chevy 400 compresion ratio - 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 01-19-2007, 09:38 PM
mad55chevy's Avatar
cutouts and 7k shifts = cops
 
Join Date: Sep 2003
Location: boston
Posts: 60
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
chevy 400 compresion ratio

Hi,

I was wondering what it would take to knock back my compression to about 8.5:1 so I could screw on a procharger and run it at about 5-6 psi.

heads I am running now are Dart iron eagles w/ 215 cfm intake ports, and 72 cc chambers. pistons are speedpro H616p's, yeah, I know their hypereutectic's, but I'm not going to run big boost for now. I will change the pistons when I rebuild the motor later on. engine is .030 over, and I would run a much milder solid flat lifter cam than the .630 in. roller in it now.

Is there a head reccomendation that would knock the compression down to reach my goal, or do my pistons have me stuck here?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 01-19-2007, 10:43 PM
Registered User
 
Join Date: Apr 2006
Location: FL
Posts: 96
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
what compression do you have now?

i don't know those heads but the only way would be to open up the chambers on the heads and wack the tops off the pistons. if you've got 10to1 you'll need to lose 13cc some where to go down to 8.5to1.

best bet is to wait until you get new pistons.

edit sorry i did see where you asked for different heads. if you post what your compression is know i'll tell you what size chamber you need to look for.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 01-19-2007, 11:46 PM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 13,321
Wiki Edits: 326

Thanks: 839
Thanked 1,153 Times in 952 Posts
According to a chart on flatlander's, your c.r. is 9.99 with 72 cc heads. It also shows a c.r. of 9.62 with 76 cc heads, the largest that I know of for a small block. Looks like maybe there's a piston change in your future. Using the calculator on KB, with a bore of 4.155", stroke of 3.750", 72 cc heads, Chevrolet 10185054 head gaskets (4.166" X 0.041"), zero deck and 30 cc dish in the piston, you'd be at 8.498....that's about as close to 8.5 as I can figure for you.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 01-20-2007, 03:51 PM
xntrik's Avatar
Save a horse, Ride a Cowboy.
 
Last photo:
Join Date: Jul 2005
Location: Arkansas
Posts: 5,131
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Some people (Steve Dulcich) have had success with thick copper head gaskets. This usually necessitate a thicker or even 2 intake gaskets on each head.

It works. Since deep dish pistons don't have quench anyway,

the combustion effects seem to be ok by using a thick head gasket on a quench head.

That's what I would do.

Usually 5 psi is acceptable on 9/1 compression, especially with a centrifugal blower that is rpm dependent and does not build as much boost at lower rpms.

You might ask the blower companies for recommendations.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 01-20-2007, 04:18 PM
mad55chevy's Avatar
cutouts and 7k shifts = cops
 
Join Date: Sep 2003
Location: boston
Posts: 60
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
thanks guys.

the engine builder claims I am at 10.2:1, and the deck is .020, fyi. I think the head gasket is at .030 or .037.

Run 2 head gaskets?? really? I am curious if that would hold together for a couple of blasts down the track. hmm.

looking into building a bullet proof short block, but all I can find are 350's around here. I love the 400 cube SBC. it's got the torque down low to push my sled.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 01-20-2007, 04:30 PM
xntrik's Avatar
Save a horse, Ride a Cowboy.
 
Last photo:
Join Date: Jul 2005
Location: Arkansas
Posts: 5,131
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by mad55chevy
thanks guys.

the engine builder claims I am at 10.2:1, and the deck is .020, fyi. I think the head gasket is at .030 or .037.

Run 2 head gaskets?? really? I am curious if that would hold together for a couple of blasts down the track. hmm.

looking into building a bullet proof short block, but all I can find are 350's around here. I love the 400 cube SBC. it's got the torque down low to push my sled.
NO, NO, NO, I did NOT say that.

I said, thick copper headgaskets, which raise the head up off the block farther,

which also makes the heads farther apart,

which will necessitate thicker intake gaskets...... often 2 intake gaskets on each side. It is a put-it-on and measure the intake gap.


This has been done for years and gaskets are made for this purpose.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 01-20-2007, 04:51 PM
CNC BLOCKS NE's Avatar
CNC Blocks Northeast
 
Last photo:
Join Date: Sep 2006
Location: NORTHEAST
Age: 54
Posts: 1,491
Wiki Edits: 0

Thanks: 1
Thanked 21 Times in 21 Posts
Quote:
Originally Posted by mad55chevy
thanks guys.

the engine builder claims I am at 10.2:1, and the deck is .020, fyi. I think the head gasket is at .030 or .037.

Run 2 head gaskets?? really? I am curious if that would hold together for a couple of blasts down the track. hmm.

looking into building a bullet proof short block, but all I can find are 350's around here. I love the 400 cube SBC. it's got the torque down low to push my sled.
If your looking to build a bullet proof short block you may want to start with a Dart Or Bowtie block as we have seen over the years some 400 blocks that have not stood up very well and we have NOT seen the same problems with the Dart or the Bowtie blocks as those are Bullet proof compared to a stock GM block.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 01-20-2007, 10:47 PM
Registered User
 
Last photo:
Join Date: Jan 2007
Location: Baytown, Texas
Posts: 10
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
chevy 400 compresion ratio

I've built a few 383 with the help of a compression simulator found on this site http://cochise.uia.net/pkelley2/index.html
A blower motor will need to be designed from the crank up with attention to CR. Steel crank, forged dish pistons, stage 2 rods or better, blower friendly cam with less overlap, and a good flowing head with the right size CC.
I prefer to shorten the deck to minimize quench area that will help on pre-detonation that lets you run lower octain on higher compressions. I keep a minimum of .040 clearance for head to piston interference without any problems so far.
WORLD makes a good block that can go up to 427+ with the right parts.
Lots of $$$$$$ and lots of luck.
Arlo
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:
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
SBC 350 superiority rebuttle...was:POWERED BY CHEVY, WRITTEN ON A FORD, (from 'Engine Oldsmolac911 Hotrodders' Lounge 50 01-12-2011 11:00 PM
Chevy 350 to 400 trans combo Rockey Meo General Rodding Tech 5 09-14-2006 03:46 PM
Powerglide trans to 400 Chevy motor K9sicem Transmission - Rearend 3 07-09-2006 09:43 AM
XE274H cam sound like? Heads Choice? Help me decide on combo for chevy 400 Warrant Engine 10 03-01-2006 03:58 PM
chevy heads desireable for the rebuild of a 400 for my 3/4 ton 86 2x4. nh32u Introduce Yourself 4 12-17-2005 07:31 PM


All times are GMT -6. The time now is 02:14 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.