General Information

 

So, how does a rotary engine work, anyway?

There are some terms specific to the rotary engine that may help you understand its operation, or that you may want to refer to when viewing the table below.

Rotor:

A rotor is a somewhat triangular shaped engine component. It is roughly equivalent to the piston of a conventional engine, except that it has a total of three combustion surfaces (located between each apex) to the piston’s one (the top or face of the piston).

Apex:

Each rotor has three apexes, which are the points of the triangular shape of the rotor.

Eccentric Shaft:

The rotors drive the eccentric shaft, which is the equivalent of the crankshaft in a piston engine.

Rotor Housing:

A rotary engine consists of a sandwich with several layers. The rotor housing is one such layer that is the same width as, and contains a rotor. The inner shape of a rotor housing, which the rotor’s apexes follow, is called a peritrochoid curve. These housings contain the exhaust ports*.

Side Housing:

A side housing is another layer of a rotary engine sandwich that is much like the bread of a regular sandwich. Every rotary engine has exactly two of these as they are the layers that cap each end. These housings generally contain intake ports.

Intermediate Housing:

The intermediate housing is found between two rotor housings. Because the rotary engines found in RX-7s have two rotors, they have only one intermediate housing. Intermediate housings also contain intake ports*.

*Note: There are some rotary engines, called ‘peripheral port’ engines, that have their intake ports in the rotor housings and none in the side/intermediate housings. Mazda has reportedly developed a rotary with all side ports, including the exhaust ports, for use in the RX-01.

This photo is of a TKT Banzai 3 rotor engine prior to assembly. The front row, from the left, is the intake plenum, the two turbochargers, a side housing, a rotor housing, an intermediate housing specific to three rotor engines, another rotor housing, the intermediate housing common to two and three rotor engines, the last rotor housing, the other side housing, and the three rotors. Notice the exhaust ports in the rotor housings.


How the rotary engine works.

Other Comparisons to Piston Engines:

Displacement:

Rotary engine displacements seem small when compared to piston engines of similar power. In fact, both displacements are measured the same way. Displacement is the sum total of positive combustion chamber volume increases for one complete revolution of the main shaft (crank or eccentric). In a piston engine, this means the total amount of space swept by its pistons. In a rotary, it is easiest to think about the difference between the maximum and minimum volumes for a single chamber multiplied by the number of rotors (where each rotor has 3 chambers). Remember that the rotor actually revolves at one third the speed of the eccentric shaft, which is the reason only one chamber’s displacement is used in the calculation. The difference in power is due to the fact that the rotary uses its full displacement to produce power for each revolution of the eccentric shaft while only half the displacement of the piston engine is producing power for each revolution of the crankshaft. Other differences also play a role; rotaries do not have the losses of reciprocating motion and there is no valve train to power.

Combustion Frequency and Power Stroke Duration:

When you consider the facts above, you will see that on a rotary, each rotor fires once per eccentric shaft revolution. In a piston engine, only half of the combustion chambers fire for a given revolution. This means that a 2-rotor engine fires as often as a 4-cylinder engine. However, the power stroke duration in a rotary is 50% longer, it being 3/4 of a main shaft revolution to the piston engine’s 1/2. This makes a 2-rotor engine similar to a 6-cylinder.

Where does the turbo fit in?

Turbocharging is the exhaust-driven form of supercharging, wherein air is forced into the combustion chamber. When more air is available, more fuel may be burned, producing more power.

Mechanical supercharging involves a belt- (or sometimes gear-) driven air pump of one of two types, Roots or centrifugal.

The Roots type supercharger typically sits on top of a large V-8 engine and pumps air down into the intake manifold by the intermeshing of worm gears.

The centrifugal supercharger spins a fan-like blade to pump air through a pipe to the intake manifold. It’s placement options are more flexible so this type is more widely used.

The centrifugal supercharger may be driven by a belt (as described above), an electric motor (new technology), or by an exhaust driven turbine. This last form is turbocharging.

The Turbocharged Rotary Engine

In the above diagram you can see a series of turbine blades being propelled by the force of the exhaust gasses rushing out of the engine. These blades are connected, via a shaft, to a compressor which forces air into the intake via an intercooler. The intercooler is an air-to-air heat exchanger designed to cool the air which has been heated during the compression process. Cool air is denser than hot air and dense air is the goal of turbocharging.

Notice that the behavior of the intake airflow arrow differs in the turbocharged engine diagram from the normally aspirated engine previously shown. The size of the intake (and exhaust) airflow arrows signifies flow in volume and speed. In the normally aspirated engine, this is dependent on the vacuum created by the change in volume of the combustion chamber. Near the end of the intake “stroke” of the rotary engine, the volume of the combustion chamber nearly stops expanding, dramatically slowing the draw of air. In the turbochanged engine, the force of the turbo continues to ram air into the still open intake port, pressurizing the chamber with air, unlike the slight vacuum in the normally aspirated combustion chamber. With more air to mix with, more fuel may be added, and more power produced.

Prior to the turbocharger is the wastegate, a vacuum or spring held trap door which leads to a shortcut around the turbine half of the turbo. When turbo boost reaches a preset level, this door is gradually opened to bleed off the exhaust pressure, avoiding overboost. The diagram shows this wastegate in an open position.

When less power is needed, the turbine naturally ceases pressurizing the air and the combustion chamber’s vaccuum draws air in. Thus a turbocharged car can produce more power on demand without using more fuel under less demand.

How are the turbos configured?

The 3rd generation Mazda RX-7 has the world’s first production twin sequential turbocharged engine. The key word here is sequential. In every other automotive twin turbo setup, the turbos provide boost simultaneously. Each of the turbochargers in this type of application is generally smaller than the one turbo used in a single turbo setup. A small turbo accelerates quicker, suffering less from “turbo lag” than its larger counterpart and, as a result, produces less power and torque but sooner and at lower rpm. Fitting twin turbochargers in sequence produces better results as the first turbocharger receives the full force of all the exhaust gasses (instead of sharing with the other small turbo) and gains speed much quicker, which enhances throttle response and increases low speed torque. At a predetermined speed, the second turbocharger is called upon to add more boost. With the twin turbos in full operation, exhaust gas flow resistance is greatly reduced, contributing to higher power output.

Assuring a smooth transition from single to twin-turbo operation as been an inherent problem with the implementation of a sequential turbo system. If the secondary turbo is not spinning at a high enough speed when it is brought in, the whole system “staggers”, temporarily failing to produce enough torque for a smooth change-over.

Mazda’s rotary engineers attacked this problem with a vengeance and perfected a solution to this technical challenge. In the primary boost stage, when only he primary turbocharger is operating, a portion of the exhaust gas is led to the secondary turbocharger, spinning it into a “pre-operation” mode. The boosted air from the secondary turbo is not required at this stage, so it circulates in an essentially closed intake chamber. Left in this condition, the turbo would eventually go into what is called “surge”. This phenomenon is accompanied by a rapid temperature rise at the entry and exit of the compressor, which would harm the turbocharger if prolonged. In order to preclude this surging condition, a bypass valve is opened to form a loop in which the air circulates.

The secondary turbo maintains a pre-operation speed of around 100,000 rpm. However, this is still not high enough to effect a smooth transition to twin-turbo operation. The secondary turbocharger must accelerate faster. This is achieved by deliberately inducing surging by closing the bypass valve and letting the compressor spin within a closed chamber. This sends the secondary turbo’s speed to as high as 140,000 rpm. When this speed is attained, the secondary turbocharger receives its full share of exhaust gas, and, at the same time, a control valve opens, allowing the secondary turbocharger to start supplying boosted air, adding to the primary turbocharger’s. As previously stated, surging is harmful if prolonged, but in this transition state, it only lasts a few seconds, and therefore has not detrimental effect on the engine’s durability and reliability.

The RX-7′s 13B engine used twin Hitachi HT12 turbos with a 51 mm, 9 blade turbine and a 57 mm, 10 blade compressor. The turbine and compressor blades are a curved “high-flow” type that offers less resistance to air and gas flow. This results in faster turbine and compressor spin-up at high rpm.

The twin turbos are mounted on a cast iron exhaust manifold which has been named “Dynamic-Pressure” manifold by Mazda’s rotary engineers. This manifold is elaborately shaped to minimize the distance between the exhaust ports and the turbochargers’ entry paths, improving low speed boost by as much as 25 percent.

A special blueprinted, balanced, and contoured version of this same unit is used on our race cars. These units are capable of producing higher boost levels for extended periods.

Always remember to properly warm up and cool down your turbo and they will reward you with trouble-free operation.

What about handling?

Good balance is the key to great handling. Although the 3rd generation RX-7 is admittedly a good handling car, it is still a compromise. At Pettit, we seek perfection, and for this reason, we have developed a complete line of suspension components that allow you to fine tune your car’s suspension to your driving style. However, some tuning can be accomplished by changing alignment settings and tire pressures.

Alignment is critical on any car, especially on a performance car like the RX-7. We’ve seen new cars that are slightly out of specification, so it is a good idea to to have your alignment checked prior to high speed maneuvers or track events. The following recommendation come from our own testing, as well as from conversations with customers who compete in all different types of events. Remember, this is only a guide.

Recommended alignment settings
Handeling
Whenever making adjustments or changes in chassis setup make only one change at a time and be sure the change makes an improvement. This way you can see the effect of each change on the car. It is also a good idea to record these changes.


How to choose the right brake pads

 

Coefficient of friction:

A dimensionless indicator of the friction qualities of one material vs. another.  A coefficient of 1.0 would be equal to 1g.  The higher the coefficient, the greater the friction.  Typical passenger car pad coefficients are in the neighborhood of 0.3 to 0.4.  Racing pads are in the 0.5 to 0.6 range.  With most pads the coefficient is temperature sensitive so claims that do not specify a temperature range should be viewed with suspicion.  The optimum is to select a pad with a virtually constant but decreasing coefficient over the expected operating range of temperatures.  As a result, the driver does not have to wait for the pad to heat up before it bites, and the pad fade will not be a factor so that modulation will be easy

Now that we have a foundation we can see that finding the pad of the right material and heat range affects your braking efficiency.  You don’t want a race pad for the street, because you have to heat it up to its appropriate heat range before it bites.  Not too far off from racing tires where the operating range is higher, so getting them to stick requires more heat.

The difference is here you pick a pad for your car based on driving habits, much like you would with tires.

If you are on the brakes non-stop and generating excessive amounts of heat then you want a pad and rotor combo designed to bite or grip at higher temps.

On the street we want bite right now thus a pad with a lower operating temp, and the trade off is fade at higher temps, (excessive braking or high speed braking) or reduced bite.

Hawk HPS Brake Pads:

The Hawk HPS Brake Pad is designed to provide you with advanced braking characteristics for the street.  Some of the features of this pad are; extremely low brake dust and a high friction (torque) either hot or cold. They are virtually noise free and are very gentle on your rotors giving you a long brake life.  This pad is designed for high performance street use and will provide the best combination of performance and reliability.

Hawk HP Plus Brake Pads:

The Hawk HP Plus Brake Pad can take the heat of the track, and still provide a good street able pad. This brake pad is designed for the serous street and autocross enthusiast.  It features an extremely high friction output making it worthy of club racing and auto crossing.  However, due to the dramatic friction levels produced by this brake pad in order to achieve “race level” braking: rotor wear, pad wear, noise and dust may be increased.

Hawk Blue (9012) Brake Pads:

Medium/High torque racing brake compound.  They provide low pad and rotor wear with good modulation.  Designed for road racing and rally applications where heat is between 250 and 1000 degrees Fahrenheit.

 

 

 The Guide:

 

“The Guide” is a summary of information and knowledge from over 30 years of experience improving and racing rotary powered vehicles as well as the observations and ideas from customers and colleagues alike who share a passion to learn about and/or improve anything and often, down to the smallest details. These individuals of every race, creed and color on the planet are true enthusiasts, small but global group where knowledge and ideas are openly shared for mutual benefit.

 

 

 

The Guide although primarily intended to help RX7 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 Guide, like any noble effort is a work in progress with mistakes, errors and omissions, please feel free to offer corrections and input. We may occasionally forget to thank contributors in a timely manner but please know that the Pettit team & staff as well as anyone who may use & benefit from the information are thankful and greatly appreciate the time and efforts from all contributors. We will do our best to keep the contributors list current. If your name is missing, let us know. “guidelist@pettitracing.com”

 

 

 

 

 

The Legendary RX7

 

When production started in 1991, who would have thought that after 4 decades the RX7 FD could still provide a driving experience superior too many new world class machines. No doubt the sleek & sexy aerodynamic shape with silk smooth turbo rotary power helped create its legendary status as well as one of the most sought after sports cars on the planet. Sleek, powerful and deceptively fast the RX7 FD delivers speed and excitement with every drive. more

 

 

 

Basic Common Sense:

 

 It is 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. If you trust your life to a mechanical thing it should be mechanically sound and up to date on maintenance, clean fluids and filters, brakes, suspension and tires all good and working properly. 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. .

 

 

 

Safety: 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 new  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 vehicle! “Safety First”

 

Before you upgrade:

 

Before upgrading or adding more upgrades,  scheduled maintenance and all the  common problems should be a thing of the past. 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 / performance problems, typically if it is not running right, upgrades don’t help, every FD can perform beyond expectation in nearly stock form, always correct problems then add upgrades for improvements, not to correct drivability / performance problems.

 

 

Since there are countless upgrades available for FD’s, possibly more than any other car, driving style, goals and budgets usually determine how the project progresses. For DIY, we recommend  installing upgrades in logical stages and often 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.

 

 

Over the years we have found that raising boost levels (more boost) should only be considered after all the above mentioned items are working properly and consistent, and you have good drivability & performance with smooth effortless acceleration from light to full throttle. more, Once  proper operation with min boost is achieved it is a good idea to put a few hundred miles on over a few days to be sure everything is consistently working right.

 

 

At this point the delivery of power and the level of performance will usually scare passengers, while providing a fun and exciting driving experience for those behind the wheel, even with a minimum boost setting the FD is deceivingly fast, this is when tire condition, brakes and suspension are critical factors, do not fail to realize their importance, a small problem at speed can turn fun to fatality.

 

 

Basic Recommendations:

 

 

Always keep up with scheduled maintenance routines as outlined in the owner’s manual.

 

 

Upgrade chassis and engine ground points with our FREE KIT. Just call and ask for one. 

 

 

 

Always use premium fuel and some lubricant with every fill up, our Protek-R fuel lubricant is proven for over 20 years by customers around the world, it cuts friction and wear adding performance and longevity. We actually use it in the gasoline for our piston engines, many folks disagree but think about this, diesel piston engines may run a million miles, gas piston engines never get close, both use nearly the same parts and materials but diesels have 3 times more compression, more stress and loads etc. so why is it they last the longest…………diesel fuel is oil!!  There is no doubt using fuel lube in gas piston engines will more than double its longevity.   more

 

 

 

Whenever possible open the oven door (hood) this stops the baking process and improves longevity for all under hood components. We have many customers that have proven this works; their cars continue to perform flawlessly year after year. 

 

 

 

 Fuel filter, Countless premature engine failures are caused by dirty fuel filters; don’t let this happen to you. Poor fuel quality also contributes to engine failures ALWAYS USE PREMIUM FUEL!!!

 

 

 

 Install a turbo boost gauge!  This is the only way to be sure the turbos are working properly. We produce several Kits.  All are easy to install, and come pre‑wired with detailed instructions. 

 

 

 

Safety: 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 new  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 vehicle!

 

 

 

RX7 FD’s with a history of problems

 

Nearly any RX7 FD can be setup to deliver a balance 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  Overheating: Cooling system & high operating temps

 

2  Seal failures:  Oil Metering System & lubrication

 

3  Air box failure: Dirt & abrasives in, engine wear accelerated

 

4  Ignition System, wires, coils & plugs

 

5  Calibration & Tuning with minimum boost set

 

6 Thermal Management & radiant heat control

 

7 Intercooler Efficiency & ICD losses

 

8 More boost

 

 

 

#1 TheCooling System  has become a top priority, Since mid July ‘2010, we have seen more cooling system issues than ever before, either summer heat, ageing components or a combination of both may play a part with several new 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 and a key factor in optimizing the FD. Proper cooling is extremely important, nearly any engine can be damaged from overheating.

 

Whether you’re a new owner or an 18 year veteran, nearly every RX7 will need some cooling system update’s and upgrades. We have several simple & easy procedures and a few inexpensive parts that have proven to get the cooling system working at peak efficiency. more  

 

 

 

#2 Oil Metering System

 

Use fuel lubricant. Proven around the world for over 20 years Protek-R  reduces friction & wear adding  performance & longevity. Developed in the late 80’s for our racing efforts and first released for sale in 1990.  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. There is no doubt that Protek-R provided the added performance and longevity needed for every victory including the US GT-2 Road Race Championship in ’98. more   

 

 

 

#2A Flaky Oil Gauge:

 

The oil sending unit is below the oil filter and aprox 5 x larger than the 1/8″ npt nipple that attaches it to the block, thus a nice moment is created, then harmonic frequencies thru the RPM ranges and pulsations from the oil pressure regulator perhaps cause  the wire connector to loosen grip on the terminal,  usually a little squeeze on the connector to tighten it up helps.

 

 

 

#3 OEM 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 at the speed of sound more

 

 

 

#4 Calibration & Tuning

 

This,  applies primarily  to FD’s with ongoing drivability / performance issues where a pile of money spent at dealers and various shops either didn’t help or made problems worse.

 

Common sense again dictates that when poor performance or drivability problems are present at light throttle and at minimum boost levels,  attempting repairs and/or testing with ECU controlled boost can add to inconsistencies as the ECU tries to compensate for other problems as well as put unnecessary stress on internal engine seals & components,  this typically shortens engine life or worse, may cause a catastrophic failure. more

 

 

 

#5 Cool Power,

 

 

 

 Are You Wasting Horsepower?

 

 

 

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 their cost. Auto manufacturers go to great lengths to reduce heat radiation from exhaust and turbo systems on 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 racecars.

 

 

 

RX7’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, this leaves exposed radiant heat to blast the lower intake. On 3rd Gen setups it usually favors the front runner, this superheats the charge for the front runner just as it enters the port, not only does this raise the charge temperature in to the danger zone, but makes you think the engine is running rich, “tuners” unknowingly lean the overall mixture to compensate, but then the cooler rear rotors is dangerously lean. 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.

 

 

 

Stop wasting horsepower !!  Pettit Racing is producing new Cool Power Thermal Management System Kits designed to fit most RX7 single turbo kits, a kit for the factory twin turbo setup as well as individual components that work for any vehicle and a multitude of applications.  These kits are easy to install and the benefits are priceless. We also have.

 

All  Pettit Racing Cool Power Kits and components use the latest proprietary technology for thermal protection, these materials do not emit or expose the driver to harmful substances.

 

 

 

The Thermal Barrier Panel or “TBP” is made from non-woven thermal insulation and is created specifically for use in areas where minimum space is available. The Thermal Barrier Wrap or “TBW” is made of woven thermal insulation, both types resists temperatures up to 2000 degrees F.  Both materials contain no asbestos, are non flammable, will not corrode, and resist mildew and deterioration.

 

 

 

The Cool Power Kit for single turbo setup includes:

 

A custom Thermal Barrier Cover, fits around the turbo hot section, it is reinforced with inconel wire, assembled with stainless steel staples and has proven to be a very durable and long lasting part.

 

A stainless steel heat shield, fits between the lower intake and the turbo system, is layered with thermal barrier panel. The simple design retains an air space between lower intake and shield, further reducing heat transfer.

 

15-foot roll of Thermal Barrier Wrap, “TBW” for the down pipe with enough material to wrap front section of the mid pipe.

 

2 Thermal Barrier Panels, “TBP” are precut for the floorboard area just above the hottest section of the exhaust system and are designed to reduce heat transfer in to the passenger foot well and floorboard area. This can make a significant improvement in occupant comfort level.

 

2 feet of hi temp metal tape, which is used to seal the panel edges.

 

3 Stainless hose clamps to secure the wrap

 

 

 

The Cool Power Kit for twin turbo setup includes:

 

A 15-foot roll of Thermal Barrier Wrap, “TBW” for the down pipe with enough material to wrap front section of the mid pipe.

 

2 Thermal Barrier Panels, “TBP” are precut for the floorboard area just above the hottest section of the exhaust system and are designed to reduce heat transfer in to the passenger foot well and floorboard area. This can make a significant improvement in occupant comfort level.

 

2 feet of hi temp metal tape, which is used to seal the panel edges.

 

3 Stainless hose clamps to secure the wrap

 

 

 

Cool Power for Single turbo setup                       $349.99

 

Cool Power for Twin Turbo setup            $149.99

 

 

 

 

 

 

 

#6 Intercoolers 101 

 

 “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… The facts are simple physics, air to air intercoolers can only improve two variables, reduce pressure drop and / or reduce the rate of charge air temperature gain.**

 

 

 

This is a common misconception because the notion you can gain some 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 themselves, but nearly always prefer selling parts that generate the highest profits and commissions even when though those parts might provide little or no performance  benefit. It is not unusual   and may be unaware they provide little benefit.

 

 

 

I/C upgrades that reduce pressure drop provide more power by delivering more  boost to the engine and gains from reducing the rate charge air temperature increases are from denser air (more oxygen) entering the engine at a given point than before upgrading.

 

 

 

I/C efficiency is directly related to ambient conditions (the weather) and air flow volume through the I/C, the laws of physics dictate that the exchange of heat via ambient air can not add HP but rather slow down the rate at which power is being lost to the rising temperatures**   Under certain conditions when ambient temps are cold enough for temp gain to stabilize, then more power overall is produced than could be with a smaller I/C

 

 

 

**As air molecules are compressed to create boost, the friction from the molecules being squeezed together generates heat, the I/C’s job is to cool it back down.  So the cooler the air is entering the turbo the cooler it will leave the I/C and enter the engine. cooler denser air allows more volume to be packed in the combustion chamber at the same boost setting,  this results in a bigger bang, IE (more hp).*** .

 

 

 

So the I/C’s job is to reduce the rate that charge air temps rise and slow down the rate your power is being lost, so 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 as well as have no provision for cool outside air feed to turbo(s), because of this many front mount intercooler kits can be less effective than the stock system.

 

.

 

For example, with the RX-7 FD, using the stock I/C and a Pettit Cold Air induction @ 10 psi  with ambient temps at 85deg the air entering the turbo is aprox. 90-95 deg F, the compressed air leaving the turbo is around 190-210deg F, if the stock I/C only drops the air temp say 30-35 deg, then charge air temp  = 160 deg

 

 

 

 

 

Air in at 90F.

 

@10 psi + 100F

 

stock I/C – 30F

 

charge air =160F

 

 

 

 

 

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

 

 

 

Air in at 190F.

 

@10 psi + 100F

 

FMIC I–100F

 

charge air =190F

 

 

 

That example shows the stock I/C to deliver 30deg 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 80deg day we could expect air in to turbo @ 90-95deg (from cold air induction) after turbo say 190-210deg, the CCIII intercooler drop min 80-90degF, charge temps = 100 deg,

 

 

 

 

 

**

 

***provided ignition & fuel requirements are correct.

 

 

 

#7 More Boost……….coming soon

 

 

 

 

 

RX 7 FD Cooling System

 

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 and 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 RX7 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 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.   

 

 

 

Cause and Effect

 

When a leak occurs and the coolant level drops just a couple of inches, the temp gauge sensor is no longer immersed and even though the engine is getting hotter and hotter the gauge displays a normal reading. 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 exhaust port melts away.

 

 

 

Cooling System Upgrades and Recommendations

 

In the past the most common cooling system failure was the plastic air separator tank, they are  well known to split  in half without warning, the coolant pumps out and after a few minutes,  the engine is 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 the mini cap is the same size as the engines. Our upgrade is round, usually silver or black with a large cap & usually a red vent lever.

 

 Besides replacing the plastic air separator other simple inexpensive but important upgrades that every RX7 needs is our  82C / 180F thermostat and 85C / 185F fan switch, together they can reduce operating temperatures 30C / 40F.  

 

 

 

Coolant Loss

 

Coolant loss can occur for several reasons, most common is the plastic air separator tank, when they split rapid coolant loss occurs, but typically leaks usually starts out small and go unnoticed until it is dripping on the ground or your engine is overheating. Coolant  leaks can occur if any of the following items fail:

 

 

 

  1. Air Separator Tank
  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

 

 

 

 

 

1 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 unexpected coolant loss and overheat the engine, this can also result 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.  Add some needed integrity to your cooling system, simple to install in 30 minutes or less and always in stock.

 

 

 

2 Coolant o‑ring seal failures will typically occur from overheating causing coolant loss with no external leaks. White smoke (steam) and or misfire on start up usually means coolant seals have failed.

 

 

 

3 The RX 7 FD Radiator is a quality part, but few are still in use due to the plastic tanks failing. Leaks are usually from the tank to core seal; any time overheating occurs it shortens the radiators life. They can be repaired, but an all aluminum unit is a better choice.

 

 

 

4 Most hose leaks occur next to the clamp, pressure swells the hose against the clamps edge and it weakens eventually failing. Cutting back a little hose and re-clamping will usually buy some time and avoid a major leak. Our HD Silicon Radiator Hose Kits are rated for 65 psi, 5 times more than normal system pressure.

 

 

 

5 The Cooling fans and relays are another common problem, when they fail temperatures and pressures rise,  the pressure cap releases coolant and within a few minutes its overheating. At that point continued operation can result in engine damage. There are four relays powering 2 fan motors for low thru high speed operation. They are controlled by the fan switch,  A/C and/or  ECU.   We commonly service and replace connectors, relays and motors. 

 

 

 

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

 

  

 

7 Core or freeze plug leaks are only common on engines with a neglected and rusty cooling system

 

 

 

 

 

Calibration & Tuning  steps:

 

 

 

Minimum Boost: The first step is to set the boost to minimum level, this sets the boost to a minimum level helping to systematically isolate and correct problems hopefully without causing more damage.  

 

 

 

Step 1, No boost testing:  , All testing to correct drivability problems that are present at light throttle when negative manifold pressure (vacuum) or “0”  (no boost) is present should be corrected before attempting to use boost, once proper operation is achieved (ie: idle & drivability smooth & consistent) with all off boost driving, good progress is made and Step 2, minimum boost testing can proceeded with confidence.

 

 

 

Step 2, Minimum boost testing:   With a wide band AFR connected we recommend adding 2 psi at a time until the desired boost is reached and verifying correct & stable AFR’s each time.

 

 

 

The following list shows many common items / procedures for original RX7’s  that we often perform to reduce operating temps and improve safety:

 

 

 

Upgrade plastic air separator tank to aluminum
Eliminate recall jumper harness on fan motor relays
Upgrade oem 92C / 198F  thermostat to 82C / 180F thermostat
Upgrade oem 98c / 209F fan switch /to 85C / 185F fan switch
upgrade oem rad hoses to hd silicon
upgrade turbo cooling, AST & bypass / transfer hoses to hd cooling line
eliminate AWS (accelerated warm up)  it causes hi revs on cold starts
replace drive belts, they look original
Eliminate PVC valve
Replace hardened vacuum / pressure lines
Bypass oem PC & WG duty sols for min boost setting
relocate sequential turbo systems pressure control ck valve
add overboost safety circuit failsafe
Upgrade chassis & engine ground with our free kit
upgrade old original rubber brake lines to dot ss teflon
upgrade flush and bleed brake system, fluid, pads , etc may be original