Look at my pistons - 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 11-08-2010, 12:58 PM   #1
Elite Member
Thread Starter
iTrader: (17)
 
Join Date: Aug 2007
Location: Fort Myers, FL
Posts: 2,790
Total Cats: 128
Default Look at my pistons

I pulled my stock 99 head off a couple days ago and wasn't all that excited about the way the pistons looked. My old motor looked brand new when it came apart but this one has a lot of carbon on it. Is this the result of a bad tune? Detonation? Any advise on what to change?

Stock 99 motor w/ 130k miles, gt2560 @ 12psi the last 5000 miles or so. I'm running lean at cruise, around 16:1 then it tapers down to 11.5:1 at full boost.



pdexta is offline   Reply With Quote
Old 11-08-2010, 01:05 PM   #2
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,833
Total Cats: 1,786
Default

there looks to maybe be det on the edges and middle of the piston tops.
Braineack is offline   Reply With Quote
Old 11-10-2010, 04:31 AM   #3
Newb
 
Join Date: Nov 2010
Posts: 24
Total Cats: 0
Default

grimy...
kevinism is offline   Reply With Quote
Old 11-10-2010, 07:22 AM   #4
Junior Member
 
Join Date: Oct 2008
Location: Manchester, UK
Posts: 274
Total Cats: 0
Default

How did your plugs look during the times of running this tune? Your spark would also be helpful for cruise and full boost. Do you run WI, intercooler etc?

I'm running 11.8:1 at full boost (only 7psi though a charger) but 15.5:1 at cruise. My plugs are a nice tan colour.
CRAIGO is offline   Reply With Quote
Old 11-10-2010, 08:47 AM   #5
Elite Member
iTrader: (12)
 
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 6,868
Total Cats: 66
Default

I'd take a coarse cloth and wipe the carbon off, that's the only way you'll really see the condition of the metal.

Mine went from-


EnginePiston3Flash by AnonymousNamelss, on Flickr

To this after a wipe down-


IMG_8350sm by AnonymousNamelss, on Flickr


I know I had a lot of carbon...from running rich and burning oil...and yes, the 01+ 10:1 comp. pistons are supposed to look like that. They don't have the nice machine marks like all the other 1.8/1.6 pistons. The only detonation are the very light pot marks on the right cylinder between the exhaust valves. The other piston is det. free.
Doppelgänger is offline   Reply With Quote
Old 11-10-2010, 10:45 AM   #6
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

I see detonation, maybe you should pull some spark or run a tick richer on cruise.
hustler is online now   Reply With Quote
Old 11-10-2010, 12:03 PM   #7
Elite Member
Thread Starter
iTrader: (17)
 
Join Date: Aug 2007
Location: Fort Myers, FL
Posts: 2,790
Total Cats: 128
Default

Quote:
Originally Posted by kevinism View Post
grimy...
That was my biggest surprise, when I pulled the motor out of my old car it looked almost new. I was concerned to see so much carbon junk.

Quote:
Originally Posted by CRAIGO View Post
How did your plugs look during the times of running this tune? Your spark would also be helpful for cruise and full boost. Do you run WI, intercooler etc?

I'm running 11.8:1 at full boost (only 7psi though a charger) but 15.5:1 at cruise. My plugs are a nice tan colour.
The plugs looked fine to me, but I'm no expert. I can post some pics later. Spark is 32-36 at cruise (depending on RPM) and tapers to 16 degrees at WOT. This is on 93 octane (which looks to convert to 98-99 on your side of the pond) so I don't think it's terribly aggressive. I've got an intercooler, no WI.

Quote:
Originally Posted by hustler View Post
I see detonation, maybe you should pull some spark or run a tick richer on cruise.
I'm putting in my '95 bottom end so hopefully the slight compression drop helps a bit. I think I am going to add a bit more gas at cruise though. Thanks for the input guys.
pdexta is offline   Reply With Quote
Old 11-10-2010, 12:21 PM   #8
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,653
Total Cats: 1,559
Default

I don't see evidence of detonation but it does look like you are burning oil. Dopple is right about removing carbon to really see what the pistons look like. What does your IM look like inside? Is it oily? Are you drawing oil through your PCV? Do the intake valve stems have carbon build up on them? Are you running adequate crankcase ventilation?

Carbon build up on your pistons will cause hot spots that will promote detonation.
sixshooter is offline   Reply With Quote
Old 11-10-2010, 02:58 PM   #9
Elite Member
iTrader: (11)
 
Join Date: Feb 2009
Posts: 2,982
Total Cats: 10
Default

Double check TDC. IF you aren't really at 10 degrees of timing when you set your MS to 10 degrees; You could end up with big problems. It looked like det to me, but if not, that's a lot of carbon for only 5k.
miatauser884 is offline   Reply With Quote
Old 11-10-2010, 03:11 PM   #10
Junior Member
 
Join Date: Oct 2008
Location: Manchester, UK
Posts: 274
Total Cats: 0
Default

I'm interested to find out for sure if it's det or not. I run 38-39* of timing during cruise and my boost is not as significant as yours at only 7psi but I also don't have a huge restriction in the exhaust path either
CRAIGO 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 57 07-19-2017 05:11 PM
OTS Bilstein to motorsports ASN conversion stoves Suspension, Brakes, Drivetrain 5 04-21-2016 04:00 PM
NEW-Wiseco Piston, K1 Rods, Supertech Valves & Spring/Retainer, TB&C pedals Rudes333 Miata parts for sale/trade 17 11-05-2015 02:16 PM
WTB Stock NB Pistons pdexta WTB 0 09-28-2015 12:18 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 09:03 PM.