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For the second time in this thread, adding liquid to the cylinders will always increase compression since that liquid can't be compressed. You're effectively making the combustion chamber smaller. If you already have leakdown numbers showing you where your leakage is then it's a totally pointless test IMO.
The engine is totally fine. Stop worrying and start tuning cause that **** didn't look pretty,
I feel like you're thinking of and copying Aidan's thread title there.
Next steps are definitely tuning it and sending it.
Edit: Annndddd there it is. Except it looks like someone got lazy now even the guise of amusement has been stripped of the pretense and veered flat out into insult. Strong work.
Last edited by ridethecliche; 09-07-2018 at 03:23 PM.
For the second time in this thread, adding liquid to the cylinders will always increase compression since that liquid can't be compressed. You're effectively making the combustion chamber smaller. If you already have leakdown numbers showing you where your leakage is then it's a totally pointless test IMO.
The engine is totally fine. Stop worrying and start tuning cause that **** didn't look pretty,
Retard the wet, sticky hole?
A half teaspoon of oil decreases the cylinder volume enough to affect compression by 30psi? Unlikely.
Originally Posted by ridethecliche
Sure. Now that I have hot dry numbers, I can redo hot wet for the hell of it to close the loop.
Also, 100 wheel sounds a bit low from an NA 1.8, especially 99 and up with a megasquirt.
In fact, I am making all of 118WHP with a VTCS IM. I have a VICS ready to go on over the winter to see if I have an intake restriction.
Yeah, the way i see it for a compression test. If I drop in the oil and it goes up by a solid amount and things get more even, then it's definitely the rings. If it doesn't normalize relative to the others then the valves are what's keeping it there. That's my understanding of it anyway. Theoretically the valves should have affected the cold compression as well, so it would be strange for it to be even when cold if the valves were causing the problem.
A half teaspoon of oil decreases the cylinder volume enough to affect compression by 30psi? Unlikely.
No one specified how much oil but I have commonly heard people stating you should put in a "capful" or a teaspoon.
A miata combustion chamber should be somewhere between 50 and 55 cc. A teaspoon is about 5 cc. That's 10% just from the oil. I stand by my statement that there is nothing to be learned from a wet compression test when you have already done leak down.
I thought the oil went into the cylinder to seal against the rings? I didn't think that much would have as large an effect on volume as you suggest.
I think the added info is it shows how much of the effect may be due to the rings. If it goes up a bunch I know the rings are the issue. If it doesn't, then it's another data point for exhaust valves.
A friend pointed out that I may have damaged the exhaust valves if my timing had been off like it was for a bit. Vtechkiller didn't seem to think so, but the head didn't have this issue when he was using it.
If nothing else, it's 30 minutes of my time. Not much to lose. I kinda want the satisfaction of knowing. I mean, I just learned to do a leakdown. Might as well learn to do a complete compression test!
I kinda agree with Spartan. If your comp and/or leakdown is bad you're yankin the head anyway, and if you're yankin the head you better pay the $40 to have it leak tested anyway, and if it's not your head then it's your block. So wet test, imo, doesn't show much. At least that's why I've never done it.
I may be crude in my thinking, but i dont really give a damn about compression much anymore. 8.6:1 will look like a deflated dick anyway, unless you put 24 volts to the starter.
1.0 Leak down, is power loss. For the most part, you dont get great compression and **** leak.
2.0 Forget about compression, it just makes you loose sleep.
3.0 10% leak is just fine, might even self heal (rings)
4.0 Tearing into a motor because of 10% is Pinout-leaky-retard syndrome
5.0 Extremely unlikely you damaged valves from cam/crank timing.
6.0 ADDING OIL TO A LEAKDOWN TEST IS VERY RETARDED. It will just fluff numbers and skew thinking by adding another variable.
7.0... still thinking.
Has a bore scope been down this turd hole yet, just to see?
feel free to use that next time you chat with a gastroenterologist.
It'll fluff numbers by helping the rings, not the valves though, right? What I've seen written is that if it goes up by a lot then it's the rings, if it doesnt go up by a lot then it just proves us all right by saying that it was the valves as the leakdown indicated.
The thing that makes it a bit more interesting is that it captures the characteristics of a warm motor. My cold vs hot compression numbers are pretty different. Leakdowns are done on a cold motor so some of the things may be off.
TLDR; I understand that doing wet compression is going to fluff up the compression numbers, but doesn't it help point a finger?
On the note of fingers... @Ryansmoneypit... On my surgery rotation one of the attending's told us all that "if you've got a finger and they've got an anus, they're getting a rectal". Fortunately or unfortunately, I'm likely done with the 'butt stuff' part of my training. I may grab one of the usb phone boroscopes on amazon soon... you know... for science!
Also, it hasn't seen a boroscope, but I've done like 5 oil changes (in 2-3k miles) and haven't seen anything concerning. I actually bought a fine reusable coffee filter that I run the oil through while draining it in addition to looking for shiny things.
I thought the oil went into the cylinder to seal against the rings? I didn't think that much would have as large an effect on volume as you suggest.
How much? I literally just did the math for 1 teaspoon.
Originally Posted by ridethecliche
It'll fluff numbers by helping the rings, not the valves though, right? What I've seen written is that if it goes up by a lot then it's the rings, if it doesnt go up by a lot then it just proves us all right by saying that it was the valves as the leakdown indicated.
How much is a lot? What's your guess and what is it based on?
Do you not see the problem here? Do you not see how much better the info is from the leak down test?
Originally Posted by ridethecliche
Leakdowns are done on a cold motor so some of the things may be off.
If the motor has substantial leakdown, you can tell where the air is escaping by listening closely or feeling for air movement at the other spark plug holes or oil fill cap.
One thing to be careful of with leakdown tests is that the quick disconnects on the fittings often leak a little bit. On mine, you need to wiggle it around a bit to get it to seal. You can also easily end up with valves that are slightly stuck open on a piece of carbon -- when the motor is running it would just get blown out, but with it stopped it doesn't. You can work around that by turning the crank back and forth a bit while you've got a little pressure in the cylinder. Essentially, the leakdown tester is never going to give you a number that's too high, so I just fiddle with it while testing and record the highest number I see.
Spartan, I should clarify that I did it on a cold motor, but that's because I've seen it done on motors sitting on a stand when I looked up videos. I also can't really see myself taking the exhaust off on a piping hot motor and Google fu showed mixed results.
Soooo, did I do it wrong?
I took all the spark plugs out at the same time too. That wasn't wrong was it?
Womp.
Last edited by ridethecliche; 09-07-2018 at 07:57 PM.
Did the wet compression test. Cylinders 1, 3, & 4 went up to 175-180. Cylinder 2 went up to 160.
I added some more oil to cylinder 2 for the lulz and it came up to 175, which echoes what everyone was saying in that adding too much oil can give false readings. Point being pretty sure it's the valves at this point.
Calling this chapter closed for now. I have good baseline numbers for everything so that's that. Likely just going to run things as is till I have a reason not to.
Got ebc working today and going to start tuning that to hit 12 psi, then up it to 15 and finally 20. Going to take a while but I'm really hoping that I can get things tuned well enough to be running at 300, even if it's just for a couple of VD pulls. Car feels way faster now with EBC.... It's amazing what spool can do. I'm looking forward to running it at 12-14 and seeing if I can compare it to dyno of my old setup. My old laptop died so I'm crossing my fingers I have the files somewhere otherwise I'll just have to use images I've posted to compare.
Also got a check valve installed in line with the pcv.
Side note: friendly reminder that the car smokes after a wet compression test.. I scared the **** out of myself when I started the car in the garage!
Going back to the drawing board with the EBC tuning. It's been so long that I have to start totally from scratch. I've hit boost cutoff pretty hard with a few recent pulls so it's back to the drawing board. Starting here: https://www.miataturbo.net/megasquir...oop-ebc-94391/
Found the 'noise' from my EBC was between 10-55 at 19.5 hz. But it's time to jump back into setup mode and start all over again. Dang... I forgot how nice it was to have things dialed in on the old setup.
Used car weight 2400 and my weight 180. Pull was done in 4th gear with a 6 speed and 3.9. Hits 240kpa at about 4k rpm.
Need to optimize some more. I want to get the torque curve nice and flat, but I'm just about maxed out with the current 2.5 bar map sensor. I want to adjust the timing and vvt, but I think I need to rent dyno time if I want to do a decent job with the timing. I expected things to be a bit higher at 20 psi...I'm pretty content though.
09-07-2018, 01:19 PM
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