mpg

[BigRedFord04]

i've seen on that body style truck that a TB spacer and a full K&N kit cause the air intake to rub against the fan shroud. check into it before you go spending $$ on all this stuff.

[eight]

I think you're slightly mixed up there David. We understand that why lower temp air makes more power is because its more dense so its like running a bigger motor. So to make the same power to move the truck, the intake air velocity is lower than stock so that equals less restriction. But then since the air is more dense, the throttle is more closed, and that's the biggest restriction on an engine. It would be great if we could figure a way to make a gas engine work without a throttle. I think it could be done by recyceling the exhaust back into the intake, now if such a system would actually increase effiency I do not know.

A big reason of the low effiency is all the heat (energy) lost to the cooling system. A perfect motor wouldn't need a cooling system because all the combustion energy would be converted into useable power. Running the engine as hot as possible without damage will get the best effiency. I'm not saying to swap to a higher than stock temp thermostat, but definately stay away from the low temp ones.

[uglyota]

Originally posted by eight
Running the engine as hot as possible without damage will get the best effiency.

Originally posted by Fredo
This....this idea is Horrible Peter.

I bet the smart people at GM figured this out, and included the correct, "super high efficiency" thermostat with his truck...no extra charge

[BigRedFord04]

i understand where you're coming from kopecki, but i dont see how extracting more heat from the engine via the cooling system affects efficiency. that energy doesnt get used anyway does it?

[eight]

Originally posted by BigRedFord04
that energy doesnt get used anyway does it?

Correct. So try not to produce what doesn't get used.

[uglyota]

so you want to be able to make the same energy with less fuel and less "rapid expansion" like that david? and thus less heat generation, but to do that wouldn't you have to get rid of some of the other things that rob power, like internal friction?

edit: going home now...you guys figure this out while I'm gone, aight?
I'm confident that with enough keystone and a welder, Kopecki could solve world hunger

[stx4wheeler]

{Quote}
I'm confident that with enough keystone and a welder, Kopecki could solve world hunger [/B][/QUOTE]

this much i do believe to be true.

[AgDieseler]

The engine produces energy in three forms: potential, kinetic, and heat. When it comes to making the engine (and only the engine) more efficient, we talk only in terms of heat. Reducing parasitic loads like superchargers, transmissions, etc. deals with the kinetic end of things. We can assume the change in potential energy to be negligible to make things simple.

The engines gives off heat to 1) the atmosphere and 2) the cooling fluid. Ryan, you're right that a thermally perfect engine (Carnot) wouldn't need a cooling system since the heat out of the engine is zero, but the heat in is very high.

The equation is for Otto thermal efficiency: Nth = 1 - Wnet/Qin

To make this number as high as possible, Qin (heat in) needs to be as high as possible. The waste heat to the radiator and atmosphere is energy that doesn't get sent through the driveline. It's wasted energy, but a good way to reclaim some of that wasted energy is with a turbo.

In no way does this have anything to do with oxygen density or airflow velocity. I'm not saying that it isn't related. I was just mentioning the interesting opposition of what one engineering equation tells us and what shade tree mechanics have know for years.

In terms of water temps, I have run 160, 180, and 195 t-stats. I have noticed better power, fuel economy, and less smoke the higher my 195 t-stats.

PS: This is good tech stuff. Most forums will look at this question and never get into too much detail. I personally find this to be some of the most interesting engine tech. It turns out, it's also the cheapest with which to experiment.

[agjohn02]

Originally posted by eight
But then since the air is more dense, the throttle is more closed, and that's the biggest restriction on an engine. It would be great if we could figure a way to make a gas engine work without a throttle. I think it could be done by recyceling the exhaust back into the intake, now if such a system would actually increase effiency I do not know.

A big reason of the low effiency is all the heat (energy) lost to the cooling system. A perfect motor wouldn't need a cooling system because all the combustion energy would be converted into useable power. Running the engine as hot as possible without damage will get the best effiency. I'm not saying to swap to a higher than stock temp thermostat, but definately stay away from the low temp ones.

there is such a thing as a gas engine without a throttle. its called GDI or gasoline direct injection. works just like a diesel by injecting the fuel at the proper time in the compression stroke. they are problematic due to the fact that gas has such a low flash point and it is easily susceptible to detonation and ping. i found a link but didnt read it, hope it a good one:

[URL=http://www.mitsubishi-motors.co.jp/inter/technology/GDI/page2.html]

a perfect engine wouldnt have exhaust either. the 1/3rd rule is 33% goes to heat through the cylinder walls, 33% out the tailpipe in the form of heat, sound, and mass flow, and the other third is converted to mechanical energy only to lose 20% of that to friction in the drivetrain. man, cars are super innefficient.






my reccomendation on better gas mileage is very cheap. but not so simple and it could possibly throw a couple of codes in the PCM.

what you need to do is take the valve covers off and remove four rocker arms and pushrods. firing order for a sbc is 18436572, assuming that its the same for the new vortecs. remove 1467 and it'll still run like a champ. then take the oil pan off and remove the corresponding pistons and rods, hopefully it'll still be balanced. this will not only reduce parasitic friction inside the engine but reduce your displacement. for better flow in and out of the engine, remove the air filter and ducting and the exhaust manifolds. removing the manifolds cold result in a burnt valve but keep your fingers crossed and you'll be ok. dont forget to unplug the injectors, if you dont, your gas mileage will really suck for about 5 miles then it'll result in a huge manifold bomb. if it's 4wd, remove the front cv shafts and driveshaft. i wouldnt worry about the xfer case b/c then you'll have to buy parts. the only other thing i can think of is inflating the tires a bit more, to say 140 psi. this will give you less contact patch and less rolling friction with the road. fold your rear view mirrors in as well. this is about all i got for now, if i think of anything else ill let ya know. hope i helped.

[BigRedFord04]

Originally posted by agjohn02
my reccomendation on better gas mileage is very cheap. but not so simple and it could possibly throw a couple of codes in the PCM.

what you need to do is take the valve covers off and remove four rocker arms and pushrods. firing order for a sbc is 18436572, assuming that its the same for the new vortecs. remove 1467 and it'll still run like a champ. then take the oil pan off and remove the corresponding pistons and rods, hopefully it'll still be balanced. this will not only reduce parasitic friction inside the engine but reduce your displacement. for better flow in and out of the engine....

or you could just get a V6...only reduces "parasitic friction" by 25% instead of 50%, but hell, its an improvement.

Still tho...that is one of the funniest things i've read in a while. to you i award this:

[agjohn02]

(creepy monty voice on, thumbs twiddling) eggggxxcellleennnnt (creepy monty voice off, thumbs stop twiddling)

[agjohn02]

ok, im an engine nut, took thermo in school, and still remember some of it even though its been a while. so, i cant leave this hanging.

i dont remember who posted this b/c i copied and pasted it, but it doesnt matter.


Quote:
[I just finished taking thermodynamics, and I learned that the typical thermal efficiency of a spark engine is 15-20%. That comes from an equation that says you want the energy that leaves the engine (like exhaust gas temperatures) to be as low as possible, and the energy that enters the engine (like the intake air) to be as high as possible.]

this is bass-ackwards

[But as common sense has told us, we try to keep the intake temp as low as possible. It makes sense that high EGTs mean an engine is being inefficient since that comes from unburnt exhaust gases.]

first off high egt's result from a too-lean condition, to a certain point. upon detonation, egt's actually drop. you could be thinking about a turbocharged diesel or gas engine. the reason you are concerned about egt's in those is you dont want to burn up the turbo. being too rich or incomplete combustion could cause high egt b/c the unburnt fuel will ignite in the turbo. turbo's get really hot y'know. but the egt between the turbo and engine will be lower. on a n/a engine though you want high egt's for max power and efficiency. high temp is indicative of more fuel being burned, more energy. if the fuel into the engine is constant, then the higher the egt the better.


Another quote:
[The equation is for Otto thermal efficiency: Nth = 1 - Wnet/Qin

To make this number as high as possible, Qin (heat in) needs to be as high as possible. The waste heat to the radiator and atmosphere is energy that doesn't get sent through the driveline. It's wasted energy, but a good way to reclaim some of that wasted energy is with a turbo.

In no way does this have anything to do with oxygen density or airflow velocity. I'm not saying that it isn't related. I was just mentioning the interesting opposition of what one engineering equation tells us and what shade tree mechanics have know for years.]


My rebuttal:

the Otto cycle beginning after the intake stroke:

Process 1 - 2: an isentropic compression of the fuel-air mixture from bottom dead-center to the minimum volume, compression stroke, so, lets say ambient air temp (T1) enters the engine and is compressed isentropically to a (T2)

Process 2-3: a constant-volume combustion process, the air/fuel mixture igniting, this will add a tremendous amount of heat and result in (T3) all of this heat is converted from chemical energy in the fuel


Process 3-4: an isentropic expansion of the products of combustion to bottom dead center, power stroke, results in (T4) isentropic means constant potential temperature or adiabatic, no heat added or taken away, but the temp does decrease due to expansion


Process 4-1: a constant-volume heat rejection process until the temperature and pressure reach initial conditions. a little confusing but process 4-1 is actually the exhaust stroke and intake stroke, remember, we started at BDC on the compression stroke


The thermal efficiency of this cycle is found as the net work delivered by the cycle, divided by the heat added to the working substance. From this definition of the cycle thermal efficiency, we may write:

Nth = Wnet / Qadded or 1-Qrej/Qadded this was mentioned earlier, kind of

Since the constant volume heat rejection is equal to the change of internal energy in process from state 4 to state 1, and the heat added in a constant volume process from state 2 to state 3 is the change of internal energy netween these two states, we may write for the case of constant specific heats:



Nth = 1 - T1 / T2 * (T4 / T1 - 1 ) / ( T3 / T2 - 1 )

so: Qadded = (T3/T2-1)

Qadded is the amount of heat added to the process during combustion. the chemical energy from the fuel converted into heat energy. Qadded is not the heat you add from the intake charge. in the above equation, if you raise T1 it lowers the efficiency. however, in application the heat of T1 would carry throughout the process and it would not change the efficiency.

basically: the reason an engine makes more power with a cooler intake charge is because the air is denser and there is more molecules of air to react with the molecules of fuel and being a more dense charge raises the dynamic compression ratio. thats it.
warm air actually flows better because its density is lower.

this is long enough, please dont criticize any mistakes in the equations or whatnot, i dont feel like checking it, my point is Qadded does not tell you that higher intake temps are better. it tells you more fuel is better. you cant simply add more fuel though. you have to add more air.

so taking this into account:


Qadded = CNC ported heads, huge cam, and mongoloid injectors

betcha didnt know that



if im totally wrong on any of this please let me know and ill get a book out and correct myself.

[eight]

What makes the most power and what makes the most effiency are two different things.

[AgDieseler]

Originally posted by agjohn02
first off high egt's result from a too-lean condition, to a certain point.

basically: the reason an engine makes more power with a cooler intake charge is because the air is denser and there is more molecules of air to react with the molecules of fuel and being a more dense charge raises the dynamic compression ratio. thats it.
warm air actually flows better because its density is lower.

this is long enough, please dont criticize any mistakes in the equations or whatnot, i dont feel like checking it, my point is Qadded does not tell you that higher intake temps are better. it tells you more fuel is better. you cant simply add more fuel though. you have to add more air.

EGTs on diesels increase linearly (roughly) with fuel rate in naturally aspirated conditions, so that explains my confusion with gas engines.

So it's not the Qin from the air that needs to be high, but from the fuel. With a cooler intake charge there's more oxygen to burn more fuel - thus a higher Qin. Got it. I was looking at things from the viewpoint that the engine strictly pumped air (since that's how we always solved problems in class), but now I understand.

[stx4wheeler]

Originally posted by Snatch Adams
The real question is, did you see them hollow out the cats, hell, I dont even know how you hollow out a cat.

no jerry you need to learn to read better it would have cost me eighty dollars to put in two new cats, they only charged me five for the other hollwed cat they installed i am a big *** and was pretty sure that paying five dollars was a lot better than 80.