The vacuum test is just a roundabout way of checking compression. If you are directly measuring compression then I don't really see its usefulness.

Indeed. Best not to "get lost in the weeds" talking about vacuum...

I'd say a leakdown test is in order. ;)

I was just curious how it was related. As for your previous question, no it doesn't fluctuate. seems to stay pretty steady. I know while engine braking it pulls about 23-24"

Now to find time to do a leak down test...

Vacuum readings are a "constant" gauge on compression and that's why I like them. You can keep an eye on it without breaking out the tester but be careful as engine temperature and ambient conditions (temperature, pressure, altitude) all affect the vacuum reading.

If you have a good gauge (or monitor the MAP sensor) you can see a change in your average vacuum if compression drops and this is something you keep an eye on.

It was really interesting to be able to literally watch the compression come up in my new engine. When it was brand spanking new, it would only pull ~18inHg when fully warmed at idle. Over the first 400 miles, it slowly crept up to holding ~22inHg, and it has been steady for the past 1500 miles. Definitely a good indicator for if/when things start to go south.

My compression tested at 228/228/230/232 once it leveled out.

So i just broke 50,000 on my built motor and i did a compression test last night here are the results..

180
http://i206.photobucket.com/albums/b...ps2c7f3081.jpg
170
http://i206.photobucket.com/albums/b...psd33491fd.jpg
180
http://i206.photobucket.com/albums/b...ps06dd390b.jpg
180
http://i206.photobucket.com/albums/b...psa4254edc.jpg

did mine last night. sobering results
160
155
155
170

MS6
72k miles
1 full year BT
spraying meth for the past... 3-4 months?


I get ~21-22 in/mg

i've had "coolant issues" in the past where tube falls off, gets disconnected, shop that did clutch forgot to put coolant back in....
so my car has "overheated" about 3 times. I usually catch it way before the needle goes up to the top, thank god to Dashhawk and alarm set to 230*. But overheating is still no bueno. I'll attribute my shitty numbers to those instances.
Yeah leakdown test is coming up next.

MS3 - 68k miles. I'm pretty happy with my results, was fearing the worst.

170 - 170 - 160 - 160

It's unlikely you lost compression from hitting 230F coolant temps. If anything you might have a leaking head gasket from this but not compression problems.

I don't even think you have compression problems. Do you have excessive blowby? Consume oil? Did you crank until the needle stopped rising in all cylinders?

As these motors wear compression will fall off a bit but I think some of these lower numbers can also be attributed to the testing procedure and tester itself.

230F, not C. Silly Canadian.

My compression test numbers before buying the car:
190 - 165 - 150 - 175

I have noticed that since I started running 18PSI, it seems like I've been losing/burning more oil. Every fill up (about 1 week/200-250 miles), I lose about 1/4 of a quart of oil. I assume that is PCV related, since it only started happening after turning up the boost, but an OCC should put an end to that, if that's the case.

Clearly there is something up with cylinder #3 , but I have not done a leak down test. The car seems to run fine overall, maybe a slightly rough idle, but it also has not had the valves cleaned yet and needs a new VVT actuator/timing chain. It makes pretty good power, but @cld12pk2go; pointed out that I seem to be making lower numbers than he would expect. However, I'm also right on par with my old speed3 with the same mods in terms of crank horsepower, so I'm not too sure what to think.

Honestly, if anything, I expect it to be a cracked ringland. The oil loss and low compression point right at that. I will do a leakdown test sometime soon and try to figure it out. The best part? The dealership tech who did the test stated "the engine is in very good health" on the work order. It's pretty much outside of Mazda's specs even if you don't count the highest cylinder. It has received a healthy amount of beating over the last 3 months, so I may do a compression test next time I pull the TMIC, just to see if it has changed.

I figured as much about the headgasket, no sign of poopoo coolant in my oil.

I can't tell if i have excessive blowby because i only drive .8miles to work, I get a TON of water in my OCC so I have to drain it nearly weekly in the "winter" due to the milkshake machine I have going on in there.
The intake tract was never connected until I installed the Cobb prototype inlet hose, but I did have a crankcase filter, never absorbed any oil on it though. Doesn't look like the hose has anything in it really either, just a very thin film (light vapors?) inside.

After reading through the entire thread, i saw that some of you guys cranked up to 20 times... i think I only did 3 to 6 at the most. Even though it was levelling off pretty decently. Maybe I'll get a second tester to try this out again.

thanks for the input.

Check for head lifting.... does coolant come out of the over flow or past the cap after hard driving? when the car is cold start it up and see if the water shoots out of over flows really fast.....

Nope, none of that. I think something may have been a little off during the test. car is probably fine.

thanks though.

Guys and gals, cylinder 3 takes more cranking than the other ones to bring up the compression on the gauge. Don't just crank 3 times. Crank until the needle stops rising with foot to the floor (14-18 cranks) and all spark plugs out.

If you want to do a more thorough test do a leakdown.

the "gals" part was for me huh?

I stopped because friend said the needle stopped after about 6 cranks.

like i said, i'll try it out again and i'll be a little more thorough. we did this when going out to eat and decided to do it on a whim since he had the tester in his car. We were pretty hungry so maybe we were rushing a bit.

Still, they're within tolerance spec and arent horrible numbers, so i feel somewhat OK about that :)

180 180 150 180

cranked 3rd alot with hopes and dreams.

Oil in the intake?

Yessir.

:frown:

sorry to hear man..although not definitely a ringland at this point. I would check piston height next.

What is your oil consumption?

I don't really go through much, MAYBE half a quart every oil change (I do 3-4k miles rotella t6)

Don't have any clutch pedal vibes if you're alluding to a bent rod. Will do a height check though.

yeah it looks eerily like my compression results and mine ended up being a ringland. No idea what a slightly bent rod would look like as far as compression results go nor if it would cause vibes.

But you can drive indefinitely on a cracked ringland but NOT with a bent rod...IMO at least, so it's good to rule the rod out.

I cranked over the engine about 10-11 revolutions...

Compression check results:

Driver side to Passenger side (I forget the numerical order)

182-176-174-177

4.5% delta between max/min. I can live with that at ~500whp.

http://i77.photobucket.com/albums/j6...psde7696a8.jpg

I love these motors...

to measure for a bent rod could I just insert a metal rod into each cylinder and mark off where it exits the valve cover? Then see if the corresponding cylinders match? Or is this not accurate enough to diagnose a bent rod? Makes sense in my head but I don't have experience working on cars other than the speed :dunce:

That will do the trick if its bent enough...I went overboard and used a dial gauge b/c I could find no appreciable difference using a screwdriver, which just confirmed I didn't have a bent rod...lol

my anal retentive results can be found here.

http://www.mazdaspeedforums.org/foru...ml#post1662597

Well if the bent rod is ruled out, what does one do? My leakdown test was inconclusive and my compression test was 160 accross the board. I ruled out a bent rod by neasuring with a long piece of paintball macroline.

I figure might as well start VTA the crankcase and start prepping for rebuild or stocking out and trading in. :rolleyes:

Sent via smokey turbo.

afaik, you're looking for differences. I'd be happy with 160 across the board.

truth...having equal numbers is more important than what the actual number is.

160 might just be the tester used.

VTA the crancase still allowed me to make decent power and mileage but I could fill up my SSP can in a few minutes.

After I stocked out, the excessive blowby caused a misfire in cylinder #4 (from bent, burned valve) and the engine went to shit in a few weeks.

Sent via smokey turbo.

A bent or burned valve isn't going it cause blow by. What did the bent valve have to do with anything? You would just lose most of the compression in that cylinder.

The burnt valves just caused lots of smoking and oil consumption (45 psi). I suspect multiple broken ringlands causes the blowby, haha.

Sent via smokey turbo.

Ahh, I see. I didn't realize you had a bent valve and cracked ringlands. Sorry.

Anyways, I tried to do a compression test today, but the HF tester I bought was apparently DOA... Too bad I ordered it 5 months ago. The gauge just sat at zero while cranking. FUCK. So while I had the plugs out, I took some pictures and checked them out. Clearly something is going on in cylinder 3. The old plugs didn't look like this when they came out and I've only recently started losing oil, so I assume it has something to do with modifications and higher boost. Maybe a bad PCV valve? Anyways, here are the plugs:

http://farm9.staticflickr.com/8097/8...39de0885_b.jpg

http://farm9.staticflickr.com/8514/8...edab213b_b.jpg

http://farm9.staticflickr.com/8097/8...b001a546_b.jpg

http://farm9.staticflickr.com/8245/8...eabc4588_z.jpg

Did you put any anti seize on those plugs prior to instal?

why does #3 require more cranking?

Yes, on all of them. Why? There is a little antiseize on them in the pictures, but most of that is definitely oil.

Yeah, that is definately not a good sign ...

Yeah, it seems that whatever is happening was probably caused by me as the old plugs I pulled had little to no signs of oil contamination. I'm wondering if the PO(s) ran low octane gas most of its life and ended up damaging a ringland. Then I came along and cranked up the boost and timing and it finally gave. Not really sure at this point though. I guess I should start selling the aftermarkets parts I have accumulated to fund a rebuild. :ugh:

Personally I would run a vented OCC and then start saving up for the rebuild. I was able to run for almost 6 months like that and I had ridiculous amounts of oil going into the catch can. I would avoid selling all of your aftermarket parts since it is a pain to collect in the first place.