Pistons - Please

Discussion in 'Forced Induction - 5.0L V8 Engine' started by schmeky, Oct 13, 2019.

  1. Woopaloop

    Woopaloop Well-Known Member

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    It depends on the fuel largely, diesels can run 15:1 compression with huge boost levels and last for 500,000 miles.

    E85 is a great fuel and is pretty widely available, it also works very well with additional compression. I wouldn't call it exotic, if anything I anticipate that it will become more available and cheaper in the future
     
  2. EFI

    EFI Well-Known Member

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    Diesel engines are also built much much stronger than a gasoline engine.

    Using off the shelf forged pistons, rods, crank in a Coyote block with 15:1 compression and huge boost and it will knock itself to death just idling...much less actually getting into load and boost.
     
  3. OP
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    schmeky

    schmeky Well-Known Member

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    Beano,

    I appreciate your post. I tend to agree. Technology has progressed to an amazing level, allowing 11:1 to 12:1 CR on engines to work with 91 and 93 octane.

    I have not ordered any pistons yet since I am still on the fence on 12:1 and boost. I have heard E85 until I could cough up a biscuit, and I know everyone is trying to be suggestive. But ain't no E85 where I am, so this is not an option. 93 is everywhere in my region, so this is what I have to work with.

    But what you say is on point. I read of the broken motors from piston ring land failure, which I personally attribute to detonation of the 12:1 and boost combo.
     
  4. Toy Cobra

    Toy Cobra Well-Known Member

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    Yes sir
     
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  5. Toy Cobra

    Toy Cobra Well-Known Member

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    They are 12:1 from the factory, low compression is old school thinking. With e85 and modern day intercooling you can get away with a lot more. You can either run low compression and high boost or make the same power with high compression low boost. The problem with low compression and a blower is that you can only spin a blower so fast and that limits your power output.
     
  6. gimmie11s

    gimmie11s Well-Known Member

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    Exactly.

    Not to mention the gained efficiency in direct injection (2018+) and modern combustion chamber design... 9:1?? lol... way too low
     
  7. OP
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    schmeky

    schmeky Well-Known Member

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    I think I'll see what the 2020 GT500 compression ratio is and how many pounds of boost. This should be a good general baseline for a 93 octane build.
     
  8. EFI

    EFI Well-Known Member

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    The predator engine is 9.5:1 compression with 12lbs of boost in the GT500.
     
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  9. gimmie11s

    gimmie11s Well-Known Member

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    You treed me.

    exactly.
     
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  10. engineermike

    engineermike Well-Known Member

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    I’m personally for lowering compression if 93 is your game. Just some food for thought:
    - Predator is 9.5
    - hellcat and demon are 9.5
    - trinity is 9.0
    - ford gt is 9.0
    - focus st is 9.3
    - raptor is 10.0

    You will always be able to make more power at less compression and more boost assuming you can make more boost. I would think 16-18 is doable on the 6-rib but correct me if I’m wrong. I don’t think over 10 is safe at 12/1. 16 psi on 10/1 would be safer and more powerful.

    Another thing to consider is increasing the cid because that doesn’t require more octane to make more power.

    I think the greatest hurdle would be optimizing the tuning since there are so many things to get right in the ecm when changing that much about the engine.
     
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  11. OP
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    schmeky

    schmeky Well-Known Member

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    Just as I have been thinking . . . . . . 12:1 and boost with inconsistent 91/93 pump gas is like balancing on the edge of a razor blade.

    Looks like a 10:1 static compression ratio engine build with 10-12 pounds of boost is more reasonable. I have 2019, 5.0 coyote complete engine with 11K miles hanging on my engine stand. Was pulled from a rear ended, totaled GT. Think I'll follow the engineering of Ford on the compression ratio.

    Thanks for the replies.
     
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  12. Beano

    Beano Well-Known Member

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    @engineermike: Exactly my thoughts until it was pointed I am old-school, haha.

    Seems a few doesn’t really understand the ratios between static CR and total CR, max boost vs fuel limitations, and a few other factors, at least if you are hoping to have a reliable boosted setup.

    Anyway, as per Schmeky’s last post above, seeing that you will be limited by Octane on a 12:1 CR boosted build, dropping CR to 9 or 9.5:1 and upping the boost will give you more power under the curve (higher average) than with a higher CR/lower boost.
    Of course, if we have access to good enough fuel, wrt octane, which will allow you to run your ‘selected’ boost at a higher CR, that will be the ideal.

    In naturally aspirated form, I would suspect a 3% power increase for every full point the CR is raised....

    ‘Anyway, a good discussion, nice to see the modern engines leaning to the same direction still as 2 decades ago, but allowing a higher static CR under the same boost levels, typically even 1.5 - 2 full points CR actually. Better CR chamber design, fuel distribution and fuel quality obviously all contributors to that....

    Cheers,
    Beano
     
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  13. BlueCollarDaily

    BlueCollarDaily Well-Known Member

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    How did these work out for your on balancing were they close to same Bob weight?

    I do understand the compression debate but cylinder pressure is cylinder pressure, lower compression and higher boost will almost always yield more heat where is the cross over to turning rotors faster or the physics adding heat by compressing more air before it enters the chamber to make up for lack of compression....there will be a sweet spot I'm tempted at dropping to 11...
    One think that would stop me from going down to 9.5 is the 99.9% of the operation of the engine will NOT be in boost....literally boost is 3-10 seconds 10x a month....I like the snap of the 12 to 1 DI, especially on a tiny engine....
    The Predator is larger displacement and that helps it, so does the DCT....I would expect a 9.5 predator build to feel as nimble with my 19 a10...but I'm not bullish on it for sure....
    I do find it odd how everyone assumes e85 is everywhere and no one wants to pump fuel out a drum for a near daily....I guess build it and they will come truly is genius....not that we haven't used it since it come out but Ford built an engine that NEEDS it with a fuel system requiring no modifications to run and it INSTANTLY took over the conversation......lol....smart...
    I'm not trying to take over the world I'll be looking for 800whp so I'm similar to the OP, except I won't have the 5.2l to rely on to mitigate some of the part and WOT throttle power drop from going down to 9.5 to 1, nor will 12psi make 680 wheel the Predator does on a 5.0 coyote much less 800whp...wouldnt we he right back at 16-18psi making the cylinder pressures seen similar? More torque it it comes in sooner I guess? I'm more comfortable dropping to 11 for daily plus weekend warrior or staging 12 since I dont have lofty goals....( makes 728 wheel on 11psi on 93 scale that up to 5.2l would be better )...just keeping it starting after 3 engines in 5k miles will he goal number 1
     
  14. 80FoxCoupe

    80FoxCoupe Well-Known Member

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    I'd rather run more compression. Conventional methods yield conventional results....
     
  15. Toy Cobra

    Toy Cobra Well-Known Member

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    They were all very close and balanced out easily. For me e85 is easily available and it’s not my daily so it was a no brainer. With modern intercooler higher compression is not as much as an issue as it was in the past. I run a procharger D1x stage 2 and with the base 4.88 pulley on a stock engine made over 800 to the wheels. Now with a 3.90 pulley I made 1050 but am planning on going up slightly with some larger injectors and an upgraded intercooler.
     
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