Good to see someone using "bugger" :-)

I agree, provided that gas is sealed off during acceleration then it is only present during lift off and cruise it simply does not matter. The residue on the inside of the manifold (unlike the intercooler) could actually be positive and keep the air cool and isolated from the hot ally. I'd say that was a very minor effect though, and only on the boundary layer anyway. It is unsightly though, and dirty. But, it's also a pain in the rear to put a catch can there... so...

It would be the last thing I bothered to do.

Fred.

 

I put the check valve on the IM to prevent any boost from ever entering the catch can and/or crankcase. I don't see the need for any other....

 

It's been covered before but I thought I'd add it to this thread for future convenience... GTX PCV from dealer, $16 shipped, made in JAPAN of all places, and it is indeed plastic (the housing is polymer, innards are steel, just like the non-OE crap). It holds 30+ psi with a slight leak but not "much". Shake the valve, re-test, no leak. Guess it depends on how it seats... but a check valve will make this moot.



To quote myself:
I looked around for info on injector contamination and it seems as though it's almost exclusively caused by fuel. I couldn't find anything mentioning PCV vapors contaminating injectors... anybody know anything to the contrary?

 

Yeah - it seems what you really want is a good PCV valve ( E301-13-890A ?) where the factory put it, and a catch can on a VTA/VT-air-cleaner and call it done. The catch can is to keep oil of of the intake, and the PCV valve should do the rest, including providing what I'd like to coin "Positive Crankcase Ventilation". Seems like a good thing. :-)

I might just pick up one of those nice valves. I'll see if I can get that on mazdacomp.

I would like to put a bigger hole on the VTA side of things. Maybe I'll pull the valve cover and enlarge it. Any point to enlarging the hole going to the manifold? I doubt it, the PCV is going to be the bigger restriction anyway.

Am I missing something here?

 

yeah, the VTA side is probably too small to flow what is required at high sustained load. That IS the case on the FE3 anyway. Any good pics of how the miata cam cover is?

 

doesn't this just take use back to putting a filter on the driver's side of the valve cover, and a gtx valve on the other side?

 

It sure does!

Is there a problem with that? Adding brain's check valve wouldn't hurt, but if the PCV is up to the task, then why worry about it? And, it should be up to the task, it's made for a turbo car.

The only other thing is the catch can, placed between valve cover and turbo-intake, the slight vacuum helps clean vapors out of the valve cover, and the enlarged hole certainly can't hurt.

If there's something that doesn't do, please post it! Otherwise, it's the first system, simplest system which:

1) Puts a vacuum on the crank case under moderate throttle
2) Prevents the idle from walking due to leaked air through breather
3) Precents pressurizing of crank case from manifold
4) Prevents spilling of oil into turbo intake and IC piping
5) Gives an outlet for crank case pressure under high load conditions.

 

I'm with abe and always have been in favour of an enhanced OEM setup. You want clean air cross flowing through the engine under moderate throttle conditions. I'd be tempted to allow a restricted feed of air from the engine to enter the manifold under heavy vac conditions and form part of the idle air supply, however due to the lower O2 content of crank case gasses that would probably result in an unstable idle under different conditions.

4. it will only do with a really good catch can
5. it will only do well enough if the hole(s) is/are big enough.

Hence, on the FE3 I would do something like what rob has on his.

• stock PCV (possibly with check valve) from RHS to intake (drivers side is which side again guys??? :-p)
• stock breather enlarged and fed to the turbo inlet via a good catch can setup that doesn't let ANY oil through.
• extra breather to exhaust venturi system or just filter via catch can.

That way you get cross flow at moderate throttle, cross flow at high throttle and solid breathing at high throttle with no/little restriction.

I know for a fact that I've got crank case pressure issues as I found oil sprayed horizontally quite far away from the hose i left hanging off the cam cover. I'd like to resolve that properly before I do much further thrashing of it.

Fred.

 

Ages ago, Braineack said the vacuum between filter and turbo inlet was ~1-2 inches...

So enlarged holes aside, I did some "testing" on this a few minutes agoo...

On my car, the vacuum between a brand new K&N and the turbo inlet was negligible, almost immeasurable, probably <1 inch. From this, I feel it's safe to say that adding a catchcan here, especially if it's steel-wool-impregnated, would drop that value to zip. This immeasurable vacuum will do nothing in terms of scavenging, on my car anyway.

Of course in boost the pressurized gases would get forced through... just don't count on an asspile of vacuum.

Scavenging is really only taking place on the cold side. And air will be going into the VC through the hotside vent to compensate for the draw from the PCV.

I don't expect any of this to change anyone's mind on the setup they choose.. but stock seems pretty ******* good (with a check in the PCV line).

If my vent line going to the intake shows considerable oil, I suppose a catch would be in order but I'd expect crank case pressure to rise as a result. Compromise I guess.

 

Correct, either it is just releasing the gas generated and keeping pressure low with flow past piston rings, through block/head and out into turbo inlet/the world OR it's drawing fresh air in through the turbo inlet and sucking dirty air into the engine.

A you want to keep the air in the engine clean and dry and keep the water and co2 that make your oil acidic out
B you want to ensure you don't get excess pressure in there during boost

B is the reason people ditch the PCV half. The double the flow out of the head during boost when the PCV would be shut. However they ruin A because of it.

BTW, the NA FE3 that I saw blow a dip stick out had no PCV and BOTH dumping to under the car through 3/4" hose... still pressurised to all hell. Hence enlargement IS necessary if you are flogging the car like a dead horse...

It's good to get this nice and clear, many thanks to Rob for instigating it. I'm appreciative of his work.

Fred.

 

I sure as heck wouldn't have expected a lot of vacuum on the intake. But I guess you could put a little venturi type restriction in there ahead of the turbo if you really wanted, I'm sure it would do wonders.

Mainly I dump it into the air cleaner to burn what fumes I can. Anything I can do to not beat the environment more than I need to to have my fun is good.

Really a belt driven or electric pump is the answer if you NEED to have vacuum on the crank case, most other things are a joke under real power.

I think the secret to a good catch can, like the secret to a good muffler, is dead volume, unfortunately. So lots of space, lots of twisty turns, and some stuffing. It'll be a hell of a lot better than my 3/8" hose.

 

so after two months of speculation who here besides m2cupcar is actually going to get around to building one soon?

 

nice job, but why not a can thats a bit more shinny like stainless steel? Both will work the same, but stainless steel is nicer to see.

 

If there is any vacuum at the turbo inlet your air inlet plumbing SUCKS badly and you are losing power. Like abe says, it's just to burn the vapours. The only reasons to not put it in there are octane dilution and oil film on the intercooler.

 

shouldn't there at least be lower pressure there because of the fast moving air into the compressor?

 

Movement alone doesn't generate pressure differences. You need a restriction for that. if you put a venturi tube in there it would create a vacuum for you though, but I'll be stuffed if I'm putting something restrictive in the way of my turbo inlet.

 

I'm a little late to this party, but have read everything thorougly and have two questions.

What's the difference between the manifold side and the breather side?

As far as I know, they both utilize the same baffling system into the valve cover. Why not simply plug one of the holes, and run your whole valving system off the other if #1 is the favorite consensus?
The small amounts of boost we're talking about making it's way into the crankcase can certainly be vented fast enough through just one of the openings in the valve cover, no?

Oh yah, and how the hell is everybody actually attaching a hose to the little rubber grommet where the PVC valve normally goes?

 

The breather side typically has a much better longer baffle chamber arrangement.

Because you lose the PCV operation and don't gain any extra flow.

I firmly believe that "boost is pressurising my crank case through the PCV" is a load of bollocks and that all the "pressurising" is being done past the rings.

I think "certainly NOT" is the consensus there. In fact I'd go so far as to say that using both of the stockers is NOT enough either.

Fred.

 

you contradict bernoulli.




v = velocity, p = pressure. as velocity goes up, pressure goes down.

so you can have pressure drop in the intake without a restriction.

plus there will be a pressure gradient at the turbo inlet as you get closer to the compressor wheel. remember it is not the turbo that sucks air in, it's the ambient pressure that pushes it into the turbo because of the low pressure region at the inlet.

 

You fail reading comprehension.

If velocity stays the same pressure stays the same. Movement alone (without change on rate of movement etc) does not generate pressure differences.

Your equation is only valid away from any walls of say an intake tube and also only to incompressible fluids. The air in your intake satisfies neither of those requirements.

You are right that there will be a pressure gradient leading into the compressor, however its contour would be something like the inverse square. If you applied a still body of air to that vacuum source you might be able to detect it. With a steady state equilibrium reached where the speed of the air moving in and the pressure differential across it (it's invalid to say that it is sucked in just the same as it is invalid to say that it is pushed in) that makes it move are matched then the pressure drop relative to the outside ambient air should be so close to zero that you'd have a hard time measuring it. If it's not, your intake sucks.

End rant :-)

Fred.