i know the assumption is shoddy at best but i dont have any better data to go on and thus this must be the conclusion i come to

i also know that at WOT or close to WOT operations the engine will run richer which does decrease power quite a bit and uses more fuel as a result. without any empirical data or specifications we cant just pull numbers outta our ass

 

um sorry i just cant accept this from someone who claims that the sweetspot on an engine is where the power and torque curves intersect (expecially when it varies based on the units you are using) ... that would mean every single piston driven combustion engine in the world would have the exact same sweetspot ... so you can basically just tell F1 engineers and sports bikes that they're retarded

 

I understant why you desagree with me, but why you are in desagreement with your self - I do not know. If you read all your posts on this subject, hopefuly you will realize that you are consistently in contradiction with yourself.
Evry engine "swet spot" is at those rpm's at which Power curve and Torque curve are intersecting (see Manufacturers official diagrams) and that spot (RPM's) are different from engine to engine (from manufacturer to manufacturer) AT THAT POINT(RPM's) YOU WLL HAVE "DECENT" POWER AND DECENT TORQUE i.e OPTIMUM OF ENGINE OUTPUTS AND MODERATE ENGINE SPEED (RPM's) WITH MODERATE FUEL CONSUPTION - M O D E R A T E , not min. nor max. For L15A appx. 3700rpm.
With this, I rest my case.

 

... power is related to torque, they are inter related and depending on which units you use the intersection point will occur at different rpms, but if you use the same units it will always intersect at the same rpms between different cars/engines

you're just spewing out your opininons as fact but that just isnt true, for someone who considers himself an engineer you seem to lack the basic understanding of what torque and horsepower is

if you just use horsepower and ft-lb as your units every engine will have torque and power intersect at 5252 rpm

if you use Nm and kw it will interesect at another rpm

what you are proposing makes no sense

consider this

we use horsepower and torque and the intersection point is 5252rpm, now lets use torque and a made up unit called X power and X power is defined as 2 horsepower, so now the power graph is vertically stretched by a factor of 2 and the intersection point is moved to 2626rpm

from this we can tell that you're already wrong, and for the record I havn't been inconsistent in my posts, you just cant seem to interpret math that a highschooler should know

 

I don't understand how Misha is an engineer. I took basic physics (and I was so good at it, i almost considered changing, so I think I have credibility). Knife is correct. The intersection is only true if Power is horsepower and torque is lb*ft, and is ALWAYS at 5300rpm regardless of engine.

[i wrote an example how to manipulate units, but knife's "2*torque" is better, so i'll delete it]

Lets rewind a bit to something you said earlier.
Do some algebra. This equation is for lb*ft and hp.
(Torque x RPM) / 5,252 = Power
we want to find where Torque = hp. set both tq and hp with the same numberical value "x". Lets find what RPM is it when there is X amount of torque at the same time thee is X amount of power.
X * rpm / 5252 = X ; the X's cancel out
RPM = 5252

I didn't look at the fit's engine curve to find out the intersection is at 5252, b/c I don't have to. If you do simple algebra, you'll see no matter what engine, it'll intersect at 5252 (the X axis) when the units is lb*ft and horsepower. Yet you say the fit's intersection point is 3700rpm but i used algebra to prove it wrong.

Do you realize somethign special about "5252"? 5252 is actually a conversion constant. The value of the conversion constant depends on which units you use. Therefore, the "sweet spot" depends on which units you use.

 

Bingo. That's what I was trying to get to with the mythical 'PonyPower' a couple of posts back - Knife's 2x torque put it more clearly. Again the intersection point is just a matter of what your definition units are. Knife and Gordio are right on this one.

 

Engines are very dynamic and you cannot simply apply single concepts and straight lines to them. The term 'efficient' can have many different meanings. And there are whole lot more physics going on than just straight HP to torque conversions! And there are so many different camshaft profiles that you can't just say the engine is most efficient at HP=Tq. The cam is really what governs an engine's personality (power curve) and all other parts are supporting (heads, intake, exhaust, etc). Some engines don't make stink for horsepower but produce gobs of torque at low rpms (they have displacement on their side). Horsepower is simply the rate at which 'work' (torque) is performed. You can do a whole lotta work very slowly, or you can do very little work rapidly. Consider the ant vs an elephant....which has a faster rate of steps/min? But which goes farther per step?

 

we're only looking at one form of efficiency, fuel efficiency

we can figure this out by comparing power output at speed since power is the determining factor and power is correlated with fuel consumption given thermal efficiency usually stays in the same range

 

That is why I mentioned earlier that you should look into the fuel flow #s at cruise, instead of focusing on assumptions of how much power is being made. Take fuel flow and plot against speed (mph), and mix with d=r*t and you should get what you're looking for.

 

it's harder to get that data than a dyno that's why

 

Not really. A lot of machinery can calculate gasoline per second. I think this is how some cars that have built in real time mileage meters work. miles per second divide gas per second = instantaneous miles per gallon

The fit can't, b/c you'd have to redesign the entire car.

 

not really, the simplest way is just to plug into the obd and use that to figure out fuel consumption, but that really only helps in specific examples, i want a general view of what the fit can do

dyno printouts are alot more accesible than fuel consumption rate data since no one really bothers with the latter

 

I believe there are several members who have the scan gauge, and from what I recall, this gives you fuel flow...all they'd need to do is run up & down a local highway at different speeds and post what they see to give us an idea.

 

this data can be clouded by many random uncontrollable factors however

run a is not going to e the same as run b, so we're using a single (or multiple but the point is you cant have enough) test and saying that is true for the whole mean

what i'm proposing is you take away as many random factors as you can by using the dyno sheet, true each dyno run is going to be confounded by multiple factors too but they are going to be spread over the entire rev range so no one point will be significantly altered

what's important is the shape of the graph we take, because that would determine the optimum point, to do the same thing with multiple runs on the highway would take much more time and would be alot harder to make sure runs are under equal conditions, think about it, if you had to do runs down a highway to gather data you would have to travel atleast a kilometer at each speed you wanted to calculate, multiply this by each speed you want to consider (every 5km/h or so) and you're wasting an hour or two's worth of time

you can do 3 dyno pulls in much less time and would give more accurate results

 

So...

What RPM should I drive at to maxmize my fuel efficiency? lol

Don't know if it was just me, but most of the conversation went way over my head.

Take a look at HowStuffWorks' take on it:

Howstuffworks "How to Drive Economically: Tips and Guidelines"
(scroll down, talks about shifting/RPM)

 

When cruising with my 1.4L Jazz with CVT it settles around 2000-2100 rpm at almost any speed up too 80km/t (have not tried higher yet...).
So that probably means that Honda think that rpm is the most economical for the 1.4L engine?

 

[quote=xanatos;119778]So...

What RPM should I drive at to maxmize my fuel efficiency? lol

Don't know if it was just me, but most of the conversation went way over my head.

Take a look at HowStuffWorks' take on it:

Howstuffworks "How to Drive Economically: Tips and Guidelines"
(scroll down, talks about shifting/RPM)[/quote
With VTEC we have practicaly 2 engines in one - below VTEC point and above. L15A VITEC is so called 12/16. Below 3500rpm,engine operates on 3 valve per cylinder - 2 exhaust and 1 intake (in that situation intake valve is in ofset position to cylinder thus creating swirll efect of fresh air/fuel mixture which enhance combustion and utilization of fuel) With this Honda Engenieers clearly placed emfesize on ECONOMY.
At 3500rpm VTEC "kicks in" and activate 2nd intake valve (4 per cyl.) Now engine operates in POWER mode taking full "breath" of fresh air/fuel mixture trough 2 intake valves.
If you look in to L15A diagram (I don't know if there is one in Owners Manual) you can see that Torque line is horizontal between 2500 and 3700 rpm-which by defenition shows " easy/relaxed " linear operation of the engine.
Stay in that RPM range and you will be very pleased with fuel consumptin .

 

i can't even begin to describe how many errors and misinterpretations of data are in your post ...

 

How is he wrong? And how have you answered your original issue?

"ok i thought up of a method to find the best rpm to cruise at but i dont have the neccesary data to do a test"

There is no 'best RPM', because this varies with speed. If you are going on a long trip on the highway, what matters is what speed you select to cruise at...obviously this will affect how fast you 'get there'. I think most folks are interested in maximized both time and fuel efficiency. You can't maximize fuel efficiency without defining other parameters, because we all know that the absolute most fuel efficient RPM is '0'...but, if you say, I want to maximizing fuel efficiency while cruising between 60 - 75 mph, which speed is most fuel efficient, that is different. And I'll bet 60 mph is. But you don't get there as fast as 75. So you really have to consider speed/time along with fuel burn/mph and therein lies the answer to 'most efficient cruise. It is a game of tradeoffs.

 

well considering i brought up the initial issue it really makes no sense for me to answer it now would it ??

i'm tryin to get some constructive comments and inputs to fine tune my theory and possibly test it but so far i've gotten nothing

misha's wrong in that his conclusion had nothign to do with his arguments, and his arguments were at best an opinion without being based on fact

saying that the lower end of the L15A engine is based on economy is not true, the only difference between the low and high rev range is the number of valves being utilized, just because 2 valves are being utilized doesnt make it a power oriented cam, it just means the engine needs another valve to breathe efficiently. in a traditional vtec system where you actually change the cam profile you could argue that the new profile is biased towards power because it has higher valve duration and lift, in the case of our fits the reason only one valve is being used is to promote low end torque through a more uniform air/fuel mixture

2nd he says the torque curve for the L15 is pretty much flat throughout it's entire rev range not just to 3700, so saying "stay in this part of the rev range would give best fuel economy" is like saying you'll get the same fuel economy at any given speed, which is absurd

now to address your post

there IS a best RPM because your RPMs are directly related to your speed in any given gear, since we're talking about cruising the only gear we're interested in is top gear. 0rpm would give you 0miles/0gallons, this is indeterminate and is not valid, thats before taking into account that you would never get anywhere. fuel efficiency is simply defined as how much gas you use to travel any given distance. if you wanted to maximize efficiency taking travel time into consideration than that's a totally different matter and is beyond the scope of this discussion for individual preferences can hardly be measured as easily as fuel consumption.

clearly you did not read my original theory properly. you can plot how much fuel you use per any given distance using my method given my two assumptions hold, and even if they do not the basic theory still applies, their would just be the issue of gathering data at different throttle positions