Get your calculators out

[Rob Gaskin]

Ok, for all you budding 'Regularity Rally Navigators' here is a question:

If you have to average 60 mph for 2 miles and you actually do the first mile at 30 mph what speed have you got to do the second mile at?

 

[jonbills]

You've got 2 minutes to do 2 miles.
you do the first mile in 2 minutes @ 30 mph.
you need to be infinitely fast for the 2nd mile.

 

[Rob Gaskin]

You've got 2 minutes to do 2 miles.
you do the first mile in 2 minutes @ 30 mph.
you need to be infinitely fast for the 2nd mile.

Correct. I got it too, but most people apparently say 90mph!

Ok next question:

At 3000 rpm (fairly relaxed pace) how many times does a piston in any engine go up and down in one second?

And how many times do the valves open and close in that second?

 

[jonbills]

3000 rpm = 50 revolutions/second. So the piston goes up and down 50 times.
each valve opens and closes 25 times per second, unless it's a 2 stroke, in which case it's probably 50 too.

 

[Jimbo]

3000rpm devided by 60secs = 50 revs per second
50 divided by 4 stroke cycle for one valve = 12.5 so 2 valves would be 25

makes sense to me jonbills

 

[johnymd]

Cam rotates at half the speed of the crank so each valve would open and close 25 times a second.

 

[jonbills]

Which is a lot, when you think about it

 

[johnymd]

It's a lot more at the red line. Gives you something to think about when the engine screaming at North Weald today.

 

[Rob Gaskin]

Correct guys and when I was discussing this 'in the pub' recently people didn't believe me.

I'm sure Joe Public thinks that the piston goes up and down about 5 times per second - if they ever even consider it.

Old F1 engines used to rev to 18k, so each piston goes up AND down 300 times per second!

Extract from the V6 regs of about 10 years ago:

Engines are limited to 18,000rpm

No wonder the components of the engine are as light as poss.!