Should i deck the block for more compression? - 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 02-13-2012, 10:25 AM
Registered User
 
Join Date: Feb 2012
Posts: 22
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Should i deck the block for more compression?

Wondering if i should have the block decked to 0 deck height. Block is a late model truck block ('89) with eagle 383 rotating assembly -18cc dish 64 cc. Cam is a 235/249 .522/.509 107LSA @ .050. According to static compression calculator I'm right around 9.5 running a think head gasket .028. Car is intended for 91 pump gas street warrior. Dynamic compression says 7.4
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 02-13-2012, 12:59 PM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 12,259
Wiki Edits: 326

Thanks: 604
Thanked 769 Times in 659 Posts
Quote:
Originally Posted by 06-z0sick
Wondering if i should have the block decked to 0 deck height. Block is a late model truck block ('89) with eagle 383 rotating assembly -18cc dish 64 cc. Cam is a 235/249 .522/.509 107LSA @ .050. According to static compression calculator I'm right around 9.5 running a think head gasket .028. Car is intended for 91 pump gas street warrior. Dynamic compression says 7.4
An 0.028" gasket with zero deck will yield a squish figure of 0.028", a little tight and asking for trouble. Most fellows will shoot for 0.035" to 0.045" squish on a SBC, so if you're gonna cut the decks to zero, use a gasket that compresses to somewhere between 0.035" and 0.045".

Now, you can cut the block decks to 0.010" piston deck height and use the 0.028" gasket, for a total squish of 0.038" or you can cut the block decks to 0.015" piston deck height and use the 0.028" gasket for a total squish of 0.043". Or make up your own combination of piston deck height and gasket thickness, as long as they total 0.035" to 0.045", you will be doing all you can to eliminate detonation and have the motor operate well on pump gas.

For you fellows and gals who don't understand squish, it is the jetting across the chamber of the fuel/air mixture as it is squeezed from between the piston crown and the underside of the cylinder head as the piston comes to TDC. This "jetting" of the mixture across the chamber eliminates lean or rich spots and generally homogenizes the entire charge to that you get a full burn when the plug fires. Of course, you need a piston with a flat area on the crown in order to mate up with the underside of the head. Many pistons do not have enough flat area on the crown to work well. The best piston to use, in my opinion, is a Keith Black hyper with a D-shaped cup. Take a look at the generous flat area on the left side of the piston crown in this illustration......
http://www.kb-silvolite.com/kb_car/p...etails&P_id=93

Also, pay attention to the piston compression height when you are planning your build. You need to add up the piston compression height, the rod length and the crank radius (half the stroke) when you figure your static compression ratio and squish. You'll note that the compression height on the piston I linked is 1.433". If you add that to the rod length of 5.700" and the crank radius of 1.875", you arrive at a stack height of 9.008". If we measure the stock block deck height at 9.025" (the published deck height of the SBC block), then we could cut the block decks to 9.008" and the head gasket thickness would be the squish. You can count on the decks to be off by as much as 0.020" from the front of the block to the rear of the block or to the opposite cylinder on the other side of the block. Suffice to say that it will not be square unless it has been decked before by another owner.

Cutting the block decks while the block is registered on the main bearing saddle will also square the block up, so that the heads sit on the decks properly (not jacked up on one end because the block was improperly cut at the factory) and the intake manifold will come a lot closer to lining up and sealing properly. You will also be moving in a direction that will equalize the cylinder volumes and giving you the same static compression ratio across all 8 cylinders, assuming of course, that you cc the chambers and equalize them.
If all cylinders are not equalized, then you will find yourself tuning the motor for the worst cylinder, the one that's detonating.

Last edited by techinspector1; 02-13-2012 at 01:22 PM.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 02-13-2012, 03:55 PM
Registered User
 
Join Date: Feb 2012
Posts: 22
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Hey tech inspector thanks for the info! That is the exact piston that i will be using! D shaped ketih black piston with 18cc volume. Now what should i deck the block to if i use a gasket with a compressed thickness of .041" with 9.0cc compressed volume? I want to make this right for when i change heads over later to aluminum
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 02-13-2012, 05:24 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
not worth the work to pick up a little bit of compression. The power increase would be very little but the work would be a lot plus the cost for the machine work and a complete gasket set.

This is the type of thing you do before putting the engine together.

use a "compression increase power" calculator to see the power difference. it will not be much.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 02-13-2012, 07:18 PM
Registered User
 
Join Date: Jan 2011
Location: Walla Walla
Posts: 31
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
What 454c10 said.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 02-13-2012, 07:41 PM
Registered User
 
Join Date: Feb 2012
Posts: 22
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
so just leave the block at stock height for now?
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
zero deck the block ffcagle34 Engine 12 02-13-2012 03:41 PM
427 TALL DECK block icebreakr1969 Engine 20 10-07-2011 12:01 AM
Cleaning the block deck? v8hed Engine 24 03-22-2009 07:22 PM
Piston to deck clearance, and compression BourgD Engine 24 05-13-2008 06:36 AM
Deck Height, Compression Ratio, Head Gasket. KeithB123 Engine 4 03-04-2004 09:41 PM


All times are GMT -6. The time now is 05:45 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.