Piston selection 377 - Page 2 - 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
  #16 (permalink)  
Old 11-14-2012, 01:55 PM
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 377MONTE View Post
cobalt,

why am i under the impression that dish pistons are second best? maybe I am mistaken, but i figure lower compression by a whole ratio, maybe even more, would equal less power? Are my 450+ hp/tq goals still realistic with dish pistons?
The piston dish or dome volume is a means to an end. You need to lower the CR. Your choices are a larger combustion chamber, a larger dish volume, or both. There are a few heads available w/larger chambers than 64cc. But in the beginning you had specified cast iron heads having 64cc chambers, so the recommendations reflect that. That said, I hope you have the newer Platinum castings.

Using an inverted dome or D-cup piston places the dish over the deep part of the chamber, which maximizes the quench effect (there's an echo in here! lol). This is an important consideration because good quench action is the same thing as raising the octane of the fuel you burn in that the propensity for detonation is lowered in either case.

Good quench is sometimes referred to as "mechanical octane". This is why we do not recommend the factory-type round dish pistons- they do not offer as good a quench action. This is also why using thick head gaskets or lower compression height pistons is not such a good idea, unless they allow a quench in the area of 0.040" (distance from the block deck down to the toop of the piston at TDC, more on quench here).

Now you are correct in thinking that compression IS worth power. The generally accepted rule of thumb says there's about a 4% change in hp per number. So going from 8:1 to 9:1 on a 400 hp engine will add 16 hp. This is a relatively small gain to chance having problems w/detonation because the compression ratio is too high. If you have to retard the timing to prevent detonation, you will lose FAR more power and economy than you will by simply building the engine w/a lower CR to begin with. Since you have your choice of pistons, now is the time to build it using parts optimized for the application. You can thank us later.

Oh, and 450 HP is totally doable w/dished pistons and the right heads.

Last edited by cobalt327; 11-14-2012 at 02:02 PM.
Reply With Quote Quick reply to this message
The Following User Says Thank You to cobalt327 For This Useful Post:
techinspector1 (11-15-2012)
Sponsored Links
Advertisement
 
  #17 (permalink)  
Old 11-14-2012, 05:52 PM
hcompton's Avatar
Old & Furious
 
Join Date: Oct 2012
Location: MD
Age: 41
Posts: 1,074
Wiki Edits: 0

Thanks: 6
Thanked 87 Times in 84 Posts
16% is very low. I cant see you only make 16 more hp going from 8:1 to 9:1 its worth almost a 100 hp on a big v8 as long as everything is tuned for the upgrade. Heads, cam and carb. You can see this very clearly on chevy 454 engines over the years. When the compression goes down the hp drops off in gobs. Lower compression engines use less gas so its common for mfg. to lower cr to gain mpg in the 70, and 80's it made the cars slow as dirt and still didnt solve the issue. Smaller high compression engines are used now cause of its drastic effect on power output and effency(VE).
Reply With Quote Quick reply to this message
  #18 (permalink)  
Old 11-15-2012, 09:52 PM
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
You also have to remember that during the same era that CR was being lowered, the factories went to net power ratings.

As far as the validity of 4%, YMMV and that's fine w/me.
Reply With Quote Quick reply to this message
The Following User Says Thank You to cobalt327 For This Useful Post:
techinspector1 (11-15-2012)
  #19 (permalink)  
Old 11-16-2012, 06:27 AM
1Gary's Avatar
Registered User
 

Last journal entry: 383 dyno sym
Last photo:
Join Date: Oct 2010
Location: Roch,NY
Age: 66
Posts: 1,461
Wiki Edits: 0

Thanks: 192
Thanked 145 Times in 131 Posts
Quote:
Originally Posted by cobalt327 View Post
You also have to remember that during the same era that CR was being lowered, the factories went to net power ratings.

As far as the validity of 4%, YMMV and that's fine w/me.
YMMV??.
Reply With Quote Quick reply to this message

Tags
377, 383, piston, sbc, stroker

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
Piston Selection AGABE Engine 4 12-31-2011 11:26 PM
Piston Selection 31fordcoupe Engine 11 08-02-2009 05:04 AM
Piston Selection - need advice blndweasel Engine 19 03-26-2008 09:17 PM
piston selection question malibu68 Engine 6 05-16-2007 11:02 AM
Piston Selection machine69 Engine 4 05-09-2004 10:55 AM


All times are GMT -6. The time now is 03:37 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.