The Guide to Performance and Longevity

The guide although primarily intended to help RX-7 FD owners enjoy an optimum balance of performance and longevity, can be applied to all rotary engines, piston engines and most mechanical devices where applicable.

The Legendary RX-7 FD

When production started in 1991, who would have thought that after more than two decades the RX-7 FD would still provide a driving experience superior to many newer world class machines. No doubt the sleek & sexy aerodynamic shape with silky smooth turbo rotary power helped create it's legendary status as one of the most sought after sports cars on the planet. Beautiful, powerful and deceptively fast, the RX-7 FD3S delivers speed and excitement with every drive.

Don't let fun become fatality, it is a fact, that mechanical things will function as designed for a period of time, then preventive maintenance must be done. If neglected one can expect less than optimum performance or worse, a failure may occur. When you trust your life to a mechanical device it should be routinely inspected and up to date on maintenance. You should always ensure you have clean fluids, clean filters, good brakes, solid suspension and good tires. Obviously, if something is wrong, continued use will usually cause more damage and added expense for repairs. With any vehicle, suspension, brakes and fuel system problems can be extremely dangerous and should be corrected without delay. Don't let fun become fatality.                                                                                                   

Safety first: Get a fire extinguisher!       

 A must have for any and every vehicle, somewhere it’s written, “If you have it you won’t need it”, this is very good when it comes to Fire Extinguishers!

Our Fire Gone Extinguishers use the latest fire suppression technology to quickly extinguish nearly all types of fires. Makes a great gift and is truly a must have item for any and every vehicle! 

Fuel requirements

We recommend a minimum 93 octane gasoline for all turbo or supercharged rotary engines. Just one tank of low-octane fuel can cause an instance of detonation and can compromise an apex or compression seal. Basically all fuel everywhere will contain 10% or more ethanol. Ethanol is basically alcohol, great for cleaning but is probably not the best thing for engines, especially rotary engines. Another reason to use premix fuel lubricant. The BTU's contained in ethanol are about half that of gasoline which can cause up to a 5 percent reduction in power in older cars not setup to run this new fuel. Also slightly increasing your chance for detonation. Just something to be aware of, the closed loop system on cars attempts to correct this for low throttle conditions but doesn't really do anything for full throttle. This problem can be fixed with a slight bump in fuel pressure or aftermarket tuning options.

Low octane and poor quality fuel is a serious problem for turbo rotaries, unfortunately there is no simple method for testing octane and you never know if the fuel was bad until it is too late. We recommend always buying fuel from Shell or Marathon fuel stations.

Fuel lubricant (premix)

The oil metering system is responsible for lubricating the delicate apex seals, compression seals, and housing surfaces that are common to every rotary engine. Oil is fed from the engine oiling system (oil-pan) to a variable ratio-metering pump. Then it’s injected into the engine where it partially blends with the onrushing air-fuel charge. This incomplete blending and fuel-to-oil ratios of 400:1 and higher are cause for alarm. Also, unleaded fuels typically have additives designed to clean piston engines, then high combustion temperatures of the rotary together with ethanol blended fuels cause the minute film to disperse and /or vaporize leaving all your critical surfaces clean and dry without protection. This causes increased friction and wear, resulting in decreased performance and longevity. With over 25 years experience and more than 2000 rotary engines built, we know excessive wear on apex seals, compression seals and critical surfaces is caused from inadequate lubrication. Without extra lubrication added to the fuel, friction and heat will cause accelerated wear that is proven to cause premature failure of some expensive engine parts. Great for Mazda’s profits but not good for you and me.

If we expect our rotary engines to deliver top performance year after year, it is clearly evident that extra lubricant must be added to the fuel. Back in the mid 80’s we developed Protek-R fuel lubricant for our racing efforts and it was first released for sale in 1990. Since then, 30 years and counting our customers around the world enjoy reduced friction and wear as well as added performance and longevity. There is no doubt Protek-R had a major role in all our race victories, 5 championships, over 50 SCCA national race wins, many top finishes in professional endurance racing like ALMS & the Rolex 24 hr races, as well as providing the added performance and longevity needed to win the 1998 GT-2 Road Race Championship. From the Rolex 24 at Daytona, to the 6 Hrs at the Glen, we ran the same engine, nearly 130 hrs of racing. We also use premix in our piston engines, some folks disagree but think about this, diesel piston engines can make it to a million miles, but gasoline piston engines never even get close, both use nearly the same parts and materials but diesels have higher compression, more stress and higher loads. So why is it they last the longer? Diesel fuel is oil! There is no doubt using fuel lube in gas piston engines will more than double their longevity.

Boost gauge

A boost gauge is one of the best longevity upgrades you can do. Numerous times we have seen engine blow just because people trusted the OEM boost gauge. Which in the RX-7s can be notoriously inaccurate. We seen OEM boost gauges off by 20 psi or more on numerous occasions and always recommend you get an accurate gauge immediately.

The oven door

Whenever possible, open the oven door (hood) this stops the baking process and improves longevity for all under hood components. 

Before you upgrade:

Before upgrading or adding more upgrades, scheduled maintenance and all the common issues should be updated or corrected first. Upgrading a poorly maintained vehicle with inconsistent performance, drivability problems or any boost issues will not produce the expected results and could even cause expensive engine damage. We often see poorly running FD’s with several upgrades that were installed to fix drivability and/or performance problems, typically if it is not running right, upgrades don’t help.

We recommend installing upgrades in logical stages and just one at a time. This allows you to evaluate changes in vehicle dynamics from each modification, then if any problems arise, you only have to go one step back to find the cause.

Ongoing issues / problems

Nearly any RX-7 FD can be setup to deliver a balance of performance and longevity beyond expectation delivering years of reliable driving enjoyment. To achieve this only requires learning some basic techniques to keep minor issues from becoming major problems and get a few simple updates and correct some commonly overlooked details.

This is especially important for FD’s with a history of problems that dealers and various shops either didn’t help or made worse.

Most common problems listed by importance & frequency

1. Cooling system: air separator tank failures, high operating temps & overheating
2. Oil metering system: inadequate lubrication, increased wear & apex seal failures
3. Air filter box failures: allow dirt & abrasives in, engine wear accelerated
4. Ignition system: wires, coils & plugs
5. Sequential turbo system: leaks, malfunctions, overboost
6. Thermal management: radiant heat can lead to detonations

Cooling system information and recommendations

The first priority for RX-7 FD’s & nearly all liquid cooled engines is to have proper and efficient cooling. This is essential for consistent top performance, many years of longevity and driving enjoyment.

Cooling system facts

It is a well known industry fact that cooler operating temperatures usually provide the best performance and longevity for any vehicle as well as all under hood components. On the US spec RX-7 FD the cooling fan thermo switch and thermostat are factory set to maintain a minimum operating temperature of 92C / 197.6 F but with age, use and heat cycles these parts slowly degrade requiring higher and higher temperatures to open the thermostat and trigger the fans. As a result of this it is not uncommon to see temperatures of 104C / 220F and higher. Another commonly overlooked fact is that the engine temperature gauge is nonlinear and displays a normal reading from 71C / 160F all the way up to 113C / 235F, manufactures do this to avoid complaints and questions about gauge variations from driving conditions and weather changes. So by the time the gauge even moves you're already overheating.

Coolant Loss

When a leak occurs and the coolant level drops just a couple of inches, the temp gauge sensor is no longer immersed in coolant and since the leak depressurizes the system, the boiling coolant at 100C / 212F causes the gauge to display a normal reading even though the engine is getting hotter and hotter.

Rotary engines suffer the most of any engines when overheated. The brunt of heat is concentrated in the combustion area (from spark plugs to the exhaust port) super heating the aluminum rotor housing, this usually results in rotor housing shrinkage and coolant seal failure. This is also detrimental to all the accessories on the engine. We have actually seen engines run with no coolant until the aluminum around the spark plugs and exhaust port melts away.

Most coolant leaks usually start out small and go unnoticed until they are dripping on the ground or your engine is overheating. Coolant leaks can occur if any of the following items fail:

1. Air Separator Tank, thermostat & fan switch
2. Engine internal coolant seals   
3. Radiator leaks
4. Hose leaks
5. Cooling fan relays or motors
6. Water pump, housing or gasket leaks
7. Freeze plugs and core plug leaks

The OEM air separator tank is plastic and known to fail. They either split on the glued seam or the neck deforms from the pressure caps spring tension and heat cycles. If the tank splits it can cause rapid coolant loss and overheating of the engine. This almost always results in engine damage. A deformed neck reduces holding pressure allowing coolant to escape and if unnoticed can also result in overheating. Pettit’s aluminum air separator tank upgrade is a direct replacement for the stock part and is far superior to the original plastic unit. The all aluminum construction and added capacity not only makes it stronger but more effective as well. In an emergency the lever vent cap allows you to safely depressurize the system for repairs or inspection. Our AST is highly recommended for every RX-7 to prevent overheating.

Most RX7 FD’s on the road today already have our aluminum upgrade unit. Many owners have never seen an original and ordered ours before realizing their car already had one. The original plastic unit is black, with age it could appear as drab olive green. The top is square and the cap is the same size as the engines. Our original AST’s are round, usually silver or black with a large cap and usually a red vent lever.

Besides replacing the plastic air separator, there are a few other simple inexpensive but important upgrades that every RX7 needs. We recommend our 82C / 180F thermostat and our 85C / 185F fan switch. Together they can reduce operating temperatures significantly. 

The RX-7’s closed cooling system works like this, with each heat cycle coolant is discharged from the AST raising the coolant level in the recovery reservoir, then during the cool down cycle negative pressure (vacuum) continues to increase until it allows atmospheric pressure acting on coolant in the recovery reservoir to push open the pressure cap recovery valve, thereby refilling the AST. If either cap is opened before the recovery cycle is complete it will probably be necessary to top off the coolant.

In a closed cooling system you should never hear boiling, that typically means some air has gotten in and /or it's not holding pressure. First thing to check is the coolant level in the radiator and the AST, if there is any loss of coolant it it's important to find the leak and repair it.

In warm climates it can take 8 to 12 hours to complete the cycle, best time to check is first thing in the morning before starting the engine, when you remove either the radiator or AST cap, both should be full right to the top and the recovery reservoir’s dipstick should be up to the full cold line. If the system needs some coolant and the recovery reservoir is full that typically means the cycle is only half working, it's discharging the coolant when hot, but it's not recovering it during cool down. That is the most common issue and typically means the AST cap is not sealing properly. Check the AST and it’s caps upper and lower sealing surfaces, both must seal perfectly. If there's any trash or debris on the seals it could cause it not to recover. The best way to figure this out is to make sure the engine and AST are full and check/note the level in the recovery reservoir, then after getting the car hot, the level in the recovery reservoir should be higher. The next day it should be lower and the engine and AST should be full. If it is still high, the AST is probably low, until it's working properly it's a good idea to check it each time before driving. That way you can observe the level in the recovery reservoir and know that it's working right. The caps can fail as well, so that's something to mindful of. Also, since the recovery reservoir is open to the atmosphere the coolant will evaporate and need to be topped off from time to time.

The RX-7 FD OEM radiator is a quality part, but few are still in use due to the plastic tanks failing. After some time they usually leak from the tank to core seal. Any time overheating occurs, it shortens the radiators life. You should replace the radiator every 5 years or so, preferably with an all aluminum unit.

Hose leaks typically occur next to the clamp, pressure swells the hose against the clamps edge and it weakens eventually failing. Cutting back the hose a little and re-clamping will usually buy some time and avoid a major leak. Our HD silicone radiator hose kits are a much more solid option for upgrading all the old OEM hoses.

The cooling fans and relays are another common problem, there are four relays powering two fan motors for low through high speed operation. They are controlled by the fan switch, A/C and/or ECU. Most FD’s have the cooling system recall upgrade, it allows the fans to operate without the engine running via a control unit mounted behind the ECU, however, one of the recalls harnesses is located under the hood and has connectors that are not hermetically sealed. After getting wet a few times the connections can weaken then when the ECU requests high speed fans, the voltage drops and the connectors overheat or melt preventing the fans from high speed operation, which can cause overheating. We commonly service and replace the connectors, relays and motors.

Water pump leaks are less common due to better pumps and but can often leak usually when the system is cold and depressurized.

Core or freeze plug leaks are only common on engines with neglected and rusty cooling systems.

Ageing components and neglect, or a combination of both may play a part in several problems that no doubt will cause 7 owners some severe headaches. Proper and efficient cooling is essential if reliable performance and improved longevity is desired. So the proper attention to the cooling system is a key factor in optimizing the FD and all liquid cooled engines in general.

Flaky Oil Gauge

The oil pressure sending unit is below the oil filter and often the wiring is loose. The harmonic frequencies through the RPM ranges and pulsations from the oil pressure perhaps cause the wire connector to loosen grip on the terminal, usually a little squeeze on the connector to tighten it up helps.

OEM Air Filter Box

The oem filter box is well known to fail allowing dust, dirt & foreign matter to bypass the filter blasting the turbo compressor wheel with unfiltered air at the speed of sound. Another issue with the factory airbox is the air comes in from the intercooler air duct, so under moderate to hard acceleration the engine takes most or all of the air which prevents the intercooler from working. The first product we designed for the RX-7 back in 1993 was our cold air induction system, it receives it's air from the front nose opening which improves the efficiency of the stock intercooler significantly.

In 1999 Mazda also corrected the problem by feeding the airbox from a passage behind the front license plate on the new nose design.

Ignition system, wires, coils & plugs

The spark plugs must be properly tightened for the most effective heat dissipation. You can check your old plugs for flattened crush washers to see if they were properly installed. When installing the plugs, it's imperative to route the spark plug wires appropriately. When connecting plug wires to the plugs, the boot will slide until a snap is felt. If the boot resists sliding, spit helps lubricate things up.

Coil harness routing

The coil harness should be routed along the base of the coil mount exiting in front of the oil fill tube and over the top of the oil feed tube. Then you can tie wrap to the oil fill tube in position between the front trail and lead plug wires. On old coil harnesses eliminate the ground wire.

 

Plug wire routing

Looking at the trailing #2 (rear coil), the plug wire should point rear to 3:00-4:00 curving around and down connecting to the rear top trail plug. It should keep some distance from the coil’s primary plug and harness. For the FD leading plug wires, the coils top position connects #1 lead plug wire to front lower (lead) plug.The bottom coil position connects #2 lead plug wire to the rear lower (lead) plug.

 

Sequential turbo system testing, fixes & calibration

The following information relates to turbocharger failure prevention and the general acceptance that turbo failures are normal and expected.. It is common to hear I always start my car and let it run for 15 minutes before driving. Then let it run for 10 or 12 minutes to cool the turbos when I'm done. In just 1 year of daily that can add up to an extra 150 hours of use, wear and tear, unnecessary fuel consumption and as a result, more emissions.

Letting engines idle to warm up dates back to the early days of automobiles and trucks, back then you had to warm them just so they would run properly. It's one of those handed down things my dad's dad did and that's just how we do it, we don't question it.

With today's vehicles, idling to warm the engine has many negative points: only the engine warms not the driveline, tires, brakes or suspension. It causes unnecessary wear and isn't recommended anymore. Instead of idling to warm up, just drive easy gently warming everything at once.

Turbo timing cool down

Seems with turbos everyone agrees, idling is necessary to cool down the turbos. For countless years idling is how turbos has been viewed as the optimal way to extend turbo life, but is also somewhat of a farce. Idling still produces heat feeding the turbo hot exhaust, did you ever notice even after idling for a few minutes, four or five hours later the exhaust is still too hot to touch? Instead we recommend when you arrive at your destination immediately shut the engine down, then turn the key back on allowing the fans to cool the radiator. After a minute or so restart the engine for 10-15 seconds, the cooled radiator fluid circulates through the turbos and fresh oil pumps on the turbo bearings and shaft preventing carbon and coking of the bearings. Usually 2 cool down cycles rejects enough heat to prevent carbon and coking of the bearings. At the track misting water on the radiator and oil coolers while performing 5-6 cool down cycles rejected enough heat that you could touch the turbo. 

Turbo failures

Endurance road racing turbocharged rotary engines is a challenge to say the least. Our turbos seemed to be holding up well as long as we serviced them every two races, polished the turbine end of the shaft and maybe changed the bearing, otherwise after two races they would fail. We theorized such a simple device a shaft with two bearings should be much more reliable. Then after night practice for the Rolex 24 at Daytona we noticed even after 10 minutes idling the turbo was staying red hot. The instant the engine shut off the color would dull, After inspecting some failed units and doing research, we were confident that heat transfer from the turbine wheel into the bearing housing was causing the thin oil film to burn forming carbon, coking up the bearing and causing the failures.

Cool down cycles is the name for a new procedure. Once we started doing this bearing failures became a thing of the past. Now our turbos lasted many races and the occasional failure was not bearing related, it was the result of improper turbo timing.

 

Turbo on a 3 rotor 20b engine glowing after only a five minute run on the highway

 

PCV valve

The oem PCV valve on RX-7 FD’s is a standard plastic valve, if it fails to seal when you accelerate it can allow boost to pressurize the crankcase creating oil leaks. In 1995 Mazda eliminated it from the RX-7 FD’s altogether. It's recommended to remove it from any turbocharged or supercharged rotary engine and connect the crankcase breather nipple to a catch can.

Intercoolers

“How much HP gain will a larger I/C deliver?” This is a common question we hear often, however, common answers are all over the board, 15-30%, 25-100 HP etc. Common industry answers because the notion you can gain HP sells parts. Since few sales people have a complete understanding of every theory, they often repeat what they heard to facilitate a sale without fully understanding it themselves. Even when sometimes those parts provide little or no benefit The facts are simple physics, air to air intercoolers can only improve two variables, pressure drop and / or the charge air temperature.

I/C upgrades that reduce pressure drop can provide more power by reducing pumping loses, and gains from reducing the charge air temperature are from denser air (more oxygen) entering the engine at a given point than before upgrading. Using only ambient air flow they can not reduce charge air temps below ambient.

Flow rates and pressure drops are a concern when upgrading to larger intercoolers and many popular systems have elaborate piping that add extra bends and connections. Because of this many front mount intercooler kits can be less effective than the stock system.

For example, with the FD, using the stock I/C and a Pettit cold air intake @ 10 psi with ambient temps at 85 degrees, the air entering the turbo is approx. 90-95 degrees F, and the compressed air leaving the turbo is around 190-210 degrees F, if the stock I/C only drops the air temp say 30-35 deg, then charge air temp is about 160 degrees.

With most front mounts on the same 85 degree day running 10 psi boost, the air (heated by the radiator) enters the turbo @ 190-220 degrees F, making compressed air leaving the turbo is around 290-320 degrees. So even with the big I/C and a 90-100 degree charge temp drop, charge air is still 220 degrees.

That example shows the stock I/C to deliver 30 degrees F cooler charge than a typical FMIC w/o provision for cold air to enter the turbos.

With the Pettit Coolcharge III system the RX-7 @ 10 psi on 85 degree day we could expect air into turbo @ 90-95deg (from cold air induction) after the turbo it's about 190-210 degrees, the CCIII intercooler drops about 70-80 degrees F, resulting charge temps are about 120-150 degrees.

Thermal management

Thermal management technology has evolved to an art. Enthusiasts everywhere are realizing that potential horsepower and reliability gains are significant and are worth far more then the cost. Auto manufacturers go to great lengths to reduce heat radiation from exhaust and turbo systems to the surrounding components. They use multi layer heat shields, reflective barriers and even ducting of air. All manufacturers agree that proper shielding of radiant heat is extremely important. Any vehicle can benefit from this technology, especially high performance and rotary cars.

RX-7’s with single turbo setups seem to gain the most from this technology. Instead of just wasting some horsepower, with the rotary it’s easy to waste engines. Since most aftermarket single turbo kits do not come with heat shielding and most installers don’t spend the necessary time to build adequate shields, it leaves exposed radiant heat that blasts the lower intake. Sometimes this heat is targeted to one intake runner causing a lean condition to the rear rotor. When tuning the car with a wideband it is usually an average of the front and rear rotor air fuel ratios. So people dont even notice and the front rotor is enriched while the rear rotor is lean. Yet the overall air fuel ratio seems good. Causing most engines to blow the rear apex seal. Also the air temperature sensor is located upstream where the temperature is cool, therefore; you would never know that radiant heat is causing this mixture imbalance and robbing horsepower and reliability. 90% of the FD single turbo engines we open have rear rotor failures which further attests to this condition.

Pettit Racing is producing Cool Power Thermal Management Systems designed to fit most RX-7 single turbo kits. These kits are easy to install and the benefits are priceless. We also have a kit for the factory twin turbo setup as well.

 

We will be adding more information to this section soon as we compile and comb more data from Pettit Racing's long history with the rotary engine.