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454ci question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Ditchdigger, Mar 30, 2003.

  1. Ditchdigger

    Ditchdigger Registered Member

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    Hi,
    Here's the situation!
    I'm doin a rebuild on a 454ci,
    and its the early 454s and the heads are 118cc
    and I'm wandering if I should spend the xtra money and raise the compression to around 9:25.1 or so
    I think original is 8:5.1 or lower.
    If I did I would be getting HigherComp. hypereutectic
    pistons which means I would have to balance also!
    OR shave the heads and go with original cast and not balance
    but some guys say even an all original bigblock should be balanced? like they were never balanced real well!!
    Any help Appreciated!
     
  2. cybrfire

    cybrfire 1 ton status Vendor GMOTM Winner

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    I'd say bump the compression a little. Really wakes up the big block. Your 9.25:1 is right in line with reality and driving daily also. I'm doing the same rebuild right now and my engine guy who is also my uncle and I trust emplicitly with my motors told me that was the only way to go.
     
  3. Ditchdigger

    Ditchdigger Registered Member

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    Thanks for your input!
    Which way are ya goin for to raise the compression?

    Hope your build goes well /forums/images/graemlins/thumb.gif
     
  4. Lonnie

    Lonnie 1/2 ton status

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    If you didn't rebuild the heads as of yet, then find a set of 1970 or earlier oval port heads from a car or pickup. (no peanut port HD truck heads... these are large chamber) These have a combustion chamber of approx 96-100cc. With flat top pistons, you will get approx 9:1 to 9.25:1 compression depending on head gasket choice. This will save your piston/balancing costs.
     
  5. Ditchdigger

    Ditchdigger Registered Member

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    yep, I rebuilt the heads, and there being hot tanked
    as of right now, so these 118cc I will have to use.
    one thing I was wandering if you shave the heads
    do they also shave the intake so they still match up?
     
  6. fortcollinsram

    fortcollinsram 1/2 ton status

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    I think you only have to shave the intake to match if you shave like .015" or more of the heads...your engine guy will tell you for sure...I shaved .010" off my heads for my BBC and the intake fits fine...Mine was more of a cleanup cut rather than trying to raise comp. I thnk you take off like 1cc of combustion chamber volume for every .004" you shave off...Since I shaved off .010" my chamber volume went from about 118 to about 116.5cc...

    Chris
     
  7. Ditchdigger

    Ditchdigger Registered Member

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    Anyone know how much I could shave these heads and
    still be in the safe margin .020?
    or rather what the lowest cc is possible on these 118cc heads?
    could you get in anywhere near 9:0.1 with flattops
     
  8. fortcollinsram

    fortcollinsram 1/2 ton status

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    [ QUOTE ]
    still be in the safe margin .020

    [/ QUOTE ] What do you mean by this? A competent machinist can angle mill .050" off your heads and match up your intake and it would seal fine...I think the biggest concern would be valve to piston clearance...If you are running like .120" Piston to valve clearance and shave .050" off the heads, you are cutting it a little close /forums/images/graemlins/crazy.gif I but that you won't have any issue with that however unless you are running like a .680" lift cam...Are you stuck on flat tops? Since they are open chamber heads, there is a decent selcection of domed pistons for your application....Did you buy the pistons al ready? But when you are looking at angle milling heads and upping the cc from 118 to like 110 or so, you are looking at a lot of $$$ as far as set up and machining cost..If you guy is already into the head job a bit and you still want pretty high comp with FT pistons, look at selling you current heads and getting a set of closed chamber head with like a 100cc chamber...

    What is the casting number on your heads that you are wanting to use? I personally feel it is paramount to select components based on what head you will be using and the intended use of the motor...

    Chris
     
  9. Ditchdigger

    Ditchdigger Registered Member

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    Thanks for that PM by the way!fortcollinsram!

    I haven't ordered the pistons yet!
    The heads are 73-85 oval port open chamber
    118cc, 256/114 ports!
    I might be lookin at some shaving because the machinist told me of some burn marks on face, probably same as you
    As far as the truck goes its not a daily driver just here and there and towing a boat or sumpin, and it would mainly be highway.
    but, if I'm going to get highercomp. pistons I will have to get hypereutectic right?(minus forged)
    and then I would have to balance too?
    but I spose a guy has to balance these bigblocks no matter what.
    This is the only way I can think of, and I spose its still cheaper than shaving heads maybe.

    I'm stuck between a rock and a hard place /forums/images/graemlins/eek.gif
    Do I shave heads and go with original flattops and not balance OR do I go with hyper. pistons and balance and not shave?
     
  10. b454rat

    b454rat 1/2 ton status Premium Member

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    What is the casting number on the heads?? If there are 041, they are one of the best factory oval port heads to run. Port the heads, 2.18/1.88 valves, open up the exhaust side, and these heads will rip. I had a set of these on my motor, with .133 dome gave me just about 9 to 1 compression. If you shave alittle off, then it will bump it just a little, that would be about perfect for a street motor. Go with Keith Black hypereutectic, forged is kinda much for a street motor, and expensive. Definatly balance the motor, you would be surprised how far off some of that stuff will be, it will run smoother and last longer. If you are getting new pistons, the price shouldn't be much different on higher compression. Of course, if you go to 12 to 1 it will. Most places will have the compression listed, say 9:1 up to 11:1 with a 108cc to 119c. Have the heads shaved to clean then up. If you go too much, then have to shave the intake, and the pushrods might be too long and cause interferance or binding on the rockers/springs. Hope this helps your decision.
     
  11. fortcollinsram

    fortcollinsram 1/2 ton status

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    Personally, I would balance no matter what...you'd be surprised to see how may BBC's are grossly out of balance from the factory...and as soon as you change any component in rotating assembly, you MUST balance if you want you engine to have any life expectancy at all...

    I got .010" off my heads b/c they were warped and needed a cleanup cut..If yours are warped, get a cleanup cut (.005" or so)...

    Are you getting you block bored or anything like that? Personally I would just go with a cleanup cut on the head, so domed hypereutectic pistons like THESE, some decent rings, some mild port and polish work on the head and let it run... I am using the SpeedPro Hypereutectic Flat tops in my 454 I am building...Again, if you replace ANY of the rotating assembly (rings, pistons, rods) GET THE MOTOR BALANCED...I had my BBC internally balanced for my rebuild....The fact that the rods and pistons I am using are so much lighter than stock required Dave (my engine guru) to make swiss chees out of my crank and harmonic balancer...he literally drilled like 8 LARGE holes overall in the counterweights and balancer to get that biatch runnin smooth...I am kinda of a perfectionist and I either do all or nothing when it comes to motor stuff...Don't spend the time and $$$ just to have the thing rattle itself to death in 30,000 miles...

    Chris
     
  12. fortcollinsram

    fortcollinsram 1/2 ton status

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    And the casting number is just the number (like 14096188 or 10114156)The is under the valve cover...you can tell a lot of stuff about a head from the casting number you can check out www.mortec.com to see all the listings and such...

    Chris
     
  13. ratlover

    ratlover 1/2 ton status

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    If you got 781 heads(people refer to the last 3 numbers of the casting # when talking about heads) wich there is a good chance they are then you have a great set of factory heads.

    You should get your motor balanced any time you change components. Even a flat top cast piston from one manufacturer will probably be a much different weight even though they look the same.

    Go with the hyper pistons. Forged require more piston to wall clearance because they expand more than hypers or straight up cast pistons and this isnt the best for a daily driver. Plus at your power level you have no need for forged.

    and if you shave 3cc off your head you are looking at boosting your compression by around .2 or less.

    I have a 454 short block built 40 over, and balanced in my garage. Hyper pistons with 10-1 or so with 118 heads, egal rods, AIT balancer, ARP main studs, crane cam that should allow you to run on pump gas. Oil pump, basicly all you got to do is throw your heads and pushrods at it with a distributor and carb and then buy my valve covers and edelbrack performer rpm airgap manifold. Its never been ran its just taking up space untill I get my chevelle done. I'll sell it to you for about what I have in it. /forums/images/graemlins/wink.gif
     
  14. monte0172

    monte0172 1/2 ton status

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    You can shave your heads 40 thousandths of an inch and all will fit and give you .5 compression if you want to go more than that simply shave your intake to match. Any reputable race car engine builder will tell you this.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Dunno what they make in the way of *head* (whoops /forums/images/graemlins/smile.gif) gaskets for the BBC, but on the SBC, you can get gaskets down to .015" from the "standard" .03x thick ones.

    Cheap way to bump compression up for sure, I've seen nothing saying that it's a bad way to go either.
     
  16. ratlover

    ratlover 1/2 ton status

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    I think you mean head gaskets not intake.

    By just using a shim type head gasket you can alter your quench considerably. You can make your motor have less power and be more prone to detonation with the wrong quench than by having the right quench and a lower compression. Not saying a shim type gasket will screw up your quench, it might make it right. Only way to know is to check it.
     

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