Engines

[bleh]

alright i was pretty sure that swept volume was displacement. so in effect the bmep offers a comparison of the bottom end of an engine, given that the heads are near identical. well at least thats the conclusion one should come to when applying the formula. its a good formula for me to understand conceptually.

the numbers i picked earlier were fairly arbitrary, but its all good as long as we are all learning. however, while on that topic, that is what you would get if you boost a civic type r motor to 14-17psi with a t3/t4. unfortunately below 3krpm will be just like driving a normal ctr.

i have a nice tangent worth mentioning, but i want to see what people say first. while we are on the subject of how much rpm it takes to make horsepower, who knows why the term for horsepower even exists?

[Anzeige eBay]

Hallo Speedster25,

 

kennst du schon Engines (Anzeige)? Dort ist vieles zu finden.

 

Verschiedenes über Autos Ersatzteile (Anzeige) | Verschiedenes über Autos Zubehör (Anzeige)

[Speedster25]

I have found a car that has 113.5nm/l as a naturally aspirated engine. This is the TVR Cerbera Speed 12. I'm not sure if it was produced or just a concept, but it has the highest amount of horsepower and torque for a naturally aspirated V12. By means of this I would say, that 120bhp/l and 120nm/l, are the limits to a naturally aspirated engine.

[bleh]

120 are by no means the limits. torque per displacement is garbage since a motor with the most torque per displacement could be very peaky. and im pretty sure those 600cc bikes with a buttload of hp have a lot of power per displacement.

i guess you guys are just too lazy cus i know you know why horse power exists. if you have a motor that can rev high and have torque at the higher rpms you can gear the transmission shorter thus yeilding more torque plainly through the conversion. haha i did it in one sentence! quite run on though. anyway an arbitrary example:

you have:

motor A that makes 300 ft/lbs all the way to 6000 rpm

and

motor B that makes 200 ft/lbs all the way to 9000 rpm.

for the sake of simplicity lets skip over the actual gear ratios and say that the transmissions for each motor adjust such that both motors will reach redline at 30mph,60mph,90mph...

given all other variables are equal(driver, weight, cd, traction, etc.) both cars will accelerate at exactly the same rate.

so how do we let people know that the motor A is just as good as motor B? multiply the torque by the rpm and divide it by some constant to make the pretty number realistic looking. brilliant marketing.

[LateNightCable]

Brilliant mathematics dear Watson.

Also, take into account the work the engine is expected to perform. If I wanted to haul an Airstream trailer, I would take motor A.

Racing on a high-speed curcuit, where a 9,000 rpm redline might do you some good, motor B would be a smart choice.

[reggid]

120 are by no means the limits. torque per displacement is garbage since a motor with the most torque per displacement could be very peaky. and im pretty sure those 600cc bikes with a buttload of hp have a lot of power per displacement.

i guess you guys are just too lazy cus i know you know why horse power exists. if you have a motor that can rev high and have torque at the higher rpms you can gear the transmission shorter thus yeilding more torque plainly through the conversion. haha i did it in one sentence! quite run on though. anyway an arbitrary example:

Yes we all know about power and advantages of gearing . No one is claiming that Nm/L determines how fast a car will accelerate thats a different topic all together.

We are simply noticing that about 115Nm/L for NA seems to be about the limit regardless of hp/L.

So if a manufacturer says they'll bring out a new engine with 6L we can assume that the torque will be limited to about 600-650Nm regardless if it makes 600 or 800hp. Its just an observed trend more than anything else.

[bleh]

reggid: im pretty sure there are plenty that are unaware of what horsepower really is, and that it has very little to do with the actual physics of acceleration. i am not accusing you or being uneducated, but should anyone in our limited audience be uniformed....

so is holding to the trend of nm/l a good measure of efficiency?

[reggid]

so is holding to the trend of nm/l a good measure of efficiency?

Yes and no! Theoretically thermal efficiency is increased by increasing compression ratio. Off the top of my head the engines with high Nm/L also have higher compression ratios so theoretically the Nm/L may provide some indication of thermal efficiency. I'm not game enough to categorically say the Nm/L is directly correlated to thermal efficiency but i am no expert in the area.

I suppose in theory you could find the airflow and hence fuel flow into the engine at the peak torque rpm and find how much heat is added and compare to the power output. But you need the volumetric efficiency (how well the cylinder fills with new charge from inlet) of the engines at the respective rpms to find the actual mass of air and fuel added per cycle. So a higher volumetric efficiency is a key factor which is dependant on several factors.

[bleh]

:)i agree.

[Thunf]

Yes and no! Theoretically thermal efficiency is increased by increasing compression ratio. Off the top of my head the engines with high Nm/L also have higher compression ratios so theoretically the Nm/L may provide some indication of thermal efficiency. I'm not game enough to categorically say the Nm/L is directly correlated to thermal efficiency but i am no expert in the area.

I must ask something on this! Thermal efficiency is increased by increasing compression ratio? There might be somthing I don't think about here... but higher compressionratios would heat up air more before ignition. Colder air in the mixture would get better efficency. When compressing gas, what you get is heat! More compression, more heat - as you know! But as I said I have certaily missed a factor or two...

A NA engine with 12:1 compression ratio would heat up air-fuel more than a 10:1 NA engine?

You know that turbos often uses intercoolers for increased efficiency as air heats up because air gets compressed...

Lighter engine internals would allow engines to rev more, heavier internals would give more Nm but less revs then also hp... if we are talking same stroke and bore, right?

[Speedster25]

Take a look at these two Ferrari's (their engines):

Ferrari Enzo

5.998 liter V12

660 bhp

485 ft. lbs. (655 nm)

Ferrari F430

4.308 liter V8

483 bhp - 490 bhp (claimed by Ferrari)

343 ft. lbs. (465 nm)

Enzo

110 bhp/l

109.2 nm/l

F430

112.1 bhp/l - 113.7 bhp/l

107.9 nm/l

The V8 is just as good and perhaps better than the Tipo F140 V12 engine in the Enzo.

[Anzeige eBay]

Hallo Speedster25,

 

schau doch mal hier zum Thema Zubehör für Verschiedenes über Autos (Anzeige)? Eventuell gibt es dort etwas Passendes.

[thepolarfoxqx]

The F430's V8 shares a lot of basic design principle with the type 140. it's no surprise they have similar performance characteristics. just like mercedes' 3.2L V6 has similar characteristics to it's 4.3L V8, they share basic design principle. As for more compression, yes - it does heat up the air in the cylender more, but it also makes the mixture more volatile, and the explosion in the cylender occurs at a higher reaction rate, creating a faster, harder force. The contents of the cylender burn faster, the energy is released more quickly with more force over less duration. This is good in high revving cars, because there isn't much time for combustion at 9k rpms. High compression lets engines remain efficient at higher rpms. Lower compression yields a cooler temperature and a more powerful overall combustion cycle. high compression engines also have more power to fill cylenders, as the downward stroke of the piston creates more suction, the cylender more completely fills. This is unimportant at very low rpms, but as you increase at all, you will feel this effect. Is higher compression more efficient in the strictest sense, no, but it does allow for more power to be created in the right circumstances.

[Thunf]

Engines as we see them are efficient when the waste heat is low and power is high, ofcourse it's more than that also involved depending on what you want. However, I discussed wasteheat with someone over here and he said something about an american who made a raceengine and used wasteheat in a closed system in the 60', anyone heard of it?

[bleh]

Lighter engine internals would allow engines to rev more,

true?

heavier internals would give more Nm but less revs then also hp

..false?

<---confused

[reggid]

Thermal Efficiency is increased by increasing the compression ratio but there are limitations. If compression ratio is too high knock occurs as well as alot of heat transfer and dissociation of combustion products which reduce efficiency. Diesels are not more efficient than petrol for the same size and compression ratio, its the lack of knock that enables them to use high compression ratios and hence get better efficiency (up to 50-55% and is the most efficient way to convert fossil fuels to power currently available, adiabatic diesel is even better but very complex to configure).

[Thunf]

Spot on there reggid! I knew I lost some factor! Ofcourse diesels are a good example to explain that higher compression makes more efficient combustion. yes, diesel fuel demand that and wouldn't knock if lower.

But for given fuel like petrol there is certainly allot of optimation and factors involved for deciding what compressionratio you want for the engine. Motorcycles have very highcompressionratios around 12:1 because it's optimised for high revs, you want more knock in high revs as you said.

Putting a motorcycleengine in a car you would need to gear it for high rpm at all time because the engine would stall when trying to pull the car in the lov revs. Also when using highrevs you get a frequent knock, each fullthrottle-knock delivers heat, you would get allot of heat from an engine on constant high rpm. As motorcycles, and light sportscars, highrevving engines doesn't need to be put under load when cruising - you can well have such an engine. I'd say the same with overpowered cars, they are seldom for a long period of time under full load. But having a 700cc (0.7l) 110 hp@9000+ rpm small engine in a 1500 kg car is not a good idea, as it must be under load pretty constantly, and when it's under load you get heat.

It's all become very clear!

[thepolarfoxqx]

you really don't ever want knock, but you can avoid it by structuring valve and ignition timing just so and efficiently shaping the cylender heads. With gas direct injection, it becomes even easier, because you don't shoot fuel in until you're ready to set if off. Diesel engines are very heavy and large compared to their output, but are fuel efficient. That goes with their low RPMs too. turning slowly, they can fully burn and use all of the fuel. Part of their efficiency too is the fact they use diesel fuel over gasoline.

[LateNightCable]

But having a 700cc (0.7l) 110 hp@9000+ rpm small engine in a 1500 kg car is not a good idea, as it must be under load pretty constantly, and when it's under load you get heat.

There are engines which are designed to run reletively efficiently under full throttle or close to it for extended periods of time, and they can be found in aircraft. Indeed, the 700cc engine mentioned above would not be at all efficient in a 1,500 kg. car, but with enough cooling, anything is possible.

At this point, I must ask, what is the root of what we are all talking about here anyway? It seems pretty loose, that is, what are the criteria for efficiency we are looking for? A simple solution to the efficiency debate, would be the realization that there is no most efficient engine. But rather there are very many ways of building an engine to perform efficiently in it's given task. Weather it be hauling, racing, low emissions, etc. If not, then the perfect combustion engine would surely have been invented by now, and we'd all be using the same one for every purpose.

[bleh]

A simple solution to the efficiency debate, would be the realization that there is no most efficient engine. But rather there are very many ways of building an engine to perform efficiently in it's given task. Weather it be hauling, racing, low emissions, etc. If not, then the perfect combustion engine would surely have been invented by now, and we'd all be using the same one for every purpose.

ding ding ding we have a winner. no most efficient, but there are a few that happen to really suck. however, i wont do any finger pointing

[thepolarfoxqx]

well, if you'd like me to start pointing at engines i really think suck, I have a long list, as many of you know.

[LateNightCable]

Hmmm, starting with the BMW straight-six, what a POS!

KIDDING!

Anyway, many engines that really "suck" in efficiency, are actually pretty great in other ways. Those 6+ liter motors out there producing insane amounts of thrust will never win any efficiency awards, in that respect, they suck. But they can be found under the hoods of some of the cars we all talk about. The venerable Bentley 6.75, big Ferrari V12's, Mercedes 6.0 twin-turbos -19 miles per gallon at best - pathetic, quad-turbo 16 cylinder Buggatti - the very model of excess.

And in this thread, they all certifiably suck!

[Speedster25]

LOL. That's just the way things go. The bigger the engine is the more fuel it wastes.

[wEstSide]

Hearken the VLB (Very Lean Burn) engine. According to a few it could be one of the most efficient engines. http://www.vlbengine.com/

[reggid]

I think that fuel consumption figures are misleading for comparsion of engines alone because it depends what vehicle the engine is in, so they don't give any indication of real engine efficiency but rather the vehicle efficiency. It takes more energy to move a 5000lb car at 100mph than does a 3000lb car of the same shape and size so the engine in the 5000lb car is going to be less fuel efficient even though the engines may have the same thermal efficiency.

Don't confuse fuel efficiency with thermal efficiency. The former is usually in the form of a volume of fuel used/distance travelled and the latter is a power output/energy input from fuel. So one relies on the vehicle parameters (rolling resistance, drag, transmission efficincy etc)and the other simply relates to the engines performance. But increasing the thermal efficiency does give more power for the same fuel consumption, its just that fuel consumption can be misleading.

[thepolarfoxqx]

ok, but some engines are less efficient overall, some are more. The car and setup does make a big difference. An engine i think is just generally awful in terms of its efficiency, volvo B230F, which produced 114hp from 2.3L, and moved a 3,000lb car to 60 in 11.3, got a rated 20/24, and in my experience with a 740, never did better than 18. Compare this to the Jaguar AJV8 4.2, which makes 294hp from 4.2L, and in a 3,800lb XJ-8 get 20/28 and runs a 6.6 0-60. One of these engines is more efficient than the other one.

[Thunf]

Ok, but this one is a bit of a mystery....

From AMS TV test:

E500 Elegance 306 hp - weight 1835 kg - testconsumption: 14.3 l/100 km

545i 333 hp - weight 1783 kg - testconsumption: 14.7 l/100 km

It wasn't an error because they confirmed in the text that the Stuttgarter consumed less fuel and weights more.

and it does not end here!

S500 306 hp - weight: 2000 kg - testconsumption: 15.4 l/100 km

745i 333 hp - weight: 2025 kg - testconsumption: 15.0 l/100 km

same engines as above!!

You are so right folks, that if the right engine is in the right vehicle - at then we can look at efficiency. Looking at engines alone doesn't mean much. But as Polarfox said, there are certainly exceptions. There are engines that throws gasoline out from the exhaus like crazy. The Fiesta i use to drive has a Zetec 16V Yamaha-Ford Engine, it consumes 6.2 l/100 km (38 mpg) in average of a full tank, the other engine choices you can get you will have 2Valves / cylinder "pole-engine" (or what it's called) and much less power and much wrose consumption.

I know also that a Ford Mondeo 1.6i consumes allot more than 1.8i engine... even if it's identical but the bore.