Pre-boost compression/leakdown test results - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 09-09-2012, 11:54 PM   #1
Senior Member
Thread Starter
iTrader: (7)
 
RedCarmel's Avatar
 
Join Date: Oct 2011
Location: Horse and Buggy, PA
Posts: 689
Total Cats: 18
Default 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.
RedCarmel is offline   Reply With Quote
Old 09-10-2012, 11:42 AM   #2
Slowest Progress Ever
iTrader: (26)
 
thirdgen's Avatar
 
Join Date: Oct 2007
Location: The coal ridden hills of Pennsylvania
Posts: 5,812
Total Cats: 184
Default

Quote:
Originally Posted by RedCarmel View Post
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.
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?
thirdgen is offline   Reply With Quote
Old 09-10-2012, 11:49 AM   #3
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,892
Total Cats: 1,792
Default

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.
Braineack is offline   Reply With Quote
Old 09-10-2012, 12:34 PM   #4
Senior Member
Thread Starter
iTrader: (7)
 
RedCarmel's Avatar
 
Join Date: Oct 2011
Location: Horse and Buggy, PA
Posts: 689
Total Cats: 18
Default

Quote:
Originally Posted by thirdgen View Post
To correct the above quote, the air wasn't coming out of the intake, it was coming out of the valve cover breather.
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.
RedCarmel is offline   Reply With Quote
Old 09-10-2012, 12:46 PM   #5
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,892
Total Cats: 1,792
Default

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.
Braineack is offline   Reply With Quote
Old 09-10-2012, 12:52 PM   #6
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

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.
JasonC SBB is offline   Reply With Quote
Old 09-10-2012, 01:04 PM   #7
Slowest Progress Ever
iTrader: (26)
 
thirdgen's Avatar
 
Join Date: Oct 2007
Location: The coal ridden hills of Pennsylvania
Posts: 5,812
Total Cats: 184
Default

Quote:
Originally Posted by Braineack View Post
when I do leakdowns I like to slightly move the crank +/- a degree or two to make sure the valves are sealed.
I did that, thinking the same thing as you.

Quote:
Originally Posted by Braineack View Post
there's no way you have 50% leakdown and those compression numbers.
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.
thirdgen is offline   Reply With Quote
Old 09-10-2012, 11:38 PM   #8
Senior Member
Thread Starter
iTrader: (7)
 
RedCarmel's Avatar
 
Join Date: Oct 2011
Location: Horse and Buggy, PA
Posts: 689
Total Cats: 18
Default

So I'll just go ahead and boost then.
RedCarmel is offline   Reply With Quote
Old 09-11-2012, 01:07 AM   #9
Slowest Progress Ever
iTrader: (26)
 
thirdgen's Avatar
 
Join Date: Oct 2007
Location: The coal ridden hills of Pennsylvania
Posts: 5,812
Total Cats: 184
Default

That's the spirit!!!
thirdgen is offline   Reply With Quote
Old 09-11-2012, 01:35 AM   #10
Junior Member
iTrader: (6)
 
Join Date: Nov 2010
Location: Three Rivers, Ca
Posts: 176
Total Cats: 4
Default

Quote:
Originally Posted by RedCarmel View Post
So I'll just go ahead and boost then.
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.
RayinNorCal is offline   Reply With Quote
Old 09-11-2012, 08:56 AM   #11
Senior Member
Thread Starter
iTrader: (7)
 
RedCarmel's Avatar
 
Join Date: Oct 2011
Location: Horse and Buggy, PA
Posts: 689
Total Cats: 18
Default

Quote:
Originally Posted by RayinNorCal View Post
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!
RedCarmel is offline   Reply With Quote
Old 09-11-2012, 09:17 AM   #12
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,892
Total Cats: 1,792
Default

Quote:
Originally Posted by RedCarmel View Post
So I'll just go ahead and boost then.
MOAR BOOST!
Braineack is offline   Reply With Quote
Old 09-11-2012, 11:00 AM   #13
Senior Member
Thread Starter
iTrader: (7)
 
RedCarmel's Avatar
 
Join Date: Oct 2011
Location: Horse and Buggy, PA
Posts: 689
Total Cats: 18
Default

Quote:
Originally Posted by Braineack View Post
MOAR BOOST!
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.
RedCarmel is offline   Reply With Quote
Old 09-11-2012, 11:44 AM   #14
Slowest Progress Ever
iTrader: (26)
 
thirdgen's Avatar
 
Join Date: Oct 2007
Location: The coal ridden hills of Pennsylvania
Posts: 5,812
Total Cats: 184
Default

I should use klotz in my fuel so my exhaust smells like my buddies intoxicating motocross bike.
thirdgen is offline   Reply With Quote
Old 09-11-2012, 05:16 PM   #15
Junior Member
iTrader: (6)
 
Join Date: Nov 2010
Location: Three Rivers, Ca
Posts: 176
Total Cats: 4
Default

Quote:
Originally Posted by RedCarmel View Post
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!
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. :-)
RayinNorCal is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 Today 09:00 PM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM
3rd Time's a Charm...hopefully. zephyrusaurai Meet and Greet 2 09-28-2015 11:59 PM
Are my coils failing? viriiguy General Miata Chat 5 09-28-2015 08:39 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 11:37 PM.