Big block hemi and boost guys - Hot Rod Forum : Hotrodders Bulletin Board -- 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
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 12-11-2008, 08:26 PM
Join Date: Mar 2003
Location: Alabama
Posts: 165
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Big block hemi and boost guys

To my knowledge you can build a boost motor @ 9:1 compression. Even higher sometimes like the new vettes. But anyways I know a guy who ordered a 472 Hemi crate motor 9:1 compression and he says he cannot boost the motor because it is 9:1. My thought is that any motor can get it, just how much can be the difference. He says that he called the company he purchased the motor from and the say NO WAY.. He would have to o ring the heads and change the pistons for lower compression. All the bottom end of this motor is forged. It is iron headed and the 525 horse version.
What are your guys opinions?

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 12-11-2008, 09:18 PM
8-71 blown 461 Rat on E85
Last photo:
Join Date: Jan 2008
Location: Detroit michigan
Posts: 59
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I am not a big fan of forced induction atop a engine designed to operate naturally aspirated.Of course the iron head hemi @ 9/1 would survive with a few lbs of boost..but does it have a blower friendly cam,increased top ring gap,3 angle ss valves..preferably inconels on the exhaust side??
Probably not..that is why the builder is steering your buddy to a n/a setup.
yes to your question tho..a few lbs of boost from an undriven 6-71 would not be harmfull and sure as heck does not need o-ringing.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-12-2008, 01:33 AM
camaroman7d's Avatar
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 48
Posts: 2,246
Wiki Edits: 0

Thanks: 3
Thanked 10 Times in 10 Posts
Fatblock is on the money. If you want a blown enine that performs build the engine for it. Far to many people throw blowers on engines that aren't set up correctly and then wonder why it runs hot or doesn't make any power. For an engine of that size it would need a minimum of an 8-71. Ideal compression is 7.5-8.5:1 sure, he can run a blower with 9:1 but, as Fatblock mentioned he will only be able to run a few lbs of boost not really worth the $5000 it's going to cost to put a blower on it.

O rings are not needed. To be honest these days with MLS head gaskets you very rarely would need to O ring a block/heads for any application.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-12-2008, 02:26 PM
OHD's Avatar
OHD OHD is offline
Last photo:
Join Date: Sep 2008
Location: outhouse
Posts: 285
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The clearances are more on blown motors bearings, ring gaps, and the cam is different. Just to name a few.

Comp for a blown motor on gas runs from 6.5 to about 8 to 1 depending on the amount of boost and speed the blower is driven. Once the static compression gets over 13-13.5 to 1, oring. MLS gaskets will not hold it.

Multiply the blowers first number(s) by the 71 to determine what size the motor was it was built to feed. That was at low rpm of about 2K. IE 4X71 6X71... 10X71 14X71.......

Determine your engines air needs at the rpm level it will run and size the blower to those numbers. Larger slows the needed blower speed down and saves hp and heat levels. Just remember it takes major HP to spin a blower at high speeds....

PLUS, there are also MAJOR differences between street forged parts and blower forged parts. IE a street cheapie forged crank runs 7-800 bucks, a pro forged crank runs 2500-3800.....THAT IS JUST THE CRANK.......

The cheapie PARTS installed in a street type motor are NOT for blown applications and will turn that 14K Hemi into 500 bucks of scrap, real quick.

Last edited by OHD; 12-12-2008 at 02:39 PM.
Reply With Quote Quick reply to this message

Recent Engine posts with photos
Gear in this thread - Powered by O'Reilly Auto Parts

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


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

All times are GMT -6. The time now is 08:14 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright 1999 - 2012. All Rights Reserved.