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Max Torque limit of an M20

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    Max Torque limit of an M20

    Anyone know what the max torque the stock rods can handle for an M20?

    I've read that its around the 430wtq mark, and am wondering if you kept the torque figures low at peak torque, and ramped boost in afterwards, could you achieve a much higher horsepower figure while keeping the bottom end together?

    Im currently using an M20/B27 bottom end, 280/274 cam, 6266, e85, and ms3 pro evo. Im hitting about 20psi around 4200rpm and about 18* of timing, and it holds it to redline. Its holding together so far and feels like its closing in on about 450whp. Im curious if maybe I could ramp boost to 25psi or so after peak torque (which should be around 4500rpm?), and keep the torque within its limit?

    I've seen a relatively stock bottom end M20 hit 647whp that the swedes built I think, and am curious if this was their method?
    Last edited by SLEEPYDUB; 07-18-2019, 06:05 AM.
    - AXIS POWERS - 2JZ E30 Build
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    #2
    Why bother? Are you really able to put down the 450hp you have now?
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      #3
      you can certainly help the rods out by limiting torque at lower rpm areas and the peak value. if you are using the 130 mm rods you're probably not going to get much guidance
      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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        #4
        Originally posted by digger View Post
        you can certainly help the rods out by limiting torque at lower rpm areas and the peak value. if you are using the 130 mm rods you're probably not going to get much guidance
        Thanks digger for the useful reply, I am using the stock 2.7 130mm rods. I am going to try my best to keep the torque low in the lower rpm range and peak torque, and see if I can squeeze out some more power up top.
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          #5
          A fairly effective way of limiting peak cylinder pressure is by pulling advance or boost in that range then feeding it back in to make more peak horsepower at high rpm. Put it on the dyno, find the torque peak, and keep it where it's safe (current torque level?) while adding boost after that point with EBC. If you can't control the boost that well (some setups can't), pull a few degrees of advance at the torque peak when you turn the boost up to keep the torque peak where it is. I know of cars that do this from the factory with boost and/or timing, such as some of the whiteblock turbo Volvos, which will bend rods if you just turn the boost up all over instead of limiting it at lower RPM.

          Originally posted by AndrewBird View Post
          Why bother? Are you really able to put down the 450hp you have now?
          Look at this guy's sig, I don't think he's too interested in converting all of the power into acceleration
          @turbovarg
          '91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
          [b u i l d]
          [Car of the month: April 2018]

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            #6
            Originally posted by varg View Post
            A fairly effective way of limiting peak cylinder pressure is by pulling advance or boost in that range then feeding it back in to make more peak horsepower at high rpm. Put it on the dyno, find the torque peak, and keep it where it's safe (current torque level?) while adding boost after that point with EBC. If you can't control the boost that well (some setups can't), pull a few degrees of advance at the torque peak when you turn the boost up to keep the torque peak where it is. I know of cars that do this from the factory with boost and/or timing, such as some of the whiteblock turbo Volvos, which will bend rods if you just turn the boost up all over instead of limiting it at lower RPM.



            Look at this guy's sig, I don't think he's too interested in converting all of the power into acceleration
            Varg, I use a 4port ebc with my MS3 to control boost. It works pretty good despite using a rapidspool manifold which is notorious for creep, so i just have a declining duty cycle to keep the boost consistent. Ive got a good little dip in timing around max torque, which starts around 4000 and ends at 5000, where it ramps back in. I will try this method out and couple the torque limit by limiting the boost in that section as well.
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              #7
              one of the issues you face is that at higher rpm the cylinder pressure which is what hurts the rod doesn't follow the torque output as nicely due to reduced efficiency, more heat and more tendency for combustion issues so the proposal you are putting forward is not foolproof. just bear that in mind and tread carefully
              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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                #8
                Thanks for the headsup digger, i will keep that in mind
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                  #9
                  Cylinder pressure vs rpm... Speaking in generalities, since specifics depend on the engine itself and tune. Highest peak pressure tends to occur at or around the torque peak, then peak pressure tends to decrease as rpm climbs. The timing of the pressure peak itself also varies with engine rpm, without respect to ignition advance, tending to occur progressively earlier until around the rpm at which peak torque occurs and then later after peak torque. The optimum time in the stroke for the peak of pressure to occur is several degrees ATDC, later and you lose torque, earlier and you risk engine damage. The objective when tuning is to maximize the cylinder pressure, to a point, and move it to that most optimal position in the stroke. Advancing the timing not only increases the peak cylinder pressure but moves it closer to TDC. The attached plot shows the above, albeit rather poorly labeled, cylinder pressure varying with respect to crank position, without respect to ignition advance which was fixed at 18BTDC (very important for the purposes of this comparison!). The other plot shows the rough location of peak torque for the research engine for reference when using the other figure. This is general behavior for a 4 stroke gasoline engine, specifics are highly dependent on many factors but this general behavior will apply to an M20 just as well as it applied to the single cylinder test engine.

                  Originally posted by SLEEPYDUB View Post
                  Varg, I use a 4port ebc with my MS3 to control boost. It works pretty good despite using a rapidspool manifold which is notorious for creep, so i just have a declining duty cycle to keep the boost consistent. Ive got a good little dip in timing around max torque, which starts around 4000 and ends at 5000, where it ramps back in. I will try this method out and couple the torque limit by limiting the boost in that section as well.
                  You know by now that at these levels it's best to be conservative to avoid crossing the line. This is something you'll just have to dyno tune. Pulling a bit of advance around peak torque is common practice but you might have to pull more to actually limit peak torque. It's good that you have decent boost control because that will help.

                  Your creep issue is interesting. I have boost creep so bad that my duty table has a steep slope and with the wastegate actuator unhooked I can make 12psi at redline :) I'm somewhat surprised that you have creep with a nice external wastegate, but then again depending on your setup it's possible that you just have a very nice exhaust to boost pressure ratio which will reduce the effectiveness of a wastegate setup with routing that involves drastic changes in direction.
                  Attached Files
                  Last edited by varg; 07-19-2019, 06:56 AM.
                  @turbovarg
                  '91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
                  [b u i l d]
                  [Car of the month: April 2018]

                  0c8b7c9527af628a346878feb14bf757

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