Hi Boosters

I have a (several) 2004 Holden Rodeo ute with the Isuzu V6 3.5lt 6VE1 engine.

These engines are well documented drinkers, am wishing to turbo the engine for better economy.

1- Is it viable to improve fuel economy by adding <6psi boost (standard fuel system/ecu can handle/tolerate)?

2- is twin turbo more efficient than a single turbo for economy?

Was going M90 SC, but they always cost energy!

Am thinking small turbos to spool up by 1200rpm
More torque would be desirable, but not chasing HP

Your thoughts and advice are welcomed, tia

 

I just recently turbocharged my 1999 Toyota 4Runner with 3.4L V6 (5VZ-FE) motor. I did it for better towing ability though, not for fuel economy boost. The amount of money you'll spend turbocharging will not justify the fuel savings you might see. You'll be able to buy A LOT of gas with the money spent on a turbo setup.

1. The max boost isn't really going to matter for what you're trying to do. The fuel economy savings comes from being in vacuum and the turbo helping the engine breathe. Once you're in boost, you're drinking fuel. As far as whether your stock fuel system and ECU can handle boost, I think most on this forum will have no idea. That question would be better suited to a forum/group that has a wider knowledge base of your vehicle in particular. Most of us don't know what the stock fueling system of a 2004 Holden Rodeo is capable of. I know in my case, my 4Runner came stock from the factory with (I think) a 80lph fuel pump. I upgraded to a 255lph pump. I also replaced my stock 245cc fuel injectors with 315cc injectors out of a Toyota MKIII Supra. The injectors are almost 30% larger than stock, but the ECU is able to dial back the fuel trims to control the injectors without setting off a Check Engine Light. For closed loop fuel tuning, I have a Split Second AFR sensor calibrator that spoofs the upstream air-fuel ratio sensor into thinking the motor is running lean, and therefore richens up the mixture. I'm targeting 11.5 AFR when in boost in closed loop. Open loop, where the ECU isn't paying any attention to the upstream air fuel ratio sensor, the larger Supra injectors have me at 10.0 AFR.
2. No idea, I'm sure others with better understanding of turbo engine theory can comment more on this. But again, I'm gonna say that the added cost of twin turbo isn't going to pay itself back anytime soon with whatever fuel savings you see.

 

Turbos do not reduce fuel consumption. They increase it.

A naturally aspirated (N/A) engine will have a brake specific fuel consumption (bsfc) of around .45, under boost you will be around .55

You are also artificially increasing displacement, more displacement, more fuel. For instance an N/A 3.5l at 100% volumetric efficiency (VE) will consume 3.5l of air every 2 revolutions, and requires enough fuel for that air. At ≈7.5psi of boost that engine is consuming 5.25l of air, and needs the fuel to keep up, plus the additional fuel requirement (.45 vs .55 BSFC).

You are also restricting the exhaust and intake side of the engine. So you are paying a penalty when off boost.

If you want better fuel economy from a turbocharged engine you need to make the engine smaller, and more efficient so it will make up for its thirstiness when off boost. You would be better off to change your gearing, add and auxillary overdrive, or increase the efficiency of the engine itself. Either way, you have a long way to drive to make up the cost of the gearing.

 

I respectfully disagree with this post. If cruising along on the highway, and OP is able to be disciplined and not push the motor into boost all the time, then the turbo will reduce the pumping loses of the engine while cruising along in vacuum. The blurb about artificially increasing displacement assumes that he's going to be in boost all of the time, which if he's cruising along the highway, he shouldn't be. The turbo will allow for more power to be on tap, and if the OP chooses to use that power, then fuel economy will nose dive. If OP has the discipline to not use the additional power on tap, keeps driving habits the exact same, and keeps the engine out of boost, then fuel economy will somewhat increase. I am not this disciplined, and pushing the motor into boost makes me grin ear to ear. It will not increase fuel economy enough to justify all the money spent on turbocharging though.

 

So your saying the fuel economy is going to improve just by adding a turbo (intake and exhaust restriction) and staying out of boost?

Can you explain how this works?


Of course a turbo increases fun factor, that's why we do it.

 

Turbo will add slight resistance to exhaust, yes. Not sure I agree with you on restriction on the intake side though. It's not like the turbo isn't spinning just because the engine is in vacuum. When cruising along, there's still exhaust flow that's spinning the turbine, and therefore the compressor is flowing some air. So I don't see the restriction on the intake side. Tell me what I'm missing here.

The turbocharger is capturing heat energy that would otherwise just be going out the tail pipe and converts to mechanical energy. Even with the engine in vacuum, that is providing airflow to the engine resulting in reduced pumping losses.

Benefit I've also seen with the turbo is that when cruising along the highway, I can now pull hills in higher gear in this brick of an SUV, instead of having to downshift to lower gear to maintain speed. All while staying out of boost.

 

Fascinating.

 

If it got bad mileage from the factory , a turbo wont change that.
If the motor is small for the vehicle its in, mileage will suffer.

A good look into the tuneup in the light load , low speed and cruising areas can increase fuel economy.
Factory tuneups sacrifice milage for emissions.

Robb, regardless of turbo , if the engine is at full vacuum, pump losses are the greatest cuz the throttle blades are fully or mostly closed. Under low load the turbo wont move significant density to change N/A.
At a load point you stated going up a hill (or even near zero vacuum), not needing to downshift, means the throttle has been opened some and load increases, causing the turbo to increase air denisty, before an actual boost reading. The engine will make more torque and hp because this without boost, still at the cost of more fuel consumed to make that addition torque.

 

Years ago when I was landing speed racing with the ECTA at Maxton, Bill put a 2.3 in his 66 mustang, first NA then added an early 80's carb/turbo. He said on the drive from WV to NC it got better mileage with the turbo.

 

thinking more about this as far a mileage.

lets say slight load increasing air density at low throttle would increase air density before the throttle blade , helping it take in more dense air, coupled with lower rpm without the need to downshift, could lead to better mileage because of lower rpm fuel usage.
Or even a smaller turbine that is more sensitive to load increasing the air density even more yet than say a larger turbine at lower throttle and rpm.

 

I have no doubt we could craft specific scenarios where a turbo will get better economy, but the average will not be in your favor. Ultimately it takes a certain amount of power (air and fuel burning in the engine) to overcome incline and wind resistance. You are doing that by increasing effective volume of air and fuel being pushed through the engine every second, a turbo does it with boost, and NA engine does it with RPM.

An NA engine on flat land in whatever gear at a fixed pedal load will get better economy than an identical engine with a turbo in identical conditions.

A turbo is a loss, it is a second engine. The favorite saying of the internet is a turbo runs off of free "wasted" power, that's not really true. Yes, it is more efficient than other types of boost, but it is not free.

The people who claim they started getting better economy after a turbo probably installed a vacuum/boost gauge and changed their driving habits, trying to stay out of boost as much as possible, which meant they were keeping their throttle inputs light and smooth. The average guy will install a turbo and fall in love with the extra power and use it, ultimately using more fuel in the same vehicle. I know every time I install boost on something my economy goes to the dogs, at least for a while. And it is never as good as it was NA, even years later.

If you want to increase your economy try installing the vac gauge without the turbo, start paying attention to it, see what that does for you.

 

I think you articulated this better than how I was trying to say it.

If I'm reading this correctly, you're essentially saying that to produce X amount of power, there's no difference in fuel consumption rate whether you increase the RPMs (effectively downshifting) and have less throttle input, or maintain higher gear and have higher throttle input (more engine load). Am I understanding you correctly?

 

Nope. It is a broad statement. You need x amount of air, you get it either from increasing charge density or from increasing RPM. I am making no statements about efficiency of either.

Throttle input is not a good predictor of efficiency change between a turbo and NA engine. Vacuum (or boost) in the manifold and load do serve as good predictors though, you can produce the same mass flow at a much lower throttle input on a turbo vehicle. They are not comparable, the throttle is only a gate, it behaves differently when under boost. What I am saying is you can't say "my throttle position is less with the turbo so I must be getting better fuel economy". You have to look at the airmass and fueling requirement.

Speaking of which, boost in general improves the efficiency of things like cylinder heads and intake manifolds. It has it's place and can be a very effective way to increase the power density of an engine. But that is not the same thing as increasing the efficiency of a vehicle.

 

Lets look at it a different way; Carnot's theorem is summarized as follows:

The greater the difference in temperature between a fuel’s combustion temperature and that of its surroundings, the lower the thermal efficiency of an engine. In other words, the greater the difference between the temperature of burning fuel and the metal and air around it, the greater the energy loss. The greater the difference in temperature, the greater the inefficiency of an engine is a fact proven by Carnot’s Theorem.

The Carnot Limit is the amount of energy produced during combustion that becomes mechanical energy. That limit is determined by the difference in the heat of combustion and the temperature of the elements and atmosphere around the combustion process. The greater the difference between the temperature of burning fuel and the ambient temperature of the environment around the combustion process, the lower the Carnot Limit.

You can prove this pretty easily, dyno a car with a 160° thermostat, tune it to the limit, then run the same car with a 195°, tune it up. The 160° car will make more power. Unfortunately cars tend to produce fewer emissions, and drive around better at 195, so that is more the modern standard.

By increasing boost you are increasing heat in the engine, that seems intuitive enough. The longer you are in boost, and the more boost you produce the more the combustion chamber heats, so something like a long grade a boosted engine is paying a greater penalty in heat. The more heat, the less energy can be extracted from the same mass of fuel.

You can see proof of this by logging coolant temps of a loaded vehicle under boost and the same vehicle without boost. This is part of why we see a ≈20% increase in BSFC in an engine running boost. Obviously that is a generalization, less boost will require less fueling. It can be partially mitigated by improving the cooling of the engine, but a given engine is going to have a thermal transfer efficiency that it cannot exceed: you can only pull so much heat out of the combustion chamber in a given amount of time.

You also keep more heat in the engine due to having a higher backpressure than boost pressure (more spent gases remaining in the chamber, which is also more heat), this can be mitigated to an extent with a large, efficient turbo... but it isn't going to want to spool in cruise conditions anyway. Ever seen a dyno run of a turbo engine where the manifolds are glowing red hot? Think of how much heat is in that cylinder and head.

Yes, the same naturally aspirated engine is generating more heat due to more RPM, but that heat is not in the combustion chamber as much as it is in a turbo engine, it is primarily frictional losses. The calculations are complex though, way beyond my skill or desire. But I can tell you from logging the same vehicle boosted and not, under cruise control, on the same grades that the boosted engine is making considerably more heat.

So even if the turbo energy was truly free you would still see an increase in fuel consumption.

Look, I am not trying to trap or trick anyone. I am not having an argument for the sake of it. At this point I feel like we are getting in a rabbit hole, and all of this information is publicly available. I know the internet, and car advertisements are telling us that a turbo is a magical specimen that inherently improves everything about our lives... but since when does a rational person trust the internet or advertisements over physics, thermodynamics and common sense? We have clearly lost the OP at this point as well.

I love a turbo engine, but at a certain point I admit to myself that it is because I like the power, and turbo noises, I like getting sideways and leaving block long elevens. I am not going to see an uptick in mileage on any boosted vehicle, not with my driving habits.

If you want better economy drive like it. You can find ≈15% just by slowing from 75 to 65 on the highway. And that is free.

 

turbo does not improve economy. I have thought and modeled about this for a looong time and i wish they did but they do not.

The reason turbo engines are 'economical' is because they are smaller displacement than other engines with the same power, making the downsizing of the displacement a gain in economy while the turbo is a loss, but the net is a gain because turbos don't hurt economy that much.

If you'd like a detailed explanation of why turbos do not improve economy I Will give a detailed break down of where energy goes and what the turbo does.

 

1. He is not talking about boost he is referring to cruise condition. Why is everybody stuck on boost brake specific... why would anybody argue that a turbo is more fuel efficient in boost? I would not respond to somebody saying anything like that , you couldn't help them.

right

wrong and totally different thing. First of all its backwards from what the first paragraph stated (a 160*F thermostat is a greater difference and therefore less efficient and yet the less efficient engine makes more power in your given example).
Second of all the increased power from a cooler jacketed engine (if any) is due to air density change. Not changes in efficiency. Higher temperature air contains more energy and will make a more efficient engine. Higher temperature coolant jackets make a more efficient engine and improve economy and power when fuel quality can acceptably reaction rate in that condition. Higher temp oils thin out and friction often improves as parts reach their ideal operating shape when fully warmed, there is a fraction of efficiency embedded into the parts design available at only the correct range of temperatures and changes with alloy and design. Higher temperature engines are the modern norm, pushing high as possible temperature in every combustion process, every power plant in the world, higher temperature is more efficient, fuel vaporizes more easily, higher temperature air takes up more space which improves velocity and therefore low speed cylinder distribution and engine smoothness operation.

There seems to be some confusion over the difference between efficiency and power. When the engine is become more powerful it will generally lose efficiency. Ex. Adding boost ruins the brake specific fuel consumption, so does a big cam upgrade, the word 'efficiency' must be carefully defined here: are we discussing the efficiency of bringing in more air per unit displacement? Or the efficiency of holding on to that air? Or the efficiency of the conversion of fuel into power at the tires? An engine may become a more efficient air pump because of a big cam at high rpm while simultaneously becoming much less efficient at converting fuel into power at low speeds, and the user is discussing low speed cruising conversion of fuel to power while everybody else is talking and posting about efficiency of breathing air mass at high rpm - totally garbage in garbage out discussion!

Wrong. Heat is energy and more energy is more economy and more extraction. The reason you erroneously assume the opposite is because you are thinking about gasoline specifically. Not all engines use gasoline and rely on low temperatures to maintain a safe combustion process. You are not thinking globally, you are pin pointing a cherry picked example of an engine octane limited by cheap gasoline fuel with too much compression. If the same engine uses E85 fuel the compression can be increased dramatically along with temperature and this will help extract more energy from the fuel because heat is energy, more energy input = more energy potentially output.



I don't keep going. pay attention

 

I'm not really sure what Carnot's Theorem has to do with real world application of the topic at hand? While I understand that gasoline ICE engines are something like 20-25% efficient, I doubt it makes much real world difference in the context of what the OP is asking. While I did take several physics classes years and years ago in college, and I admit that I'm not a physicist, to me appears you copied and pasted the first two paragraphs of where I quoted you from this article, stating in a nutshell that the greater differential between fuel combustion temps and surrounding material temps, the greater inefficiency of the engine due to heat absorption of the surrounding material. Are you not then stating the exact opposite in the third paragraph quoted above about "proving" Carnot's Theorem with the example about the 160 degree engine (greater temperature differential) running better than the 195 degree one (less temperature differential)? You've lost me... My understanding of why a cooler engine performs better is due to other reasons, nothing to do with Carnot's Theorem. For example, a hotter engine bay heats up the intake charge more (hotter air, less dense air charge, less air in the combustion chamber). And hotter engines are more prone to detonation, and the ECU will therefore command less timing resulting in less power.

 

haha its a copy and paste? Priceless

One thing I've never done 50,000 posts is copy and paste anything. and usually the shit you find out there is wrong anyways.

 

This whole thing feels like a troll, I am out. Good luck!