This site indicates for every "1" compression increase, HP also increases 4%. So increasing to 18:1 means aprox a 30hp increase or 215HP.
With the temp here in Minnesota reaching -10*F last week, and normally is around 10-20*F in winter, I'm really curious to see how Mazda engineers overcome the cold start with HCCI.
I just wonder what kind of a beast of a starter that thing is going to require! Or if it will use an initial spark to kick it off or something.
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So if increasing compression makes for more power why did Mazda reduce the compression ratio for the diesel?
Although they did increase the ratio for the petrol. Can someone explain.
Lowering the compression ratio on the diesel allowed them to make the engine lighter, produce less NOX emissions (no urea after-treatment) and it allowed for a higher readline.
It also allows for more fuel to burn closer to the top of the cylinder stroke, improving the amount of work done by the fuel.
The power improvement for compression increase also isn't nearly as much as CX-sum wrote.
Going from 17:1 to 14:1 you'll only see a ~4% drop in power. Not hard to make up for that with more boost.
You might see a 4% increase in power for 1 point compression increase when you step up from 7.0:1 to 8:1 in a turbo engine, but once you hit higher compression ratios the increase gets lower.
Plus there's this "Optimization of Combustion Timing by Lowering Compression Ratio
When the compression ratio is lowered, compression temperature and pressure at TDC decrease. Consequently, ignition takes longer even when fuel is injected near TDC, enabling better mixture of air and fuel. This alleviates the formation of NOx and soot because the combustion becomes more uniform without localized high-temperature areas and oxygen insufficiencies. Furthermore, injection and combustion close to TDC result in a highly-efficient diesel engine, in which a larger amount of actual work (or, a higher expansion ratio) is obtained than in a high-compression-ratio diesel engine(Fig.2)."
That said Mazda was probably okay with balancing out some HP for increased MPG and maybe better emissions as per above? I mean that engine already has ample TQ.
Last edited by CX-5um; 01-11-2017 at 02:14 PM.