Oil Filters & Metering Oil Pump

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The installation of a remote oil filter mount eases engine installation and removal.

Oil Filters

We recommend the use of the stock Mazda oil filters for all applications other than serious race cars. The only undesirable feature of the factory oil filter is the internal pressure bypass. If the engine is cold and the RPM is high, the pressure differential might exceed 14 psi., causing the filter to bypass some contaminants that the bearings likely can't handle. To avoid this, always warm up the engine gradually and fully before running at high RPM.

Remote Mount Oil Filters

For serious racing applications, remote, non-bypass filters perform better than stock filters/mounts. We recommend installing a remote, double oil filter assembly on the return line from the oil cooler.

The remote filter mounts we offer allow installation of temperature and pressure senders away from the engine block, thereby simplifying engine installation and removal. Use of the FRAM HP-2 model non-bypass filters will provide both excellent filter capacity and elimination of the bypass. One other filter possibility is the FRAM HP-6. It is larger in diameter the HP-2, but only one filter is necessary, thus making it easier to mount. The only limitation to this filter is that it has an internal pressure bypass set for 22 psi. However, this is high enough that bypass is unlikely to occur in reasonable use.

Rotaries can also be run with a dry sump oil system; that is, an oil system that pumps the oil out of the bottom of the engine into an external tank, then picks it up from the tank and supplies it to the engine. The primary reason for doing this is to gain clearance under the engine, or to allow the engine to be lowered (the pan is commonly replaced with a flat plate). If the tank is well designed, this system also aids oil cooling by removing the air from the oil before cooling.

Metering Oil Pump

The metering oil pump is a useful but misunderstood component of a rotary engine. It rarely gives any trouble, although people commonly try to blame the metering oil pump for high oil consumption. In fact, if the pump fails, it usually simply stops operating. The only likely exception would be if the linkage from the carburetor, or injection throttle body, becomes hung up in the "full throttle" position in 1988 and earlier models.

This condition is quite easy to diagnose. If the problem is not in the linkage, the rotor oil seals are the most likely source of trouble. As a general note, later model rotaries commonly get 2,000+ miles per quart of oil. If oil consumption exceeds one quart in 700 miles, the engine probably needs an overhaul. The factory recommended setting for the metered oil volume has generally been getting lower and lower.

Metering Oil Pump Rates

The metering oil pump found on all 1989-95 RX-7s is an electronic unit that cannot be externally adjusted to change oil flow delivery; however, if you require additional oil flow, you can completely remove this electronic unit and fabricate a cover plate with an adjustment screw mounted in it to allow manual adjustment of the oil flow. This cover plate replaces the electronic control.

The metering rates for stock engines vary, so consult an appropriate shop manual for your car’s specifications. In normally aspirated racing vehicles we use either a setting of 5cc/5minutes (total flow - 2,000 RPM, warm engine, arm in the "full throttle" position) on the metering oil pump or premix 3.5 oz of good quality synthetic oil (preferably 2-stroke motorcycle "oil injection" oil) to 5 gallons of fuel. The requirement for turbo engines in racing is high enough that use of a metering oil pump is impractical. Therefore, we premix up to 22 oz of oil to 5 gallons of fuel in a 600 HP 2-rotor. If you are not pressing your engine this hard, you can use proportionally less oil.

RX-8 - Race Tips

While undertaking development work on the RX-8 Renesis engine for SCCA T2/T3 use, we decided to introduce extra oil into the fuel to monitor the effect. To our surprise, this additional oil increased power! Further dyno testing found that by adding 10 oz. of Royal Purple 2-Stroke Oil to 6 gallons of fuel, we gained an average of 1.7 HP from 2000-9000 RPM, along with an increase in peak power of 4 HP. We validated this increase by changing back to a "non-oiled" fuel - and the power returned to the previous level. Later, we tried the same test with another brand of synthetic oil with nearly the same results.

For racing applications, the addition of a high quality synthetic oil increases power and most certainly decreases wear. The only negatives are the cost of the oil and an increase in the tendency to foul the spark plugs. (Note: We have not performed these tests on non-RX-8 engines yet, these results are unknown.)

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