Different Pistons - Does it need rebalanced? - 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> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 03-13-2013, 07:49 PM
S10 Racer's Avatar
http://www.warsprints.com
 

Last journal entry: W.A.R. (Wingless Auto Racing) Sprint Car Racing
Last photo:
Join Date: Nov 2007
Location: At The Dirt Tracks
Age: 55
Posts: 1,810
Wiki Edits: 0

Thanks: 3
Thanked 51 Times in 46 Posts
Different Pistons - Does it need rebalanced?

Hey guys,
Just got parts ordered for my motor. A little history is the rotating assy. was balanced in the old motor (383 SBC) and the crank and rods are going into the Dart SHP 4.125 block. The old pistons were KB 123 Hyper pistons that had been balanced. The new pistons going into the Dart block are SRP forged dome. My question is do you think I need to be concerned about any weight difference between the two pistons and is it necessary to have the assembly balanced again with the new pistons since the pistons are part of the reciprocating weight and not rotating weight?
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 03-13-2013, 08:03 PM
vinniekq2's Avatar
Registered User
 
Join Date: Jun 2012
Location: BC,Canada
Age: 56
Posts: 6,740
Wiki Edits: 0

Thanks: 236
Thanked 619 Times in 602 Posts
a bsolutely.
yes
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 03-13-2013, 08:43 PM
Landshark928's Avatar
FrankenPorsche
 
Last photo:
Join Date: Feb 2010
Location: Pensacola, Fl
Age: 45
Posts: 459
Wiki Edits: 0

Thanks: 0
Thanked 13 Times in 9 Posts
+1 on rebalancing
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 03-13-2013, 09:10 PM
spinn's Avatar
More dogs than bones
 

Last journal entry: This makes a huge difference
Last photo:
Join Date: Oct 2004
Location: midwest
Posts: 2,212
Wiki Edits: 0

Thanks: 0
Thanked 67 Times in 65 Posts
Yes its a good idea.

Define NEED and I can give you a better answer.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 03-13-2013, 09:22 PM
Semper Gumby
 
Last photo:
Join Date: Feb 2007
Location: Vancouver, BC
Posts: 329
Wiki Edits: 2

Thanks: 129
Thanked 105 Times in 86 Posts
Will it need to be all re-balanced?

No - For idle speed. Of course if it might someday be run above minimum idle speed then a complete rebalance is mandatory.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 03-13-2013, 09:55 PM
How fast is fast enough?
 
Last photo:
Join Date: Jun 2005
Location: St. Louis, MO
Age: 28
Posts: 8,236
Wiki Edits: 0

Thanks: 12
Thanked 220 Times in 205 Posts
A more accurate answer is- it depends. If there is significant weight difference between the pistons it can lead to a balance issue. If its not a large difference then it may not be noticed at all or only at low rpm. Most 350s on the road are not finely balanced, they just shoot for "good enough" and it works out just fine.

That being said there are cases where balancing has shown to increase power... There are also cases that shows balancing decreasing power so a case can be made for either side. A lot of race engines are intentionally overbalanced and a few that are under. Unfortunately there is no easy rule for deciding your case.

Find the weight difference and if its only a small amount then just run it as is.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 03-13-2013, 10:25 PM
1Gary's Avatar
Registered User
 

Last journal entry: 383 dyno sym
Last photo:
Join Date: Oct 2010
Location: Roch,NY
Age: 66
Posts: 1,445
Wiki Edits: 0

Thanks: 190
Thanked 145 Times in 131 Posts
I'm on the side of re-balancing.Many of the high dollar race piston set with floating pins so you can swap out pistons come in a set of ten so as to not effect the balance.I am saying for longevity of bearings balance is critical.It's not only at idle,but at the top end where unbalance is amplify or multiplied.

Back when I pounded balance pins into H/B'ers,the good enough factory spec was not even close to what guys did for their high performance application.I promise you all there are no Super Stockers running unbalanced.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 03-13-2013, 11:02 PM
BOBCRMAN@aol.com's Avatar
Member
 
Last photo:
Join Date: May 2002
Location: Holly, michigan
Posts: 7,951
Wiki Edits: 0

Thanks: 13
Thanked 218 Times in 207 Posts
Find out the weight difference. The new forgings will probably be lighter. Lighter is good. Up to ten grams light would be great. Called overbalancing.

Left turn racers do it all the time with no evil problems. Some engines love it.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 03-13-2013, 11:05 PM
S10 Racer's Avatar
http://www.warsprints.com
 

Last journal entry: W.A.R. (Wingless Auto Racing) Sprint Car Racing
Last photo:
Join Date: Nov 2007
Location: At The Dirt Tracks
Age: 55
Posts: 1,810
Wiki Edits: 0

Thanks: 3
Thanked 51 Times in 46 Posts
Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Find out the weight difference. The new forgings will probably be lighter. Lighter is good. Up to ten grams light would be great. Called overbalancing.

Left turn racers do it all the time with no evil problems. Some engines love it.
Yeah, we're left turn "dirt" racers for sure.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 03-13-2013, 11:13 PM
1Gary's Avatar
Registered User
 

Last journal entry: 383 dyno sym
Last photo:
Join Date: Oct 2010
Location: Roch,NY
Age: 66
Posts: 1,445
Wiki Edits: 0

Thanks: 190
Thanked 145 Times in 131 Posts
My opinion is there is a direct correlation between how well a engine is balanced and how fast it rev's.

The Super Modified's engines we have built are finely balanced.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 03-14-2013, 04:45 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 595 Times in 545 Posts
Quote:
Originally Posted by S10 Racer View Post
Yeah, we're left turn "dirt" racers for sure.
As has been said already, forged pistons are often lighter than cast. You have both piston assemblies- weight them both including rings and pins and see where you are.

See that the new pistons, wrist pins and rings all weigh very close to each other (static weight matched). Then calculate the difference in balance percentage by using the balance card from when it was originally balanced.

As a comparison, the difference of 1% under/over balanced on a reciprocating assembly weighing 1500 grams is 15 grams. So you have some leeway until you get anywhere near too far out.

BTW, often differences in reciprocating weight can be corrected by just using different pins.
Reply With Quote Quick reply to this message

Recent Hotrodding Basics 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
do you know what pistons i have? ralph hart Engine 1 10-10-2005 06:12 PM
pistons 78 chevy truck Engine 2 10-22-2003 06:00 PM
ID these pistons please. HemmiGremmie Engine 1 10-13-2003 10:02 PM
Do I need to have my 383 stroker rebalanced if I replace the balancer? Rodrunner Engine 1 07-03-2003 05:15 AM
Pistons DoubleVision Engine 7 04-24-2003 04:57 PM


All times are GMT -6. The time now is 04:23 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.