Turbo or no turbo

[Bird]

Well, I said I had no technical knowledge. Of course, in the most modern times, maybe additional fuel is used to meet emissions standards, so I don't know whether a turbo helps fuel economy or not now. Many years ago, starting about 1980 or 81, part of my responsibilities included supervising 19 wrecker companies who had contracts to tow for the city. In the beginning, 18 of the 19 companies were using Chevrolet wreckers, while one used Fords. They were all gasoline powered trucks (except for their heavy duty stuff, of course). Then Ford came out with the 6.9L diesels and within 2 years, all 19 companies had replaced every one of their standard duty wreckers with diesel powered Fords. Every company liked them, although they all said they were really sluggish on acceleration. Now I had also been an RVer for several years and subscribed to some RV magazines. For both the 6.9L and later the early 7.3L Fords, Banks and ATS sold a lot of aftermarket turbos to RVers that everyone said increased power, acceleration, and fuel mileage. Now I've heard and read the same thing several places, but the EPA standards that required catalytic converters on cars didn't apply to diesels for several years. So perhaps, with the new emissions standards, and the means by which those standards are met, better fuel economy may no longer be a benefit of turbos.

 

[toddler]

Sort of kinda maybe. If you are putting along in a smaller displacement turbo engine and putting along in a larger displacement natural engine, yeah the smaller displacement will use less fuel. If you are putting along the turbo isn't doing anything. The turbo needs heat to turn it faster and do it's thing. Hot gases expand faster than cold gasses.

More fuel equals more power, not more air. More air allows more fuel to be burned, thus more power. The turbo compresses more air into the cylinder, raises the effective compression, more o2 and you can burn more fuel. Same as a larger displacement natural engine pulls in more air and can burn more fuel.

There is a reason my little 3 cylinder 26hp tractor burns 1/2 gallon of fuel an hour and my BIL's Ford 6600 with a natural 80 or so hp tractor burns a couple gallons or more.

I agree with this. But my understanding is that in a turbo diesel, there are several more factors. As load increases, the gas temp increases and the higher turbo speed can allow more fuel to be injected, essentially on an as needed basis. Also, as air pressure becomes less at higher altitude, the turbo can add more air by compressing it, which maintains the required amt of oxygen to burn the fuel efficiently.

So while you clearly need more fuel if you add more air, the turbo seems to optimize itself for both altitude and load. I also thought that at higher compression, you increased the temperature and burnt the diesel fuel more completely/efficiently. In a gas engine you may actually need to waste some fuel to keep the vapor temperature down, otherwise you get pre ignition. So older gas turbo engines ran richer than a non turbo's and exhausted more unburnt gas. I don't think that is still the case for gas, and I don't believe in a diesel that this was ever a problem. Something about cooler exhaust temps never requiring a gas wasting situation.

Engineers, please correct anything I said that is incorrect.
Thanks,
Todd

 

[RobJ]

Well, I said I had no technical knowledge. Of course, in the most modern times, maybe additional fuel is used to meet emissions standards, so I don't know whether a turbo helps fuel economy or not now. Many years ago, starting about 1980 or 81, part of my responsibilities included supervising 19 wrecker companies who had contracts to tow for the city. In the beginning, 18 of the 19 companies were using Chevrolet wreckers, while one used Fords. They were all gasoline powered trucks (except for their heavy duty stuff, of course). Then Ford came out with the 6.9L diesels and within 2 years, all 19 companies had replaced every one of their standard duty wreckers with diesel powered Fords. Every company liked them, although they all said they were really sluggish on acceleration. Now I had also been an RVer for several years and subscribed to some RV magazines. For both the 6.9L and later the early 7.3L Fords, Banks and ATS sold a lot of aftermarket turbos to RVers that everyone said increased power, acceleration, and fuel mileage. Now I've heard and read the same thing several places, but the EPA standards that required catalytic converters on cars didn't apply to diesels for several years. So perhaps, with the new emissions standards, and the means by which those standards are met, better fuel economy may no longer be a benefit of turbos.

You are right Bird, the non turbo engines needed more power, in a RV that may be traveling in the mountains. But anytime you ask for more power there is a cost. I can get much better gas mileage doing 50 vs 70. But who wants to drive 50 on the highway?

"Better gas mileage" was always the final sales trick to sell something. You know I can get better mileage by putting magnets on my fuel line?!!! hehe.

 

[dynasim]

I am under the imnpression(don't know) that the turbochargers help with emmisions by keeping the fuel to air ratio right, and possibly by enabling the recirculation of exhaust into the inlet.

Again, I don't know this for sure.

Chris

 

[RobJ]

I agree with this. But my understanding is that in a turbo diesel, there are several more factors. As load increases, the gas temp increases and the higher turbo speed can allow more fuel to be injected, essentially on an as needed basis. Also, as air pressure becomes less at higher altitude, the turbo can add more air by compressing it, which maintains the required amt of oxygen to burn the fuel efficiently.

So while you clearly need more fuel if you add more air, the turbo seems to optimize itself for both altitude and load. I also thought that at higher compression, you increased the temperature and burnt the diesel fuel more completely/efficiently. In a gas engine you may actually need to waste some fuel to keep the vapor temperature down, otherwise you get pre ignition. So older gas turbo engines ran richer than a non turbo's and exhausted more unburnt gas. I don't think that is still the case for gas, and I don't believe in a diesel that this was ever a problem. Something about cooler exhaust temps never requiring a gas wasting situation.

Engineers, please correct anything I said that is incorrect.
Thanks,
Todd

The old gas turbo kits installed had a lot different cars back then. You could use water injection or nitrious to cool things off. It's a LOT different today with computers in cars. Ever wonder what keeps your car running smoothly when you crank it up first thing in the morning on a 30 below morning? No choke to set, that computer is flooding the engine with fuel to keep it lit.

I agree on the altitude comment. But at altitude I think the turbo will only compensate "some" for the lost air. with less o2 in the air at altitude I don't think it will get you back to sea level o2 levels. I believe it would have to considerbly raise the boost psi and the wastegate may not let that happen....damage to the engine and all. None of the diesels I worked on had a wastegate of any kind, I think that has something to do with the application of the turbo in a car/truck and the speed up, slow down thing. Dunno about that one.

I still believe the main reason for a turbo is for more power. If the mileage was noticeable with a turbo vs a non, then why wouldn't every car have one or people try and sell me one of those instead of magnets.


Rob