Quote:
Originally Posted by Sleeperz
Mazda Sky engine 13:1 runs 87 octane.
He calls the 14:1 CR "groundbreaking," though it's a lesser 13:1 in U.S. engines to accommodate our 87-octane regular gas. A "breakthrough" combination of technologies – including direct multi-hole injection, dual VVT, new-design pistons, a unique 4-2-1 exhaust system, shorter combustion duration and delayed ignition during start-up – prevents knock.
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What is groundbreaking is how the engine has a typical output with peak torque at 4k RPMs and peak power at a modest 6k RPMs. Most engines that use that high of compression either require high octane and/or extremely high cam profiles. The Prius engines use 13:1 static compression ratio but they make far less than 100BHP per liter. The drawback is that the early '12-'13 MZ3 Skyactiv without the 4-2-1 header does take a hit below 4k RPMs. The CX-5 has the Skyactiv headers while the '12-'13 MZ3 uses traditional headers.
Too much compression can actually hurt power and torque as pre-ignition becomes an issue. Economy engines will typically run pig rich at high RPM/load anyway, to protect the engine. But it's not uncommon for a regular tuned engine to run better on midgrade or even Premium. What with VVT and VCT being commonplace.
Quote:
Originally Posted by ae86stunt
Whats it caused by? 
Main bearing and journal bearings becoming loose, Duo to detonation.
I am a mechanic. But dont take my advise. |
So you're actually a technician?
They are probably talking about the specific sound. Pinging sounds a bit different from rod knock. Hammering vs popcorn popping. Pinging can cause bearings to wear out but you typically don't get rod knock until after pinging or detonation.
Quote:
Originally Posted by bestwheelbase
Detonation can be a cause (not the only one). But the cars are designed to not have catastrophic failure due to one street driven tank of 87, right?
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91 AKI is recommended but 91 AKI is
required. So no, a tank of sub-Premium could result in long term damage or possibly void the warranty in the event of catastrophic failure. All it would take is sending out a sample of the fuel to confirm.
Note that 100 RON(94-95 AKI) is more commonly available overseas than it is here. Whereas we have places like Cali and the thirteen states that follow CARB where 91 AKI is the only Premium available.