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--- camshaftsbp [2022/01/02 16:32] – [Quotes] imakeyoufast
+++ camshaftsbp [2022/01/03 09:41] (current) – [Quotes] imakeyoufast
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 ====== Camshaft Theory BP ======
+We had never too much lift ([[https://youtu.be/NZEoIy0_rqc?t=1297]])
+- DBilas
+**IVC, IC intake valve closes (at)**
+  * The significant value to estimate the target power rpm of the camshaft
+  * Later IVC -> More time to overcome the pressure differential, usage of the high velocity gas, favors HIGH RPM
+  * Too late IVC -> Cylinder pressure > Manifold pressure, loss of power (but efficiency gain through better expansion (reverse Flow Atkinson Cycle [[https://en.wikipedia.org/wiki/Atkinson_cycle]])
+**OL, O/L overlap (OL duration = IVO + EVC)**
+  * Overlap can be used to evacuate the remaining intert gas out of the cylinder
+  * Free Flow Exaust -> Inertia of the exhaust gas helps via scavenging effect
+  * Positive Pressure Intake -> Inertia of the intake charge pushes the remaining inert gas out
+If air or intake charge is pushed into the exhaust, NOx / HC emission increase. Also precious charge is wasted, resulting in higher BSFC.
+**EVO exhaust valve opens (at)**
+  * Too early -> Gas goes through the exhaust valve and doesn't participate in piston downforce -> power loss
 ===== Rotrex Specific =====
 ==== Consultation with Jeff David, who developed a Rotrex specific Camshaft for Honda K22 ====
+**Preparation**
 In my experience it's a combination package. For the bolt on's like inlet manifold, TB, exhaust headers and exhaust system use what a good/excellent NA build would choose.
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   * Free Flow Catless: 4 PSI Backpressure ([[https://forum.miata.net/vb/showthread.php?t=553290]])
   * Metal Cat, 2,5" Exhaust, Resonator and Magnaflow Muffler: 5-5.5 PSI @ 10 PSI MAP @ Redline,  ([[https://www.miataturbo.net/engine-performance-56/i-measured-exhaust-backpressure-59103/#post749282]])
+**Blow Through / High Overlap**
 As it's important to trap the fuel/air on the valve overlap, higher lift and longer duration NA cams tend to loose power due to blow through.  Specific fuel consumption goes crazy as well. On the K22 going from stock to Stage2 NA cams was +50% injector flow. Power was almost the same.
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 So I would try the mildest inlet cam you can find, hopefully with more lift than stock. And a stage 2 exhaust cam as a starting point. Fit a venier exhaust cam gear to advance it's centre line. Position based on dyno tuning but 6 degs advanced is a starting point depending on the duration.
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 k24madness Rotrex Setup ([[https://www.miataturbo.net/engine-performance-56/295whp-rotrex-c30-74-a-75473/]])
+I asked for grinds with around .400 lift and duration between 210-230 @.050
 WebCam grind #264 intake and exhaust, 110LSA, 108in, 112ex.
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 - k24madness
+----
+The BP powerband shape is very sensitive to duration @.003. The few degree increase from a 4W to a 5A shifts peak torque a few hundred rpm. We found that an Integral stage 1 NB2 cam with a bit more lift but 10° more duration at .003 was no faster on track than the stock cams even though it made a bit more peak. If it is a 5 speed or driven on street with a stock longblock, we prefer stock cams for best driveability. Breathe on the longblock or do a full I/H/E +ECU and you can afford a little more duration as the low end improvements from the other stuff over up the losses from cams. For instance, the Tomei's we offer on a stock engine with just an ECU, are awful.
+Add I/H/E + ECU with the Tomei's, particularly with a 6 speed and you have a great balance between powerband and peak power.
+- emilio700
+----