How much HP is gained for each increased point of 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 12-07-2004, 03:49 PM
Member
 
Join Date: May 2004
Location: Miami
Age: 37
Posts: 85
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Question How much HP is gained for each increased point of compression?

If I'm going from 9.8:1 to 11.1 how much HP gains am I looking at?

Also is there a special cam needed for higher compression? Would I be able to run my current cam and set-up on 93 octane?

Pontiac 455 bored .040 over
Edelbrock Performer intake
Comp XE Cam 240/256 507/510 LSA10
2600 stall,
750 holley, vac snd
stock 6x-8 heads, 3 angle valve job (going to 6x-4 which is going to increase the compression)
stock bottom end
373 gears.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 12-07-2004, 04:40 PM
firestone's Avatar
http://teamrfc.gospelcom.net
 
Last photo:
Join Date: Nov 2003
Location: Fenton MI
Age: 32
Posts: 1,743
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
From what I have heard, you can assume around 20 hp per point of compression. This is just an estimate, and will vary. As far as you combonation running on pump gas, the only way that you will have any chance is if you are going to be running aluminum heads, and your quench is right (distace from top of piston to deck of head, should be around .045).

Adam
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-07-2004, 04:47 PM
stepside454's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: St. louis area
Age: 47
Posts: 1,074
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
it depends on the rest of the combination....lower RPM engines will have less impact than higher RPM engines as far as total increase in power.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-07-2004, 06:19 PM
Max Keith's Avatar
Member
 
Last photo:
Join Date: Jul 2003
Location: Fort Madison,Iowa
Age: 66
Posts: 2,391
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
how much hp?

How much gain for each increase in ratio depends on the engine, how its built, head design, etc. There is not hard fast rule on it.
Higher compression shows its greatest effects at higher rpm, where the breathing time is much shorter, and cylinder filling isnt quite so good.

With your engine setup, cam wise, you will probably see some good gains from going to the higher compression. The biggest concern is whether you can run that high on 93 octane, due to other factors like combustion chamber size, etc.
Around these parts, with a steel head engine, about the maximum anyone is running with any big blocks (427 and up) is about 10-10.5:1. Thats with a heavy cam and steel heads.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 12-07-2004, 06:35 PM
Mad Maggot's Avatar
The lean mean donut machine
 
Last photo:
Join Date: Aug 2004
Location: Red Deer, Alberta, Canada
Age: 31
Posts: 386
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
compression increases also help with large cams in the lower RPM ranges. It helps when the overlap is hurting performance... More compression from a diminished charge will feel like the cylinder is filled more completely than at a lower compression level. It will make large cams seem less radical or enable engines to operate more smoothly at lower RPM. It will also help torque and vacuum slightly as well.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 12-07-2004, 06:43 PM
lluciano77's Avatar
Short changed on common sense
 
Last photo:
Join Date: Jun 2003
Location: california
Age: 37
Posts: 3,548
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I can't remember the exact specs. I have it written down somewhere. The way it works is you get 4% more power each point from 7:1 to 10:1. From there each additional point nets around 2%. I know that is close enough for what you are asking. If you want I can go digging through the archives and get the article, but I am in the ballpark.

You can't say how much hp. Every engine will gain more or less. That is why it is more accurate with a % of hp.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 12-08-2004, 07:28 AM
Member
 
Join Date: May 2004
Location: Miami
Age: 37
Posts: 85
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thanks for all the replies thanks to everybody for the great help...
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 12-09-2004, 01:15 PM
Member
 
Join Date: May 2004
Location: Miami
Age: 37
Posts: 85
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Just wanted to know if it is possible to run this set-up on pump gas 93 octane?
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 12-09-2004, 03:14 PM
Member
 
Join Date: Aug 2003
Location: calgary canada
Posts: 727
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thats gonna be very border line for sure you may have to knock back the timing a bit on pump gas which will take away any gains you made from the increased compression.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 12-09-2004, 05:26 PM
camaroman7d's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 47
Posts: 2,245
Wiki Edits: 0

Thanks: 3
Thanked 9 Times in 9 Posts
Robinson Robin, I think you hit the nail on the head. With iron heads and 11:1 it is not going to run on pump gas (and if it does it won't for long). You honestly need to be in the area of 9.5-10:1 to run iron heads on pump gas (I think that's about the practical max). The slight gain you "might" get from 10:1 to 11:1 will be negated with reduced timing and broken parts.

Royce
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 12-09-2004, 05:58 PM
killerformula's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Carburetor
Last journal entry: Clean up
Last photo:
Join Date: Oct 2003
Location: Northeast
Age: 34
Posts: 3,485
Wiki Edits: 3

Thanks: 13
Thanked 27 Times in 18 Posts
Bah humbug!!! lol. ANyway I run about 10.5 or 11:1 on the street. I admit I have had someproblems with spark knock, but I think I've got them taken care of, and we noticed the plugs to look a bit lean, so it needs a bit more fuel anyway. That coupled with a new set of 3.73 gears in leu of the 2.73, and I think I'll be fine. It depends a lot on the car and the conditions. I wouldn't want an 11:1 truck motor that will be towing a boat, but in a car, you're much better off. I run 93 and some marvel mystery oil, but I also admit that I've had to come down to that from mixtures of 110. I also haven't CCed my heads, so... who knows. But I think it can be done...

K
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 12-09-2004, 07:39 PM
67 Deuce 4 Me's Avatar
Bowtie or Die!
 
Last photo:
Join Date: Dec 2004
Location: TN
Age: 43
Posts: 637
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I read somwhere that 1 point increase in comp usually nets an average of 15 hp. I have no proof. But I did read it somewhere in a pile of my old mags.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 12-09-2004, 07:57 PM
lluciano77's Avatar
Short changed on common sense
 
Last photo:
Join Date: Jun 2003
Location: california
Age: 37
Posts: 3,548
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by camaroman7d
Robinson Robin, I think you hit the nail on the head. With iron heads and 11:1 it is not going to run on pump gas (and if it does it won't for long). You honestly need to be in the area of 9.5-10:1 to run iron heads on pump gas (I think that's about the practical max). The slight gain you "might" get from 10:1 to 11:1 will be negated with reduced timing and broken parts.

Royce
I have said it a million times now. My 400 is 11:1 with iron heads and 91 octane gas. My timing is set at 18o initial and 16o mechanical.

What you gain from 10: to 11:1 is more vacuum, better throttle response, better gas mileage, and more power.

You have to do your homework before attempting to go over 10.5:1.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 12-10-2004, 12:42 AM
camaroman7d's Avatar
Member
 
Last photo:
Join Date: Dec 2003
Location: Vacaville, California
Age: 47
Posts: 2,245
Wiki Edits: 0

Thanks: 3
Thanked 9 Times in 9 Posts
lluciano77,
How did you calculate your compression ratio? Were the heads cc'd, pistons cc'd, how far is the piston in the hole, how thick is the head gasket? What is your quench? Without actually measuring, which most people don't do or have the tools to do (home builders). There is no way for you to know your TRUE compression. If you buy a set of heads that are supposed to be lets say 64cc, when you actually measure them they can/will be from 63 - 66cc in some instances. The same goes for pistons.

If you are estimating based on what the advertised compression ratio of the pistons are, then you can easily be 1.5 points off. there are a lot of "11:1" engines running around and in reality they are closer to 9:1.

I am not trying to start an argument you, may have very well measured everything. I just have a hard time believing you are running 11:1 with iron heads on 91 octane.

While the engine is new you might get away with it for a while but, once you start building up carbon and the compression goes up slightly this will end the party. Nevermind a bad load of gas.

If your engine is actually 11:1 with iron heads more power to you. I can tell you I have seen first hand what happens to "true" iron headed 11:1 engines on the street (broken ring lands, hammered bearings, poor performance).

Just cause you "have said it a million times" doesn't make it a fact.

Royce
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 12-10-2004, 07:52 AM
Member
 
Join Date: May 2004
Location: Miami
Age: 37
Posts: 85
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
lluciano77


Sent you a PM

If not pump gas how about aviation fuel? I have a gas station that sells it for air boats. Aviation fuel is what octane? 110?

Last edited by granprix76; 12-10-2004 at 07:52 AM.
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



All times are GMT -6. The time now is 11:07 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.