Mazda Speed 6. Manual — part 7

01 ENGINE

30

Fuel Octane

The MZR 2.3L L3T engine has a high compression ratio for a turbocharged vehicle
of 9.5:1. Typically turbocharged engine compression ratios are in the range of 7.5:1
to 8.5:1. This engine also has high boost pressure from the turbocharger 15.6 psi.
Typical turbochargers boost from 5 to 12 psi . When you combine a high compression
ratio and high boost, the result is a higher compression engine, somewhere in the
range of 11:1. Higher compression engines require higher octane fuel.

Using lower than 91 octane fuel is not recommended. Lower octane fuel must be
injected and ignited earlier. Less timing advance results in lower power and more heat.
This engine should be run with 91 to 93 octane, 93 is ideal for its compression ratio.
There are several disadvantages to lower octane fuels, less power, more heat, lower
fuel economy, more carbon deposits. 89 octane should only be used in an emergency
if 91 octane is not available.

The engine management system is able to seemlessly modify the ignition timing and
fuel delivery for the entire range of fuel octane from 89 to 93 without detonation. It is
also designed to protect the engine from damage due to lower octane fuel. When low
octane fuel is used, the fuel delivery and ignition timing are retarded and power output
is reduced. Continued operation with low octane fuel can result in increased engine
intake air temperatures, when temperatures exceed safe levels, the PCM commands
the turbochargers waste gate regulator solenoid off at 4200 rpm. With the wastegate
regulator solenoid off, the wastegate opens earlier to reduce heat. A customer using
low octane fuel in hot climates may describe this as a loss of power over 4000 rpm.

02 SUSPENSION

31

Suspension Modifi cations

18” X 7” Alloy wheels with 215/45/18

Vehicle overall height reduced 0.4”

Shock dampers tuned

Spring rates increased:

Front- 25%

Rear- 37%

Stabilizer bar thickness increased:

Front- 23 to 24mm

Rear- 21 to 23mm

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02 SUSPENSION

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03 DRIVELINE/AXLE

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Objectives

After completing this section, you will be able to:

Explain Active Torque Control AWD

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