Scott Speirer wrote:
Just found this article on the SAE website by Jack Yamaguchi ...
http://www.sae.org/automag/global_viewpoints/01.htm
Some interesting information. I can't tell when it was written. Sounds like it was
before the announcement of the Evovle and RX-8. In the last paragraph, is Jack
saying that Mazda is owned by Ford?
Scott
snips...................
the world's first such turbo installation. The engine produced 190 kW (255 bhp) at 6500 rpm and
294 N*m (217 lb*ft) of torque at 5000 rpm. Two years later, power output was increased to 198
kW (265 bhp).
By unwritten decree and industrial agreement, no Japanese manufacturer offers passenger car
models with engine output greater than 209 kW (280 bhp). Imported marques are not a party to
this domestic consensus, so for them the sky's the limit. Some members of the industry limit
output of their larger displacement or more powerful powerplants. Others try to attain the limit by
tweaking up their engines. Honda, for example, has made the mark, adding 0.19 L to the Acura
NSX's exotic quad cam V6.
Now Mazda has joined the 280-bhp club. The latest 13B-REW produces 209 kW (280 bhp) at
6500 rpm, an increase of 11 to 13 kW (15 to 18 bhp) obtained above 5000 rpm. Torque output is
also improved by 20 N*m (15 lb*ft) in the critical mid-speed range above 2500 rpm, peaking at
314 N*m (231 lb*ft) at 5000 rpm. New turbochargers, improved apex seal lubrication, freer
exhaust, enhanced cooling, and more elaborate engine management are cited as bringing these
benefits, while the engine's internals are inherited from the previous version.
The turbocharger, two of which are used in the sequential setup, is a new Hitachi instrument
with an abradable compressor sealing and an "ultra high flow" turbine design. The abradable
compressor housing sealing has been in U.S. markets, Toyota being among the first to use it in
the MR-2 sports car, some years ago. It was one of more promising items in the menu that
Mazda's rotary designers had prepared a few years ago to get more power out of the
13B-REW, but, according to Yamamoto, the company was in a dire financial state, and the
design team could not dare ask for the expensive turbocharger. The Toyota unit had plastic layer
hot-sprayed onto the housing's surface, a methodology hardly suitable for large-scale
production, therefore costly.
Hitachi has since come up with a new built-up construction of the compressor housing. A
formed plastic inner sealing element is bolted onto the main housing, and then machined. The
turbocharger is assembled, and run up to 100,000 rpm, abrading the inner surface of the plastic
seal, obtaining the closest clearance between the compressor and housing. The new abradable
turbocharger has an 80%-plus efficiency, whereas a typical instrument's efficiency is about
75%, according to a Mazda designer. This brings down the compressed air's temperature by
10°C, or about 10%, at the exit of the compressor. Air temperature is still in the region of 110°C
(230°F), which is further cooled down by the air-to-air intercooler in the RX-7 installation.
The latest trend in high-performance turbo technology is a "diagonal flow" turbine. Mazda
asked Hitachi to come up with several candidates of this design, hoping it would boost the
engine's output. They did not quite match the rotating piston engine's unique characteristics.
Back to the tube, as it were, to research basic flow dynamics. The fruit of the toil is the
"ultra-high-flow" turbine, with its blade length extended and its shapeless acutely curved,
enlarging gas passage and reducing flow resistance. Turbo response in the low speed zone has
been greatly improved. The turbocharger adopts a smaller diameter turbine, 50 mm (1.9 in.) now
versus the previous unit's 51 mm (2.0 in.), again reducing inertia mass. The new "ultra
high-flow" turbine realizes about a 10% gain in efficiency, according to Mazda's turbo engineer.
The twin ultra-high-flow turbochargers supply a maximum boost of 74.7 kPa (10.8 psi) at 6500
rpm to the previous high-flow instruments' 62.7 kPa (9.1 psi) at the same rpm.
The rotary's reliability under the severest conditions was well proven in Mazda's competition
activities in the late '80s and early '90s, including an outright win in the Le Mans 24-hour race
for sports racing cars in 1991. A road car is subjected to a different kind of stress, said a Mazda
designer responsible for the engine's innards, especially when the 13B-REW's output is
increased to 209 kW (280 bhp). Possible problem areas are higher combustion temperature and
pressure. The former could be dealt with by the cooling system's heat dissipating capacity. The
latter was thought to exert extraordinary pressure on the engine's gas sealing.
Apex seal lubrication became a critical issue. In a race engine, oil supply to the rotor housing by
means of injection was precisely monitored and controlled, whereas in the production unit, a
larger amount is supplied, just to be on the safe side. Some of the lubricant is fed into the trochoid
chamber through a metering nozzle. The previous nozzle's oil passage was 2.0 mm (0.08 in.) in
diameter. Negative pressure created in the rotor chamber would cause all the oil within the
nozzle to be sucked out. When the engine accelerated rapidly, oil supply could not keep up with
the speed. To prevent oil starvation, the previous system supplied a larger amount of oil to be on
the safe side. In the new metering nozzle, the passage diameter has been reduced to 0.08 mm
(0.003 in.), halving its volume of 0.0005 L (0.03 in3). A new rubber seal is also inserted to fill a gap
within the nozzle body where oil used to be sidetracked. Now, there is still some oil left within the
nozzle after each suction, so that the lubrication system responds to the apex seal's requirement.
ln the exhaust system, the front tube gauge has been reduced by 0.5 to 1.0 mm (0.02 to 0.04 in.)
so that flow passage is increased while retaining the tube's outer diameter. The main silencer
has also been redesigned. These changes result in about 10% reduction - about 13 kPa (1.9 psi)
- in exhaust gas resistance.
The third-generation RX-7 had come off Mazda's rigorous development test programs on the
bench and on the demanding Global Road Circuit section of the Miyoshi Proving Ground with
flying colors. Yet, there was one arduous test left undone. When the car was taken to a race
track near Tokyo known for its tight turns requiring short bursts of speeds followed by fierce
deceleration, the pride of Mazda's rotary rocket team quickly cooked its powerplant when
pushed to the limit. Subsequent investigation revealed that air temperature at the entry area had
risen to as high as 50°C (122°F). Fresh air for the engine's consumption was taken from the
single intake that also fed to the air-to-air intercooler. On wide-open driving, airflow reversed
its course from the intercooler and went straight into the engine's intake. The intercooler was
acting as an inter-heater! In the updated RX-7 with a designed fascia, fresh air is taken through
a separate, dedicated duct guided by a newly installed airguide. Air temperature at the engine's
intake entry area has been halved to about 25°C (77°F), which adds about 7 kW (10 bhp) to the
output.
The front-end's opening areas have also been increased by factors of 2.1 for the radiator
opening, 1.8 for the intercooler duct, 1.8 for the oil cooler, and 1.6 for the front brake cooling duct
intake over the previous RX-7. The radiator's core depth has been increased to 27 mm (1.1 in.)
from the previous one's 25 mm (1 in.). The 209 kW (280 bhp) engine had its fin-pitch changed
from 1.1 mm (0.04 in.) to 1.3 mm (0.05 in.). Twin cooling fans' blades have also been increased,
one from five to seven blades and the other four to five blades, while the high-speed electric
motors' consumption has been changed from 160W to 120W.
The central computing unit operates on the same logic; however, its data parameters have been
greatly increased. The CPU centrally and precisely controls air/fuel ratio, ignition timing and
boost pressure. Mazda continues to offer the 194 kW (260 bhp) and (190 kW (255-bhp) with
automatic transmission) version of the 13B-REW, on its rationale that not everyone wants 209
kW (280 bhp). All external modifications are shared with the higher-power engine, except the
turbos, and oil metering nozzles.
more snips..............
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