Mazda RX8 Rotary - Completely Different Beast

[OVERKILL]

The rotary engine was also used by OMC in snowmobiles.

Horsepower is torque at RPM. The higher in the RPM range an engine makes peak horsepower, the less torque it has to make to get there. Rotary engines, by nature, like RPM, and by design, make power very high in the RPM range. This means they do not make a lot of low-end torque, but they do not need to.

Two cars of equal weight, with the same HP, geared to take advantage of where they make peak power, will run the same timeslip. While in application, this may not prove to be a viable setup, it is factual. Gearing a car that doesn't make peak power until 9,000RPM optimally for the dragstrip is going to make it basically undrivable on the street. Gearing a big-ol V8 that tops out at 5,000RPM on the other hand, is much easier.

The effect Turbo's have on an engine's torque curve (quite helpful) is one of the main reasons they are used so extensively (and effectively) on small displacement engines, and why they worked very well on the RX7......

 

[Gary Allan]

Does the rotary suffer from high rpm continuous operation? Pardon me for my ignorance here (maybe I missed it in reading), but I would reason that you don't have the issues that reciprocating engines have with inertia and changing directions and acceleration/deceleration curves and whatnot.

 

[OVERKILL]

Gary: I believe that the RPM limit imposed upon modern rotary engines is somewhat superficial; But I don't know enough about them to give any sort of reasonable expectation as to what their actual RPM range potential is.

 

[Doug Hillary]

Hi,
Gary - In my exposure it was always the drag factor of the seals - mainly the side seals. The tip seals do have a speed to size factor of note. Modern and emerging technologies have made sealing such things a true cost/benefit exercise today

The revs are a factor of the Wankel engine's internal gearing - shaft to rotor speed. Forget normal reciprocating engine principles except for Otto's. And you are correct of course about the inertia and imbalance factors inherent in the "normal" engine families and to a large degree abscent from Felix Wankel's design

Balancing torque to power again is more a factor of many emerging techologies in Wankel's engine today - these are all solveable at a price. The real issue is liquid fuel consumption
and yes, Mazda have run LPG and other gases in prototypes

Oil use was/is programmed in and adjustable, and no doubt easily ECM controlled

Most major engine makers of the time took up R&D licences off Wankel. Some still hold them..................

 

[Doug Hillary]

Hi,
Gary - Sorry but I meant to add this to the above Post:

"Don't forget that only or so 30 years ago the "first" life of a turbocharger was around 80kkms (50k miles) - better seals, bearings and lubricants were all just parts of the fix for that!"

 

[artificialist]

Originally Posted By: aquariuscsm
I know absolutely nothing about the RX8`s,but the last generation RX7 turbos are insanely fast! Incredible cars. They`re getting very rare. I can`t even remember the last time I saw one. Was the last year they were made limited number production?

The third generation Mazda RX-7 (FD3RS) was sold in the USA from 1993 to 1995. I'm fairly sure that tougher smog tests introduced in 1996 ended the sale of the RX-7 in the USA.

The rotary engine has very limited means of creating a homogeneous air fuel mixture, and the burning fuel has to travel across a wide combustion chamber. That, plus the 13B series rotary had a port setup that behaved like a standard 4 cycle engine with a huge overlap cam. The OE had to control it with exhaust back pressure, otherwise the HC emission would be even worse than it already is. Too bad that limited power severely.

The 3rd Generation RX-7 was sold in Japan from 1993 to 2002, because their smog tests are not as tough to pass. At some point, horsepower was increased, and an improved twin turbo setup solved huge reliability problems with the earlier design.

The renesis engine had relocated ports to address smog, however, I have not seen anything that can be done to address the huge surface area to volume ratio that leads to low thermal efficiency.

 

[digitalSniperX1]

Hello Doug,

Can we ask a bit of your expertise on this never ending rotary engine oil synthetic vs. conventional debate.

Of course, Mazda recommends that synthetics not be used. I use a group III product, probably applying erroneous logic in that I believe the recommendation against synthetic use in the rotary applies to PAO based synthetics (I may be wrong, but doesn't most if not all 5W-20's have oils in them that today are classified as synthetic without using PAO)?

What's your opinion on the topic? Is group III ok to use? Any light shed on this from a person with your expertise would be greatly appreciated.

 

[Doug Hillary]

Hi,
digitalSniperX1 - I would not hesitate to use a prescribed viscosity G111 lubricant

Remember that the lubricant's task in a rotary engine is somewhat different from that in a reciprocating engine

 

[digitalSniperX1]

Hello Doug,

Well thank you for confirming my plan even if I devised it via flawed reasoning. It's somewhat of a guess I suppose.

I'm mixing 5W30 and 5W20 Amsoil XL during the summer months. Straight 5W20 in the winter.

I suppose the logic in doing so is that outside the US, Mazda recommends 5W30 for this engine. I'm not sure if that has anything to do with formulations being different in other countries because as stated by Amsoil, 5W20 oils are required to have lower ash formulations than are the higher viscosity products.

I'm thinking it has little to do with high temps as it's generally hotter here in summer months than in Europe for example.

There are RX-8 owners who swear by using 10W-40 or even 20W-50 products. I'm not in their camp as I do not believe engine failure modes have anything to do with viscosity unless one has an advantage over the other in clean burning.

 

[byez]

After much research I have decided to run a "Oil Metering Pump Adapter" with an external reservoir for a dedicated two-stroke oil.

http://www.rotaryaviation.com/oil_injector_pump_adaptors.htm

This basically ends the debate over the use of synthetic as only the two stroke is injected to be burned off. Anyone have any thoughts on such a device?

 

[digitalSniperX1]

From what I've read it's a very good upgrade. The only negative is that without a doubt, it'll void your 100,000 mile/8 year warranty since Mazda has not certified the device. I think this warranty applies to all RX-8's sold in North America. If you purchased one used, you'd want to have its service history.

Last I heard though, Richard Sohn (I've talked to him on the phone directly) hasn't been responding lately. Hope he's ok, he sounded like he's getting up there in years.

 

[digitalSniperX1]

Here, check this out.


http://www.rx8club.com/showthread.php?t=102271

 

[byez]

Just heard about the retroactive 8 year/100,000 mile warranty, that is good on Mazda for doing this. Do you think this adapter would void that warranty though?

 

[digitalSniperX1]

I afraid it would void the warranty. I'll let you decide on the ethics associated with such a mod/deleting it.

 

[byez]

Nevermind, just re-read your post.

Do you know if the warranty applies to Canada? Would you need proof of all oil changes?

 

[digitalSniperX1]

On the 100,000 mile warranty, I think it's applies to all North American RX-8's.

Proof of all changes? Depends on many factors. Knowing where the previous owner had his service peformed wouldn't hurt. If you purchased it from a Mazda dealer, esp if it's a certified car would probably seal the deal on your warranty issues (you'd be good to go assuming the dealership followed the rules on certifying the car).

Having a good relationship with a good Mazda dealer would be helpful if you developed the need for warranty assistance.

It's my understanding that Mazda is very particular in applying these warranties. They will do more research to make sure the owner followed the rules/recommendations than they'd do with other cars.

A link for warranty information:

http://www.rx8club.com/showthread.php?t=147287&highlight=100,000+mile+warranty

One last thing, Mazda informed all owners of this warranty and wanted them to respond (not necessary in my case I have that good relationship with a dealer). You'll want to get hold of that at a Mazda dealer if possible (and it applies to Canadian vehicles).