Back in the 80’s and 90’s I installed a number of the Car Tech turbo systems in Mazda RX7’s. Most of these systems included a Street Ported and turbo-prepped 13B engine, these installations were fairly simple systems with carbuerators producing impressive power. I am currently building one of these cars and the revisit of a carbuerated 13B engine in a first-gen. Turbo RX7 should be interesting. My upcoming blog will include the project along with pictures.
There was a lot of chatter last year about a new RX7 (redesigned) from the Mazda folks. This car would feature a redesigned 13B Rotary engine with better fuel economy, lighter and producing around 300hp naturally aspirated. The latest however is that we are not likely to see any new Rotary automobile from Mazda in the U.S., at least for some time to come. We enthusiasts are really disappointed with the news….can you imagine putting a Turbo on one of those? Looking at the bright side of things however, I see Rotaries out there going up in value due to the fact that they are no longer coming into the country and there are still good deals on used Rotary Engine Mazdas.
It’s unbelievable but thus far in 2014 I’ve seen more clean 1st generation (1979-1985) Mazda RX7’s than I have in many years. People I know are getting them on Ebay from all over the country, some modified with Holley, Dellorto carbs. and even old Car Tech Turbo systems. 2nd gens (1986-1990) are still around but it’s 3rd gens (1993-1994) that have the best resale value. Dollar for dollar Mazda RX’s still yield the most performance for the money. I am currently building a few 1st. gens for my customers which I will blog about in the near future.
Rotary enthusiasts; there is a new RX7 coming for 2015. We don’t know exactly how the car will look. Word is that the engine will develop 300hp naturally aspirated (no turbo). This new Rotary Engine is designated 16X. It offers 30% better mileage, lighter all Aluminum Housings, direct low pressure fuel injection which means the Injectors will be located strategically at the top of the Rotor Housings. Direct injection will occur later in the intake cycle. Engine Block weight should be under 200 lbs, which sounds fantastic. Overall engine height is the same but the Rotor Housing’s width will be about as narrow as that of a 12A Rotary (1st gen. RX7). Trochoid surface will probably extend more into the water cooling jacket making it effectively taller inside than older 13B’s creating a “longer stroke engine” with accompanying improved torque figures, fuel economy and improved oil consumption.
This all sounds too good to be true but I think it’s going to happen; the Rotary following remain strong and surprisingly, there is considerable interest coming from new and younger enthusiasts. Can you imagine a 16X Rotary with a Turbo? wow!
Porting the intake and exhaust on Mazda RX7 RX8 RX2 and the rest is how we improve a Rotary’s “breathing” thus increasing power and efficiency. Porting includes changing the aerodynamics, shape and surface smoothness of intake and exhaust ports, which results in changes in intake and exhaust timing; not unlike a cam change in a piston engine. The main purpose of this blog is to address questions about different kinds of porting and how they affect your street rotary engine car. Let me begin by saying bigger is not always better for “street porting”. Companies like Racing Beat offer great street port templates which I highly recommend. Basically degree of port size and configuration depends a lot on the size of intake e.g. carburetor size, throttle body size and the flow capacity of the exhaust system. To maximize all-round engine performance, volumetric efficiency must be maintained. For instance, installing a 750cfm carburetor on a stock rotary with a stock exhaust will give less overall power than a 490cfm carb., the latter being a better match for the system. Simply put, for any engine speed and load there is an optimal balance between intake size, port size and exhaust flow; things need to be matched. I remember someone building a 1st gen. RX7: large polished ports, a huge turbo, over-sized intake and a 4in exhaust system, that resulted in a car than ran only a little better than a factory Turbo II RX7. Street RX’s in my opinion give better all-around performance with conservative street porting (Racing Beat e.g.), a three inch exhaust that includes a pre-silencer, turbos not larger than T60. Maximum carburetor size should be about 600cfm. Bridgeporting or semi-bridgeporting a rotary for street may produce more peak power but overall drivability, economy are sacrificed not to mention the necessary loud exhaust which in time will become irritating. It all depends on how you plan to use your RX; do you want a “sleeper” daily driver, weekend only racer or a track machine.
What is the best way to break-in a rotary engine?
This is a question that may have more than one answer depending on who you ask. I am offering my opinion which is based on ideas gleaned from 30+ years of working on early rotary-engine Mazda RX2, RX3, RX4, Cosmo, Rotary Pickup, and later RX7 and RX8’s. My formula for break-in is this simple; “the longer the better.” The factory recommends about 600 miles for most models. I believe Rotaries are somewhat broken-in at 600 mi. but experience has taught me that if one wants to get the maximum benefit of a break-in period the figure is around 3000 miles. I’ve seen builders who mercilessly rev engines after building them to get engine internals to “seat”, and conversely, I’ve driven Rotaries owned by women and people that barely rev them thinking that high rpm’s are damaging. The latter run the best by far. I’ve built hundreds upon hundreds of Rotary engines-most of them high-performance builds and have personally noted that 3000 miles is the magic break-in figure where maximum engine performance is realized. So how does one break-in a fresh Rotary Engine? for the street simply drive normally and avoid really hard acceleration. When you get close to the end of your break-in mileage gradually increase engine load and revs. For racers you might want to let your engine “sit”and run for periods at different rpm’s. I believe you will like the results. I will talk more later about synthetic oils vs conventional oils in Rotaries.
1993-1994 Mazda RX7s like previous RXs seem to develop problems unique to their generation e.g. early second Turbo 2s have vibrations in the drivetrain more specifically, imbalances associated with the transmission. Third gens. (93-94) RX7s are plagued with instrument (gauges) problems and speedometer- odometer issues are common. I am working on a automatic 94 rx7 that has a working speedometer but an odometer that recently stopped showing. There are some places here in Florida that claim to be able to bring these units back to life. I made the decision to do some investigations including online threads to tackle the odometer issue. In this particular the engine check light was on and flashed 6 times for speedsensor malfunction. First order was to replace speed sensor (after checking wiring) which sells for $271.0 from the mazda dealer, result; nothing changed. I removed instrument cluster which is quite a job to check speedometer- odometer itself. To my delight, there it was a burnt 1000uf Capacitor just what folks online said I would find, I got the Capacitor online soldered in and also another Cap. of lesser value that’s been known to fail. The grand result was that the odometer worked! but only for a few minutes after starting the car. No codes came up from the computer though, but there must be other problems in the speedometer circuit board and my guess is that the culprit is probably a diode but which one. Ahhhh the saga continues……. I will post anything else that I find provided that I sum up the courage to go back into the 94 RX7’s instrument cluster….what a job!
The subject of my blog; the 2004 Mazda RX8 is now ready for sale. I blogged the entire engine building process for this car previously. The RX8 has less than 300 miles on the new engine so the new owner will be able to break it in. I will post pictures soon and discuss details about the car. Price- $7200.00 Tel.# (954) 865-2607
A few things to look for when buying a used Mazda RX8. Body inspection is fairly straightforward; like any other car look for rust, structural damage, accident history etc. Drivetrain; the engine is the biggest unknown when purchasing a used RX…. the first thing is how does the car start-up from dead cold and how does it restart when hot. In the case of cold start look for excessive blue smoke from the tailpipe; this is an indicator of worn oil control rings inside the engine and or how bad the oil seal “o” rings are. Either case suggest an old engine in need of rebuild or maybe an engine that was run with low oil pressure. Compression on a Rotary Engine can only be checked using a genuine Rotary Engine Compression Tester. Standard gauges can’t work because they measure only one pulse from each Rotor, the right tester will differentiate between the three pulses per rotor which is unique feature of Rotary Engines. In general, compression is not a tell-all because compression readings can read normal while an engine is consuming excessive oil or has overheating issues. Low compression is usually manifested when there are hard-starting problems when an engine is hot. Of course the engine flooding-hard starting issues (when cold) that i blogged about previously are associated with tired engines with low compression.
Mazda Rotary Engine RX cars have been sold in the U.S. since the early seventies and have had a significant number of die-hard followers. There is something very special and almost addicting about Rotaries. Maybe that’s from their design which gives them the uniqueness of being the only production car with a non-piston rotating gas engine with exceptional power and smoothness. Mazda discontinued it’s only production Rotary-Engine car exported to this country (RX7) in 1994 but ten years later (2004) brought the Rotary back in the form of the RX8. I am constantly reminded of the Rotary’s allure when I see so many young people who are knowledgeable and enthusiastic about the used Mazda RX7 or 8 that they own or are about to buy. I will discuss what to look-out for when buying an RX7, RX8, or even older models in my upcoming blogs.