Jeff Conner

I just purchased a 1994 Monster Miata with a freshly built MRM, non-boosted 331 stroker. The engine is supposed to have two thousand miles on it, which I think the documentation provided to me supports. There is so much blow by at WOT that it blows the PCV valve out of it's rubber grommet at the back of the intake. Factory Cobra intake and manifold. I've cleaned the birds nest, put in a new valve, redirected vacuum (twice), put in an oil catch can, even ran vacuum to the tit on the oil filler tube (which caused the car to make a metallic noise under load, emanating from what sounded like the value right below the intake. I can also hear a fairly loud clacking under WOT at about anything over 3500 rpm. I had read that excessive blow by can cause detonation, which the noise could conceivably be. Running a mixed tank of 93 octane and 98 octane. Today, I cut a PCV value open and gutted it with the plan of increasing flow. I have put high temp rtv on both the rubber grommet and the empty pcv shell and will drive that tomorrow and see what it does. I have not done a compression or leak down test. Exhaust pulses can be felt strongly with the car at idle from six feet in back of the car, which to me would seem inconsistent with rings not seated. I think the compression of this engine is probably pretty high. I'm having some difficulty sorting this problem and am open to suggestions. Also, if there is further information that might be helpful, please ask.

gagoft

with that much blowby, compression and leakdown would be my first priority.

Jeff Conner

I think I've worked through the PVC problem. Now to clear the tank and fill with 98 octane fuel to take care of detonation. If this works, I'm a happy camper. In the event that anybody cares, I hollowed out the PCV valve in order to flow more crankcase pressure. Drove it a little hard yesterday and did several WOT runs and nothing popped out. Oil has also ceased flying around the engine compartment. I understand the function of the PCV and potentially preventing discharge of gases inside the crankcase, but I spoke to an older gentleman who used to drag race in CA, claimed to be number 1 in his field, and advised to do this. Said he had done this repeatedly without issue. I will keep my fingers crossed.

V8MiataMike

I usually ensure I have an operational PCV system, start the engine and then put a clean rag over the oil fill hole on the valve cover. With a good engine, no vacuum leaks, etc., you should see the rag being slightly pulled into the oil fill hole. This indicates the crank case has a vacuum. While the engine is still running, pull the PCV out and you will notice a change in how the rag is no longer being pulled in but rather being pushed out.

At WOT there will be very little engine vacuum and the PCV is supposed to close so that all that oil does not get pushed into the intake. But that is also when the other hose connected to the valve cover that goes to the intake canister/tube/throttle body (connected before the throttle blade) takes over to create some vacuum as at WOT it should produce some vacuum to the crank case.

Back in the day they used draft tubes that went down under the engine so that at driving speeds it created a venturi effect to create vacuum to the crank case but the oil/vapor it pulled out just dumped on the ground and it did nothing when the car was not moving forward! The PCV system was put in place to burn off that collected oil/vapor as opposed to dumping it. But some kind of vacuum source is required to remove crank case pressures for sure however with excessive blow by, it can not handle the volume...

tbone heller

High volume oil pump filling the top end of engine?

Jeff Conner

I'm guessing that there is a high volume oil pump. When I pull the vacuum line from the bottom of the intake, oil pours out. Replacing pump with a lower volume unit might cure this? Thank you for your thoughts.

Gunpilot

I had a similar issue and found this: Oil Baffle for Cobra lower Intake - Ford Mustang Forums : Corral.net Mustang Forum

I removed my Cobra intake and found I did have the smaller oil baffle. I used the template and cut my own large baffle out of aluminum and riveted it in. No more problems.



Template here: http://eectuning.org/forums/viewtopic.php?f=17&t=14019

V8MiataMike

I have the high volume Melling on my 5.0 setup - Martin's oil pan - no issues...

Jeff Conner

Yes, this car has a Martin pan on it also, specially designed to clear the 331 stroke. I'm thinking a baffle under the intake may be a likely culprit of excessive oil in the top of the engine. I want my mommy.