More midrange torque with exhaust camshaft adjustment on nc miata

As an experiment, I have been trying new things with camshaft timing. On my Corolla, I have a 3SGE 2.0L with variable valve timing on intake camshaft, I've moved the exhaust camshaft from the factory position to 16 degrees retarded. What this has done is increase overlap of the exhaust with the intake valves. This allows the exhaust to effect the intake filling cycle. The engine gained torque throughout the mid range as well as a bit above 6000rpm.

I decided to try a version of this on the Duratec 2.0L in my 2007 Mazda Miata MX5 NC1. This job requires removing the valve cover in order to access the exhaust cam sprocket. Once accessed, I rotated the engine till the camshaft could be locked against the cylinder head, which will be aligned with the crankshaft as factory specifies. I then loosen the exhaust cam sprocket center bolt (21mm) and rotated the crankshaft clockwise one tooth on the harmonic damper. The damper has a tone ring which is a 36 tooth with gaps missing teeth to indicate position to the computer. 1 tooth of the crankshaft tone ring will equal 10 crankshaft degrees.

I put everything back together and performed an initial start. Initial impressions are that the engine idle is nearly completely un-effected. I performed a test drive while logging engine values. I found that the MAF values are higher at peak and in mid range, indicating more cylinder fill.

Over the next few days, I performed a change of engine tune. I viewed logs and made changes as necessary. I found that I was able to add more intake cam advance via the VCT settings and gained more torque in the 1800-3500rpm range. More power is made during peak torque between 5000-6000rpm. Peak torque is made at 5400rpm vs 5100rpm prior to cam timing change. Peak power moved from 7100rpm to nearly 7500rpm and more air is being pulled in from 6000-7000rpm range. Overall, I believe more gains can be made with further timing changes made to the exhaust cam.

After driving for a week and observing behavior, I have found that the ignition timing needed to be reduced by 1-2 degrees due to the increased cylinder pressures which would indicate a higher rate of cylinder fill.

Surprisingly, or perhaps unsurprisingly; more torque and mid range was made than extra peak horsepower. This has made the car more drivable at average daily driving rpms. After

evaluating fuel range changes, I have not noticed a significant difference above or below what I usually get for mileage.

-Anthony Lleras

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DISCLOSURE: I purchased all these items with my own money and the company had no prior knowledge to this promotion. All opinions are my own.