Welcome to the North American Subaru Impreza Owners Club Tuesday April 13, 2021
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
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.

* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Thread Tools Display Modes
Old 02-14-2021, 04:29 AM   #1
Scooby Newbie
Member#: 417103
Join Date: Mar 2015
Default Go boom or no?

I'm trying to figure out what head gasket thickness to make use of on my car- and I think I need a bit of help or a sanity check of my thinking.

I has a typical subaru head gasket issue + overheating ended up in a warped block and my first complete enginge reubuild on my own.

My machinist didn't keep a record of on how much was milled off the block or heads so I determined the depth of cut from the block as being 0,36 mm making use of the calculated piston (201mm - 39.5mm - 130.48mm - 30.71mm = 0.31mm pistons below deck) to deck height using dial indicators so I'm fairly sure its accurate. Im pretty sure 0,1mm was skimmed from the heads (again machinist didn't write it down), but I'm not sure how to determine that other than CCing the heads. Ideally I'd like the quench clearance and the compression ration to be close to stock as this motor will be abused on track, and I want to be able to drive it with the stock map.

I found a spreadsheet (http://www.submariner.org/thepno95/T...0-%202017.xlsx) that calculates CR, quench clearance and a variety of other metrics specifically for an ej 257. With no grinding to the head or the block it gives the following data with a stock 0.51mm gasket cr 8.37:1, quench clearance 0,84mm. The compression ratio of 8.37:1 seems awfully high compared to the quoted 8.2:1 I've seen in the Subaru factory manual. But does that really matter - I'm pretty sure that answer is no.

Essentially I shaved 0.46 mm off the mating surfaces, Most of that off the block (0,36mm). So 0.51mm (stock gasket) + 0.4mm to replace the amount material removed results in a 0.9-1,0 mm gasket.

If I plug that data (amount head and blocked shaved + plus a gasket of 0.9mm ) into the spreadsheet I end up with a CR of 8.4 and a quench clearance of 0.81 mm, Pretty damn close to the stock rating of cr 8.37:1 and quench of 0.84 on the stock motor.

So then finally the questions:
Do I need to 100% know that the head had 0,1mm taken off of it to proceed? - I'm pretty sure this is correct and the heads were in good shape and I asked him to take the minimum off. (deep down I know the answer is yes)

If not:
Am I good to go with this setup 0.9mm gasket?
Will fuel trims in the stock map be able to adjust the now slightly lean running engine due to bumped up CR?
* Registered users of the site do not see these ads.

Last edited by anon0mouse; 02-15-2021 at 10:24 AM. Reason: Clarity
anon0mouse is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.

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

All times are GMT -4. The time now is 03:19 AM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2021 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.