Comp ratio what octane
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Comp ratio what octane

  1. #1
    Senior Member schiada flatty's Avatar
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    Default Comp ratio what octane

    I was wondering what octane I would get away with running if I went with another set of L88 427 pistons just ones designed for the open chamber heads this time around.

    Could I buy C12 and just mix it a little with 91 pump gas. If so what ratio.

    These are the pistons I'm thinking of going with. Heads are 990 open.

    Speed Pro TRW Chevy 427 ZL1 L88 COPO Forged Dome Coated Pistons Set 8 030" | eBay

    or these if I want to run just pump gas alone

    Speed Pro TRW Chevy 427 425 435 HP Forged Dome Coated Piston Set 8 11 1 1 030" | eBay
    At $100/ hp plus injection oil it's just to expensive to go that slow!
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    Quote Originally Posted by schiada flatty View Post
    I was wondering what octane I would get away with running if I went with another set of L88 427 pistons just ones designed for the open chamber heads this time around.

    Could I buy C12 and just mix it a little with 91 pump gas. If so what ratio.

    These are the pistons I'm thinking of going with. Heads are 990 open.

    Speed Pro TRW Chevy 427 ZL1 L88 COPO Forged Dome Coated Pistons Set 8 030" | eBay

    or these if I want to run just pump gas alone

    Speed Pro TRW Chevy 427 425 435 HP Forged Dome Coated Piston Set 8 11 1 1 030" | eBay
    when the l88 was in cars they ran on pump 100 so would say that would be the octane I would shoot for, or you could run av gas it will all depend on tuning there is no set rule for static compression to octane it all depends on your whole package
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    gn7
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    Quote Originally Posted by bowtiebro View Post
    when the l88 was in cars they ran on pump 100 so would say that would be the octane I would shoot for, or you could run av gas it will all depend on tuning there is no set rule for static compression to octane it all depends on your whole package
    When the L88 was in cars, they could get away with most premium leaded gas under most conditions. Chevron white pump and Sunoco 260 was pushing more like 105, and that's what most people ran in them. Also, the L88 was aluminum headed when it ran that piston.

    But hey, if SHBH says the can run that second piston with a CC head, you should be able to run the first when with a OC head. It only comes out to about 12.5 to 1. Walk in the park for pump gas. If your SHBH.


    Personally, I think you're walking a tight rope with the second piston on pump gas at 10.5 under the best conditions. Mixing fuel with that piston might make a little sense. Bothering to mix it with the first is a waste of time and money. You just be better off running it on straight 110.



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    Distinguished Member David 519's Avatar
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    I probably wouldn't buy a set of pistions without the dome volume specified so I could calculate exact CR. GN7 probably knows but I thought the L88 was a closed chamber motor. Closed chamber pistons in an open chamber head is gonna hit the CR pretty good. Again, I'd want to be able to calculate it.
    My circle boat has a spec 427 that's supposed to be a modern clone of an L88 and it made the most power on 110 octane. I won't run it on anything much less than 105ish fuel. Regardless, I'd be real careful running the swill that qualifies as 91 octane pump gas in anything over about 10:1.

    Crap, GN treed me!! Got sidetracked by one of my millwrights interupting my PB time
    Last edited by David 519; 03-24-2014 at 06:25 PM.
    Quote Originally Posted by gn7 View Post
    ....... David 519 is 100% correct........

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    .....I think people forget that racing is supposed to fun. Losing shouldn't be discouraging it should motivate you work on your pile to make it faster.....
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    gn7
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    Quote Originally Posted by David 519 View Post
    I probably wouldn't buy a set of pistions without the dome volume specified so I could calculate exact CR. GN7 probably knows but I thought the L88 was a closed chamber motor. Closed chamber pistons in an open chamber head is gonna hit the CR pretty good. Again, I'd want to be able to calculate it.
    My circle boat has a spec 427 that's supposed to be a modern clone of an L88 and it made the most power on 110 octane. I won't run it on anything much less than 105ish fuel. Regardless, I'd be real careful running the swill that qualifies as 91 octane pump gas in anything over about 10:1.

    Crap, GN treed me!! Got sidetracked by one of my millwrights interupting my PB time
    First design L88 was a closed chamber head with a round exhaust port. 2nd design in 1970 used the ZL-1 OC head(077) and piston. The 2nd design was never offered in a car, it was a crate engine like the LS-7 454.
    But because they sold so many more of them, a lot of people thing of the L88 as a OC alum head engine.

    EDIT: The '69 year Camaro ran for close to 18 months. The 2nd Gen Camaro was release as a 70 1/2. There is a chance that some 2nd design L88s made their way in to later Camaros if someone knew the magic boxes to check for a COPO. But the majority of OP chambered L88s were sold in crates.



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    Last edited by gn7; 03-24-2014 at 07:12 PM.
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    Quote Originally Posted by gn7 View Post
    When the L88 was in cars, they could get away with most premium leaded gas under most conditions. Chevron white pump and Sunoco 260 was pushing more like 105, and that's what most people ran in them. Also, the L88 was aluminum headed when it ran that piston.

    But hey, if SHBH says the can run that second piston with a CC head, you should be able to run the first when with a OC head. It only comes out to about 12.5 to 1. Walk in the park for pump gas. If your SHBH.


    Personally, I think you're walking a tight rope with the second piston on pump gas at 10.5 under the best conditions. Mixing fuel with that piston might make a little sense. Bothering to mix it with the first is a waste of time and money. You just be better off running it on straight 110.
    thanks for all the info again gn7. I think I might grab a set of those L72 pistons. Running 110 in a lake boat might get a little expensive. As it is I can burn through a 10 gallon tank of 91 in about an hour.
    At $100/ hp plus injection oil it's just to expensive to go that slow!
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    Quote Originally Posted by gn7 View Post
    But hey, if SHBH says the can run that second piston with a CC head, you should be able to run the first when with a OC head. It only comes out to about 12.5 to 1. Walk in the park for pump gas. If your SHBH.

    So what are you trying to say? Mine won't run on 91 without detonation? Opps what did it hurt?What Good thing i didn't say my deck is only 8-10 with the new block

    Where do you come up with 12.5-1?

    Spec on the op's second choice is 10.18-1 @116.9cc And while i have not verified it there is a good chance that number if figured with oem head gasket.
    Figure by the time the op has to flycut the pistons it should be a solid 10.0-1 motor.

    I wonder how long the op ran the combo he had before it hurt itself? The ones with the material removed from the pistons to clear the intake valve.Kinda odd...where the piston broke, right where the material was removed.
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    So what are you trying to say? Mine won't run on 91 without detonation? Opps what did it hurt?What Good thing i didn't say my deck is only 8-10 with the new block

    Where do you come up with 12.5-1?

    Spec on the op's second choice is 10.18-1 @116.9cc And while i have not verified it there is a good chance that number if figured with oem head gasket.
    Figure by the time the op has to flycut the pistons it should be a solid 10.0-1 motor.

    I wonder how long the op ran the combo he had before it hurt itself? The ones with the material removed from the pistons to clear the intake valve.Kinda odd...where the piston broke, right where the material was removed.
    I didn't say anything like that. I said you are SPECIAL. The rest of us mere mortals can't get away with that shit.



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    Quote Originally Posted by gn7 View Post
    I didn't say anything like that. I said you are SPECIAL. The rest of us mere mortals can't get away with that shit.
    "Special'? not on this thread. Care to offer an opinion as to how i am able to run this combination without having problems? I sure as hell don't know why,i don't think it all that close to the edge, i pull the plugs every time i take it out. Maybe i just don't run it hard enough?
    "A liberal paradise would be a place where everybody has
    guaranteed employment, free comprehensive healthcare, free
    education, free food, free housing, free clothing, free
    utilities, and only law enforcement has guns. And believe it or
    not, such a place does, indeed, exist: It's called prison."

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    Maricopa County Sheriff's Office
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    Quote Originally Posted by gn7 View Post
    I didn't say anything like that. I said you are SPECIAL. The rest of us mere mortals can't get away with that shit.
    In case it matters, it's right on the edge. 2 gal. 87 octane and 10 of 91 and i took off up river after D/S. I ran from the dredge to the sand bar and back...8-10 miles spinning 6500+ and i bounced it off 7k rev chip a couple times earned me a few speckles on 3 of the plugs in the head that's milled .030. Air temp probably didn't help, it was plenty cool and i had a set of 12 series champion plugs in it. I stuck a camera down the plug holes, other than the quench area being a little cleaner than last time i looked it looked ok. Deck is 8-10 with an 022 head gasket that is probably mashed to 020 after being reinstalled so many times

    Kinda odd, that head picked up a few lbs. on compression test. I don't track each cylinder, i just average each side and they are always pretty even. One side usually hits 150 and the other 160 and it went 165.

    I figure colder plugs, hotter air and straight 91 octane to be my safety margin although that is the first time i have ever had a chance to run that long/hard, no wake boats and some wind chop is the shitz...
    Last edited by SoldHondaBoughtHondo; 05-11-2014 at 12:26 PM.
    "A liberal paradise would be a place where everybody has
    guaranteed employment, free comprehensive healthcare, free
    education, free food, free housing, free clothing, free
    utilities, and only law enforcement has guns. And believe it or
    not, such a place does, indeed, exist: It's called prison."

    Sheriff Joe Arpaio
    Maricopa County Sheriff's Office
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