Hondaklubben

Annat forum... skrev:Honda are currently talking about trying to make it rev to 7,000 rpm. As a technical exercise, this is impressive, but it could have one of three big disadvantages as far as my engineering knowledge extends. To do this without the head literally being blown through the bonnet due to the massive compression ratio of a diesel compared to a petrol, they'll either have to massively increase the strength of the engine at the top and bottom end which means you end up with an engine even heavier than the usual diesel. This will have a big negative effect on handling and weight obviously, which will hit fuel economy.

Secondly, they could lower the compression ratio to avoid this, but this then negates much of the advantage of diesel which is that the explosive force it provides is done with far less fuelling than petrol, hence the gains in fuel economy. So you have a 7000rpm diesel that isn't much more economical than it's petrol equivalent for a lot of extra complexity, weight and R&D money.

Thirdly, a 7000 rpm diesel is going to generate far more internal friction and heat than any other diesel on the market. Not only does this mean frictional losses will be much higher and power lower than expected, but also could have negative effects on the reliability aspect.