piston cr - 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 03-30-2005, 05:49 PM
Member
 
Join Date: Mar 2005
Location: kitchener, ont canada
Age: 39
Posts: 55
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
piston cr

having trouble finding a post or a method for determining an engines compression ratio. the engine rebuild was done several years ago and i can't recall what pistons cr i bought. however i seem to remember having the option of 9/-9.5/-10 : 1 ratios and knowing myself i'm sure i would have went for the 10's. these are 350 sbc .030 flat top pistons with 4 valve reliefs ontop. the heads are 64 cc and i'm wondering if (short of removing a piston) if there is a way to determine cr . for example by doing a cylinder compression test are there compression numbers that would typically equate to certain "ballpark" cr. anything at all. thanks for your time.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 03-30-2005, 06:11 PM
bracketeer's Avatar
489 Lemans
 

Last journal entry: Street Legal
Last photo:
Join Date: Dec 2004
Location: Courtenay, BC, CehNehDeh
Age: 55
Posts: 2,139
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
http://www.jepistons.com/pdf/2002-srp-chevy.pdf

10.3 to 1 compression with a 5.7 rod, .030 bore, 64 cc head, and 4 valve relief piston.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 03-30-2005, 06:27 PM
Member
 
Join Date: Mar 2005
Location: kitchener, ont canada
Age: 39
Posts: 55
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
piston cr

sorry, i was unclear before. how do i check to confirm that the pistons are 10:1 ratio. i was hoping to confirm the pistons and cr that i have. i am not 100% certain that they are 10:1 but that is what i thought i had. thanks again.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 03-30-2005, 08:55 PM
Max Keith's Avatar
Member
 
Last photo:
Join Date: Jul 2003
Location: Fort Madison,Iowa
Age: 66
Posts: 2,391
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
figuring compression ratio

First you need to know the compression height of your pistons, that is the distance from the center line of the wrist pin to the top of the piston.
Second is rod length.
Third the deck height of your block.
Subtract the total of 1/2 your stroke, the rod length, and compression height of your piston from the deck height of your block, which is the distance from the centerline of the crank to the deck of the block.
This will tell you how much unswept area you have in your cylinder.
Figure the displacement of the bore and thickness of your head gasket.
Find out the CC's of your valve reliefs.
Convert the volumn of your cylinder to CC's, as well as all the other dimensions.
Add all these figures together. If you are running a domed piston, subtract the CC's of the dome from the total of the unswept area.
Unswept area is that area left for combustion when the piston is at top dead center.
Generally, this applies to the valve reliefs, the difference between piston top and the deck height of the block, cylinder head gasket, and combustion chamber.
Divide the total figure by that of the unswept area, and you have the compression ratio.

IE: 350 CID engine (SBC for the Bow Tie brigade). (4 inch bore X 3.48 inch stroke)
1 cubic inch = 16.39 CC's.
One cylinder = 716.39 CC's
Head gasket (rough numbers) thickness = .050", diameter of cylinder hole, 4.1". = 10.8 CC's.
Combustion chamber size= 64CC's
Valve reliefs,= 6 CC's.
Cylinder relief ( rough guess0 .020" = 4.12 CC's.
716.39 + 10.8 + 64 + 4.12 = 795.31 CC's.
Divided by the unswept area, 10.8 + 64 + 4.12 = 78.92. = 9.08:1 compression ratio.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 03-31-2005, 06:13 AM
Hotrodders.com Moderator
 

Last journal entry: PICTURE TEST
Last photo:
Join Date: Jan 2004
Location: york pa
Age: 52
Posts: 2,795
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
pistons

If you did a cylinder psi test, and you could tell me where the cam was installed, per intake degrees i could get you close. But with out that info the only way to know is pull a head and CC everything.... Or find the part numder of the pistons you installed..

Keith
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
stroke to rod ratio jacobm99 Engine 28 12-16-2013 05:46 PM
383 vs 350 TheCiscoKid Engine 86 05-03-2008 03:10 PM
327 in 88 Truck pete379 Engine 101 01-19-2006 09:03 PM
longest rods in std deck 454 bbc?? deuce_454 Engine 11 01-30-2004 10:06 AM
Cam Help black66 Engine 3 05-12-2003 06:15 PM


All times are GMT -6. The time now is 01:13 AM.


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.