Is low rpms + high load bad for an engine?

[WRXtranceformed]

Ah I dunno, what kind of Subaru does she own ?

My car didn't actually make an audible noise. Well, maybe it did but my exhaust probably droned it out. I could tell it was knocking because it was bucking like crazy at WOT

[CaptainHenreh]

Click and Clack says

Click and clack are retards.

[Andy]

Click and Clack says

Click and clack are retards.

Hey hey. They make one too many jokes and the people that call are retarded, but come on, they know their shit.

[JackoliciousLegs]

i do premix... but there's no concencus... is there?

[Rex4life]

in my completely un-educated opinon. i would believe pre-mixing takes out the need of high rpms to properly lubricate

[BLAIR]

kinda off topi but it was a big no no when driving a 996 turbo.. 993 turbo..or even an s4 to go fullthrolle at lowe rpms. they told me never to floor it on the highway in 6th gear..always downshift

if not.. motors go BOM

[BLINGMW]

kinda off topi but it was a big no no when driving a 996 turbo.. 993 turbo..or even an s4 to go fullthrolle at lowe rpms. they told me never to floor it on the highway in 6th gear..always downshift

if not.. motors go BOM

I can't imagine a late model porsche or audi that wouldn't have the computer control to deal with the situation. I'm quite sure that if you were in 6th, even as low as 1k RPM, and floored it, it would figure it out and slowly pull itself out of it. I'm not saying that's great for the bearings, but you could probably do it a thousand times in a row if you really wanted to.

[Krush]

Well, internal comubstion engines run most efficiently at WOT.

Where the hell did you hear this, cause you are completely misinformed.

When the engine is cold, just taking it easy on it is the best way (shift at normal economical rpm and don't hammer down on the throttle). There already is oil circulating, so that's not the concern. Granted if it's really cold out (below freezing) the oil is gonna be substancially thicker.

Lugging an engine is always bad. Main concern with cold engine is that all the tolerneces are not correct. But, for all intensive purposes, if you just hop in the car, start it up, and take it easy till it gets warm, you'll have no problems.

[CaptainHenreh]

Well, internal comubstion engines run most efficiently at WOT.

Where the hell did you hear this, cause you are completely misinformed.

You sir, are misinformed. Internal Combustion Engines run most efficiently at WOT. It's a fact. You cannot argue with physics. Intake restrictions reduce efficiency, as pumping losses are increased. And an air throttle plate is one big, fat restriction. This is one reasons why diesels are more efficient than gasoline -- they don't have throttles. (the other reason is the more energy in diesel fuel -- but that doesn't relate to this discussion)

Your statement relies on one definition of "completely misinformed" that I'd been unaware of up until this point.

[BLINGMW]

Well, internal comubstion engines run most efficiently at WOT.

yeah, 'fraid he's right. Sure, a car may gulp triple the fuel at WOT than it would at 1/3 throttle, but it's making more than triple the power.

[CaptainHenreh]

Well, internal comubstion engines run most efficiently at WOT.

yeah, 'fraid he's right. Sure, a car may gulp triple the fuel at WOT than it would at 1/3 throttle, but it's making more than triple the power.

It doesn't even have to gulp triple the fuel, if it's geared properly.

Take, for example, my lovely Metro. At cruising speed, in fifth gear, going along the highway, I routinely keep my go-foot pretty much planted to the floor. My revs do not increase that much, nor does my speed, particularly. (55HP and overdrive will do that to you) BUT, the engine is not wasting energy fighting against my throttle plate, since it is open all the way -- there's no restriction there.

Don't blame me, blame Newton. It's all his damned fault.

Now, if you've got a car that actually goes faster when your foot is planted, then yeah, you're going to gulp fuel at a higher rate than if your throttle plate were closed. But your engine will be doing more useful work per unit of fuel at WOT than not -- IE, engines run most efficiently at Wide Open Throttle. Period.

[BLINGMW]

haha, do you really keep it almost planted on the highway? that's awesome. :lol: Wanna race? (I may have found the only car in the club I could take) :thumbup:

ps, anyone remember that tall guy with the big hat that used to show up to NASA autocrosses in his black covertable metro? That thing was sweeeeet. :wink:

[CaptainHenreh]

haha, do you really keep it almost planted on the highway? that's awesome. :lol: Wanna race? (I may have found the only car in the club I could take) :thumbup:

ps, anyone remember that tall guy with the big hat that used to show up to NASA autocrosses in his black covertable metro? That thing was sweeeeet. :wink:

Unless I'm going down a hill or I've got her in the wind, fifth gear requires WOT 90% of the time.

[Krush]

Discussion time?

An internal combustion engine is a heat engine. Efficiency of a heat engine is simply the work output divided by the heat input. In this case the heat input is the energy content of the fuel. You may also measure this efficincy by taking the work output divided by the mass of fuel input.

The efficiency you are speaking of is volumentric efficiency. This has to deal with the theoretical maxium amount of air that can be pumped thru an engine. The max volumetic efficnecy occurrs at WOT, but VE is NOT how an engines effiency is measure, it's thermo, as mentioned above.

Peak thermal effiency almost never occurs at WOT.

Diesel are more effiency mainly for 2 reasons. First, they have substancially higher compression ratio. Higher CR = higher efficiency (this is primary reason). Second, diesels control power output by meter FUEL not AIR. Gasoline engines use a throttle plate to control output. To insure proper combustion, an nominal air/fuel ratio of 14.7:1 must be attained (notice nominal0.

In a diesel, there is no throttle (like you mentioned). Natually the engine has greatter volumetric efficiency, but this isn't the primary reason that diesels rock. Instead of having the maintain that stoicmetric ratio, a diesel just injects enough fuel to maintained the desired RPM set by the governer (ultimetly set by the operator). Essentially, under no load conditions a diesel engine is running extremely lean the exhaust consists of mostly air. This is why a diesel will take FOREVER to obtain operating temperature if you just let it sit and idle.

You also mentioned diesel fuel has a higher energy content than gas, which is true, but this has nothing to do with thermal efficiency, only with MPG.

Lastly, there is mechanical efficiency, but that does not factor into this discussion.

[.RJ]

Peak thermal effiency almost never occurs at WOT.

Thats where the most power is made. It is most "efficient" at WOT.

[Krush]

I found a link that I had bookmarked that give a brief explanation of the 3 effiency types.

We are bascially arguing different things (go figure)

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[Krush]

Peak thermal effiency almost never occurs at WOT.

Thats where the most power is made. It is most "efficient" at WOT.

"efficient" doesn't mean most power made, it means burning least amount of fuel to make power. Peak effiecinecy usually occurs at the peak in the toque curve.

Friction losses in an engine increase with the square of the RPM...that needs to be considered as well.

BIGASS low speed ship diesels spin at 100rpm and attain almost 50% effiency (meaning near 50% of the energy content of the fuel is turned into mechanical energy)

[.RJ]

"efficient" doesn't mean most power made, it means burning least amount of fuel to make power. Peak effiecinecy usually occurs at the peak in the toque curve.

You're now saying two different things.

First its not at WOT, now its at peak torque.

In thermodynamic terms, efficiency is turning fuel into power - not conserving the most amount of fuel. And this happens at WOT.

[JackoliciousLegs]

kinda off topi but it was a big no no when driving a 996 turbo.. 993 turbo..or even an s4 to go fullthrolle at lowe rpms. they told me never to floor it on the highway in 6th gear..always downshift
if not.. motors go BOM

You know what man, I read about that on the RX7club forums. It may have something more to do with boosting in high load, low rpm situations... Ugh... either way, I never plant my foot in 5th gear. I've heard of too many rotaries blowing that way. I always downshift. I think I'll continue to do that... also, I'll probly just continue to baby it until it's fully warm (read: piss people off).

My torqueless car is hard to drive around town w/o boost.

[CaptainHenreh]

First its not at WOT, now its at peak torque.

In thermodynamic terms, efficiency is turning fuel into power - not conserving the most amount of fuel. And this happens at WOT.

Which was exactly what I was saying. Hypothetical. Let's say you could gear an engine to run at it's peak torque RPM all of the time, while varying the gearing to increase or reduce speed.

What you're saying is that this engine wouldn't care whether or not the throttle plate was open or closed, that it would run just as efficiently either way.

This is where I am saying that you are wrong. Or not wrong, really. You've just latched on to a point and you refuse to concede.

If your car is geared so, you can be at WOT at any RPM. If you are at your peak torque (where you say thermal efficiency is highest) and your gearing can keep you there, your engine will be more efficient at WOT.

You've been dancing around this, and saying "nuh-uh" but you haven't really addressed it. If an internal combustion engine, especially a gasoline engine, has to fight against an intake restriction (I.E. has a low VE) then the result is reduced efficiency, however you choose to measure it. Mechanical, Thermal, or Volumetric. ICE engines run most efficiently at WOT. For your reference, of course, and this may be where the confusion lies, WOT stands for "Wide Open Throttle" not "High Ass RPM" or anything else. "Wide Open Throttle" means, "With the throttle plate wide open."

I don't appreciate the insinuation of my ignorance. I don't say something is a fact unless I'm damn sure it is a fact.