A number of issues related to the rotary engine have been raised in this thread. Having installed my 13B in two vehicles, I have some experience with this engine and it's unique characteristics. Here is a lits of the main ones as I have gleaned them from the thread
1. Expensive
2. Expensive to overhaul
3. Power produced
4. Split timing
5. Exhaust issues
6. Apex seal wear
7. Hard to work on
So hear we go:
Issue 1: Expensive
There were a couple of examples in the thread of engines available. $500 from a junk yard with transmission, and $1200 JDM engine on ebay with transmission and electronics. I purchased my engine from Bruce Turrentine in South Carolina for $4950. It included several modifications, including a mild street port, removal of the oil filter boss (for use with a remote filter), and lightweight 9:7:1 compression rotors. This engine was installed in an airplane and flown until I wrecked the plane (another story). So is this expensive? I just checked Ebay for Ford V6 engines Buy it now prices. They range from $165 to $2695. The high end one is a "High Performance Ford 3.8 Mustang 4.3 V6 Stroker Engine". The same search for rotary engine has a price range of $4500 to $1350. So my conclusion is yes there is a cost penalty of maybe 2:1 and/or you may have to be a little more careful shopping around for a good deal. BTW, compared to a typical aircraft engine like a Lycoming or Continental, under $5K is a super bargain. The plane wreck had nothing to do with the engine either. It was my piloting skills.
Issue 2: Expensive to overhaul:
One example of a rotary rebuild was mentioned at $12000, but that was for an engine that produced almost 3X it's stock power. Let's look at some real world numbers. You've picked up a rotary engine at the junk yard, and take it apart. First if the rotor housing are bad, then you are looking at about 1K for both housings if you have to buy them new. There is alway the option of scrounging around for good used ones. Even more money if the center or end housing and/or the rotors are bad. But let's just assume you need a basic overhaul. New apex seals, and set of 'O'-rings. I know of a source for the complete 'O' ring kit for $163, and another $70 or so for the gaskets needed. A set of Apex seals and springs can be had for $225. So total cost for the rebuild will be $163+$70+225 = $458. A few other items are needed such as sealant, etc. So make it $500. Quite a bit less than $12000! Those parts are available from
http://www.rotaryaviation.com/ That's also where I purchased my ECU and Engine monitor (EC2 and EM2).
Issue 3: Power produced
Some of the early 13B's were rated at 140 HP. It's pretty easy to pump up the power to 180 -200 HP with minor modifications. Various levels of "porting" from "mild street" to a "bridge" port. The bridge port is very aggressive and to my understanding not a good idea on a street car. Bruce rated my engine at 193 HP at 6000 rpm with the mild street port and 9.7:1 rotors. But a lot depends on the intake and exhaust tuning as well. Rotaries tune a lot like a two stroke engine. Intake and exhaust lengths can make a lot of difference. With the setup I have now the intake is probably tuned to something like 9000 rpm, which means I will never see that peak. My ECU has a 7500 RPM cut out. 9000 isn't practical in an aircraft application. now the thing is, it's possible to boost a rotary to incredible power levels. If you haven't seen it, here is a video of a 4 rotor engine turning 1664 HP on a dyno:
http://www.youtube.com/watch?v=0BGGBU2Lpyo. That's only 800 HP for a 2 rotor.
Issue 4: Split timing
This has been brought up before. It's my understanding that the split timing is used to reduce HC emissions. It's not a big contributor to power production. I have the ability to kill either the leading or trailing ignition on my ECU. It's done only for testing purposes. Killing the trailing plug make almost no difference in power production. Killing the leading plug causes a significant reduction. I do not have split timing capability.
Issue 5: Exhaust issues
No doubt about it, the rotary exhaust runs hotter at full bore. Notice the exhaust pipes in the video above when they hit peak power. Another thing that sometimes happens with the rotary is that some unburned fuel will ignite in the exhaust which can lead to higher temps. The typical exhaust temps of the rotary can run around 1800F, maybe 100 or 200F higher than a piston engine. I will be putting some extra shielding around my exhaust to keep heat away from the rest of the car. My exhaust system will be build out of thick walled steel tubing. I'm talking 0.120 wall thickness. The aviation guys tend to go more to 321 stainless as they can use thinner material and save some weight. An aircraft engine runs at 75 -100 % power for long periods of time. It only take about 30 HP to run down the highway at 60 MPH no mater what engine you have which also makes it easier on the exhaust.
Issue 6: Apex seal wear
The problem isn't really so much seal wear as it is carbon gunking up the slot the seal sit in. The seal then gets stuck so can't seal. This is mainly due to Mazda's system of injecting crank case oil into the rotor housing to lubricate the seals. The simplest solution for this problem is to junk the entire oil injection system and use 2 stroke premix at 3/4 to 1 ounce per gallon of gas. The premix burns a lot cleaner and does a good job lubricating the seals.
Here is a quote form one long time rotary engine user:
"I have owned six rotary powered cars starting in 1973 two of which have had over
300,000 miles. The engines were still running fine when I sold them.
The rest of the car will turn into a rusted hulk long before the engine
dies. However one must not let the engine over heat
or run out of lubricating oil both for the apex seals and the
bearings. You must also keep the air filter in good shape and not
allow objects to enter the engine intake system." Paul Lamar (see
http://www.rotaryeng.net)
Paul know how to take care of a rotary engine.
7. Hard to work on
This is probably the most incorrect of the issues.
OK, the real problem is the unknown. But just take a look at what's involved The rotary is a sandwich of 5 pieces which are bolted together. Front housing, rotor housing, center housing, rotor housing, end housing. In the sandwich are two rotors and an eccentric shaft. There are a few other pieces, like the oil pump and apex seals and springs, but compared to a 4 stroke piston engine the parts count is way down. The eccentric shaft is bullet proof. Never heard of one breaking or even wearing out. Like anything else, one has to pick up the special tricks that make the job easier. Knowing how to keep the apex seals in the right place while you slip everything together, and how to keep the 'O' rings in place are a couple of the things I've heard about that can cause major grief. (Remember, I didn't build my engine.) There have been several of the aviation guys that have built a junk engine for practice, then built an engine they were going to fly behind. In one case the builder had some issues that resulted in redoing the engine a second and third time. He was having problems with the 'O' ring seals. But he did learn. Resources to help, Bruce Turrentine sells a video on rebuilding the rotary. A good place to start
One other issue:
Sometimes you will see references to apex seal fractures. These happen and they can be costly. The rotor housing will probably be rendered unusable. It is caused by detonation. The thing is, it is almost exclusively a problem for turbo engines. It would be a very rare event in a NA engine.
Certainly the rotary engine won't be everyone's cup of tea (understatement). And all of it is heresy to the "Stock" and "Factory Original" folks. I'm expecting my rotary Alpine to be a fun car that I can travel in. We shall see. So far I've driven it around an empty parking lot once.
I hope to see a lot of you Alpine enthusiasts at one or more Alpine events in the next year. If all goes well I should have the rest of the pieces put together, paint and interior done by spring. I have been off on my estimates before.
Bob W.
