Article: adding a turbo to improve efficiency

[LostCause]

Yes, good explanation.

- LostCause

[JohnnyGrey]

Isn't the fuel economy advantage getting a smaller engine than you would have, then add a turbo? In other words, puting a turbo to what you have adds more power - but no fuel economy.

Exactly right.

For all you guys that think downsizing isn't necessary, running a 2 liter engine at atmospheric pressures (let alone under boost) provides WAY TOO MUCH POWER to make use of in an FE context.

That BSFC sweet spot does not need to get bigger, it needs to move South on the map!!!

Tiny motors let us run at or near atmospheric pressures without putting down excessive power. That means we can run with greatly reduced pumping losses (not to mention weight, reciprocating mass, and friction) without getting speeding tickets. The only reason that turbo is there is so we can take our tiny 1.3L engine on the highway without being demolished by a semi. Get it now?

[LostCause]

Originally Posted by JohnnyGrey

Get it now?

I get it.

I still think it's foolish to say downsizing is the only choice. The best choice, maybe. The only choice, no.

- LostCause

[Duffman]

To say that there will be no gain is really not true either, if you lived in a hilly area it might allow you to hold OD or more likely the TC locked on an automatic. The power can be used when accelerating as well. It really depends on the engine you are starting with, if its a chrysler 2.2L chances are it can use the power, if it is a 5.0 mustang chances are it wont. Making the island bigger increases the potential to be operating in conditions that put you on the island, also if you look at the island in post 60, the island is also a hint wider as well with the turbo.

On a diesel a turbo should always help.

[JohnnyGrey]

Here's a downsize + turbo success story from 2002:

VW Jetta VR6
5spd Manual
Regular Fuel
200HP
2.8L
17/26 MPG
$2708 in fuel per 15K miles

VW Jetta 1.8T
5spd Manual
Premium Fuel
180HP
1.8L
21/29 MPG
$2402 in fuel per 15K miles


Turbocharging the VR6 wouldn't do anything for its fuel economy, but you'd have a stupidly fast car. Also, the base N/A 2.0L is cheaper to run than either of these powerplants.

Notice I highlighted the cost. When talking about fuel economy, that's the number that really matters, not gallons. So the turbo engine not only has to overcome the MPG numbers of its N/A counterpart, but it has to do so by a margin that justifies its more expensive fuel. This is one rare example where a turbocharged engine provides a lower cost of ownership than one of its N/A counterparts.

The Subaru Impreza has an N/A 2.5L and a 2.0T that both get 18/25 MPG. The turbo is more expensive to run because of its fuel requirement, but it also provides more power. If Subaru was aiming for efficiency rather than performance, it would have opted for a 1.5T or smaller. Subaru downsized by only 0.5L where VW took it down a whole liter.

[JohnnyGrey]

Making the island bigger increases the potential to be operating in conditions that put you on the island, also if you look at the island in post 60, the island is also a hint wider as well with the turbo.

It's not worth it at all. While accelerating, I can stay in that island from 5mph all the way up to 80mph turbo or not. I can't stay in it while cruising. You know why? Because I can't use that much torque. The island needs to be brought south, so I can stay in it without accelerating, just like I said before.

If you really understand the concept of torque, then go ahead and explain to us why P&G is more efficient than cruising, and use the map to back up your points.

[Duffman]

I dont know why you keep coming back to torque, if you have read any of my other posts you should be able to infer that I know the physics of how a car is propelled down the road. I live in the flat lands and I can still hit hills that will kick the torque converter out of lockup on a automatic equiped ride on the highway in most directions of travel. As I said 2 posts up the merits of a turbo largely depend on the power to weight ratio of the car you are starting with and if you live in a hilly region you can use the power. If you look at the diagram in post 60, the shapes are not distorted only enhanced with the turbo, because the shapes are enhanced FE certainly cant go down so what is the problem? If FE goes up in hilly regions and doesnt go down on the flats then it must go up depending on how often you can use the extra power.

Remember most people on this board are driving metros and civics, there not endowed with an overabundance of power where a turbo addition is pointless.

[LostCause]

Originally Posted by JohnnyGrey

So the turbo engine not only has to overcome the MPG numbers of its N/A counterpart, but it has to do so by a margin that justifies its more expensive fuel.

Not every turbo engine needs high octane fuel (Miller-cycle).

Not every down-sized turbo engine needs to run high octane fuel all the time. If you read the whole post, MIT developed a dual injection system that uses pure ethanol during acceleration and 87 during cruise.

You are definately right that through conventional modes of thought and technology, downsizing and taking the hit of premium is the only choice. If you look at industry and automotive research firms, you'll see some are willing to think outside the box.

The conservative big three are the ones I've seen really pushing down-sized turbo-diesels and gas engines. It took Mazda to bring us the wankel and the miller-cycle. It took Honda to bring America the hybrid. It took Toyota to bring us the parallel hybrid. It took GM to do nothing.

Originally Posted by Duffman

...because the shapes are enhanced FE certainly cant go down so what is the problem? If FE goes up in hilly regions and doesnt go down on the flats then it must go up depending on how often you can use the extra power.

Great observation. I hadn't considered that.

- LostCause

[JohnnyGrey]

I dont know why you keep coming back to torque

Because torque makes up the Y axis of the charts you fail to comprehend. How can you keep referring people to charts you can't read yourself? I can't keep pointing out facts to you that you quietly ignore because you don't want to admit you don't know what I'm talking about. Get a clue about what torque is, how it relates to the map, then come back to the discussion. If torque wasn't crucial in BSFC, it would be a 2d plot, not a 3d map. I'm more than happy to explain what things are, and I've done so many times in this thread, but I'm not going to argue with the uninformed.

[Duffman]

Originally Posted by JohnnyGrey

Because torque makes up the X axis of the charts you fail to comprehend. How can you keep referring people to charts you can't read yourself? I can't keep pointing out facts to you that you quietly ignore because you don't want to admit you don't know what I'm talking about.

Actually the other axis is BMEP, not torque although they are proportional, but it shows how much you are actually paying attention I guess. A reading of TORQUE is entirely pointless when you have no clue how much is required to push a vehicle down the road and the TORQUE required to push a car at 60 mph is not the same TORQUE to move it at 80 mph, so again without any other information the x axis is effectively unitless because it provides no information, its the shape of the plot that provides any usefull information to this post.