of pressure being pushed.

Maxthe7man

It still can have blowby and ingest oil internally.. If you keep the oil pan area(crankcase) eqivalent in a vaccuum, you would reduce the chance of pushing oil past the side seals on the rotor face on the intake phase...
Think past the obvious...Max

Directfreak

iTrader: (2)

I read somewhere (can't remember where) that some people put a boost reference into the breather neck to equalize pressure and virtually eliminate blow-by.

I am in the process of looking for a small catch-can for oil-blow-by. I was thinking of using a small one used for power steering use. If someone has more info on this please speak up.

Or, If I am wrong about the reference line, please let me know. Or - what small catch can you guys are using.

setzep

Also lower oil pan pressure will keep your turbo happier, aids in the oil drain line.
In a lot of japanese 7's I've noticed they just bolt on a volume chamber (like directfreak is talking about) onto the top of the oil fill then run a large diameter tube off the top of the volume chamber to a filter. I'm guessing it works well. Be a lot better than just leaving the oil filler neck open for contamination to find it's way into the oil pan area.
I guess running a vacuum in the oil pan would be that much better than having a well vented one but is it worth it to hook up a air pump to do just this? Maybe a PCV valve is something to think about. It would only work good untill you got in the boost though...hmmm

nice sig Alex

turbostreetfighter

as somw of you know i just went through this delima with my rac car and i finally got through it. first of this does effect rotaries, i dotn think that we need and air pump but then again i have not tried. ok, i had to plumb dual -8 lines out of the filler neck and into a 1.5 quart catch can and then i put a small breather filter on top of the can...this was still not quite enough vent for 30 psi so i took a vacuum pull coming from the inlet of the turbo and plumbed it into the top of the catch can causing a slight pull on the system even with the vent filter. what my car was doing before i did this was making soo much pressure in the pan that it was clogging up the oil drains and making the turbos smoke. at first i had the catch can hooked up to one of the outlets on the filler neck and drew a vacuum from the turbo but it was only good for around 20 psi!! a PCV valve only works while the engine is pulling a vacuum so as soon as you go into boost it closes ,eleminating a vent.

yeah nice sig alex!!!!

MWW

Maxthe7man

Yeah I am not sure I like idea of putting a mechanical driven air pump back on, but an electric vacuum pump from a diesel truck may work ok..
As far as oil blowing out, my last motor was ok to about 14 psi, past that, it literally hosed down the engine bay with oil, often I would turn off the profec and run lower boost around town just to stop it from rustproofing itself with synthetic oil.
I dug up another Car craft from sometime ago, with a dyno test of engines with mechanical crankcase evacuation, they made 10 hp more with a smog pump sucking on the crankcase then without it, and thats on a naturally aspirated motor, I would think the difference on a force fed motor may be the same or a bit more..
I think moroso is making pumps specifically for this purpose now...Max

setzep

But woulden't that 10 extra hp come from the less pressure behind the pistons therefor no gains for us?

Hmm... a small electric air pump that turned on under boost, never thought of that. With that you could still run a pcv valve so you'd still have evacuation durring non boost if you didn't want to run the vac pump all the time.

Maxthe7man

I think power actually comes from fact of again reduced blowby which contaminates and diluting the intake charge, which then has the effect of reducing volumetric efficiency.... Some aerodynamics would come into play, but probably not that much..Max

setzep

I guess I'm just used to my V-8 buddies talk about how they need to evacuate there oil pans because it will free up some hp and stop all those damn leaks their small block chevy have. Never thought about the oil contamination effect.

suganuma

ya, i had problems on a road track with the BOV spitting oil b/c either i need a restrictor in my oil feed line or the oil drain isnt working too well right now. this was with just running a line from the turbo inlet to the oil filler neck with the other nipple on the filler neck plugged. i later cracked an apex seal due to other problems, but i was planning on putting in a catch can in the line going to the turbo inlet. this would give the crankcase vacuum all of the time with it increasing as more boost is being created.

are you still running yours with a vent in the catch can marcus?? so the way i was running it before is good to about 20 psi? hmm...maybe i do need that restrictor then ( i was only running 15 when fooling around and only 10 on the track that day)

are you saying that taking it off of the filler neck WITH a filter on the catch can is better than not having a filter?? I would think that a sealed setup would work better....but then again look at what ari and steve are running and they dont seem to have too much trouble

Directfreak

iTrader: (2)

[thinking out loud]

How about a line to a from the oil filler neck,
to a vented catch can (with a little breather on it),
which then drains to the same drain as the oil return line?

That way the whole thing would be automatic, and you'd never have to drain the catch can?

Or even better, since I am using a single - I could use the "other" return hole (normally used for the twins) on the rear plate for the drain. I have it blocked off at the moment, but could put a fitting on it for this purpose.

Or can I use the two tubes on the filler neck. One for blow-by, and one for return. Just putting some kind of one-way valve into the return line.

Ooooh. I am starting to like this idea..

[/thinking out loud]

80-CU.IN.T

This is exactly what I was planning on doing. I was using a coke can for a temporary container. I know pretty ghetto but a quick fix for the time being. I also think I popped a side seal during dyno. I wasn't involved with the tuning and couldn't see the graphs when they finished. That is what I thought caused my blow by during boost 14 - 15 LBS. I thought that pulling a small vacuum even with a breather would help. It is nice to see someone already thought of it and it works.

Thanks - (I have learned a lot from you and others. Keep it coming)

setzep

Alex- What about just mounting a catch can right on to the oil filler tube (where the tube comes out of the center plate at the two bolt flange) and having a vent/breater filter at top. It would self drain back into the center plate eliminating the need for a separate drain.

Remember all those pic's of the japan FB/SAs someone posted a while back (2-3 months?) in the 1st gen sec? I think I saw some pretty intresting looking setups in those pics.

twokrx7

iTrader: (1)

The vented catch can topic is very old, many have been doing it for several years now. It works, is needed, and you cannot have too much flow capacity to your vent ... more is better.

Many folks running around 15 psi find a small pressure hose (I use 3/8") to a vented bottle or small tank is more than enough. Running this system back to the suction of the turbo is optimum, however, you need to tap into the top of the filler neck to minimize oil carry over.

My system ties into an aluminum oil filler cap and routes to a ss can which has a small K&N vent filter. The can usually has about 3/16" of oil in it but the level has never risen in four years! Under high boost runs it does vent some blow by ... you can smell it!

Directfreak

iTrader: (2)

twokrx7, can you (or anybody else) post some pics of your catch can setups?

Thanks.

Maxthe7man

I have seen the numerous catch can threads and such.. But from what I understood in the original article I was reading, was that in high boost applications, intake suction nor atmospheric venting was enough to evacuate the volume of blow by in order to stop oil migration into the combustion chamber which caused detonation, the worry wasn't really about the oil spew externally, but how to control oil and pressure within the motor itself in order to stop oil from slipping by the various combustion chamber seals, now in a piston motor that would be 3 or possibly 4 set of rings, in a rotary, thats the side seals, which we only have one per face, plus the oil control rings, which do not have near the sealing area in terms of width of the average piston ring..
When some motors pop for no apparent reason, I am wondering if its oil ingestion that is causing the detonation and not some tuning glitch... If I had a dollar for every thread I have read, including my own, that said "my motor popped, a/f's were 11:1, timing was 12 degrees boost was 14 psi " yada yada yada... Is the evacuation of the crankcase being overlooked when it comes to higherboost levels..
I found another magazine today that said the same thing, its this months Hot rod with a twin turbo chevy on the cover by Troy Trepannier, it reitterates what was said in Car craft about forced induction applications and mechanically scavenging the crankcase in order to ward off detonation problems cause by oil vapours. Its no secret that oil contamination of the intake charge lowers fuel octane..
Have a look at this:
http://www.aerospacecomponents.com/vacp.htm
Every Rx-7 I have ever owned turned th oil black quickly, and always wreaked of gas when drained, which tells me blowby in a rotary is pretty common..Max

twokrx7

iTrader: (1)

Don't forget that the side intake ports are inside the side seals at times. During these instances the oil control rings are the only seals to prevent pressurization of the crank.

Directfreak

iTrader: (2)

I think I found my solution.


Jaz Mini Catch can with Breather,

S2-13BT

DF, that looks like an oil/air seperator (maybe). Where you retain a cars PCV valve. Basically you run the ventilation line to the seperator then continue the line back to it's original location in the intake system of the car. It strips the oil from the air passing through it by way of a filter of some sort. Then drains back to the sump. That makes it a low maintenance system.

The ones I've seen don't vent to atmosphere, so I'm a bit confused.

The other option is the catchcan. This is just a can with an airfilter on top and an inlet. You completely remove the PCV and run the ventilation line into it. You have to periodically empty it and it can smell pretty bad in some instances, because it's vented to atmosphere.

Pete, AKA Rice Racing simply has a small filter as shown in the pic atached straight to the small pipe coming of the oil filler pipe. I assume this would work OK.

Overall, it's a very good idea, because retaining the stock system will coat your inlet pipes and I/C with a film of oil reducing the cooling efficiency.

Sorry for the long post.

turbostreetfighter

everyone seems to agree on the subject, but i think one of the problems is the actual size of the nipples that are already on the filler neck...they are just too small!! as far as recirculating back on to the oil pan, i think that is a bad idea, most of the vapors that go in to the can have more fuel in it than oil. i know when i drain my catch can it is FULL of straight methanol and no oil at all!!! the jaz tank looks like it would work great but i would drill two .375 or .5 " holes, tap them and use fittings.
some vent to atmosphere and some dont , i found that when i did not vent to atmosphere not enough pressure was released so i vented it and the problem was solved!

S2-13BT

I would add that I agree with turbostreetfighter. I am going to run a catch can and empty it when need be. For me it will be illegal, because it makes a big difference to emissions but it's worth it IMO.

Bad2ndgen

Im working on a part to help evacuate your crankcase. and it works with boost....in fact thats what makes it work. I'll keep you posted.

80-CU.IN.T

Hey - The Coke can is my idea

silvr94r2

iTrader: (3)

You don't happen to have an orange FD do you? I just remember his having a coke bottle there as a catch can.