Paul,

 I have enjoyed reading your email list over the past few
 months, and I have learned a lot about rotary engines. There
 is no question in my mind that this is the engine I will use
 when I start to build my plane. However, I have a few questions
 that I am trying to answer.

 The first thing I am curious about is whether P-Porting an
 engine dramatically affects the life span of the engine. I
 ran into a website that claimed that P-Porting causes "excessive
 noise, extensive intake mods, very poor drivability and fuel
 consumption, relatively short engine life, is very expensive,
 and results in a narrow power band". The website can be found
 here:

 http://www.mazdarotary.net/porting.htm

 Obviously they are focused on automobiles, not planes, so
 some of these comments may not be relevant to airplanes.
 They mention other kinds of porting on this site, including
 mild porting, extended porting, bridge porting, and J porting.
 What are your thoughts on this issue? Will P-Porting have a
 negative effect on engine life? If so, how much (ball park)?

 Would it be better to use another less aggressive form of
 porting to get some increase HP if we wanted longer engine life?
 I am inclined to use P-Porting, but I want to make sure I can
 get 2000 hours out of the engine if I go this route. After all,
 it is a lot of effort and expense to go through this each time.

 Next, I was curious if it would be better to start with a
 13B from an RX-7, or to go to an RX-8 (assuming money is not
 the issue)? How about the 16B, is that engine available yet?
 Is there a difference in HP between the NA 13B and the NA RX-8
 engine? In your opinion, if you were an inexperienced newbie
 looking for a two rotor engine in the 225 HP range, what option
 would you select, and how would you acquire an engine?

 Finally, I am baffled by the fact that Mazda does not sell
 "crate engines". However, it seems there are plenty of new
 parts for these engines on the market. Is it possible to
 simply purchase all the engine parts new from Mazda and assemble
 your own new engine, or is that prohibitively expensive? Are
 there companies out there that do exactly this?

 I apologize in advance for all the questions, but these
 things just run around in my head all the time, and you are
 clearly the most knowledgeable person to ask. Thanks again
 for your excellent email list.

 Dave Stoddard
 Future Cozy MKIV Builder

 No need to apologies. All questions are welcome.

 The guy is in the biz of porting engines. What else can I say
 other than it is a lot on nonsense. The 13B exhaust p-port
 is ten times harder on the apex seals than any intake p-port
 ever could be. The intake p-port actually cools the apex seals
 which normally run about 500 F near the center. The fuel
 consumption is actually lower in a p-port as less HP
 is used to suck in air. The guy is a grinder and not
 an engineer :)

 IMHO the 16B will be vapor ware into the near future.

 The over all cost of the p-port winds up cheaper as there are
 no suitable manifolds out there for all the variations
 of side ports. Just to name a few, there is an old four port RX4,
 six port 13B, four port 13B turbo, Cosmo four port, RX8 four port and
 RX8 six port. What intake manifolds there are... are too short
 and mostly for carbs. People wind up kludging intake manifolds
 and wind up with disappointing amounts of HP.

 I think a P-port RX8 engine is the best of all worlds.
 It runs as well as a stock 13b in our RPM range and
 is quieter with a cooler exhaust. The intake manifold
 is cheaper and lighter. The slide throttle cost
 the same as a throttle body.

 Mazdatrix will sell you all of the parts. Same goes for
 Mears Motors in Lubbock Texas.
 http://www.mazdatrix.com/
 http://www.mearsmotors.com/


 Read the whole web site as there are other links and lots
 more info on there.

 Paul Lamar


 Paul,

 I'm sure its been covered before but humor me. Why do you advocate PP intake
 ports on an engine that presumably is then going to be breathing limited
 with side ports on the exhaust side (RX8 engine)? Seems to me that in the
 interest of HP the best choice would be an older 13B with PP on both intake
 and exhaust? Show me where I'm wrong (purely from an HP perspective). As you
 know I'm well aware of the noise issues with the 13B PP exhaust ports (mine
 are turbo housings without splitters).

 Mike Wills

 It is quite simple when one looks at the pressure differences involved.
 On the intake side one has only a few psi difference to suck air into
 the engine. The amount of HP generated is directly proportional to how
 much air one can get in the engine.

 On the exhaust side one start's with well over 100 psi and one is pumping
 that out of the engine to only 15 psi at sea level. 85 psi difference.

 It is far more important to streamline the intake and tune it using
 organ pipe theory to archive a 120% volumetric efficiency which is what
 you get with a tuned P-port.

 I was pleasantly surprised to get about the same HP on the P-port
 RX8 as we got on the p-port 13B. We tested both on the Mazdatrix dyno
 with a similar muffler system. The RX8 had a slightly higher compression
 ratio. Both had the same Weber 51 mm carb. If anything the exhaust manifold
 on the RX8 was worse than the tuned header we had on the 13B.


 Paul Lamar


This is precisely why conventional reciprocating engines _all_ (as far
as I know) have more intake valve area than exhaust valve area.
Ford's 3 valve engines have two intake valves and one exhaust.
Audi/VW 5 valve engines have 3 intake and 2 exhaust valves. I guess
one other factor for these poppet valve engines is that a smaller
exhaust valve might be easier to cool.

Mazda has had the port size relationship backwards until the Renesis.


Matt-

Strictly on the basis of port area I don't think so Matt.

The 13B P-port exhaust is smaller than it looks. In a six port 13B
you have to add the area of 3 side intake ports for each rotor.

The RX8 side exhaust ports are 17% more area than the 13B p-port exhaust.
That could be another reason we are not losing more power in the
RX8 intake P-port engine.

Port area of course is not the whole story as the air can be going through
there up to 400 MPH. A straight shot is therefor better than a bunch of
right angle turns.

Charles Taylor at MIT did some work on this subject years ago.
Note curve 2 which is the VE of an aircraft engine that did
rather well. Modern engines with multiple intake valves can do
better but not as good as a rotary p-port at 120% VE.

Paul Lamar