quote Originally posted by Joseph Upson: What makes it possible for the earlier shift into top gear on the turbo motor for lower rpm and not the naturally aspirated motor? or better yet, what other changes not associated with the turbo are being made to the turbo motor to afford it better fuel economy and why wouldn't it also be done to the NA motor to avoid the added expense of the turbo since it wouldn't be necessary for the bump in mpg? Turbos = low end torque. Low end torque = ability to shift into top gears sooner without lugging the motor and therefore the ability to turn lower rpm burning less fuel while maintaining the same speeds. You are acknowledging the benefits in your statement, you're just attributing them to something other than the actual cause, the turbo.

The turbo isn't the cause.

http://cartuning.ca/product...grandprix&engine=ls4

Notice under "In the Box" it includes "4T65E transmission shift kit" as one of the many changes that comes with installing the Cartuning LS4 turbo kit. Installing only the shift kit (with TCM program changes), and none of the other bits, will also likely net you a couple MPG difference. But 2-3 is really an insignificant change. There are way too many variables involved to just say "the turbo is what does it."

What I am attributing the increase in MPG to, is the most likely cause, given the set of changes involved in the installation of this kit. That is all there is to it.

And making the direct statement of "Turbos = low end torque" is nonsense. It depends on the turbo, how it's installed, how it's tuned, etc… There are way too many variables involved to make such a blanket statement.

quote Originally posted by Joseph Upson: At cruise speed the exhaust back pressure is probably insignificant and the compressor is likely moving enough air to exceed the need so that lighter throttle input is needed to maintain cruise speed. That amounts to a bump in pumping efficiency due to utilizing hot exhaust gases that otherwise would be pumped out the exhaust and not used at all. Thermodynamics at work, recovering some of the lost energy to do more work.

The turbine is harnessing only mechanical energy, not thermal energy - so its reducing exhaust velocity / mechanical potential by the same amount its adding mechanical potential to the intake stream. It seems that at 100% efficiency, you'd get no benefit - but since there's always friction and other losses, you'd see a reduction in fuel economy.

This is ignoring the reduction in compression ratio was well, which by itself is significant from a efficiency standpoint.

Again, i'm only talking about steady-state cruise with the same gearing with identical displacements.

Sheesh guys. Keep it simple. I'm NOT talking about shift points, different gearing, or other mods, or anything else like that. I'm talking about adding a turbo to a NA engine & getting more MPG at cruising speed because the engine can be more efficient with the turbo. I think that was the original question, was it not? But yes, all the turbos we used to install also meant a different exhaust system, since we were going from two small exhaust pipes to one 3" downpipe split into two 2 1/2" exhaust pipes & turbo mufflers (or in some cases two 3" pipes for dual turbo cars). But the mileage would still be better than if you just changed out the exhaust system alone.
And no, the exhaust back pressure on the turbo does not take away from the boost pressure to negate the increase in intake pressure. The boost overcomes the exhaust pressure 'cause, after all, it's boosting more pressure than the exhaust has. Ever noticed that the exhaust valves are always smaller than the intakes? That's because after burning the fuel there is less gases exiting the engine than entered it. The gases were turned into energy to push the piston down.
I'm not speculating here (like some others): I'm just telling you that you CAN get better mileage at cruising speeds (steady highway speeds) with a turbo installation if done right.
~ Paul
aka "Tha Driver"

Custom Fiberglass Parts

I just can't see it that way, Paul.

The whole point of a turbo is to increase the amount of air flowing into the cylinder each cycle. If the gear ratios, tire sizes, trans slippage are all held constant, then it takes the same number of cycles (revolutions) of the engine per mile. If the engine is inducting more air, unless the fuel/air ratio is made more lean, the engine MUST use more fuel per mile....even worse, most forced induction engines are run RICH to avoid detonation!

I suppose that if the effective compression is increased by the turbo, the amount of power created for a given amount of fuel might increase slightly, but generally speaking, more air = more fuel = reduced mileage.

quote Originally posted by Tha Driver: Sheesh guys. Keep it simple. I'm NOT talking about shift points, different gearing, or other mods, or anything else like that. I'm talking about adding a turbo to a NA engine & getting more MPG at cruising speed because the engine can be more efficient with the turbo. I think that was the original question, was it not? But yes, all the turbos we used to install also meant a different exhaust system, since we were going from two small exhaust pipes to one 3" downpipe split into two 2 1/2" exhaust pipes & turbo mufflers (or in some cases two 3" pipes for dual turbo cars). But the mileage would still be better than if you just changed out the exhaust system alone. And no, the exhaust back pressure on the turbo does not take away from the boost pressure to negate the increase in intake pressure. The boost overcomes the exhaust pressure 'cause, after all, it's boosting more pressure than the exhaust has. Ever noticed that the exhaust valves are always smaller than the intakes? That's because after burning the fuel there is less gases exiting the engine than entered it. The gases were turned into energy to push the piston down. I'm not speculating here (like some others): I'm just telling you that you CAN get better mileage at cruising speeds (steady highway speeds) with a turbo installation if done right. ~ Paul aka "Tha Driver" Custom Fiberglass Parts

You're misunderstanding what I intended about exhaust pressure. To simplify it, if you install a turbo that does not produce anymore back pressure than the stock exhaust system, there is no reason to assume the turbo will increase the work of the engine in expelling exhaust through it.

At this point nothing short of a step by step formula will prove the efficiency gain with the turbo.

I have to disagree with you on exhaust pressure not taking away from boost pressure because the most efficient systems are on race cars and I'm pretty certain that at some point on practically every production turbo car if tested you will find exhaust pressure is higher than boost pressure at some point, the only way to get around it is build more exhaust volume into the system which will make the turbo contribution less and less streetable because of the rpm level that must be reached before exhaust pressure accerts enough force to build boost. As the exhaust pressure increases the ability to expel exhaust gasses decreases because you have opposing forces at play with a changing ratio of force. The classic example of this is an undersized turbo for an engine application.

You have to choose the effective range and build around it.

As for exhaust valve size, my understanding is that they are smaller because 1, you merely need to open the valve and gasses will rush out in a far greater proportion than air will rush in when the intake valve is opened and 2, the tremendous forces on the valve after the combustion process warrants a smaller diameter to reduce the load on the camshaft lobe since the larger the valve trying to open against the pressure the greater the lbs/square inch trying to keep it closed.

Far more exhaust gas will blow out of the cylinder than it can pull in. On combustion the volume of gas in the cylinder increases several times compared to what was pulled in. So there is no way you can have a lower quantity of exhaust gases than intake gases unless the mixture doesn't fire. Again this is delving into thermodynamics.

It's getting over my head but it's good tactful discussion.

quote Originally posted by Tha Driver: And no, the exhaust back pressure on the turbo does not take away from the boost pressure to negate the increase in intake pressure. The boost overcomes the exhaust pressure 'cause, after all, it's boosting more pressure than the exhaust has. Ever noticed that the exhaust valves are always smaller than the intakes? That's because after burning the fuel there is less gases exiting the engine than entered it. The gases were turned into energy to push the piston down.

This is not quite true. Also check your camshaft(s). You'll notice the exhaust duration and lift, are generally greater than the intake side. The burning of the fuel in combustion doesn't create less gases. It actually creates more. The expansion of gases forces the piston back down the cylinder, producing power. Also, as the air is sucked into the cylinder during the intake stroke, it does expand slightly, due to the surrounding heat in the head and cylinder, because all of the heat is not pumped out through the exhaust, along with the combusted air/fuel mixture. It's a lot of math, but the volume of gases in the cylinder basically remains constant before and after combustion. Some of the combusted mixture also does not stay a gas, but becomes a solid, especially if there is any oil in the mixture. Then you get baked on carbonation inside the cylinder, which is undesirable, and decreases the efficiency of the system.

Of course, if your engine was 100% efficient, and everything you said was entirely true, then a turbo would be useless, as you couldn't increase the efficiency beyond 100%.

Maybe I don't understand the functin of the shift kit. I was under the impression that it was to give a firmer hold during the shft to save the clutches from increased wear. Less slip during the actual shift. Is there slippage after the shift has been made in a stock transmission? After the shift the loss is in the tc and before it locks up right?

quote Originally posted by dratts: After combustion there is more gas? Isn't it the same amount, just larger volume, less dense?

Part of the petrol/ethanol/whatever fuel you're using, becomes a gas when it is burned. The volume is the same, because you can't fit more volume in a cylinder, than the volume of the cylinder, otherwise you will throw a rod or cause some other severe damage. What changes are the elements in the gas, and the density of the gas as a whole. For the purposes of this discussion though, the really important part is the volume, which stays close enough to 1:1 throughout the process that the minor differences aren't interesting to argue here.

IIRC, it is Boyle's Law that states P*V*T= constant. So, since the temperature is much higher after combustion and the volume of the cylinder is constant (until the piston moves) the pressure increases (which is what pushes the piston). As the exhaust gas exits the cylinder, it drops in pressure to ambient, so the volume of the gas must increase.

quote Originally posted by imacflier: IIRC, it is Boyle's Law that states P*V*T= constant. So, since the temperature is much higher after combustion and the volume of the cylinder is constant (until the piston moves) the pressure increases (which is what pushes the piston). As the exhaust gas exits the cylinder, it drops in pressure to ambient, so the volume of the gas must increase.

The volume of gas increases, but not from the volume of the cylinder. It increases from the volume of the compressed gas which fills the combustion chamber, as ignition happens immediately after compression. As the gas expands, it pushes the piston down the cylinder, but before the piston reaches BDC, the exhaust valve opens, and the exhaust gas begins to flow out of the cylinder.

In the case where the exhaust valve does not open (as happens when DoD/AFM is engaged on those engines so equipped), the combusted gas fills the cylinder when the piston reaches BDC. Because the volume cannot increase beyond what the cylinder can contain, the pressure must increase. This increase in pressure is what allows DoD/AFM to function appropriately, as it provides a compressing and expanding gas for the piston to rebound against, to avoid extraneous vibration and loss of power when engaged.

Ok, some corrections in order here.

First off, ignition begins *before* TDC, that's what timing advance means, advance of Top Dead Center. The fuel is already mostly burned by the time the piston arrives at the top of the cylinder.

Secondly, the primary push on the piston is *not* from the expanding combustion gases. In fact, not a whole lot of the push comes from that. The primary push comes from thermodynamic expansion of the air in the combustion changer resulting from the heat released by combustion. That air is mostly nitrogen with some argon and CO2. The O2 is consumed by combining with the H in the fuel, and some is bound up with the C to make CO and CO2. It's why it's called an "Internal Combustion" motor, the heat is released inside the engine whereas a steam engine is an External combustion motor.

The more air by mass there is in the cylinder, the more push occurs from heating it. Colder air is denser, so more mass gets in the cylinder, that's why carb'd cars ran better in winter in many cases. Super chargers and turbochargers also increase the mass of air in the cylinder.

quote Originally posted by JazzMan: Ok, some corrections in order here. First off, ignition begins *before* TDC, that's what timing advance means, advance of Top Dead Center. The fuel is already mostly burned by the time the piston arrives at the top of the cylinder. Secondly, the primary push on the piston is *not* from the expanding combustion gases. In fact, not a whole lot of the push comes from that. The primary push comes from thermodynamic expansion of the air in the combustion changer resulting from the heat released by combustion. That air is mostly nitrogen with some argon and CO2. The O2 is consumed by combining with the H in the fuel, and some is bound up with the C to make CO and CO2. It's why it's called an "Internal Combustion" motor, the heat is released inside the engine whereas a steam engine is an External combustion motor. The more air by mass there is in the cylinder, the more push occurs from heating it. Colder air is denser, so more mass gets in the cylinder, that's why carb'd cars ran better in winter in many cases. Super chargers and turbochargers also increase the mass of air in the cylinder.

Correctings in order, indeed. Ignition timing obviously depends on what the timing is set to (as do lots of other things depend on various settings). Discussing the process of combustion with advance of 0 degrees simplifies the discussion though. The mixture should still be burning when the piston reaches TDC, even with advance set in. If it's not, then you are probably advanced too far. The piston needs to be fairly near TDC, for the engine to be remotely efficient. Combustion too early or too late can cause lots of problems, as I'm sure most of us in this discussion are aware of.

And as for the expansion pushing the piston, we are saying the same thing, though I was trying to limit the technical spectrum of wording. The "combustion gases" (not sure where you got that phrase exactly) presumably aren't expanding to push the piston, since they've already fully combusted and expanded, assuming that you mean "exhaust gases" by that. The thermodynamic expansion of the volume of air in the chamber happens due to the burning of the compressed mixture. If you set ignition timing to fire at or near (before or after) BDC instead of at or near (before or after) TDC, you would be lucky to burn anything at all, as the compression happening afterward would put the fire out, much like stepping on a burning match will extinguish it.

And yes, the increased mass of air/fuel in the cylinder from adding a super or turbo charger, will create more push on the piston when combusted. That is exactly why they increase the power output.

quote Originally posted by dobey: Part of the petrol/ethanol/whatever fuel you're using, becomes a gas when it is burned. The volume is the same, because you can't fit more volume in a cylinder, than the volume of the cylinder, otherwise you will throw a rod or cause some other severe damage. What changes are the elements in the gas, and the density of the gas as a whole. For the purposes of this discussion though, the really important part is the volume, which stays close enough to 1:1 throughout the process that the minor differences aren't interesting to argue here.

Right! I can't believe i suggested that there would be more volume in a sealed cylinder. The pressure that drives the piston is from the combusting gas trying to expand it's volume though right? Isn't that what an explosion does?

quote Originally posted by dratts: Right! I can't believe i suggested that there would be more volume in a sealed cylinder. The pressure that drives the piston is from the combusting gas trying to expand it's volume though right? Isn't that what an explosion does?

That's what heating air does. The combustion in the engine isn't an explostion. If the mixture explodes, you have detonation, which can be very bad for the engine. The burning of the fuel/air mixture, heats the air, causing the expansion, though. But it can only expand to the volume of the cylinder containing it.

I don't want to get into an argument here, but I didn't say that combustion was an explosion. I meant that the gases are trying to expand LIKE a controlled explosion. Since they are contained they create the pressure that does the work in an internal combustion engine. As far as I know the combustion is LIKE a controlled explosion in effect.

[This message has been edited by dratts (edited 10-20-2011).]

quote Originally posted by dratts: I don't want to get into an argument here, but I didn't say that combustion was an explosion. I meant that the gases are trying to expand LIKE a controlled explosion. Since they are contained they create the pressure that does the work in an internal combustion engine. As far as I know the combustion is LIKE a controlled explosion in effect.

Sorry. The way you worded your question implied that you were saying it was an explosion. I suppose you could say it's like a contained explosion, given that the combustion is contained within a closed cylinder. But aside from them both being in a closed container, they're not really anything alike. I'm not sure what a good analogy would be, and I tend to try and avoid analogies, similes, and metaphors in technical discussion, as they typically only serve to cause confusion.

Thanks for all the post and disscusions. It seems that a small turbo would atleast gain you quite a bit of power without losing much if any MPG. We can keep this disscusion going but I would like input on another question on the turbos.

What size turbo and mods would it take to get 100 HP added to the stock 240hp, looking at around 350hp. Im thinking I would like too keep the torque in the lower to mid range. With a PR engine, I don't feel good about running too high in the RPM range. Gas mileage is still a plus.

Anything wrong with this idea or have a better one, please let me know. Thanks

Steve

Okay well If you make any changes to your motor you will see a difference in how it performs weather good or bad depends on how you set it up the key here is the tuning. If you do not properly dyno tune the motor after a change you should see a reduced positive effect or even a loss of power. now if you put a small turbo with no change to your injectors but increased your fuel rail pressure to equal the boost. IE if you are running 25 psi fuel pressure and you add a 5 lbs boost you would have to increase your fuel pressure by 5

If you make changes to your motor with the tuning set up for economy and the fuel you are using then you could see an increase in MPH along with increases along the power band but the best way to save gas is to drive consistently and combine any trips together, avoid accelerating/braking hard and a bunch of other tips.

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You are not prepared

[This message has been edited by hawkebat (edited 10-21-2011).]

Some years ago Smokey Yunick (remember him?) did extensive research on a zero boost turbo system. The function was to heat the air/fuel charge, vaporize the fuel, and induce more swirl to the intake, thereby increasing fuel economy significantly.

quote Originally posted by larry mimbs: Some years ago Smokey Yunick (remember him?) did extensive research on a zero boost turbo system. The function was to heat the air/fuel charge, vaporize the fuel, and induce more swirl to the intake, thereby increasing fuel economy significantly.

I don't think it was zero boost. Claimed 250 HP from a Duke, & 50 MPG (& this with a 4-speed: think what it would do with an overdrive). You'll need boost for that. It's a perfect example of better mileage with a turbo, but he did use hard rubber/low rolling resistance tires on it too.
http://gafieroclub.org/smokey.shtml
~ Paul
aka "Tha Driver"

Custom Fiberglass Parts

Question, Has ANYONE here ever tried to actually make a vaporizer? I had a friend of mine make and run one years ago and although I can not attest to the 35 mpg, I can say that it did not feel or sound anything like a 400cid V8. It was ALOT smoother than that. I also know what all he used and it is small and simple if anyone is interested. ( and here comes the flaming)

Steve

quote Originally posted by JumpStart: Question, Has ANYONE here ever tried to actually make a vaporizer? I had a friend of mine make and run one years ago and although I can not attest to the 35 mpg, I can say that it did not feel or sound anything like a 400cid V8. It was ALOT smoother than that. I also know what all he used and it is small and simple if anyone is interested. ( and here comes the flaming) Steve

The way Smokey's vaporizor worked, was sending fuel in with the air, through the turbo. And, injecting fuel into the compressor of a turbocharger is not generally a good idea. Turbos can get very hot, and gasoline is pretty well flammable. Smokey's hot vapor duke apparently had many fire issues throughout its lifetime.

The system my friend made had no fire issues and no turbo. Basically he used a constant velocity carb from a motorcycle mounted to a square funnel by way of a short rubber hose. (The carb being suspended by the hose) The wide end of the square funnel was mounted to 3 heater cores with 4 gaskets, 1 between each core and between the core and square funnels. The second square funnel on the otherside of the cores tapered back down to a round short tube and was attached to a 90deg elbow that turned down into an adapter where the carb used to be. The heater cores had coolant circulating through them which heated the air/fuel mixture after the carb (no vapor lock) and just before the intake.

He also used an atomizer on the fuel line but I dont know how much difference that made. Like I said, There was no proof to me that it was getting 35 mpg but he wasnt the type to lie either and he was a little aggrivated that it wasnt getting better mileage. It sounded nowhere near stock and riding in it, it felt more like an electric motor.

Steve

quote Originally posted by dobey: gasoline is pretty well flammable.

Gasoline is not flammable but im sure you knew that. I think gas vapors self combust at about 500 degrees.

[This message has been edited by JumpStart (edited 10-23-2011).]

quote Originally posted by JumpStart: Gasoline is not flammable but im sure you knew that. I think gas vapors self combust at about 500 degrees.

Flammable does not mean self-combustible. It simply means combustible. A turbocharger where the turbine side gets very hot, could easily ignite a fuel/air mixture on the compressor side, where the compression itself also adds some heat to the mixture.

For what it's worth, you don't need to heat gasoline to vaporize it. The flash point of gasoline is about -45℉. With modern electronic fuel injection, and fuel rail pressure at 65+ PSI, the tiny amount of fuel that gets sprayed into the intake air stream is almost instantly vaporized anyway. Direct Injection makes that even more true, with fuel rail pressures over 300 PSI, and being injected into the combustion chamber rather than the intake stream. Smokey's system provides more risks, than benefits.

quote Originally posted by dobey: The combustion in the engine isn't an explostion.

quote Originally posted by dratts: I meant that the gases are trying to expand LIKE a controlled explosion.

If anyone cares, in normal burning the flame propagation rate is lower then the local speed of sound in the medium (in this case, the air/fuel mixture), while in an explosion the propagation rate is supersonic. The objective in an internal combustion engine is smooth burning with a flame propagation rate substantially lower than the local speed of sound.

[This message has been edited by Marvin McInnis (edited 10-24-2011).]

quote Originally posted by dobey: The way Smokey's vaporizor worked, was sending fuel in with the air, through the turbo. And, injecting fuel into the compressor of a turbocharger is not generally a good idea. Turbos can get very hot, and gasoline is pretty well flammable. Smokey's hot vapor duke apparently had many fire issues throughout its lifetime.

That's ridiculous. Folks have been making pull-through systems for decades - maybe close to a century. The only problems I've ever heard of is when idiots run them through an intercooler & had a backfire explosion (NOT a good idea to have an intercooler system full of a fuel/air mixture!).
A pull-through system allows you to not have to make a bunch of mods to the carb to pressurize it (because you're not), & not have to modify the fuel pump system to add more pressure there.
~ Paul
aka "Tha Driver"

Custom Fiberglass Parts