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RevTalk and Radiators...
I keep getting car questions on and off but can never reemember them when I want to ask. I'll keep it at these and see if I can think of any later.
1) I've heard that less revs means better quality engine. For example if a Corolla is doing (cruising at) 100 km/h, it would do so at probably 2000 revs but a Lamborghini would do so it at 1000 revs or less. Based on this, I'm very confused as often members here and the Top Gear crew prefer "more revs" as something of a driving experience and I dont' get it at all. Can anyone explain this? Why would anyone want "more revs" if it means the engine is more stressful?
2) I've seen many-a-time water come out of a new bus radiator whenever it stops. Is it a manufacturing fault or is the radiator designed to let stagnant water out, or does it just stop working when the bus brakes? It's fairly common on the public transport busses here.
Cheers.
- spi
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[QUOTE=spi-ti-tout]
2) I've seen many-a-time water come out of a new bus radiator whenever it stops. Is it a manufacturing fault or is the radiator designed to let stagnant water out, or does it just stop working when the bus brakes? It's fairly common on the public transport busses here.
Cheers.
- spi[/QUOTE]
are you sure this isn't condensation from the aircon?
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[QUOTE=spi-ti-tout] I've heard that less revs means better quality engine. For example if a Corolla is doing (cruising at) 100 km/h, it would do so at probably 2000 revs but a Lamborghini would do so it at 1000 revs or less. Based on this, I'm very confused as often members here and the Top Gear crew prefer "more revs" as something of a driving experience and I dont' get it at all. Can anyone explain this? Why would anyone want "more revs" if it means the engine is more stressful? [/QUOTE]
What you have there is gearing, not the engine.
A Corolla that has a maximum speed of, say, 120mph will be geared so that it will presumably be running close to max revs in top gear at 120mph; 8000rpm for the sake of argument.
At 60mph (just under 100km/h) in the same gear the engine would be at 4000rpm.
A Lamborghini is geared to do over 200mph. If the Lambo were pulling 8000rpm at 210mph in 6th gear, in the same gear at 60mph the engine would only be running at 2285rpm.
Gearing is largely linked to the power and torque outputs of the engine.
If you need, say, 100bhp to overcome the friction and drag forces encountered at 100kmh, then the engine in a 150bhp Corolla-esque car will be reving pretty hard. A Lambo will produce 100bhp at much lower revs, which is what enables it to have taller gearing than the Corolla.
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[quote=spi-ti-tout]
1) I've heard that less revs means better quality engine.
[/quote]
Thus proving the point Diesel engines are better :D
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[QUOTE=spi-ti-tout]Based on this, I'm very confused as often members here and the Top Gear crew prefer "more revs" as something of a driving experience and I dont' get it at all. Can anyone explain this? Why would anyone want "more revs" if it means the engine is more stressful? [/QUOTE]So when you want to go faster, you don't need to downshift, if you're out for a fast drive you want to keep revs up in the powerband
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[QUOTE=drakkie]Thus proving the point Diesel engines are better :D[/QUOTE]
The same applys to large V8s in American cars, does that mean they are just as good?
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[QUOTE=spi-ti-tout]1) I've heard that less revs means better quality engine.[/QUOTE]
I'd say a good quality engine is one that lasts and has a good power delivery (both in quantity and quality).
I like my engines to be revy. I get bored with engines that have a linear output (you never find a sweet spot). I also dislike those that run out of breath short of the redline.
By my standards an engine that lasts the same than another and revs higher is a better engine.
About the water in the buses... you are in the wrong forum! ;) :D :D
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[QUOTE=clutch-monkey]are you sure this isn't condensation from the aircon?[/QUOTE]
I have no idea tbh, but the water doesn't just drop, it coems out in a flow from the front and (sometimes) from the back.
[QUOTE=Coventry]All that he said.[/QUOTE]
So, the rev output has absolutely no linking with the quality of engine.
Based on what you've said then, I'd like to ask this question. A Porsche Boxster can do, as a maximum, 5500 rpm max (according to James May). Why are the revs so short and does this mean top speed is affected? Or are shorter revs more "brutal" and "aggressive" than higher ones?
[QUOTE=magracer]About the water in the buses... you are in the wrong forum! ;) :D :D[/QUOTE]
What?! I don't think I'll find anything in the Aussie forums :p
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1 Attachment(s)
[QUOTE=spi-ti-tout]Based on what you've said then, I'd like to ask this question. A Porsche Boxster can do, as a maximum, 5500 rpm max (according to James May). Why are the revs so short and does this mean top speed is affected? Or are shorter revs more "brutal" and "aggressive" than higher ones[/QUOTE]
According of the picture attached (dashboard of a new Boxster S), the redline starts at 7,000rpm.
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[QUOTE=spi-ti-tout]So, the rev output has absolutely no linking with the quality of engine.[/QUOTE]
The rev output of the engine, i.e., the maximum revs that the engine can achieve is linked to quality.
An F1 engine can do 19,000rpm - you need very high quality materials and manufacturing techniques to do this: to stop bits of the engine hitting each other/bending/breaking etc,.
The revs that you achieve at a particular speed & gear in a car is nothing to do with the quality of the car's engine, but is governed by the gear ratios.
[QUOTE=spi-ti-tout]Why are the revs so short[/QUOTE]
At a complete guess I'd say it was due to the flat 6 configuration.
Useful Stuff About Configurations: [url]http://www.e31.net/navmisc_e.html[/url]
[Quote=spi-ti-tout] and does this mean top speed is affected?[/Quote]
Depends on gearing & power.
You need power to overcome friction & drag.
For a certain ammount of power you can get a certain ammount of speed.
You need to have the gearing set up so that the wheels can actually turn that fast at the correct engine revs.
E.g., if you need 500bhp to get your car to 200mph, and it produces 500bhp at 5000rpm, your gearing needs to work out so that when the engine is at 5000rpm the wheels are turning at 200mph.
Obviously if you have top gear set to do 250mph at 5000rpm, you probably won't get to 200mph, because the get the wheels at 200mph, the engine would have to be at 4000rpm, which might only generate 450bhp, which is only enough power for, say, 185mph; that would be your top speed.
With the correct gearing you should be able to get a vehicle to the same top speed whether you power it with an engine that produces 500bhp@1000rpm, or 500bhp@10,000rpm.
[Quote=spi-ti-tout]are shorter revs more "brutal" and "aggressive" than higher ones?[/Quote]
Depends on what the engine is.
A big 26 tonne marine diesel producing 5000bhp at 1000rpm isn't going to be remotely "brutal" or "aggressive" as the moving parts are very large, therefore more difficult to accelerate.
A 2.0-litre V8 weighing 75kg producing 500bhp to 10,000rpm will be more brutal because the moving parts of the engine are easy to accelerate.
However, a 26 tonne diesel engine with a max. engine speed of 10,000rpm would be just as sluggish, and a 75kg V8 with a max. engine speed of 1000rpm would be just as fast.
(I think...)
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[QUOTE=clutch-monkey]are you sure this isn't condensation from the aircon?[/QUOTE]
Just confirmed, it is. Heat is transferred to the water which is let out so the bus doesn't overheat.
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[QUOTE=spi-ti-tout]Just confirmed, it is. Heat is transferred to the water which is let out so the bus doesn't overheat.[/QUOTE]
lol thought so :) some of my (admittedly female) freinds freak out because they think they're car has some sort of leak
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OK, remembered another one. Two actually, forgot the 4th.
3) Why do the revs go down for a second when you change gear? I know it's because torque is suddenly suspended when the firewall disengages with the clutch and connects again with the other gear. I just need to know the thing exactly.
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Do you mean during a gear change or after you've made one?
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[QUOTE=h00t_h00t]Do you mean during a gear change or after you've made one?[/QUOTE]
I think he means during the actual gear change.
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[QUOTE=spi-ti-tout]OK, remembered another one. Two actually, forgot the 4th.
3) Why do the revs go down for a second when you change gear? I know it's because torque is suddenly suspended when the firewall disengages with the clutch and connects again with the other gear. I just need to know the thing exactly.[/QUOTE]
Are you talking auto or manual?
And the fire wall isn't a part of the transmission.;) :)
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[QUOTE=Coventrysucks]The rev output of the engine, i.e., the maximum revs that the engine can achieve is linked to quality.
An F1 engine can do 19,000rpm - you need very high quality materials and manufacturing techniques to do this: to stop bits of the engine hitting each other/bending/breaking etc,.
The revs that you achieve at a particular speed & gear in a car is nothing to do with the quality of the car's engine, but is governed by the gear ratios.
At a complete guess I'd say it was due to the flat 6 configuration.
Useful Stuff About Configurations: [url]http://www.e31.net/navmisc_e.html[/url]
Depends on gearing & power.
You need power to overcome friction & drag.
For a certain ammount of power you can get a certain ammount of speed.
You need to have the gearing set up so that the wheels can actually turn that fast at the correct engine revs.
E.g., if you need 500bhp to get your car to 200mph, and it produces 500bhp at 5000rpm, your gearing needs to work out so that when the engine is at 5000rpm the wheels are turning at 200mph.
Obviously if you have top gear set to do 250mph at 5000rpm, you probably won't get to 200mph, because the get the wheels at 200mph, the engine would have to be at 4000rpm, which might only generate 450bhp, which is only enough power for, say, 185mph; that would be your top speed.
With the correct gearing you should be able to get a vehicle to the same top speed whether you power it with an engine that produces 500bhp@1000rpm, or 500bhp@10,000rpm.
Depends on what the engine is.
A big 26 tonne marine diesel producing 5000bhp at 1000rpm isn't going to be remotely "brutal" or "aggressive" as the moving parts are very large, therefore more difficult to accelerate.
A 2.0-litre V8 weighing 75kg producing 500bhp to 10,000rpm will be more brutal because the moving parts of the engine are easy to accelerate.
However, a 26 tonne diesel engine with a max. engine speed of 10,000rpm would be just as sluggish, and a 75kg V8 with a max. engine speed of 1000rpm would be just as fast.
(I think...)[/QUOTE]
F1 engines can go 19000 rpm cuz they have a really short stroke, the piston speeds in an f1 engine arnt much higher then a "regular" performance engine say s2000 or audi's v10 in the rs4
generally a higher redline means more power and thus top speed
and i didnt understand anything you said after that
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[QUOTE=spi-ti-tout]OK, remembered another one. Two actually, forgot the 4th.
3) Why do the revs go down for a second when you change gear? I know it's because torque is suddenly suspended when the firewall disengages with the clutch and connects again with the other gear. I just need to know the thing exactly.[/QUOTE]
when you shift up, you're going into a longer ratio, think about it
if your first gear is 1:1, then at 1000rpm engine speed your wheels are going 1000rpm, now lets say ur 2nd gear is 0.5:1, your engine rpm must be 500rpm for the wheels to go at 1000rpm
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The revs drop because (unless you're flatshifting) you take your foot off the throttle and as the engine is disconnected from the drivetrain, there's nothing to keep the engine spinning so it loses momentum and hey presto, the revs drop
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[QUOTE=KnifeEdge_2K1]when you shift up, you're going into a longer ratio, think about it
if your first gear is 1:1, then at 1000rpm engine speed your wheels are going 1000rpm, now lets say ur 2nd gear is 0.5:1, your engine rpm must be 500rpm for the wheels to go at 1000rpm[/QUOTE]
Hmn, I'm a bit confused as I don't think this is what I was actually asking. Does this have anything to do with the temporary decrease of revs (down and back up again) when you shift gear (in a manual - thanks johnny)
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[QUOTE=spi-ti-tout]Hmn, I'm a bit confused as I don't think this is what I was actually asking. Does this have anything to do with the temporary decrease of revs (down and back up again) when you shift gear (in a manual - thanks johnny)[/QUOTE]
As 2ndcc said, when changing gears in a manual your foot comes off of the accelerator. (Unless you are powershifting)
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[QUOTE=Rockefella]As 2ndcc said, when changing gears in a manual your foot comes off of the accelerator. (Unless you are powershifting)[/QUOTE]
I think you misunderstood. Say you're cruising at 100 mph at 2500 rpm, when you shift the needle sticks down all the way to 0 revs and then just as you finish shifting, it goes back to about 2450 rpm and starts counting. I doubt acceleration would climb that quickly back up again, unless the power was suspended and readily available again as soon as the clutch and gear made contact, or something to that extent. Or I just may be a n00b.
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You let off the gas(rpms drop), push the clutch(rpms now drop faster), change the gear, let out the clutch(the clutch grabs), and get on the gas again(rpms climb). I think I typed that right.
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4) Turning Circles
I can't really explain it properly but in my mind these cars will have the bigger turning cicles in order:
AWD/4WD
RWD
FWD
Because in FWD the power and steering is one, therefore when you try to steer both are applied at the same time. With RWD, you have the steering the power at opposite ends, so basically you require space to put out the power. In AWD, the power is divided by even more space.
Meh, I'm not thinking.
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[QUOTE=spi-ti-tout]4) Turning Circles
I can't really explain it properly but in my mind these cars will have the bigger turning cicles in order:
AWD/4WD
RWD
FWD
Because in FWD the power and steering is one, therefore when you try to steer both are applied at the same time. With RWD, you have the steering the power at opposite ends, so basically you require space to put out the power. In AWD, the power is divided by even more space.
Meh, I'm not thinking.[/QUOTE]
Actually RWD have smaller turning circles because the front wheels doesn't have to transmit power (can't remeber of the name of the parts that transmits the power to the wheels), and as result can have more degrees of steering lock.
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[QUOTE=Ferrer]Actually RWD have smaller turning circles because the front wheels doesn't have to transmit power (can't remeber of the name of the parts that transmits the power to the wheels), and as result can have more degrees of steering lock.[/QUOTE]
I was also thinking of understeer when I wrote that. If you went round a corner too fast you'd have understeer which would help because the car locks and then you can continue, so it'd be a smaller line than a RWD coming in fast as a RWD has oversteer.
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Well actually oversteer tends to tighten the line, while understeer opens it, as demonstarted by those rather basic drawings:
[IMG]http://nwalfaclub.com/track/images/understeer.gif[/IMG]
[I]Understeer[/I]
[IMG]http://home.pon.net/hunnicutt/images/oversteer.GIF[/IMG]
[I]Oversteer[/I]
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Just one thing I thought I
d point out about engine speed. F1's operate at the highest rpm for cars, as Knifedge said their piston's stroke is very short. NASCAR engines, on the other hand, rev to ~10,000 rpm, and have very long strokes. Their engines piston speed are incredibly high, about twice what the accepted safe range is.
Turning radius should not be affected by drive type, since under/oversteer only occur when traction is at the limit, and the turning radius is a a low speed. Turning radius is dependant only on the geometry of the 4 wheels on the ground and the maximum turning degrees of the front wheels. But like ferrer said it may be that due to mechanical considerations rwds generally have a greater range of steering motion, and therefore a smaller turn radius.
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To clear that up, the turning circle should be the same whether the car is fwd, rwd, awd, or just pushed by someone, because at low speeds the front and rear wheels turn in unison anyway and are not close to the limits of traction.
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[QUOTE=Bob]To clear that up, the turning circle should be the same whether the car is fwd, rwd, awd, or just pushed by someone, because at low speeds the front and rear wheels turn in unison anyway and are not close to the limits of traction.[/QUOTE]
The question came to me because of how Clarkson was moaning about the turning circle of the MRFQ400. IIRC NOBODY have ever mentioned a horrible turning radius of any EVO, atleast none that I have spoken to or read from, but that turning circle was really horrible and it was based on the stock MR, which is also AWD and shares all the same technology. I was just thinking "why?", if this has been so bad why hasn't anybody ever mentioned it ebfore.
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The MRFQ400 is a track orientated car and they generally have large turning circles.
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[QUOTE=h00t_h00t]The same applys to large V8s in American cars, does that mean they are just as good?[/QUOTE]Those V8s rev low because the people who made them stupid. Give those engines to Europeans and they put them in supercars and make them rev to 8k rpm and produce at least 90bhp/liter na.
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[QUOTE=QBridge]Those V8s rev low because the people who made them stupid. Give those engines to Europeans and they put them in supercars and make them rev to 8k rpm and produce at least 90bhp/liter na.[/QUOTE]
A 540ci goin 8k rpm, hahahha.
But those europeans do that to the engines so they get "mad money" for racing right?
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[QUOTE=QBridge]Those V8s rev low because the people who made them stupid. Give those engines to Europeans and they put them in supercars and make them rev to 8k rpm and produce at least 90bhp/liter na.[/QUOTE]
Nice collcetion of stereotypes there...
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[QUOTE=spi-ti-tout]The question came to me because of how Clarkson was moaning about the turning circle of the MRFQ400. IIRC NOBODY have ever mentioned a horrible turning radius of any EVO, atleast none that I have spoken to or read from, but that turning circle was really horrible and it was based on the stock MR, which is also AWD and shares all the same technology. I was just thinking "why?", if this has been so bad why hasn't anybody ever mentioned it ebfore.[/QUOTE]
the turning radius is a function of wheelbase, and steering rack geometry, the evo's steering ratio is 13.0:1 with 2.1 turns lock to lock, this translates to 30 degrees of steering in either direction, not much when compared to other cars, this just makes it worse when factoring in it's above average wheelbase
the designers of the evo had steering response and speed in mind, not turning radius, i dont even considerer the large turning radius a tradeoff in my mind, parking has never been a problem for me :D
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[QUOTE=QBridge]Those V8s rev low because the people who made them stupid. Give those engines to Europeans and they put them in supercars and make them rev to 8k rpm and produce at least 90bhp/liter na.[/QUOTE]
But they are fitted in rear wheel drive cars which lets them 'keep it real' unlike the europeans who make more fwd fake cars.
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[QUOTE=johnnynumfiv]A 540ci goin 8k rpm, hahahha.
But those europeans do that to the engines so they get "mad money" for racing right?[/QUOTE]I never said anything about no 540ci.
The Europeans do that because rich people buy them. There is quite a few European supercars with Chevy V8s that make good power.
[QUOTE=h00t_h00t]But they are fitted in rear wheel drive cars which lets them 'keep it real' unlike the europeans who make more fwd fake cars.[/QUOTE]American car makers don't keep it real because they fit those V8s in big ugly heavy cars with automatic trannys making 50bhp/liter. Europeans keep it real because they can take a small block Chevy V8 and put it in a supercar and make twice the power out of that engine.
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[QUOTE=QBridge]Europeans keep it real because they can take a small block Chevy V8 and put it in a supercar and make twice the power out of that engine.[/QUOTE]
So a European version makes [i]twice[/i] the power at [i]ten[/i] times the cost, I fail to see the "wow" factor.
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[QUOTE=Alastor]So a European version makes [i]twice[/i] the power at [i]ten[/i] times the cost, I fail to see the "wow" factor.[/QUOTE]
the car is ten times the cost but the engine isnt, it is amazingly simple to gain power from american engines which have huge displacement but the efficiency of a coal/steam powered train
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[QUOTE=QBridge]I never said anything about no 540ci.[/QUOTE]
You generically said american v8's. A 540ci bb is an american v8, so yes, you did say something like that. Friggin stereotypes.