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I'm running the Supertech 84mm 9:1 pistons (P4-MA84-CR9) and the Supertech rings (R84-GNH8400).
I had my machine shop gap them and they gapped them to .017 for the top ring and .023 for the second ring. I do not know the oil ring gap. I also didn't double check their work when I installed
I am dealing with excessive blow by, in the form of bad valve cover leakages, specifically at the back rear cam cap and VC bolt. Running both stock location vents as AN10 to a vented to atmo catch can. I also drilled out the middle baffle for more air flow and sealed the chambers with rtv. Still seems like tons of crankcase pressure.
My question is, anyone else running these rings and what gaps did you go with? Is my 2nd ring gap too big?
(Other possibly important info: 700miles on engine, been leaking the whole time. Leaks even at 5lbs of boost from a EFR6758. Rear main seal is dry, front crank and front cam seals also dry.)
Those ring gaps are not excessive for a forged piston turbo motor. If those numbers are real/accurate your issues are somewhere else.
Ok lets assume they are, how else would the crankcase get pressurized? The only thing I can think of is cracked head...which I can't rule out, given a couple other symptoms.
How was the engine broke in? What kind of oil? Does this engine have oil squirters?
first start, ran for about 2 mins holding the revs around 2k.
Change oil and filter.
Drove around the neighborhood getting heavy vacuum pulls for 20-30mins.
Changed oil and filter.
drove around town varying loads/rpm and no boost for 100 miles
Changed oil and filter.
Drove normally for another 150 miles, hit about 10lbs of boost max but still very easy on it
Off to dyno where it saw 24psi
Changed oil again and been driving it ever since.
It idles super solid and nothing feels "off" about it, just keeps pissing out the valve cover gasket in the back.
+1 for those ring gaps being sane assuming those are the true numbers.
There are more scientific ways of doing it, but have you idled the engine with the oil cap off and held your hand over it to confirm excessive crankcase pressure? Comparing the amount of blow-by you feel to another Miata (even a stock motor one) will help confirm the issue.
How quickly will the motor blacken new oil? My old stock motor running 10psi with 207k miles (and a lot of blowby) will turn fresh oil black in under 100 miles. Dual 10AN breather fittings and drilling out the internal crossover to ~9mm took care of blowby causing oil leaks though.
There are a few ways combustion/boost pressure can get into the crank case; piston/ring problems, valve stem issues, wonky cylinder bores, other things that I'm not thinking of off the top of my head. I imagine cracks in the head would lead to combustion gas leaking into the coolant passages long before the crankcase.
With all that porting and venting of the crank case, are you really sure you have pressure building up? How have you confirmed that? How is the sealed path out of the back of your valve cover less resistance than the vented path?
"Bad leakage" could mean very different things to different people. How much oil are you losing for how many miles of hard driving (track?/street?/etc)?
I had valve cover seal problems on an old car and eventually discovered the cover was warped.
+1 for those ring gaps being sane assuming those are the true numbers.
There are more scientific ways of doing it, but have you idled the engine with the oil cap off and held your hand over it to confirm excessive crankcase pressure? Comparing the amount of blow-by you feel to another Miata (even a stock motor one) will help confirm the issue.
How quickly will the motor blacken new oil? My old stock motor running 10psi with 207k miles (and a lot of blowby) will turn fresh oil black in under 100 miles. Dual 10AN breather fittings and drilling out the internal crossover to ~9mm took care of blowby causing oil leaks though.
That is a very good idea, I'll see if I can find some miatas locally that could let me test that out. I have the VC off right now and the oil is about 100-120 miles and the stuff thats pooled under the cams is pretty black already.
There are a few ways combustion/boost pressure can get into the crank case; piston/ring problems, valve stem issues, wonky cylinder bores, other things that I'm not thinking of off the top of my head. I imagine cracks in the head would lead to combustion gas leaking into the coolant passages long before the crankcase.
With all that porting and venting of the crank case, are you really sure you have pressure building up? How have you confirmed that? How is the sealed path out of the back of your valve cover less resistance than the vented path?
"Bad leakage" could mean very different things to different people. How much oil are you losing for how many miles of hard driving (track?/street?/etc)?
I had valve cover seal problems on an old car and eventually discovered the cover was warped.
Let me hit you with this then. I had the fab9 head studs on at 85ft/lbs per instruction. I don't recall ever getting a slipping feeling while torqueing them but at 500 miles I pulled spark plug 4 and it had oil all over it in the combustion chamber, not in the spark plug well.
I haven't been able to confirm it, wasn't sure how to honestly. I'm going to try the hand over the oil cap method just mentioned.
I am baffled why its going out there as opposed to the catch can. The can has basically nothing but does smell like oil at least. Fair enough on the oil, I'd say about 1/2 cup just driving around for 30mins and I changed the wastegate spring so its only hitting 5-7psi and thats at 30% throttle, I haven't even pushed it since discovering the leak.
Got a machinist straight edge and the VC seems fine, as does the top of the head but I need to find a shorter one since 2ft is too long to really get it on there front to back. Lemme throw some pics up...
It was coming out the back of the cam cap cover so I tried some ultra grey.
After 24hr set and a 20mile test drive it was almost dripping down from that corner and right in front of the stud behind the dip stick. I've already talked to DIY Auto Tune, who makes that ignition bracket and they said standard 55in/lb torque on those bolts and they've never had an issue, so I'm not sure its that.
Just got a new VC gasket from Mazda (again) and gonna try even more RTV and hoping for the best but I wanted to confirm the ring gap was ok.
I even took the head off and replaced that gasket thinking it might've blown. Here's what the cylinders look like, seems all the combustion is where it should be
Had a thought, you can see vertical dark marks on cyl 3 in my picture above. Would those marks be indicative of blow by through the ring gap? Cyl1 has similar markings.
I made a gauge to measure internal pressure using a gauge from a blood pressure cuff. Cheap, accurate, easy to make. It can read very low pressures ( like 1/2 psi). It may help determine where the problem is at.
That is a very interesting idea, basically what ZWAAZ was saying with actual measurements. Do you have a baseline for how much pressure yours is making?
I was at about 2 psi. Now at about -2 hg. I designed an electric vacuum pump that turns on at 2 psi pulling through the catch can. Kinda like the exhaust slash concept.
I was at about 2 psi. Now at about -2 hg. I designed an electric vacuum pump that turns on at 2 psi pulling through the catch can. Kinda like the exhaust slash concept.
It's a smog pump off a VW, (and probably many German makes). Moves a lot of air. Routing is pretty straightforward out of the valve cover with your choice of setup to catch can. Then over to the pump. The pump is controlled via a Hobbs switch set at about 3-5 psi through a relay to power the pump. I kept a one way valve through the pvc to act normally with no boost. If necessary, you may need to control the power of the pump. I did this using a heater fan control to slow the motor down some. I had to do this because in my valve cover I went the stainless scrubby sponge route and it may not be the current best practice on the subject of valve cover venting. No track days, but a 1000 miles of highway/spirited backroads driving amounted to 4-6 oz. in the catchcan.
It's a smog pump off a VW, (and probably many German makes). Moves a lot of air. Routing is pretty straightforward out of the valve cover with your choice of setup to catch can. Then over to the pump. The pump is controlled via a Hobbs switch set at about 3-5 psi through a relay to power the pump. I kept a one way valve through the pvc to act normally with no boost. If necessary, you may need to control the power of the pump. I did this using a heater fan control to slow the motor down some. I had to do this because in my valve cover I went the stainless scrubby sponge route and it may not be the current best practice on the subject of valve cover venting. No track days, but a 1000 miles of highway/spirited backroads driving amounted to 4-6 oz. in the catchcan.
That's pretty awesome. I never thought about using a secondary air pump as... just a pump haha.
An old instructor of mine used to build/race drag cars back in the day and he said they'd often run a similar setup on a lot of the engines they built (although I don't know what kind of pumps they were using). Never occurred to me that something similar might ever be done on our little 4-bangers.
09-21-2023 | 02:46 PM
Supertech Ring Gap - Blow-By Problems
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