Like Tree0Likes

how much can you drop comp with a head gasket??

Reply
Old 03-31-2011, 06:56 PM
  #1
Registered
Thread Starter
 
Join Date: Jul 2001
Location: oshawa ontario
My Boats: 31 Scarab Thunder
Posts: 4,684
Default how much can you drop comp with a head gasket??

This is actually a car application but theres tons of knowledge around here....

Theres lots of engines around for a good price with lots of good components but too high compression for my pump gas rule.....I realize a cam change would be in order but thats a relatively small price to pay for good heads, recip assy etc...

Is a full point or point and a half possible??

heres the car....
Attached Thumbnails
how much can you drop comp with a head gasket??-new-stuff-022-large-.jpg  
pullmytrigger is offline  
Reply With Quote
Old 03-31-2011, 07:36 PM
  #2
Charter Member
Charter Member
 
Thunderstruck's Avatar
 
Join Date: Nov 2000
Location: Lake Charles, LA USA
My Boats: 1998 32' Active Thunder (Sold)
Posts: 1,094
Default

http://www.race-cars.net/calculators...alculator.html
__________________
Long time cult member.
Thunderstruck is offline  
Reply With Quote
Old 04-01-2011, 01:37 AM
  #3
Charter Member # 55
Charter Member
 
Griff's Avatar
 
Join Date: Oct 2000
Location: Omaha
My Boats: .......32............. ...............Active Thunder....
Posts: 15,659
Default

The most you can reduce the CR with a thicker head gasket is about .2 and its really not a good idea to do it. It of course depends on the thickness of the current head gaskets also.
Increasing the head gasket thickness also increases the quench and can actually increase the risk of detonation.
Griff is offline  
Reply With Quote
Old 04-01-2011, 06:47 AM
  #4
Registered
Trade Score: (1)
 
Join Date: Feb 2011
Posts: 2,618
Default

Is the short block together? If not, you might be able to measure the dome thickness and mill a little bit off the dome of each piston to bring it down a little. Make sure you have an experienced performance engine builder evaluate this, but it is possible. Of course, everything would have to be balanced after this. It may be cheaper to just get some different pistons, or some heads with bigger chambers.

I am having the opposite problem. My builder CC'd the heads on my 781's and they came out to 124 cc's! That will put me at around 8.3:1 with the SRP flat tops my 489 will be running. I'm not sure if we can mill enough off the heads to bring the CR up to a more respectable 8.7+. Is that the Almighty telling me I need to run a supercharger?

BTW, I would love to have that 2-post lift in my garage!
Budman II is offline  
Reply With Quote
Old 04-01-2011, 07:53 AM
  #5
Banned
 
Join Date: Sep 2007
Location: Frankfort,ill
My Boats: 40 SKATER
Posts: 12,863
Default

Quote:
Originally Posted by Griff View Post
The most you can reduce the CR with a thicker head gasket is about .2 and its really not a good idea to do it. It of course depends on the thickness of the current head gaskets also.
Increasing the head gasket thickness also increases the quench and can actually increase the risk of detonation.
+1 with griff
get another set of pistons BIG Daddy you'll be glad you did , a local [email protected] n il shop does this bandaide .095 head gasket trick and bites them in the azz everytime good luck on your project Bro and a lil spoiled with that lift aren't we ????
RunninHotRacing163.1 is offline  
Reply With Quote
Old 04-01-2011, 10:04 AM
  #6
Registered
Trade Score: (4)
 
Rookie's Avatar
 
Join Date: Jan 2003
Location: Grand Rapids, MI
My Boats: 30 Scarab Panther, 37 Active Thunder, 34 Wellcraft Gran Sport
Posts: 3,764
Default

I also agree with Griff my situation is not ideal but I know I am safe.

What I did was some what of a band aid cause I have one head that was cut to ~118cc when my other heads were ~122cc. I went with a bigger bore MLS gasket and thicker. My block was also decked. I went from 9.7cc volume Felpro 17042 gaskets to a 14.8cc Fel Pro 1077-1 gasket. I also stayed around my max 0.060" quench . I gained 5.1cc's which is about .5 CR reduction.

Last edited by Rookie; 04-01-2011 at 07:47 PM.
Rookie is offline  
Reply With Quote
Old 04-01-2011, 10:09 AM
  #7
Registered
Thread Starter
 
Join Date: Jul 2001
Location: oshawa ontario
My Boats: 31 Scarab Thunder
Posts: 4,684
Default

Quote:
Originally Posted by RunninHotRacing163.1 View Post
+1 with griff
get another set of pistons BIG Daddy you'll be glad you did , a local [email protected] n il shop does this bandaide .095 head gasket trick and bites them in the azz everytime good luck on your project Bro and a lil spoiled with that lift aren't we ????
wow only .2 thats nothing.....so Id have to figure in a set of pistons in the equation, thanks I really had no idea about that.

Yeah I picked up the lift off Kijiji from a dealership refit....paid $1200.....had it prof installed for another $500.....good deal.
Theres no way in H ELL I would have taken on this project with the body refit without one.....Im WAY to old/lazy for that s hit!!!......truth be known if it I could of afforded it I would have dropped the two cars off at a shop and let them do all the work and come back when its done.....I dont want to build I want to DRIVE THE S HIT OUT OF THIS MUTHERFCKER!!!!!
Attached Thumbnails
how much can you drop comp with a head gasket??-new-stuff-029a-large-.jpg  
pullmytrigger is offline  
Reply With Quote
Old 04-01-2011, 10:56 AM
  #8
Registered
Trade Score: (2)
 
Join Date: Aug 2005
Location: Between A Womans Leggs in IL
My Boats: 77 donzi x18 92 formula 336 sr1
Posts: 6,321
Default Fixx

Quote:
Originally Posted by pullmytrigger View Post
wow only .2 thats nothing.....so Id have to figure in a set of pistons in the equation, thanks I really had no idea about that.

Yeah I picked up the lift off Kijiji from a dealership refit....paid $1200.....had it prof installed for another $500.....good deal.
Theres no way in H ELL I would have taken on this project with the body refit without one.....Im WAY to old/lazy for that s hit!!!......truth be known if it I could of afforded it I would have dropped the two cars off at a shop and let them do all the work and come back when its done.....I dont want to build I want to DRIVE THE S HIT OUT OF THIS MUTHERFCKER!!!!!
is e85 a option for you??? change the carb and fuel system and go run it..one down fall,,e85 from the pump vary's in octane tho, i herd it goes from the high 90's to 115..also its supposed to be mixed by the driver,,x amount of gallons of alcohol to x amount of gallons of 93 = ??
FIXX is offline  
Reply With Quote
Old 04-01-2011, 10:59 AM
  #9
Banned
 
Join Date: Sep 2007
Location: Frankfort,ill
My Boats: 40 SKATER
Posts: 12,863
Default

Quote:
Originally Posted by pullmytrigger View Post
wow only .2 thats nothing.....so Id have to figure in a set of pistons in the equation, thanks I really had no idea about that.

Yeah I picked up the lift off Kijiji from a dealership refit....paid $1200.....had it prof installed for another $500.....good deal.
Theres no way in H ELL I would have taken on this project with the body refit without one.....Im WAY to old/lazy for that s hit!!!......truth be known if it I could of afforded it I would have dropped the two cars off at a shop and let them do all the work and come back when its done.....I dont want to build I want to DRIVE THE S HIT OUT OF THIS MUTHERFCKER!!!!!
way cool trigger you got a Link ?? was gunna have one put in a year or so ago and the installer made it sound like it was harrible and he was building a space ship for the moon LOL cutting holes in the floor for anchors, new concrete, running electrik all over the place looks like a cool project need more pics
RunninHotRacing163.1 is offline  
Reply With Quote
Old 04-01-2011, 11:13 AM
  #10
Registered
Thread Starter
 
Join Date: Jul 2001
Location: oshawa ontario
My Boats: 31 Scarab Thunder
Posts: 4,684
Default

Quote:
Originally Posted by RunninHotRacing163.1 View Post
way cool trigger you got a Link ?? was gunna have one put in a year or so ago and the installer made it sound like it was harrible and he was building a space ship for the moon LOL cutting holes in the floor for anchors, new concrete, running electrik all over the place looks like a cool project need more pics
I have a thread for the car here http://www.offshoreonly.com/forums/t...e-project.html

or do you mean the lift??......4" of concrete is the general rule (I have 6) but each manufacture has its guidelines.....simple 240v to the lift , your good to go.....I called the manufacture of the lift and they gave me a list of recommended installers that they use.

Last edited by pullmytrigger; 04-01-2011 at 11:18 AM.
pullmytrigger is offline  
Reply With Quote
Reply



Posting Rules
You may not post new threads
You may not 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 -5. The time now is 11:11 PM.


Copyright 2011 OffShoreOnly. All rights reserved.