- 2.5V6 - two variations of the 2.5V6 exist, KL for ex-Japan, KL-ZE for
within Japan. The KL is a detuned variant of the KL-ZE offering power and fuel
economy of a 2.2V6 (based on the 2.0V6 output). The KL-ZE offers 200bhp and
achieves up to 94bhp/litre.
- All V6s - all Normally Aspirated V6s feature a Variable Resonance Intake
System (VRIS), the same concept as later used by Porsche on their 3.6 and Ferrari
in much more sophisticated form on their V12. VRIS first appeared in Mazda's in
their older 158bhp 2.0i-16 UK engine in 1989, it's purpose is to maximise the area
under the torque curve rather than peak figures so aiding low-end driveability.
In addition, the VRIS aids fuel efficiency and averages of 27-29mpg (Imperial)
in urban driving and up to 32-34mpg (Imperial) on the highway readily attained.
The I4 engines are special derivatives of the Miata & 1.8-I4-235bhp turbo engines.
The V6 has been used in the SuperTouring Mazda Xedos6 & 323V6-5dr (Xedos6 floorpan,
not related to the 323), and by Ford in 2.0V6 form in Mondeo/Contour. The Mazda V6
is not related to the Duratec engine which lacks a forged crankshaft. The 2.5V6
MX6 raced in several countries successfully. The IMSA 2.5V6 engines produced
430-480bhp from the 2.5V6, the 2.0V6 was 380-420bhp, all in race only form.
Engineering Data
Engine Dynamic Stress Levels
- As a benchmark, MPS
o Bore & Stroke
o Ring Loadings
Maximum-Piston-Acceleration (MPA):
Lighter rings create reduced accelerative forces, reduced ring/piston
interface overheating and reduced hammering of the piston-ring-groove. Too
light and ring longevity is adversely affected.
MPA = (rpm^2 * stroke"/2189)*(1/2A), A = ratio between rod-length-between-centres to stroke.
2.5 rod-centre-dist = 138mm; stroke = 74.2mm; A = 1.87
Both the 2.5V6 & 2.0I4 engines are engineered for longevity. The
2.5 engine is likely to be the longer lived engine subject to identical
maintenance to the 2.0 engine. Mazda V6 engines are assembled entirely by
robots, not humans, at the Osaka engine plant in Japan alongside Rotary engines.
Ford bench testing, with very minor changes, showed the V6 to be capable
of continuous running at 8900rpm - well beyond redline 7500rpm.
SAE paper "SAE920677" covers detailed design of the engine.
Engine Longevity
A USA oil company researched engine longevity using their own oil:
The V6 rivals the Lexus V8 for longevity, which is unsurprising considering
the original application was a Xedos6-2.0V6, Xedos9-2.25/2.5V6 & Sentia rotary
luxury lines. Many V6s & I4s have exceeded 350,000 miles, the only failures
on one was a Mitsubishi alternator at over 200,000 miles and the pre-Jan-1995
rear calipers on another.
The replacement for the V6 will come in two forms, a 2.3-DOHC-I4 in the Mazda-6
and a 3.0-DOHC-V6 in a larger saloon. There is of course the innovative 4 door
sports car, the RX-8, with the 250-280bhp Renesis rotary engine and potential
for a series of rotary sports cars should the market demand. The Renesis engine
is a non-turbo rotary engine using side-port exhausts to greatly improve fuel
economy, reduce emissions and improve performance.
Last Upload: 16th February, 2002. V1.50a
Engine Architecture
V6 Configurations
The V6 configuration appears in 1.8, 2.0, 2.25 and 2.5 litre displacements.
- 2.25V6 - worlds only Miller-Cycle (MC) as opposed to Otto-Cycle engine.
The Miller Cycle uses an 8 to 1 compression ratio with 10 to 1 power ratio for
improved power & reduced fuel consumption. The MC uses a twin-intercooled
Lysholm-screw Autorotor supercharger (world's most compact & most efficient)
to deliver 210-230lb/ft at 3500rpm and 0-60 of 7.9secs from the 4-speed ATX.
It effectively achieves the power of a 3.2-3.5V6, yet fuel economy of a 2.1V6.
The 0-60 time through torque-converter slippage masks the accelerative capability.
Mean Piston Speed
- V6 Engines - all-alloy DOHC 24V 60-degree V6 configuration
- Split Crankcase - as 911 flat-6 offers increased rigidity over
traditional bearing-cap solutions for high-rpm capability (7800rpm 2.0V6)
and low NVH (winning 1992 German engine award)
- Bearings - 4-bolt Mains, with a further pair of bolts at each bearing
section. Key journals & bearings are oversized regarding width. Bearings are
triple-layer heavy duty
- Crankshaft - Forged, nitrided, triple-lapped, mirror-finished
- Piston Squirters - Upper bearing journals contain piston oil-squirters
to aid cooling
- Exhaust-Valves - Stainless steel & sodium cooled
- Pistons - Lightweight to reduce reciprocating mass, piston skirts
are moly coated to reduce friction
- Head Gaskets - Stainless steel is used, with torque-to-yield bolts
- Stroke - Very short stroke creates low crank angles & low rod/bearing loads
o Mean Piston Speed, MPS
- 2.5V6 MPS = 0.167 * 2.92 * 7000 = 3170 ft/min at 7000rpm
- 2.0I4 MPS = 0.167 * 3.62 * 6500 = 3929 ft/min at 6500rpm
- F1 engine MPS = 4519 ft/min at 16,400rpm
- under 3,500 ft/min - Good reliability
- 3,500-4,000 ft/min - Stressing
- over 4,000 ft/min - Very short lived
- 2.0 Bore*Stroke of 83x92mm (3.62" long stroke)
- 2.5 Bore*Stroke of 84.5x74.2mm (just 2.92" stroke)
- For comparison F1 engines have 70x42mm (1.65" stroke)
Top-rings must balance high-rpm capability and wear, a thin ring
allows high-rpm capability, too thin and wear becomes an issue. With
reduced crank angles from a short stroke ring wear is reduced.
A 1.5mm ring is beneficial over a 1.0mm ring for high-rpm.
2.5 top-ring - 1.49mm/0.06"
- MPA Permitted = 77,000ft/sec^2
- MPA Experienced = 51,354ft/sec^2 at 7000rpm
2.0 top-ring - 1.17mm/0.046"
- MPA Permitted = 105,000ft/sec^2
- MPA Experienced = 70,157ft/sec^2
- The BMW M5 in comparison experiences MPA of 90,000ft/sec^2 on a 1.5mm ring.
2.0 rod-centre-dist = 135mm; stroke = 92.0mm; A = 1.47
- MPS-2.0 = (6500^2*3.62/2189)*(1.2*1.47) = 51,354 ft/sec^2
- MPS-2.5 = (7500^2*2.92/2189)*(1.2*1.87) = 70,157 ft/sec^2
Long Term Testing
"After 300,950 miles the Mazda MX6-V6 passed an IM 240 Exhaust Emission
Test in Aurora, Colorado, with results well within new car limits. At more
than 310,000 miles, the test engine was disassembled for inspection and
measurement. No wear was evident on valve stems and guides, main and rod
bearings, crankshaft main and rod journals, or cylinder walls. The cylinder
hone marks from original factory machining were all clearly evident. While
piston skirts showed no wear, piston rings showed an average of only 0.0015"
of face wear."
URL: http://homepage.ntlworld.com/dorothy.bradbury/probemx/p_m18.htm