Pre-boost compression/leakdown test results
 

I've been accumulating parts for my turbo build for several months now but I figured before going ahead with the install I really should do compression and leakdown testing just to make sure I knew what my engine was doing.

The engine's only got about 78k on it as of today. My car sat around as a rich guy's 3rd car for several years so I often wondered if the lack of use would impact the engine's health...

Anyway, I headed over to a friend's garage today for some help. We ran through both tests with the following results:

Compression
#1 - 175
#2 - 175
#3 - 150
#4 - 175

Leakdown
#1 - 30% (70psi)
#2 - 50% (50psi)
#3 - 70% (30psi)
#4 - 10% (90psi)

Compression test results were mostly good. Sucks about #3 (adding some oil for a wet test didn't really help the numbers) but the others looked pretty nice and healthy

Leakdown results were frustrating. For tests done on cylinders 1, 2 & 4 we could feel air at the intake. Wasn't sure where the air was going in cylinder 3.

Any thoughts as to why leakdown test results on 2 and 3 are so miserable? I'm sure we had pistons correctly positioned at TDC compression. Some other operator error??

Cylinder #3 fared worst in both tests so I'm guessing I have problems there.

We did this test the same way as I did it in this thread:
https://www.miataturbo.net/engine-pe...hat-now-64069/
Something seems screwy though. To correct the above quote, the air wasn't coming out of the intake, it was coming out of the valve cover breather.

What I don't understand is that this engine does not smoke or burn any oil, it does not take any coolant. The compression numbers don't look too bad in my eyes, (especially as compared to mine). Since this engine seems to run so well and not show any physical signs of future grenading, why such crappy leak down numbers?

when I do leakdowns I like to slightly move the crank +/- a degree or two to make sure the valves are sealed. A lot of times the crank moves from TDC once you start pushing the pistons down with air.

there's no way you have 50% leakdown and those compression numbers.

Right, thanks. I was tired and pissed off when I wrote that post.

To brains point, I think he might be right. I've heard the same response from someone else I talked to about this.

you should have the oil cap off when doing leakdown to hear the source better, but that would suggest rings, but the compression test doesn't.

especially if adding oil didnt increase the results.

Also listen at the plug holes of the other cylinders.

When you hear the hiss at the plug hole of the cylinder that is *earlier* in the firing order, that suggests a leaky exhaust valve. When you hear it at the hole of a cylinder *later* in the firing order, that suggests a leaky intake valve.

I did that, thinking the same thing as you.

That's also what I'm thinking. I mean, this engine has decent compression numbers and it runs like a top with no fluid consumption and no smoking.
There is no reason it should have those numbers. Something wasn't right with this test.

So I'll just go ahead and boost then.

That's the spirit!!!

You're going to beat me to it, Adam! I've got to hold off for awhile as we just found out we'll be moving out of town shortly. But I'm glad you'll be getting yours up and going soon.

We'll see how long it actually takes me, I still need to buy a WB02 and then I'm going to install just the Link and WB first, get that tuned, and go from there. Good luck with your move!

MOAR BOOST! :brain:

In my case, any boost is moar boost. Just ask thirdgen how lethargic my car feels when driving uphill. To be fair, I don't have a two stroke miata motor so it's gonna feel a little down on power.

I should use klotz in my fuel so my exhaust smells like my buddies intoxicating motocross bike.

Thanks. At least we won't have to be moving across the United States like you did...just to central California. And I guess I shouldn't say my build is entirely on hold...just the main kit from Begi. I'm still buying parts here and there as funds permit. :-)