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  1. #1
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    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....
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  2. #2
    Charter Member Charter Member Thunderstruck's Avatar
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    Long time cult member.

  3. #3
    Charter Member # 55 Charter Member Griff's Avatar
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    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.

  4. #4
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    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!

  5. #5
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    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 W@ukega 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 ????

  6. #6
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    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.
    No matter how pretty she is, there is a guy who is sick of her S#!t

  7. #7
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    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 W@ukega 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!!!!!
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  8. #8
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    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 = ??

  9. #9
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    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

  10. #10
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    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 my "Winston Cup" 69 chevelle project

    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.


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