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Thread: raising compression?

              
  1. #26
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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    I'm pretty sure i'm going to lower the compression from 10.2 to something, just so i can be sure i'm able to throw ALL the boost at it

    the issues isn't JUST cylinder pressures though, just the most simple one to articulate... it's also heat and .. probably plenty of other variables i'm not educated enough to know about... the cooler you can get your cylinders, the more pressure you can add (heat) before the fuels knock point will occur, the 'max' could vary a fair bit depending on specific conditions and variables you're comparing
    Yes but compressing and more and more air raises heat as well right?

    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    i think we're starting to get into slightly other topics specifically to do with the tuning though?
    Whatever, we can discuss what we feel like discussing.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
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    Yes but compressing and more and more air raises heat as well right?
    true.. but also intercooler efficiencies, methanol/alcohol injection (or nitrous if you're keen), less backpressure so SUPER hot manifold gases stay the hell away from the cylinder, turbo being efficient/in efficiency range... EGT's s staying as low as possible so the turbine wheel doesn't transfer as much heat and stays efficient (which i guess is all a byproduct of the above somewhat) .. much much more?

    really, the only way we'll get an answer to this for this particular application for a particular setup, is for someone to do it

    really, if anyone wants to try a higher compression ratio, i'd love to compare notes/figures when it happens

    either way, it's not like it'll totally ruin the N54, at worst a little less power in the top end with some more low-mid, and probably still happily make NEAR as much power as you would stock

    Click here to enlarge Originally Posted by Sticky Click here to enlarge
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    Whatever, we can discuss what we feel like discussing.
    well fair enough

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
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    Oh well of course, I assumed all things were equal other than the compression in the example.
    Sure. In my example you're running the same boost, same gas, and you TRY to run the same timing in both a low CR and a high CR. In the high CR case, the DME will likely pull timing and will potentially result in less power. (Note that there's no testing to back any of this thread up, it's all conjecture to this point).

    @Flinchy
    I mean given the MAXIMUM octane theoretically possible, an intake and turbo capable of delivering X theoretical psi and Y air flow rate (whatever you can dream of), and the stock N54 block/internals increasing the CR from an already octane limited tune will likely result in pulled timing (less power).

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    really, the only way we'll get an answer to this for this particular application for a particular setup, is for someone to do it
    Yes.

    But it's fun to debate theory, and I get to learn new $#@! in the process!

  5. #30
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    Click here to enlarge Originally Posted by trufus Click here to enlarge
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    Sure. In my example you're running the same boost, same gas, and you TRY to run the same timing in both a low CR and a high CR. In the high CR case, the DME will likely pull timing and will potentially result in less power. (Note that there's no testing to back any of this thread up, it's all conjecture to this point).

    @Flinchy
    I mean given the MAXIMUM octane theoretically possible, an intake and turbo capable of delivering X theoretical psi and Y air flow rate (whatever you can dream of), and the stock N54 block/internals increasing the CR from an already octane limited tune will likely result in pulled timing (less power).
    what about if you throw in some sort of Aftermarket management/situation where the DME won't arbitrarily pull timing when a feather sits on the car?.. assuming the tune is solid and safe (but still as much power as you can go safely)

    true, if there's a bit timing pull, any power gains are pretty moot - that would all come down to tuning though no? not like you can just throw the pistons in and leave it.

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    what about if you throw in some sort of Aftermarket management/situation where the DME won't arbitrarily pull timing when a feather sits on the car?.. assuming the tune is solid and safe (but still as much power as you can go safely)

    true, if there's a bit timing pull, any power gains are pretty moot - that would all come down to tuning though no? not like you can just throw the pistons in and leave it.
    Ah, yes. But now you've thrown a wrench in my scenario and it's different from what I described. Now you have none of the DME niceties. No stock knock prevention, only what is plugged into your new controller. The scenario is still applicable, however. How far can you go until you blow up a motor?

    Agreed its all down to the tuning, but we're talking about compression not tuning. I don't disagree that the tuning will play a role in this, but academically there is a point where, assuming you have "perfect" tuning, increasing compression ratio is NOT a valid way to increase power. The issue now is that there is a complete lack of REAL data as far as the ideal compression ratio is concerned. While its fun to debate the academic merits of increasing or decreasing the CR, there's no conclusive evidence as to which will make the most (or best) power yet.

    Bottom line is that @WDBi should spend his $$$ to experiment for us and let us know how it goes... Click here to enlarge

  7. #32
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    lol wow this thread kinda blew up.

    i was just looking around and came across this http://www.modularfords.com/f17/incr...ressure-51059/

    i what im probably going to do is wait for a good turbo upgrade to come out like the vargas set and when that happens i will port my head and build the motor and possibly raise compression i have to look into it more
    Turbo lag is the on ramp to the highway which is power.

  8. #33
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    Click here to enlarge Originally Posted by WDBi Click here to enlarge
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    lol wow this thread kinda blew up.

    i was just looking around and came across this http://www.modularfords.com/f17/incr...ressure-51059/

    i what im probably going to do is wait for a good turbo upgrade to come out like the vargas set and when that happens i will port my head and build the motor and possibly raise compression i have to look into it more
    GREAT info in that thread. This seems like the key takeaway to me...
    Therefore, for any given fuel and AFR, etc., one can make more power & torque at any given engine speed by reducing CR and increasing boost pressure, than the other way around for the same peak cylinder pressure
    Obviously there are application specific concerns (what is the maximum N54 MEP (Mean Effective Pressure) at detonation for a given fuel (and stock internals)?) but this rule makes mathematical sense to me now...

  9. #34
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    Why rather than the way other around if peak cylinder pressure is the issue? Isn't it a wash?

  10. #35
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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    it's a bit more complicated though, how much absolute pressure can the stock rods handle? how much more heat, therefore less efficiency, will the stock turbo have put into it?
    I'm going to assume that since he is talking about raising compression, one would replace both rods and pistons with upgraded aftermarket peices.


    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    more compression = more heat = hotter turbo = less efficiency in the compression
    Ethanol mitigates this greatly.


    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    however, if, yes, the factory turbo can take more compression, all well and good, but going the high comp build will cost as much (more) than RB/VargasII turbos, and you'll still end up with less power, and you'll 100% defintely be restricting them by then.

    so, yeah, if you could run more compression on stock turbos with more E85, go right ahead, but upgrading the turbos is cheaper, more effective, and will work BETTER on lower compression.
    Completely agree, but OP never mentioned he was looking for the cheapest way to make more power, he wanted to know if he was building for E85, would be an advantage to run higher CR. The answer is without a doubt, YES.
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  11. #36
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    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
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    I'm going to assume that since he is talking about raising compression, one would replace both rods and pistons with upgraded aftermarket peices.
    True, but this now costs $4k~ in parts plus labour and boring out the block.. So $5k pretty neatly just or the bottom end.. I know we're not really talking about cost effectiveness, but when you're talking about this level of cost/gain, it deserves a mention lol
    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
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    Ethanol mitigates this greatly.
    yes? And? You could either run more compression or more boost..




    Click here to enlarge Originally Posted by lulz_m3 Click here to enlarge
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    Completely agree, but OP never mentioned he was looking for the cheapest way to make more power, he wanted to know if he was building for E85, would be an advantage to run higher CR. The answer is without a doubt, YES.
    What? That's not the outcome that's been discussed in this thread?

    correct me if i'm wrong, but the n54 gets on boost around the high 1xxx-2k ish rpm, and full boost 3000ish?

    You'll only be better off power wise when your turbos are below max cylinder pressure, and you'll see most difference off boost, up high you'll probably have to pull timing, so almost no matter what, less up top, and maybe similar midrange at best

    if you want more in the mid range and peak, bigger turbos, more boost (rb turbos spool like stock almost don't they?), cost less too.. Dzenno's recent results show slightly lower compression leads to buttloads more power and a much healthier tune.

    if you want more off boost and JUST on boost, raise compression, a more pleasant daily driver, not as fast, LOTS harder to tune, less timing, less boost.

    That's what i'm getting out of this.. You can't just go crazy raising compression and expect good results, where lowering makes it a fair bit easier to get more power on-boost... It's very 'what you want' specific, as to whether you raise or lower or stay stock.. Never see redline? Well kinda strange to be doing this work or driving this car, in the first place..
    Last edited by Flinchy; 12-07-2012 at 08:30 PM.

  12. #37
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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    Dzenno's recent results show slightly lower compression leads to buttloads more power and a much healthier tune
    Unfortunately the way Dzenno did his testing the only thing we know is that e85+meth+more boost= more power. Changing several different things at once has made it impossible to tell what has done what.

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  13. #38
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    I'm not looking for the cheapest way to make power. And i just say stock turbos because im waiting for more options to come out. I am looking into doing motor work pistons, rods, and head work. So i can have fun on the turbos before nee options come and when those come it will be really worth it.
    Turbo lag is the on ramp to the highway which is power.

  14. #39
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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
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    Unfortunately the way Dzenno did his testing the only thing we know is that e85+meth+more boost= more power. Changing several different things at once has made it impossible to tell what has done what.
    he already ran E85 and meth

    more boost and timing was allowed through lowering compression to 9.93 (or whatever it was):1, more than the extra flow.. it's pretty obvious to tell what did it, not impossible at all..

  15. #40
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    Click here to enlarge Originally Posted by WDBi Click here to enlarge
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    I'm not looking for the cheapest way to make power. And i just say stock turbos because im waiting for more options to come out. I am looking into doing motor work pistons, rods, and head work. So i can have fun on the turbos before nee options come and when those come it will be really worth it.
    fair enough if you're already planning on EVERYTHING... but what the basic outcome will be, is less power on boost (once you're at a decent number of psi) and more power off boost.. probably SLIGHTLY earlier spool, and better response.

    I really do think you should do it if that's what you want, it's a cool thing!

    Just don't *expect* the same numbers you'd see on stock or lower compression, but be pleasantly surprised if they're still decent lol.

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    If you're not making more power with more compression it's because you don't have enough octane.

    MOTIV750, MOTIV P-1000 PI, MOTIV/FUEL-IT! low pressure fuel system, AEM EMS/COBB AP, Aquamist HFS-3, ETS FMIC, SPEC stage 3+ clutch/SS flywheel, BC Racing coilovers and VMR wheels wrapped in Hankook RS3s.

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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
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    If you're not making more power with more compression it's because you don't have enough octane.
    orrr.. you're having to pull timing.. (or worst case, lower boost)

    you make more power with higher or lower compression, it can't be both ways just the same... if you make more power with higher compression then it'd make sense to lose power with lower compression...

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    orrr.. you're having to pull timing.. (or worst case, lower boost)

    you make more power with higher or lower compression, it can't be both ways just the same... if you make more power with higher compression then it'd make sense to lose power with lower compression...
    If you're having to pull timing(or run less boost) it's because you don't have enough octane.

    If everything else stays the same and you lower the CR then YES YOU WILL LOSE POWER. You will have to raise boost/run more timing to make the same power. The only thing lowering the CR does is provide a pump gas friendly safety net.

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  19. #44
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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
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    If you're having to pull timing(or run less boost) it's because you don't have enough octane.

    If everything else stays the same and you lower the CR then YES YOU WILL LOSE POWER. You will have to raise boost/run more timing to make the same power. The only thing lowering the CR does is provide a pump gas friendly safety net.
    so if you're runnign pure e85, you can magically get more octane from where now?

    i thought we were talking 100% e85 in both the low AND high compression situations

    no, lowering the compression lets you run more boost and timing for MROE power, not just the same.. why do you think when evo owners swap to a 100% E85 tune, they magically gain 70 odd wheel horsepower over their pump gas tune? magic?.. raising means you have to lower both variables (or at least timing), if you've advanted the timing as far as you can before knock on 100% E85, then raise the compression you WILL have to retard it.

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    so if you're runnign pure e85, you can magically get more octane from where now?

    i thought we were talking 100% e85 in both the low AND high compression situations

    no, lowering the compression lets you run more boost and timing for MROE power, not just the same.. why do you think when evo owners swap to a 100% E85 tune, they magically gain 70 odd wheel horsepower over their pump gas tune? magic?.. raising means you have to lower both variables (or at least timing), if you've advanted the timing as far as you can before knock on 100% E85, then raise the compression you WILL have to retard it.
    Yes, lowing CR lets you run more boost/timing. In fact, like i said, you HAVE to run more of both to equal the power from the higher CR.

    Check this out
    http://www.musclemustangfastfords.co...o/viewall.html

    MOTIV750, MOTIV P-1000 PI, MOTIV/FUEL-IT! low pressure fuel system, AEM EMS/COBB AP, Aquamist HFS-3, ETS FMIC, SPEC stage 3+ clutch/SS flywheel, BC Racing coilovers and VMR wheels wrapped in Hankook RS3s.

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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
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    Yes, lowing CR lets you run more boost/timing. In fact, like i said, you HAVE to run more of both to equal the power from the higher CR.

    Check this out
    http://www.musclemustangfastfords.co...o/viewall.html
    i didn't quite understand from the aritcle how a lower compression motor had the supercharger produce less boost?

    shouldn't the supercharger be spinning at the same RPM in the same pulley/intake setup for the same boost?

    if so, that would explain a lot of the power difference, more than JUST the lower compressoin?

    this makes no sense to me and i've read it twice >_<

    "The uninitiated may be tempted to attribute the drop in power on the supercharged applications to the drop in boost pressure,"

    well, that's PART of the problem isn't it? :/
    Last edited by Flinchy; 12-08-2012 at 02:01 AM.

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    i didn't quite understand from the aritcle how a lower compression motor had the supercharger produce less boost?

    shouldn't the supercharger be spinning at the same RPM in the same pulley/intake setup for the same boost?
    The motor's breathing changed and with it the backpressure.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
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    The motor's breathing changed and with it the backpressure.
    wouldn't lower compression lead to less back pressure, so more flow?

    how would this effect the air that the blower is pumping out still? as it's not connected to the exhaust at all, only the intake.

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    wouldn't lower compression lead to less back pressure, so more flow?
    Why? I'm not entirely sure but clearly back pressure changed if the boost changed when the pulley remained the same. It has to be attributed to the compression change as nothing else changed.

    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
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    how would this effect the air that the blower is pumping out still? as it's not connected to the exhaust at all, only the intake.
    Maybe this chart can shed some light, final compression ratio:


    Click here to enlarge

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
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    Why? I'm not entirely sure but clearly back pressure changed if the boost changed when the pulley remained the same. It has to be attributed to the compression change as nothing else changed.



    Maybe this chart can shed some light, final compression ratio:


    http://www.audiboost.com/images/impo...12/nkVlr-1.png
    Yeah, but final compression ratio is whatever boost is being run * static compression ratio ?.. not actual boost productin being effected

    i can't fina any info on CR effecting supercharger output anywhere, i'm still trying though.

    i get that's the only differing factor, but i was always lead to believe that a supercharger of a certain size with a certain pulley etc. will always (well, in theory) produce the same amount of boost and airflow.. i didn't even really know that backpressure into the intake manifold was a major thing! i just thought exhaust backpressure was the main issue usually

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