bbc gear head question???
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bbc gear head question???

  1. #1
    Senior Member hotbo's Avatar
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    Default bbc gear head question???

    OKAY FELLAS HEREs what ive got going,i have 100c closed chamberes heads that brodix built,2.25 valves,1.88 ferra vavles,oval port that they have warmed over and cnc machined the chambers to unshroud the vavles,they measure exactly 100.9 on all chambers.i want 10.1 static compression cant seem to have it.heres what ive found with all my calculations
    i can run a flat top with single valve relief,it has a voulme of 3cc at zero deck with a .039 head gasket and a 4.370 gasket bore at 4.280 cylinder bore .030 over can go .060 over but doesnt add much compression.it comes to 9.376.oaky the smallest dome i can find has a volume of -12cc that jumps to 10.6-7 static my cam has a intake close of 48 degress that with the 10.6-7 adjust my dynamic compression or adjusted compression as some might say to 9.508.
    i personally think with a closed chambered head and 93 octane think this could be problematic.this motor is going in my unlces taylor lp so it has a closed engine hatch to top things off building excessive heat is a concern to me also.

    no one makes a piston with the dome size i need :smile18:i figured it up and i need a piston head volume of about -5cc to get 10.1.
    with the -12cc dome i could run into dome hitting head okay i cut dome or head,then i can run a bigger bore gakset and a thicker one well that causes horrible quench or squish whichever you preffer i am getting way from the .30-.40 that needs to be to make everything be at its best.

    im getting pissed off any ideas i can run the flat top 3cc piston and be 9.3-4 which is okay with a good tight qeunch area but damnit i want 10.1.ideas

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    Senior Member hotbo's Avatar
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    i forgot to mention that this cam is already bought so having one ground is outta the question hes outta money

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    Senior Member Bigblockbill's Avatar
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    By the -12cc pistions and cut 7ccs off

    Or Give me the heads and I will give you some eldelbrocks with 119 cc and then you have a much better pistion selection
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    Senior Member hotbo's Avatar
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    Quote Originally Posted by Bigblockbill View Post
    By the -12cc pistions and cut 7ccs off

    Or Give me the heads and I will give you some eldelbrocks with 119 cc and then you have a much better pistion selection
    well i dont think he would want to spend any more money on headsi guess i could have the -12cc pistons cut down???

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    Run the flat tops and cut the heads a little to get to your target compression ratio.

    Flat top piston and small chamber will net you the most effiicient combo if you can get there.

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    Senior Member hotbo's Avatar
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    yes its simple for a hell of alot of money to have custom pistons made

    i cant cut the heads anymore than they are right know b/c the intake valve is almost flush with the decki had a suggestion to mill the heads and redo the vlave job im assuming to sink the valves some but here we go again with spending money thats just been spent

    im about to the point of running it with the 9.4 and calling it good,b/c the closed chambered with a small dome will not be a effecient as the flat topjust agrevates me to know that i cant do this without alot of time and money that he has run out of,

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    Senior Member Boat 405's Avatar
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    Quote Originally Posted by hotbo View Post
    yes its simple for a hell of alot of money to have custom pistons made

    i cant cut the heads anymore than they are right know b/c the intake valve is almost flush with the decki had a suggestion to mill the heads and redo the vlave job im assuming to sink the valves some but here we go again with spending money thats just been spent

    im about to the point of running it with the 9.4 and calling it good,b/c the closed chambered with a small dome will not be a effecient as the flat topjust agrevates me to know that i cant do this without alot of time and money that he has run out of,
    Get ahold of Chris Straub here on the boards. He will definately steer you in the right direction. cstraub is his screen name.

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    Senior Member hotbo's Avatar
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    well im gonna cut the piston tops,scott seastrum is gonna do it for me

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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by hotbo View Post
    i forgot to mention that this cam is already bought so having one ground is outta the question...his wife won't give him any more money

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    Senior Member Woods 017's Avatar
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    What kind of temp will the motor see? I know a few guys running way more compression than that on 91 octane and haven't had any problems with detination. The key being the ambient cooling system.

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    Senior Member hotbo's Avatar
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    its in a closed engine hatch so im gonna assume pretty good,but the problem is a cc head with a significant dome is a horrible idea,afraid of detination with 10.5-10-7 on 93 with a corrected compression of 9.5-9.6

  14. #12
    Senior Member Woods 017's Avatar
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    ya i hear ya on the detination but i can think of three good running engines off the top of my head that are all above 11.0:1 on 91 onctane and have shown virtually no signs of detination. These motors will run for over a half an hour up and down the river (w/ full coolers) pull into the cove sit all day and will be driven home (w/ empy coolers ). The thing is the motors dont see over 120* of heat. If you ask around on here I'm sure a few people will tell ya the same thing. Guess it just depends on the aplication...Best of luck
    Jordan

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    the cheapest way is thow in a set of 0.060 cometic gaskets, they drop your combo about a 1/2 point.



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    Senior Member hotbo's Avatar
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    okay they are doing this 11.1 with a 100cc closed chambered head????that is tiny flame travel is terrible with a dome of any margin in them,not like a open chambered head.

    as far as throwing the .060 head gasket wow that really does not optimize the quench very good.ah hell i dont know anymore just more confused then when i started,lol!!!!!!!!!!!!!!!!!!

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