johnfm

have you done some preliminary reading? If not, consider the forces involved in accelerating the piston/conrod assembly. The faster these assemblies move, the greater the forces. With the regards to the valve train, you have valve bounce issues, which can be overcome with changes to valve spring rates.

All the engineering decisions relating to overcoming these issues then boil down to economics - they can easily engineer the engines with stronger, lighter components - but the price of the car then increases and the market narrows - hence limited numbers of highly engineered GT3s and their ilk, and rev limits of 7200 rpm for cars which in the main are used on public roads.

Just my 0.02....

Pete Lech

Essentially, the ultimate reason is that above a certain speed, the recirocating mass will come apart in an undesireable way. For example, in my '85 Carrera, a major limiting factor was the strength of the connecting rod bolts, which tended to stretch over ~7000 rpm. Connecting rods are known to come apart as well, which is why very high revving motors use titanium rods. You hear less about it nowadays, but valves can float above a certain rpm, and could hit the piston if the clearance is very close.

PV

Thanks Pete.

So the M5 is using all the higher tech stuff?

What is more important in the design decision: the valve weight or the oil pressure (spring load)?

pcar964

W R O N G ! ! ! hahaha

For max acceleration, shift at redline. Period. I'm afraid you guys don't know what you're talking about...

As far as "why don't they raise the redline," there are many factors that affect that, but here's the basic idea - redline is the point at which the engine stops making power efficiently, due to its design. You can change the effective "redline" by altering timing, advance, spark, etc... but it's not like they just build the engine and then arbitrarily decide on a redline. They could have designed the engine so that it has a 10,000rpm redline, but it would be peaky and have a much sharper torque curve. Not to mention the cost of strengthening the internals to cope.

But for instance, just because a diesel engine's redline is much lower, doesn't mean it's of inferior quality or technology. It's just the design of that engine that dictates its effective redline. Watch the Audi R10 diesels next year with their much lower redline, as they win races against cars with much higher redlines.