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Higher Comp. on my 454 ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Ditchdigger, Jan 6, 2003.

  1. Ditchdigger

    Ditchdigger Registered Member

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    Hi,
    I'm rebuilding a 454 for my Blazer and i'm Wakin her up with some performance goodies /forums/images/graemlins/grin.gif
    She's about a 75(first gen) and I think its 8.8.1 comp.?Don't know for sure, stock anyways, but I want to up it too about a good 9.5.1 and I never did it on any overhaul and these engines are so low comp. and I did a Portin and polish on it and that lowered it some,
    Anyways, My question is What can i do to up the compression, I need to do more than just get higher pistons right, oh ya not to mention How affordable is it going to be?

    Any help appreciated
    /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif
     
  2. Sandman

    Sandman 3/4 ton status Author

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    I think Flattops will give you around 9:1 depending on the heads. I kept mine there so I could run cruddy gas if I had to. You looking at different heads or a dome piston to get the compression up.
     
  3. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    The stock comp ratio is going to be closer to 7.9:1. Like Sandman said the 9:1 neighborhood is very user friendly and makes good power. I went with 10:1 with mine and it needs 93 octane and prefers 104+ octane boost as well (which can be inconvenient).

    You'll need to get the casting number off of the head and see what size combustion chamber the have. Most likely they are 119cc chambers. Find a local speed or machine shop and ask them to help you research the best piston for you.
     
  4. Lonnie

    Lonnie 1/2 ton status

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    You can find an early set of closed chamber heads from '70 & earlier passenger cars, they have chambers that vary from 96 to 110cc. This will increase your compression with stock pistons. They also flow pretty well in stock form compared to the stock truck heads. Just stay away from the rectangle port heads as they are for high RPM operation. I run a set of '67 heads on my 427 & it has 9:1 comp. with flat top pistons. Regular 87 octane works well & it runs 13's in the 1/4 on 35" tires.
     
  5. Ditchdigger

    Ditchdigger Registered Member

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    Thanks for the info, So all I need to do is change pistons?
    but, if I'm not mistaken aren't flattops original, thats what my block had were flattops with single valve reliefs(cast)and thats factory, is there anywhere on the web that I can email casting# and such to see what I need, I might see if I can get 9:25.1.
    Also, What price range am I lookin at? I'm definitely not going forged, What about Hyperuetectic?
     
  6. Ditchdigger

    Ditchdigger Registered Member

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    I found some Hyperuetectics for about $38 a piece,
    and will give me 9:1.1 with 119cc heads, but not sure on
    heads is there anyplace on the internet to find out,
    and I'm still wandering about the comp. If you get dome pistons aren't you also raising it BTDC so how can it be Higher comp.?
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Are hyper. pistons for BBC that much more expensive than SBC? You can buy 9.2:1 (64CC heads) SBC hyper. pistons for $100/set!
     
  8. fortcollinsram

    fortcollinsram 1/2 ton status

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    You can do a few things to raise the comp. ratio Since you are rebuilding the engine anyhow, you might as well do what you want, right? /forums/images/graemlins/thumb.gif Well that s what I am doing...I have a 1992 BBC that I am rebuilding...I chose the SpeedPro Hyperutectic Flat top pistons...The are also available in some moderate domes to help bring up the comp. I found my pistons on e-bay and got a set of FT pistons for $160 shipped to my door, NEW. I also had my heads shaved .010" which decrease the combustion chamber by about 2.5 cc's. You can also simply use a head gasket with a thinner compressed thickness that the one you already are using...You must also take into account that the side affects of each mod you do to raise comp. Shaving the heads more than about .015" can lead to sealing problems between the intake manifold and the head. to correct this the intake may have to be machined to correct for the shaved heads...This can add up quickly as far as machining cost are concerned. my heads were warped about .007" across their entire lenght, but I had .010" taken off do bump up the comp just a bit more. Also, a piston that has a ridiculous dome can cause problems as far the flame and airflow characteristics of the combustion chamber are concerned. But my general way of think on this subject leads me to believe the the best thing to do would be to do a little of everything, shave the heads a bit, get some flat top pistons or slight domes and it should work out for you...

    Chris
     

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