Welcome to the North American Subaru Impreza Owners Club Friday March 29, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Technical > Subaru Conversions

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.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 01-17-2005, 09:26 PM   #1
harvcharg
Scooby Newbie
 
Member#: 79738
Join Date: Jan 2005
Default Want to use 2.5 single over head pistions in a 2.5 dual over head cam motor.

Hi i have a 97 legacy outback with a dual overhead cams. You know after a while you get the pistion noise. well i have a set of 2.5 single overhead cam pistions. i was woundering if they will work in the dual over head cam moter without the pistions hitting the valves? i know the dual over head cam pistions have the square indentation on the top of the pistion. and the single over head came pistions have the small slots for the valves on top of the pistions. has anybody tried this swap or know if it will work. i am worried the the valves will hit the pistions. what do you guys think? I also know the compression will be higher. would it be so high that i would have to run 94 octain in it all the time? please let me know what you think. thanks Jim.

[email protected]
* Registered users of the site do not see these ads.
harvcharg is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 01-17-2005, 09:32 PM   #2
jamesfacts
Scooby Guru
 
Member#: 51282
Join Date: Dec 2003
Chapter/Region: SCIC
Location: Pasadena, CA
Vehicle:
98 RS
black & blue from parking

Default

They will certainly work... but I think it will be more trouble wiring than its worth.
jamesfacts is offline   Reply With Quote
Old 01-17-2005, 10:38 PM   #3
Quibron
Scooby Newbie
 
Member#: 77220
Join Date: Dec 2004
Chapter/Region: NESIC
Location: Meriden,CT
Vehicle:
2000 2.5rs Turbo
silver

Default

It wont work, the comp height is way different. However I just happen to have a brand new set of JE lo compression pistons for your dual overhead cam motor.
Quibron is offline   Reply With Quote
Old 01-17-2005, 11:19 PM   #4
Scoobie Steve
Scooby Specialist
 
Member#: 2289
Join Date: Sep 2000
Chapter/Region: Tri-State
Location: Bangor, PA
Vehicle:
1998 11.87@112mph
Subaru L Ver 6 STi Type R

Default

Quote:
Originally Posted by Quibron
It wont work, the comp height is way different. However I just happen to have a brand new set of JE lo compression pistons for your dual overhead cam motor.
I wouldnt say it wont work. The phase I pistons have a compression height of 1.190 and phase II 1.160. Thats a difference of .030. Now the phase I HG has a thickness of .060 and the phase II .023 difference of .037. If you put the Phase II pistons on Phase I rods the combo will have a neg deck height of -.030 (assuming stock deck height is 0.000) So by using a Phase 2 HG you will decrease the Quench height by .037 and actually increase the CR very slightly.
Scoobie Steve is offline   Reply With Quote
Old 01-18-2005, 01:31 AM   #5
Storm
Scooby Guru
 
Member#: 5218
Join Date: Mar 2001
Chapter/Region: MWSOC
Location: SAUL'S Motorsports
Vehicle:
96L Most Over-
Developed Beater

Default

But the phaseI pistons clear the deck @TDC. I don't remember by how much, but I can measure the amount when I get home from work. I was going to do the same thing, but decided to use a phaseII shortblock with my DOHC pistons and .027 headgaskets. The result is the need to run 94 octane...... I'm looking at north of 11.5:1 CR....

The safest way would be to install the pistons and put some clay on them prior to testfitting the heads to make sure you don't have any problems.

Americanyouth: None of my pistons have wiring....do yours?

Jay Storm
Storm is offline   Reply With Quote
Old 01-18-2005, 09:11 PM   #6
harvcharg
Scooby Newbie
 
Member#: 79738
Join Date: Jan 2005
Default will 2.5 dual over head cam heads fit a 2.5 single over head cam block?

I have a 97 legacy with a blown block. the engine has dual overhead cams. I have a 2.5 single over head cam block. will the dual over head cam head fit the single overhead cam block? will i have any interfearence with the valves hitting the top of the pistions because the domes are different? pleas let me know if this swap has ben done before and is there anything i need to know about the swap if it works. thanks Jim

[email protected]
harvcharg is offline   Reply With Quote
Old 01-19-2005, 02:31 AM   #7
Storm
Scooby Guru
 
Member#: 5218
Join Date: Mar 2001
Chapter/Region: MWSOC
Location: SAUL'S Motorsports
Vehicle:
96L Most Over-
Developed Beater

Default

This should be a seperate thread.
Quote:
Originally Posted by harvcharg
I have a 97 legacy with a blown block. the engine has dual overhead cams. I have a 2.5 single over head cam block. will the dual over head cam head fit the single overhead cam block? will i have any interfearence with the valves hitting the top of the pistions because the domes are different? pleas let me know if this swap has ben done before and is there anything i need to know about the swap if it works. thanks Jim

[email protected]
It will work. A few of us are doing just this. The CR goes up above 10:1 because the chamber is smaller on the DOHC. It's been calculated at around 11.4:1CR. It goes up if the heads have been resurfaced....like mine have. I have to run 94 octane to keep the ECU happy, and I am thinking of raising the idle to 850-900 to keep the ECU happy. Look here for more info:
http://forums.nasioc.com/forums/showthread.php?t=689708
and here:
http://forums.nasioc.com/forums/showthread.php?t=386462


Jay Storm
Storm is offline   Reply With Quote
Old 01-19-2005, 06:16 AM   #8
harvcharg
Scooby Newbie
 
Member#: 79738
Join Date: Jan 2005
Default gas octain

I do have to send the heads out. I think i would get a ping with the cheap gas correct? also if i look the heads over and decide i dont have to send the heads out will i still have to run high octain gas? this car is for my mother and you know how gas prices are. i am also trying to save some money. By the way how mutch are those pistions you have for sale?
harvcharg is offline   Reply With Quote
Old 01-19-2005, 02:26 PM   #9
jamesfacts
Scooby Guru
 
Member#: 51282
Join Date: Dec 2003
Chapter/Region: SCIC
Location: Pasadena, CA
Vehicle:
98 RS
black & blue from parking

Default

Quote:
Originally Posted by Storm
Americanyouth: None of my pistons have wiring....do yours?

Jay Storm


No, but my heads do. I thought he was going to swap heads instead of the shortblock for some reason.


To the OP: yes, you will probably need at least mid-grade gas.
jamesfacts 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
Want to use dual AVCS heads that are on my longblock in my wrx Wagonkenny Built Motor Discussion 27 03-23-2010 10:37 AM
I don't want to be the only person with this stuck in my head (mp3 link inside) Kaiser Off-Topic 17 12-19-2006 04:18 PM
I want to melt down every single 1/4 mile track in this country. rogue Off-Topic 38 11-17-2006 09:33 AM
Photomamographers! My college wants to use my photograph in a display.... Protege Menace Off-Topic 134 07-31-2006 03:48 PM
Anyone want to use a private game server for 5 hours (only select games) drkwtsn Off-Topic 17 07-13-2005 11:15 AM

All times are GMT -4. The time now is 06:27 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.