Perry Mick wrote:
I'm considering building a new engine for my plane, 2-rotor NA. Since I
want the 13B-REW front thrust bearings and the rear engine mount points,
it should be based on the 3rd gen REW engine. But since I'm not
turbo-charging, I think I should use 89-91 NA rotors and rotor housings?
Higher compression ratio and the rotor housings would have the exhaust
splitters in them for noise reduction. Hopefully these parts are
interchangable. Also looks like I would retain the 2nd gen front cover
with CAS.
Attached is an HTML page about the REW. Looks like the 2nd gen water
pump will work on the REW. See any problems with this idea?
--
Perry
---------------------------------------------------------------
13BT vs. 13B-REW: (Last revised Aug. 14, 1997)
There are two types of 13BT blocks, one from the 87-88 Turbo RX7
(FC3S GTR) and one from the 89-91 Turbo RX7 (FC3S GTX). While
the older 13BT GTR block differs a lot from the 13B-REW block,
the GTX block is some what a compromise in between. Most of the
changes made by Mazda engineers are refinements to address the
< problem areas of the previous designs. For comparision purposes,
the 13B-REW motor described in this article is the one from the
FD3S, not one from the Japan-only Mazda Cosmo.
One significant difference on the 13B-REW is the areas around
the dowel pins on the side housings. They are reinforced and
ribbed with thicker castings. This is a major problem area on
high output 13BT engines, as they tend to crack at high power
levels and is the main reason that the 13BT blocks are not
reliable beyond 400HP. Most competent rotary rebuilders will look for
this before rebuilding a 13BT motor. The 13BT GTX blocks are
said to be more reinforced than the earlier motors but not as
significantly as the newer 13B-REW designs. Before the introduction
of the 13B-REW motors, some engine builders experimented
with brazing extra metal around the dowel pins area on the side
housings of the 13BT motors.
The port sizes on the 13B-REW are extremely larger than the 13BT's,
especially the primary ports on the intermediate housings.
This is accomplished by increasing the height of the side and
intermediate housing where the ports are located and relocating
some of the coolant passages inside the housings. The larger
ports increase the duration and "lift" of the intake stroke,
allowing more air to be ingested into the combustion chamber.
While the intake ports are larger, the intake runners of these
motors are still about the same size. The 13BT intake manifold
has a surge tank plenum which is found to create too much pumping
losses because of its large volume. The 13B-REW intake manifold
is a "Dynamic Pressure Intake System" which eliminated the surge
plenum tank and has opposed-facing secondary intake runners. This
new design enhances intake flow by taking advantage of the
strong pressure waves inherant in rotary engines. The throttle
bodies on the 13BT are 3x45mm, while the 13B-REW are 1x45mm +
2x50mm.
*Intake Runners: Upper, Lower
*Plenum: 1, 2
*Runners: 1, 2
Contrary to popular beliefs, the 13BT's and 13B-REW share
many internal components. The 13B-REW rotors are interchangable with
the 13BT GTX rotors, although they don't have the same part
number and thus are not the same part. But they do have the same
compression ratios of 9.0:1 and they weigh the same. The CR
of the 13BT GTR rotors are 8.5:1. I believe the later model rotors
are manufactured from a more accurate milling technique while
the older ones are left partly casted. This is evident in the
bathtub faces of the rotors.
Almost all the internal seals and springs are the same parts
in the 13BT and 13B-REW. This includes the 3-piece cast-iron 2mm
apex seals which are found on all post '86 rotary motors, both
turbo and non-turbo. With the exception of the side seals and
corner seal springs, all the other rotor parts of the two motors
such as oil seals, rings, springs, side seal springs, and
corner seals, are the same parts. The newer design corner seal
springs are reccommended for use in all rotary rebuilds.
The eccentric shafts for these motor seem to all look the
same, but the 13B-REW shaft has a larger oil bypass/crank pulley bolt.
The newer motor surprisingly maintains the same warm-up oil-bypass
pellet as the older motors. The 13B-REW motors does have
larger front-end thrust bearings than the 13BT motors. These
larger bearing components require the use of a different front
counterweight. The larger thrust bearings allow better loading
and thus a tighter torque setting of the pulley bolt. This design
will reduce the chance of the eccentric shaft bending at the
front section, which is sometimes a problem on high-output 13BT
motors. The large thrust bearing is probably also designed
for use with the pull type clutch assemblies found in the FD3S.
The front cover of the 13B-REW has one more attachment bolt
which prevents the gasket from blowing out, which is a problem on
the 13BT motors. These front covers are interchangable between
the two motors as the bolt patterns are the same (except for the
one extra bolt on the 13B-REW). The 13B-REW motors uses crank
trigger sensors mounted on the crank instead of the crank angle
sensor (CAS) on the 13BT. The crank trigger sensors allows a
better accuracy resolution because of its wider teeth spacing.
Also, torsional flex on the crank angle sensor shaft causes
inaccurate readings. The two triggering systems has similarities in
the numbers of triggering teeth. The 13B-REW's crank trigger
has 12 syncro teeth and 1 home tooth, while the 13BT's CAS which
spins at half speed, has 24 syncro teeths and 2 home teeth.
The rotor housings on the 13B-REW motors are refined for
reliability. Since the motor is designed for higher standard output,
the wear surface on these housings has a carbon-graphite coating
which is said to exhibit 32% less friction than the 13BT
motor's fluorocarbon resin coating. The new coating actually
allows less oil to be injected into the combustion chambers, thus
the 13B-REW requires only two oil injectors instead of four.
In addition to this coating, these rotor housings has the water
passage machined around the spark plug areas to increase
cooling at the spark plug tips. This modification is similar to the
ones done on race motors.
The stationary gears on the 13B-REW are factory hardened.
They are interchangable with the 13BT's, provided that the 13B-REW's
thrust bearings and front counter weight be used. Inside the
stationary gears, the standard main bearings on the 13B-REW motors
are the multi-holes type and are locked into place by an
anti-rotation set screw. This design, similar to the "3 window-type"
bearing is pioneered in the earlier LeMans and IMSA motors.
The holes allow extra oil to flow around the oil groove thus
providing a thicker oil film for the eccentric shaft to ride on.
The 13BT has standard bearings with no oil holes. Oil pump
capacity and pressure are also increased in the 13B-REW motors.
The oil pumps are not interchangable. The 13B-REW oil pressure
regulator is interchangable with the 13BT motors and is a
reccommended upgrade when power output is increased. Also, a new oil
pan design on the 13B-REW motors helps to minimize air induction
into the oil strainger. A thinner pan with a inner bulge
maintains oil level to keep the oil strainer submerged in oil.
The 13BT GTR blocks use mechanical oil metering pumps, while the
13BT GTX and 13B-REW blocks use electronic oil metering pumps.
The water pump of the 13B-REW is probably the only reverse
rotation water pump assembly found on any Mazda rotary engine. It is
driven by the back of the serpentine belt. The water pump housing
assembly on all the rotary engines are interchangable, but the
appropriate front cover/pulleys/etc... must be used.
Fuel injectors used in the 13BT motors are 4 standard Nippondenso
top feed rail injectors rated at 550cc. Depending on
production dates, the 13BT motors had both low and high impendance
ratings. The 13B-REW motors has 2x550cc injectors for primary
and 2x850cc injectors for secondaries. This higher fuel capacity
is for higher power levels. These injectors are side-feed rail
types with high impedance so it can operate cooler. They are not
interchangable with the 13BT injectors.
The engine mounts locations of the 13B-REW are under the rear
side housing, while the mounts on the 13BT are located on the
intermediate housing. Because of this, interchanging the motors
between the FC3S and FD3S chassis is a very involved project.
The tranny bellhousing bolt patterns are the same on the
13B-REW and 13BT motors, thus the trannies are interchangable with the
appropriate clutch/flywheel assemblies.
In summary, because of these and many other refinements,
the 13B-REW is a much more potent powerplant which can easily handle
high HP output beyond for which it is originally designed for.
Many of these refinements are shared in the designs of the
20B-REW and 13B-REW of the Mazda Cosmo.
Any questions or comments? Please send email to pko@mindspring.com
Reference
* S. Tashima et al, "Sequential Twin Turbocharged Rotary Engine of the Latest RX-7", SAE paper 941030
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2003 All world wide rights reserved.