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ls block w/ b16 pistons, FI?

Discussion in 'Engine Building' started by javenger, Apr 26, 2004.

  1. javenger

    javenger Junior Member

    alright, tryin to figure out what to do! i have a b18a1 and another ls block that is bored over .02. i have a set of b16 pistons. and would like to turbo charge the motor i build. on a budget! ---- could i put the b16 pistons in the bored block with larger rings, and boost it? is that a bad idea, only would like to boost around 7-10 psi. should i just save my lunch money, and pick up some forged pistons? just tryin to learn more, so any info would help.
  2. projectxspeed

    projectxspeed Senior Member

    Using the b16 pistons in your LS motor will raises the compression. Since your using a turbo you wanna keep your compression low. I recommend selling the b16 and stick with you ls pistons. (they are great for the low psi application you have going)
  3. StyleTEG

    StyleTEG Senior Member

    The whole "you need low CR with FI" is blow way out of proportion.

    Read corky Bells book, and he specifically says that lowering your CR is NOT a good idea because it stunts off boost performance.

    Further, look into effective compression and you will see that adding pressurized air is seen by the engine the same way as adding CR.

    The only drawback to having higher CR on a FI motor, is it is harder to tune. But if you have a quality tuner at your disposal, there is no need to swap in lower CR pistons unless you plan on running ALOT of boost.
  4. phunky.buddha

    phunky.buddha Admin with a big stick Admin

    Yes, lowering CR with FI isn't always necessary.... but if you're going to run 11.x:1 compression on factory cast pistons with boost, you'd better have some extra luck in your back pocket. Those pistons aren't going to last very long if you actually want to make some power.

    Sure, lowering your static compression ratio screws your off boost performance, but it increases your threshhold for more boost without grenading the engine. On a budget- like the guy in the first post clearly states- going with high compression and boost together is NOT an option.
  5. javenger

    javenger Junior Member

    thanks for the info guys!

    now, which block should i use, stock block or the one that is bored .02 over. i'm tryin to find a set of forged pistons and rods for a good price...( that damn budget thing) . if i use the bored out block, should i get over sized pistons? or 81mm pistons and get larger rings. worried about blow by (if that means anything). or just stick with the stock block and just hone it?
  6. StyleTEG

    StyleTEG Senior Member

    I still don't completely agree Calesta, just because its not a road frequently traveled doesn't mean its not a good idea.

    Stock LS CR, running at 8 PSI is equal too

    ((8 / 14.7) +1) * 9.2 = 14.2:1 Effective CR

    Now running 11:1 but less boost you can get the same effective CR but have more off boost power.

    ((5 / 14.7) +1) * 11 = 14.7:1 Effective CR

    Further, here is a dyno of a guy with 11:1 CR, 6psi on a JRSC. Pretty impressive no?


    And the only reasons the pistons themselves would be damaged or not hold up, is if there was detonation. Again, see tuning.
  7. JDMilan

    JDMilan Senior Member

    impressive, yes.

    but back to running higher CR with FI, like C said - you don't have to run 8.0:1 compression if running boost, with the proper tuning, fuel, ignition timing, and reinforced internals - I have seen the good ole drag circuit guys running CR in the high 10's.
  8. StyleTEG

    StyleTEG Senior Member

    But how much boost are those guys running?

    Of cource there is a point where lowering your CR is a good idea so you can run more boost. But a mild CR mild boost setup makes for a great daily driver setup.

    If you are not planning on boosting a bar or more, I would look into a higher CR instead.
  9. phunky.buddha

    phunky.buddha Admin with a big stick Admin

    Yes, low boost with static compression makes a really nice power curve. This isn't the thread to debate it in. I'm not saying that it's not a good idea- but read the damn first post! He's trying to build a budget setup. You can get enough boost out of any bolt on turbo kit to overload OEM parts in a B block regardless of your tuning. Enough power can be made to melt your OEM cast pistons. Why spend the extra money to rebuild the block with B16 pistons if he's ready to go with the stock B18A/B pistons?

    He can make more power at the same effective compression because he's able to burn more air and fuel with the lower static compression engine.

    Effective compression isn't everything. It's just an indicator that helps you determine what type of combinations are open to you based on the strength of your equipment, along with the quality of your tuning. Just because an engine has a higher effective compression doesn't mean that it's going to make more power. If the lower effective compression engine is still able to burn more fuel than the higher effective compression engine, it has the potential to make more power.

    Why spend the money to swap out pistons just so you can turn down the boost on a budget turbo setup and have a nice power curve? It's not the right setup for him. That should be what you're concerned about here, not some argument on theory that really doesn't belong in a thread where someone's trying to ask a simple question.

    By the way, read the last section of my post again:

    Save your arguments and effective compression jibber jabber for a thread where people are talking combustion theory, not where a man is trying to get an answer about his engine build.
  10. StyleTEG

    StyleTEG Senior Member

    I was and always have been arguing with the second post in this thread

    Then I was debating your response here

    You were saying its a bad idea.

    I agree, if he doesn't have the money to bore and drop the slugs in then obviously don't do it. But that doesn't change the fact that you can run 11.X:1 factory cast pistons with boost safely.

    You criticize me for not reading, yet you obviously foget what you typed yourself?

    Is there not something to be learned from seeing his two options? He was considering dropping the pistons in, if you read again his budget was he didn't have money for a set of forged pistons. Not that he couldn't afford to drop the B16 pistons in. Should we try and shield him from both sides, because YOU don't think its good for a budget setup?

    It seems silly to say "don't talk about it in this thread" , when the original poster was the one who brought it up and iquired about it. Are you his father now? do you know whats best for him? Maybe we should let him decide?

    I am not aruging or debating that a higher effective compression has the potential to make more power or not. I am debating that if you keep the same effective compression through boost and static compression, but have a higher static compression, you will have better off boost power. More off boost power will create more exhaust gases, and more exhaust gases will speed up spool time. Its a win/win situation. I am debating the BS that everyone spreads in terms of "You have to be low CR to boost".
  11. phunky.buddha

    phunky.buddha Admin with a big stick Admin

    No, I didn't forget what I wrote.

    YOU obviously can't read... even where I agree with you. Geez.

    Fuck it.
  12. handlebarsfsr

    handlebarsfsr Senior Member

    if your on a budget, why not just boost on the stock block until you can afford to build it right? turbo the b18a you have, and see if you really need more boost. if so, then build up your spare block with forged internals, maybe sleeves, etc. but as always, speed costs money, how fast do you want to go?

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