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Thread: Thoughts on high Compression 4AGZE

  1. #1
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    Icon1 Thoughts on high Compression 4AGZE

    Hey,

    So I am pretty close to finishing my SC12 4AGZE build, but I had a "while I'm at it" idea to run by you guys.

    I have been tinkering on a big port head with a mild DIY port & polish and need to take it to the machine shop to have it decked for my HKS 1.0mm MLS headgasket.

    I am running aftermarket 8.9:1 Arias turbo pistons, in a silver top bottom end. Fuel & Spark will be handled by a Microtech LTX-8. FMIC, blah blah blah.

    There was a thread that 666 put up about head tolerances for his blacktop and it got me thinking. If I am going to the machine shop to plane my head anyway, maybe I should get them to deck it by like .020" and see if I can up the compression. I haven't done the calculation to see how much I need to take off, but I think I could get away with a 10:1 CR in this engine with little ill effect.

    So what's the word on high compression supercharged engines? Pros/cons? Most FI guys only say "crank the boost!" and little else. The way I see it I have a couple options for more power here:

    Option 1: Deck head to 10:1 CR, with stock pulleys for 10psi from my SC12
    Option 2: Keep CR as-is @ 8.9:1, get a oversized crank pulley and make 14psi
    Option 3: Screw the SC12, get an SC14 with a silly downstream throttle body and be obnoxiously loud all over the place

    Does anybody even still care about supercharging 4A-G's?
    Quote Originally Posted by greenie View Post
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  2. #2
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    Hey Vickers,

    I dont know how the other 4age gurus will respond but i believe the reason for more boost VS CR is because you tend to get more results from increased boost on a FI engine than bumping up the CR.

    Additionally if the FI engines naturally deal with intake temps that are higher than NA motors so you might run into issues with timing advance because of combustion temperatures being higher in a highcomp FI motor. Where as turning up the boost and adjusting your AR may be more beneficial.

    my 2 cents. Hope it doesnt sound to Crazy

    Geard.
    Collecting Parts...

  3. #3
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    Thanks Geard,

    Combustion temps will already be pretty high with the roots blower. Adding more static CR would probably just be dumb. With crank pulleys costing about as much as the machine work, I'll probably get more power by simply adding more boost. Safe and simple.

    Like I said, it was more of a "while I'm at it" kind of idea. I'd still be open to hearing the reasons for or against it though.
    Quote Originally Posted by greenie View Post
    i like to go into lordco and just yell into the mufflers they have in stock until i find one that tickles my fancy
    Wisdom from NeptuneD on choosing mufflers for exhaust note

  4. #4
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    i don't really see the benefit. On a turbo application, higher CR helps off boost. On an SC application where your boost is directly correlated to RPM, the benefit is minimal. Yea you'll probably see more power, but if higher CR is limiting you from running higher boost, than its shooting yourself in the foot. SC14 and call it a day, i say.

  5. #5
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    yea fair enough, i would definitely go with a larger SC and cams down road get it to breathe more! Eitherway sounds like it will be awesome once done!

    Geard.
    Collecting Parts...

  6. #6
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    For throttle downstream the SC (i.e., stock bluetop intake manifold configuration), I was thinking of using an external waste gate as a bypass valve for off-throttle business. Running an SC14 full-time would probably be easiest rather than playing with a clutched pulley.

    I have a 38mm turbosmart external waste gate kicking around, but I would probably need to play with springs to get it to drive right. Would it be better to use the ecu to sense vacuum and then open the bypass valve via a solenoid, or just stick with the mechanical workings via the vacuum diaphragm?
    Quote Originally Posted by greenie View Post
    i like to go into lordco and just yell into the mufflers they have in stock until i find one that tickles my fancy
    Wisdom from NeptuneD on choosing mufflers for exhaust note

  7. #7
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    My uncle in Victoria is making 200hp with a 4age/sc12 in his MR2, I can ask him what setup he's using, and what issues he had to deal with.

  8. #8
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    visean is offline Yo, troubled night in the John
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    Quote Originally Posted by bcae92 View Post
    My uncle in Victoria is making 200hp with a 4age/sc12 in his MR2, I can ask him what setup he's using, and what issues he had to deal with.
    Curtis is your Uncle?

  9. #9
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    Yup.

  10. #10
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    Yeah, don't. Low comp is best.

    SC is bad enough, don't shoot both your feet.
    BCWORKS

  11. #11
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    Instead of increasing the size of your crank pulley for more boost, consider instead, decreasing the size of your SC pulley.

  12. #12
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    SC is not bad. Very fun and reliable don't listen to me turbo pants break all the gears warren

    Sc14 is your best bet, leave compression where it is!
    Husky Situations

  13. #13
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    Quote Originally Posted by Rastaracer View Post
    Instead of increasing the size of your crank pulley for more boost, consider instead, decreasing the size of your SC pulley.
    this and low comp

    Quote Originally Posted by woodenturn View Post
    DK should ban such nonsense. 2 cents~ sr86 www.dorikaze.net/showthread.php?32933-Elizabeth

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