head gasket bore size - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 10-24-2008, 09:06 AM
GMR GMR is offline
Registered User
 
Last photo:
Join Date: Sep 2006
Location: florida
Posts: 290
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
head gasket bore size

Could someone explain the significance of head gasket bore size as it pertains to a street motor please (I understand it needs to be larger than the cylinder bore). For example, a particular head gasket for a sbc 265-400 with a compressed thickness of .040 can be had in bore size 4.060 or 4.165. If I have a 350 that is .030 over, which gasket should I use and why?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 10-24-2008, 10:06 AM
mrdreex's Avatar
Registered User
 
Last photo:
Join Date: Feb 2008
Location: TX
Posts: 316
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by GMR
Could someone explain the significance of head gasket bore size as it pertains to a street motor please (I understand it needs to be larger than the cylinder bore). For example, a particular head gasket for a sbc 265-400 with a compressed thickness of .040 can be had in bore size 4.060 or 4.165. If I have a 350 that is .030 over, which gasket should I use and why?
One thing that jumps right out is the fact you will have slightly higher (~.1) compression with the smaller bore size gasket.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 10-24-2008, 01:25 PM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 12,597
Wiki Edits: 326

Thanks: 701
Thanked 886 Times in 753 Posts
Quote:
Originally Posted by GMR
Could someone explain the significance of head gasket bore size as it pertains to a street motor please (I understand it needs to be larger than the cylinder bore). For example, a particular head gasket for a sbc 265-400 with a compressed thickness of .040 can be had in bore size 4.060 or 4.165. If I have a 350 that is .030 over, which gasket should I use and why?
What I do is measure the bore at the very top, where the machine shop has added a chamfer to facilitate starting the rings into the cylinder on assembly. I'll use a gasket with at least that diameter or larger. I don't want any gasket overhang into the bore to act as a hot spot to begin detonation. But I also don't want the gasket diameter so large that I create a "shelf" cavity between the bore and the head. Small spaces like that are a "dead zone" that will not light on ignition and will contribute to dirty emissions on a motor that has to conform to State requirements.

I might be all wet, but that's my take on it.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 10-24-2008, 07:06 PM
GMR GMR is offline
Registered User
 
Last photo:
Join Date: Sep 2006
Location: florida
Posts: 290
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thanks fellas.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 10-24-2008, 07:56 PM
Double_v23's Avatar
Horsepower Enthusiast
 

Last journal entry: Finished BMOD001FH
Last photo:
Join Date: Jul 2007
Location: Mooresville, NC
Posts: 1,495
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 4 Posts
The most important thing is to make sure the gasket bore is larger than the engine bore. A 4.060 gasket is used for anything up to a +.040 bore on a 350. The 4.165 you specified is for use on 400's with a bore of up to 4.155. (which is a .030 over 400)

If you have a gasket that is smaller than the engine bore the gasket will fail. The best idea is to find a gasket that is the right thickness and has a bore that is the closest to the actual bore of the engine without being smaller then the cylinder.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 10-25-2008, 10:48 AM
OHD's Avatar
OHD OHD is offline
Member
 
Last photo:
Join Date: Sep 2008
Location: outhouse
Posts: 285
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The 4.060 gasket
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 10-26-2008, 08:43 AM
GMR GMR is offline
Registered User
 
Last photo:
Join Date: Sep 2006
Location: florida
Posts: 290
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thanks Double_v23 and OHD.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 10-26-2008, 06:16 PM
engineczar's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2002
Location: In Flowbench nirvana
Age: 52
Posts: 1,630
Wiki Edits: 0

Thanks: 5
Thanked 43 Times in 40 Posts
Also measure the cross section of the combustion chamber and how it sits in relation to the bore. If it is larger than the bore of the gasket or is offset from the bore then you may need to run a larger bore head gasket. I've seen some heads that the chamber does sit outboard of the bore due to either core shift or machining tolerances. Just something more to check.
__________________
BSE Racing Engines
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 10-27-2008, 08:04 AM
GMR GMR is offline
Registered User
 
Last photo:
Join Date: Sep 2006
Location: florida
Posts: 290
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Good tip engineczar, didn't know that could happen, thanks.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may 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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
quench and head gasket smokin63 Engine 3 03-30-2008 08:21 PM
Master Cylinder Bore Size W/Hydroboost? krehmkej Suspension - Brakes - Steering 17 03-04-2007 05:06 PM
390 FE Blown head gasket: Thinking Man Engine 21 01-23-2007 06:31 PM
Head gasket question? GMW Engine 7 04-06-2006 01:37 AM
Bore size question 53LEDSLED Engine 5 05-12-2005 06:55 PM


All times are GMT -6. The time now is 03:07 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.