How high can a petrol engine rev.

[billyo]

What is the highest revving petrol engine that you know about? I would guess an F1 car but dont know what they go to.

Is it much lower for diesels. What about the LE MANS diesel engines? Why do diesels not rev as high as petrols?

 

[HDi fun]

i'D IMAGINE A 2 stroke sports bike with red line over 23,000rpm is the highest revving reciprocating engine.

Turbine engines run up to 250,000rpm.

Diesels reciprocating engines rarely go over 5000rpm due to the compression the require.

Diesel turbines also do 150,000 plus rpm.

 

[obi_waynne]

23000 rpm I thought 12,000 in F1 was pretty high. I suppose bike engines are different beasts to cars.

 

[HDi fun]

A sports bike is probably little more than 250cc. So there's little reciprocating mass. Hence the silly rpms

 

[Pixel]

With each year that goes by, cars are getting faster & faster.

The average diesel cars revs to about 5,000 rpm.
The average petrol car revs to about 7,000 rpm.

How do you think these statistics will change in the next 10 years?

Turbochargers and Superchargers as standard on family cars?

 

[HDi fun]

You say that bit about forced induction. I think it will become standard. All Saabs are turbocharged, as are lots of Volvos.

VW is also moving this way.

 

[obi_waynne]

Its the only way to meet the emissions figures. A NASP engine will only ever be 75% efficient wheras a turbo pushes the output to 150% of the NASP equivalent easily.

The twin charger is a very interesting concept and will no doubt become more widespread.

More efficient = better economy and that is what the makers are chasing. I suspect we will at some point all end up with noiseless electric motors with their massive flat torque curves.

(Then we'll get someone called Lekkymotor-fun joining up the forum and endlessly banging on about how good electric motors have become. And saying how much better they are than diesels !)

 

[HDi fun]

The problem with electricity is storing the stuff. Batteries are heavy. And anyone who solves this problem will wind up dead. Killed secretly either by the British government because of the massive impact that loss of fuel duty revenue will have. Or by the government of oil producing nations because such a breakthrough will render their oil seams WORTHLESS

 

[Gangsta]

there is a compound available that can absorb HUGE amounts of hydrogen in a tiny space, and very safely, the problem is that when the hydrogen comes back out it does so with such vigor that it is dangerous - but im sure they will fix that soon. any we already have the technology to make electricty from hydrogen (look up hydrogen fuel cell) im not talking about all that run your car on water stuff.

 

[obi_waynne]

Ive read interesting things on the fuel cells. It will be interesting to see what they come up with.

 

[HDi fun]

No one's going to rush any alternative fuel. Last thing the govt. wants is to lose revenue from fuel duty.

 

[jonski]

even if they did im sure they would find some sort of alternative tax to bleed us dry as usual

 

[HDi fun]

Of course they would. Let's face it - there's a very important skirmish in Afghanistan to fund

 

[pgarner]

But is that not going to pay for itself through all the oil weregoing to get. Sorry this is going to turn very political if we stick to it. better get back on topic.

How high and engine can rev depends on alot of factors,
bore, stroke, compression ratio, fuel, block material. are just some

 

[HDi fun]

Balance is critical. Theoretically a straight six has the best primary and secondary balance, but its length means that you can get torsional stresses in the crankshaft.

Valves can bounce if engines are revved too high. Double valve springs help overcome this as the two springs have different resonant frequencies.

Breathing, too. If you cant get enough air in then it won't rev. And you have to get the fuel in to match the airflow. Apparently the 1984 Sierra Cosworth had two whole injector rails (ie. 8 injectors for 4 cylinders). In road tune the second set never came into action but it maybe explains why some of these vehicles could sling out over 500bhp.

 

[Gangsta]

afaik its was only the RS500 that had the duel injector rail, although the castings for the intake manifold still have the bits there (just havent been machined out).

Thats the bit i think i know - the bit I do know is this:

the reason for 8 injectors is actually for small power. back in the dark ages we never had super accurate/non leaking/fast acting injectors like we do now. If you had 4 really big injectors in the cossie it would run good on full chat, but would idle really badly as the injectors couldnt be controlled well enough to supply the small amounts needed at idle, whilst still dumping gallons in when needed.

So when its idling, or running low boost it just runs on 4 smaller injectors, and when the requirement gets bigger it kicks in the other 4, its all about controlability.

back to high revving:
having double valve springs is a strange one, its helps produce better power by making sure the valves shut properly and quickly but also increases friction.roller rockers can help a bit too by reducing friction.

even small things can make a big difference - such as titanium (or other lightweight and strong) spring retainers (the little collers that go over the end of the valve to hold the springs in)

anything lightweight and low friction will help, 6cyl is good, very stable and doesnt need a balance shaft for high speed and low vibration.

carefully specifying things such as oil pump and sump - so that there is just enough oil to let the engine run and with just high enough pressure to prevent losses circulating oil and prevnting splash in the crankcase. well shaped crank, alowing it to 'cut' through the oil in the sump without splashing and causing drag.

thats all i can think of just now

 

[HDi fun]

Thanks for correcting me on the Cosworth Sierra. On the oil pump note what about dry sump lubrication? The main bearings don't have to splash about in the oil (or rely upon the splashing for lubrication) therefore there's less crank drag.

Am I right in saying that a V6 is NOT inherently balanced in the way an inline 6 is?