Welcome to the North American Subaru Impreza Owners Club Thursday December 25, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Built Motor Discussion

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 07-27-2008, 10:31 AM   #1
03wrxtreme
Scooby Specialist
 
Member#: 119041
Join Date: Jul 2006
Chapter/Region: South East
Location: Enterprise, AL
Vehicle:
2004 Subaru STi
WRB

Default #4 piston smoked? 100mm or 99.5mm

Well did a compression test and like so many others my #4 is smoked. Im assuming that the ringlands are cracked like everyone elses. My first question is for everyone with this problem, did you cylinder walls get jacked up. Im not sure if i should go ahead and order 100mm or 99.5s. Is there any cons with going with 100mms. Here is a list of what im getting. Do i need anything else.
CP pistons w rings
Eagle rods
cosworth main and rod bearings
ARP headstuds
Subaru gasket kit
* Registered users of the site do not see these ads.
03wrxtreme is offline   Reply With Quote
Old 07-27-2008, 02:13 PM   #2
methaddict
Scooby Specialist
 
Member#: 159738
Join Date: Sep 2007
Chapter/Region: SCIC
Location: Socal
Vehicle:
2004 WRB STi
Full Race TS, BW 8374 EFR

Default

To get the p/w clearances as accurate as possible go with 100mm and have the cylinders bored and honed to the recommended p/w clearance recommended by CP for your application.
methaddict is offline   Reply With Quote
Old 07-27-2008, 03:30 PM   #3
03wrxtreme
Scooby Specialist
 
Member#: 119041
Join Date: Jul 2006
Chapter/Region: South East
Location: Enterprise, AL
Vehicle:
2004 Subaru STi
WRB

Default

Thats what i was thinking too
03wrxtreme is offline   Reply With Quote
Old 07-28-2008, 12:53 AM   #4
jaimejrivera
Scooby Newbie
 
Member#: 112943
Join Date: Apr 2006
Default

I broke #4 ring lands as well. I rebuilt my engine with the exact setup your planning. I did the 99.5 CP pistons. My cylinder walls were ok and I didnt want to mess with my block. I was a bit concern about the machine shop getting it correctly bored.

Any way, the engine is running great and holding tight after 1 year. I doing 380 whp on a conservative tune.

Honestly, if your cylinder walls are ok... go with the stock size. By the way, your knock sensor will be hearing piston slack. I installed a Utec in order to turn down sensibility of the sensor and correct the timing curve. Stock ECU was pulling to much time at 5000 RPM.

Good Luck
jaimejrivera is offline   Reply With Quote
Old 07-28-2008, 01:17 PM   #5
kellygnsd
Scooby Guru
 
Member#: 32669
Join Date: Feb 2003
Chapter/Region: SCIC
Location: Rancho C
Vehicle:
2007 2.34LR, EFR7670
LINK G4 hybrid STi

Default

100mm would cover all bases as you can always make the bore bigger but if there is significant bore damage the only way to know would be to tear it down, inspect, and measure to see if you can still fit 99.5mm pistons. So to the short answer if you get the 100mm pistons they will work, 99.5mm might work for you. Shorter answer, Ask your builder.
kellygnsd is offline   Reply With Quote
Old 08-04-2008, 09:29 PM   #6
Innovative Tuning
NASIOC Vendor
 
Member#: 67958
Join Date: Aug 2004
Chapter/Region: Tri-State
Location: www.InnovativeTuning.com
Vehicle:
MY96 Time Attack
and 06 STI daily

Default

With CPs you'd have to go 100mm to get the proper clearance after you hone it so we'd get the block bored/honed for 100mm. We'd be happy to rebuild this for you. Your parts list is our stage 2+ rebuild. PM/Call/E-mail if interested.

-Mike
Innovative Tuning is offline   Reply With Quote
Reply

Thread Tools
Display Modes

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
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: CP Piston & Ring Bore 99.5mm for Subaru EJ255 & 257 2.5L T3H D0C Engine/Power/Exhaust 5 07-12-2010 11:08 AM
WTB: 99.5mm forged pistons.... 74KILLER Private 'Wanted' Classifieds 3 03-09-2007 10:58 PM
WTB: 99.5mm forged pistons.... 74KILLER Private 'Wanted' Classifieds 0 01-22-2007 08:50 AM
99.5mm JE pistons, Coated, Total Seal Ring conversion ImprezaRS dot com Rocky Mountains Impreza Club Forum -- RMIC 17 11-25-2003 03:43 AM
FS: spare new set of coated JE 99.5mm 8.5:1 pistons with Total Seal rings ImprezaRS dot com Private 'For Sale' Classifieds 4 11-02-2003 04:35 PM


All times are GMT -4. The time now is 05:34 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.