[Closed] Why is there a REV Counter in most cars?

Get her a Nissan Juke...they're proper street man.

When I say 4x4 I mean generic higher cars so the Tiguan, Q5 etc all come into the mix. She just likes the idea of a higher vehicle for (perceived) safety and for the ease of lifting the girls in and out.

Right. Would she listen if you showed her stats that proved road death has no correlation to size of car?

They'd be a lot more useful in conjunction with power, torque and various load efficiency plots. But that's completely at odds with the modern view that you shouldn't know what a 'torque' is let alone how an engine works.

Maximum efficiency in my car comes from keeping the revs below where the second intake valve opens. Maximum fun is at the other end of the rev counter. The bit in between is solely for A-road and motorway cruising.

It's the equivalent of a cadenceometer - only useful if you understand it.

Right. Would she listen if you showed her stats that proved road death has no correlation to size of car?

But she does like the idea of driving a car with a much higher driving position so that will always be a hurdle for me to sort out.

My mother in law is the same - has to have a **** off great 4x4 for the high driving position.

It's a "woman" thing.

Chief - depends on the engine.

Maximum efficiency in my car comes from keeping the revs below where the second intake valve opens

Not sure I agree here...! There are many factors influencing thermodynamic efficiency, if this is indeed what you are talking about.

My mother in law is the same - has to have a **** off great 4x4 for the high driving position.

It's a "woman" thing.

The high driving position of a 4x4 is lovely, much better view of the road ahead, much easier to anticipate peoples moves, much easier to get out of junctions without having only a view of the car next to you, and when some moron runs up your bum, a decent old-school 4x4 will have a minor paint scratch and shake them off. There's loads of reasons for having a 4x4. There's a few against, too.

Back to the original post - not sure why there are rev counters - probably so people can see they're being stupid and sitting at high revs, especially as many modern cars are so damn quiet you can't hear the engine. I hate that, I rarely look at the rev counter but in a quiet car you can almost forget what gear you're in they're that silent. Ultimately rev counters are not ideal in fast cars (if you're using the car in a way that requires precise knowledge of the rev counter readout, you're accelerating too fast to look at it and should really be able to tell from the engine note. Shift lights are the way forward for such cases.

Smaller/fewer inlet valves do increace efficiency, acheievable either by having 2 camshafts/sets of valves as in V-tech or with fiat's new multiair system which has hydraulic cylinders/pistons between valve and cam, so you an get away with a himalayan shaped cam that wouldn't even let the engine tick over properly and the piston forces flid through a variable damper, at low throttle openings most of the oil can escape, so the valves barely open, at full throttle the damper closes and the valves a are pushed fully open as theres nowhere for the flid to escape to.

It's to do with vapourising the fuel better, large openings allow the fuel to coalece which in turn means you have to pump more fuel in to compensate (a bit like when the engine is running cold and you have to run the choke on for a few minutes, effectively restricting the intake manifold). Which is also why big carb's/throttle bodies arn't always a good idea.

Maximum efficiency in my car comes from arranging things so that i can drive it when the roads aren't gridlocked.

Rev counter in my car is in the centre - biggest dial as well, so its often the only one I can see. I use it to keep the revs below (yes really) a certain level whilst the car is warming up. Once its warmed up, then its used to keep the revs well above that point 😀

4x4 and estate = rs4=lots of fun, 4x4 and slightly larger estate=firing god up in the morning=rs6=please please one day

Shift lights seem a good idea, particularly if you can have them trigger at different revs depending on load and target (i.e. speed or economy). Regarding economy, many v-tec type engines run lean burn 3 valve strategies at low revs, so they're very economical when kept in that range and then behave more like a fairly high performance conventional 4 valve at higher revs. The hardcore v-tec engines run 4 valve all the time and switch cams entirely, going from a fairly high performance road car tune to a race tune, the switch happening way up the rev counter.

The downside to all these revvy petrol engines is that high rev overtaking manoeuvres seem to offend far more than the same behaviour in a car of equal performance but delivered at lower revs. The upside is they sound lovely.

One thing missing from many cars these days - simple engine oil and/or water temp gauges - WHY?!!

My Land Rover doesn't have one, I don't feel like it needs one!

A speedo that, at least, made a guess at the speed would be nice though.

On topic - Rev counters, never really use it, change gear based on engine feel and need for speed. That said our VW Touran actually tells you which gear to be in on the LCD display, doesn't always get it right though.

Off topic - 4 x 4s. We've got a Honda CRV pretend 4 x 4 (owners manual says not to take off road 😆 ) and a VW Touran which is they're 5 / 7 seater. The Touran is way more practical. It easily does 60 mpg on long motorway trips, is faster and accelerates better. Driving position is equally as good as the CRV and internally there is way more space for roughly the same body footprint (with the added bonus of 2 extra seats in the boot or a huge boot). Only place the CRV scores is ground clearance which is only really an issue when driving around Gisburn Forest, the Touran will never be going in there again 😯

It's to do with vapourising the fuel better, large openings allow the fuel to coalece

Eh? How come?

I was under the impression that v-tec was variable valve timing which changed the amount of overlap between exhaust and inlet valves - more overlap for performance, less overlap for economy.

Smaller/fewer inlet valves do increace efficiency, acheievable either by having 2 camshafts/sets of valves as in V-tech or with fiat's new multiair system which has hydraulic cylinders/pistons between valve and cam, so you an get away with a himalayan shaped cam

and in BMW system they have done away with throttle valves completely and throttle is controlled by varying the lift of the valves rather than via a traditional butterfly(s) etc. Meant to be more efficient, though it is not used for M series engines...

re valve overlap - this improves fuel /air mixture being drawn into the chamber as the bigger the overlap the better the suck from the exhaust system and thus better chamber filling for NA engines, but doing this you also lose fuel/air out into the exhaust - bad for economy and emissions... good for power though

One thing missing from many cars these days - simple engine oil and/or water temp gauges - WHY?!!

Although I'd prefer to have them myself, all that most people would require is a simple warning to say that the temperature is too high or low. Even then, most people wouldn't know what to do about it anyway.

Modern cars warm up quickly and maintain temperature effectively.

Likewise for oil pressure gauges. I'd like one, but oil pressure is rarely an issue. If the oil pressure does drop, chances are that the engine will seize and need replacing.

Aristotle - my Astra (1.9CDTI 150) and the BM don't have temp gauges, the Jimny does! I want to know when my oil is warm enough to give the car some stick. As it is, I just drive it carefully for a few minutes, hope it's warmed up then have some fun (even though this is as PC as hitting kids). Seems odd that many "performance" cars don't have temp gauges.

Orange Light On - STOP Immediately... and not like my colleagues wife who thought it just meant 'take to dealer when you next have chance'....

oops

V-tec et al tend to do more than just change the timing, they also adjust lift. Back in the 90s Honda used to sell an economy oriented v-tec (instead of a diesel) which was the precursor to modern milder v-tecs with this 3 valve lean burn low rev strategy. A key part of this approach is optimising the swirl pattern by causing the right kind of turbulence at low revs (when the port area of 2 intake valves could result in laminar flow and thus poor combustion of leaner mixes).

What v-tecs don't do is provide any useful torque.

That BMW thing is clever - is it only in conjunction with direct injection?

I look forward to the next generation of petrol engines which are likely to be compression ignition at low revs, spark at high revs, for diesel economy but petrol drivability, cleanliness and performance. Mercedes are under way with this using moving crankshaft bearing mounts to give variable compression ratio.

Torque on it's own is useless, a human on a bike can provide more torque than a small car engine! Fortunately gearboxes were invented...

I found the v-tec had a 3 lobe cam profile, the third cam lobe had an oil actuated piston which locked all three followers together so it ran on the high lift option at high rpm. Simple but effective.

I look forward to the next generation of petrol engines

I've got a few ideas up my sleeve, don't worry 😉

Btw, does varying turbo boost not have the same effect as changing the compression ratio?

diesel type engines are still where the money is. More energy per mass and with a new stream of bio mass produced "carbon like" diesel (which is also better) coming into the fold all the more reason. also Gasolines can not produce the environmental savings required by legislation getting tighter..

Cellulosic bio-ethanol has a lot more potential than biodiesel I think. So we will still need petrol style engines.

Plus, petrol-electric hybrids get around many of the disadvantages of a petrol engine as compared to diesel. And petrol is a heck of a lot cleaner in terms of other pollutants.

Torque on it's own is useless, a human on a bike can provide more torque than a small car engine! Fortunately gearboxes were invented...

Yes that's all very well but catch a v-tec engine at anything under 6k rom and nothing happens. Fine for the race track, irritating on a real road.

Cellulosic bio-ethanol has a lot more potential than biodiesel I think

Years ago I used to drive an expensive car (no, not my own) and if for any reason the engine stalled, you could only tell by the rev counter dropping to zero. The vibrations and engine noise were so low when the car was not moving that you could not tell the engine had stopped.

It's to do with vapourising the fuel better, large openings allow the fuel to coalece which in turn means you have to pump more fuel in to compensate (

There's a whole heap of things you want to optimise, rather than larger or smaller being right. Smaller = greater pumping loss getting the air in through the valve. Smaller diam intakes mean restriction at higher revs but better gas momentum over large diameter, which means better cyl fill and so better VE. Ultimately your car would be throttled by the valves and have completely variable intake runnner and plenum sizes across the rev ranges. In reality they just pick an efficiency level at a speed, design for that and try to minimise the damage to the upper end power, I'd guess. Things like the toyota VVTI engines are horrible to drive "off cam", gutless miserable things despite being 190hp when allowed to be let loose. Vtech are the same, but it serves a purpose I suppose.

if for any reason the engine stalled, you could only tell by the rev counter dropping to zero.

And the row of red lights on the dashboard...... 8)

How are you hoping to make diesel from cellulose? That algae they recently found in the Amazon? Could be a fair way off. They are building large scale test cellulosic ethanol plants now. May even be finished.

Ethanol is a bit rubbish as a fuel when you put it in a petrol engine. But it has a high octane rating, so you can increase the compression ratio a lot which means you can get a lot of the efficiency back. Saab I think are also working on variable compression ratio engines for this reason.

Things like the toyota VVTI engines are horrible to drive "off cam"

Sounds reasonable. You only need the power when you're flogging it, so might as well set it up to appear at high revs.

hydrotreating my dear man - you change the entire structure of the molecule and hey presto a diesel/kero stream with far surperior properties to the incumbant..

edited to add, it can be made from various wastes - some commercial jets have already flown on the stuff (through waiver)..

One thing missing from many cars these days - simple engine oil and/or water temp gauges

Was oil temp ever common in road cars? Agree though, as unless the ECU is cleverer than I give it credit for if my engine read 20psi on the motorway/b-roads I'd be worried, but in town thats fine, would an ECU account for this?

Never understood water temp guages, unless its too high its not a problem (warning light would be more use), but oil temp is more important if you need/want to know when its up to being thrashed.

Ethanol is a bit rubbish as a fuel when you put it in a petrol engine. But it has a high octane rating, so you can increase the compression ratio a lot which means you can get a lot of the efficiency back

Hmm. A year or two ago, 'Bike' magazine modified a Triumph Daytona 675 sportsbike to run bio-ethanol... from apple juice! All they had to do was remap the injection, and IIRC it made a fair bit more power than on petrol

http://www.greencarsite.co.uk/GREENNEWS/apple-powered-bike.htm

🙂

Orange Light On - STOP Immediately... and not like my colleagues wife who thought it just meant 'take to dealer when you next have chance'....

oops

To be fair, orange lights are warnings, reds mean stop. If they've used an orange light for a fault that's immediately terminal if ignored it's a design fault IMHO. Many sensible cars have an orange warning lamp for mild faults and a big red STOP if it's a fatal fault like oil pressure.

ethanol is great but it's got some sever issues to contend with - water being one, 30% high consumption being the other along with material compatability issues...

you change the entire structure of the molecule

How?

PP - usually flex-fuel cars just change the map somehow (not sure how) and presto, you run on ethanol. However this usually results in similar performance but lower MPG - no idea if it'd be different in a motorbike. However with a turbo petrol car you can ramp up the boost no end because of the high octane rating. So some folk in the Volvo 'community' get 300bhp from their 2.0l petrol 🙂

chemical engineering - hydrotreating has been used for years to change carbon molecules to other "end products" they've relaised that a similar process can be used on biomass.. quite clever really and the only "real" contender for a "proper" renewable fuel!

some folk in the Volvo 'community' get 300bhp from their 2.0l petrol

Or just chip a T5? There's no replacement for displacement!

There's no replacement for displacement!

There is - boost!

The point is, ethanol allows much more boost than petrol. So whatever your displacement, if you have forced induction you can tweak it to get much more power than if you were on petrol.