Piston selection help...and other rookie Q?'s
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Piston selection help...and other rookie Q?'s

  1. #1
    Senior Member H20MOFO's Avatar
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    Default Piston selection help...and other rookie Q?'s

    I am in hopes of rebuilding my 557 bbc here in the near future. I ran so much shrapnel through my motor last year my piston skits/cylinder walls look like hell. I was curious as what would be a good off the shelf piston choice if I wanted to stay pump gas friendly. For me (around here) pump gas maxes out at 91......and dont want to live on the edge...so for conversation sake lets call it 88-89 octaine. Heads are alum. 119'cc.....and agin for conversation sake we will assume the motor has a good quench.

    One other dumb question....pistons currently have pressed pins....does that mean with these current rods....I am stuck with pressed pin type a set up. ( yes I am that clueless...but hope not to be shortly lol)

    Wouldn't just a set of flat tops put me about where I want to be??

    On a side note....what type of hp increase "should" a fella get by going from say 8.4 to 1(what it is now) to say 10.4 to 1.

    Hoping to reuse the custom ground solid roller cam I have....I assume to have enough ammo to take an educated guess at any of this you will need the cam specs...they are as follows

    duration at .050 int. 255 ex 265
    lobe lift int .4150 ex .4170
    separation 112
    timing events int. 21.5 53.5 ex 70.5 14.5
    duration at .020 283 296
    gross valve lift int. .705 ex .709
    degree intake lobe to 106

    also I live and run at 4200 ft.....

    If I have left out any important info let me know....TIA Kreg
    Another Hot Boat refugee

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  3. #2
    Senior Member H20MOFO's Avatar
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    I am not sure on the rods barry....if you are remembering differently ...you are probably right and I am probably wrong. They and the crank were brooks/brc if I remember right. 99 percent of the time I will be at this altitude or higher. If/when I go closer to sea level...I would be prepared to up the octaine.

    Holy vanishing post batman. lol
    Another Hot Boat refugee

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    Some guy obnoxious001's Avatar
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    So people don't have to guess,, that's a 4.375" stroke crank if I recall?

    Are you sure heads have not been cut enough to drop chamber size?

    When you say "good quench",, do you know what deck height the existing pistons are at?

    I think flat tops may get you to about 9 1/2-1, roughly speaking.

    Will you only be running it at higher altitude, no trips elsewhere?

    Are you sure about press pins in those rods, I honestly don't recall what they were, but it sounds wrong to me for some reason? Thought maybe I had photos of the parts but can't find them,, current pistons are JE, correct? You could have the rods bored and bushed, but probably more reasonable to just buy new imported H beams.

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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by H20MOFO View Post


    Holy vanishing post batman. lol
    Sorry,, I went back to edit

    Other thing, is it a standard deck block? Need that for piston choice. 6.385" rods, or longer?
    Last edited by obnoxious001; 02-15-2012 at 01:54 PM.

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    Senior Member H20MOFO's Avatar
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    Its a bowtie tall deck....having a hard time putting my hands on my build sheet.....wanna say 6.135 rods.
    Another Hot Boat refugee

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    Senior Member H20MOFO's Avatar
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    Quote Originally Posted by obnoxious001 View Post
    So people don't have to guess,, that's a 4.375" stroke crank if I recall?

    Are you sure heads have not been cut enough to drop chamber size?

    When you say "good quench",, do you know what deck height the existing pistons are at?

    I think flat tops may get you to about 9 1/2-1, roughly speaking.

    Will you only be running it at higher altitude, no trips elsewhere?

    Are you sure about press pins in those rods, I honestly don't recall what they were, but it sounds wrong to me for some reason? Thought maybe I had photos of the parts but can't find them,, current pistons are JE, correct? You could have the rods bored and bushed, but probably more reasonable to just buy new imported H beams.
    Honestly....I dont know or believe anything my last guy did or said. The quench currently sucks...pistons are almost .020 in the hole...want to fix that when I punch her out.

    Heads were bought new in 05' and I have never asked for them to be milled....he supposedly cc'd em at 119 and even stamped the front of em 119

    Not sure on rods...I will look for a pic I have/had

    I was thinking I could get away with more like 10.5 to 1 but I dunno.

    crank is 4.375...yes

    High altitude only....if/when I ever get closer to sea level....I will up the octaine
    Another Hot Boat refugee

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    Some guy obnoxious001's Avatar
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    Give me a call if you want,, or PM if you don't have my number. I went back and found the ad where I sold you the parts a few years ago. If you have been scraping debris up and down the cylinder walls,, it probably needs to be bored. With the tall deck, it probably makes sense to put a longer rod in it,, they were 6.385's according to the original post, particularly if they were press pin.

  10. #8
    Senior Member H20MOFO's Avatar
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    Can do Barry...hate to bug ya just yet. Just want to get a plan for when this thing lets go. Didnt find my build sheet....but I found a pic of it in my photobucket...says rod length 6.525. Was curious as to what you and some of the guys here would be a good pump gas piston option for me....and was curious as to what dome (cc) I would want to look for ....I realize static and dynamic are 2 different critters thats why I put up the cam specs. I have some money set aside...depending on what gains are feasible/reasonable. According to the jet dyno....I am not even 1hp per cube....I am thinking the 8.4 to 1...alum. heads....and the high altitude is smackin me with a tripple whammy.lol Based on what I see day in and day out here....I would think 750 should be a walk in the park with the rest of my junk.
    Another Hot Boat refugee

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