Turbo Boost and FE

[DRW]

Originally Posted by AlainB7

DRW, explain me how you get 46 to 53 mpg with your big Laser?

You almost make the FE of my VX with the set-up of my Galant that make 19 mpg...

Haha, it's magic!
It's all in my gaslog. Essentially I have a long boring commute, which gives me plenty of time to think of new ways to squeeze more mpg out of the car. The car is fwd with a taller 5th gear and an eprom ecu with extensive mods. I've been on the dsm-ecu list for several years, and they released a full commented disassembly which makes it easier to mod almost everything in the ecu. Not to rain on anyone's parade, but even the famous AEM EMS would be a step backwards compared to the level of control I have with this ecu.
I also drive really slow.

[suspendedhatch]

There is no reason why a turbo car can't have the same compression ratio as a stock non-turbo car if you tune it carefully.

I'm willing to bet that you could add a turbo to a N/A engine, keep the stock compression ratio, and tune it with a standalone for a pretty significant gain in both FE and HP.

[DRW]

Originally Posted by suspendedhatch

There is no reason why a turbo car can't have the same compression ratio as a stock non-turbo car if you tune it carefully.

I'm willing to bet that you could add a turbo to a N/A engine, keep the stock compression ratio, and tune it with a standalone for a pretty significant gain in both FE and HP.

I agree. The VW turbo 1.8 and 2.0 have something like 10.2:1 compression from the factory. They work well for getting good power and good FE.

I'm following the same trend with my other DSM. I'm just finishing the rebuild on it and I upped the compression from 8.3 to 9.0 I also have a 1.6 head which has smaller combustion chambers for more compression and slightly more quench area. If I can't run the same ammount of boost on it, I won't be sad since I was able to run over 30 psi (gage stopped at 30).

[dkjones96]

That's one of the ideas for the tracker. The stock engine with stock compression and everything but a turbo slapped on. The turbo should give me a little more grunt so I don't have to get out of overdrive on hills and the car won't need to keep the TC unlocked all the time to keep 75mph. Then again, I've already got a solution for the second one.

[trautotuning]

Originally Posted by dkjones96

That's one of the ideas for the tracker. The stock engine with stock compression and everything but a turbo slapped on. The turbo should give me a little more grunt so I don't have to get out of overdrive on hills and the car won't need to keep the TC unlocked all the time to keep 75mph. Then again, I've already got a solution for the second one.

And what is that? I want to know!! (I actually want a way to lock my TC earlier at like 30-35mph)

[thisisntjared]

hmm, it appears that there are some opinions that are founded on incomplete evidence in this thread and i wish i saw this thread earlier.

if there are two motors that are identical aside from a turbo, the turbo COULD get better fuel economy or it could get much worse fuel economy depending on the driver. a turbo is alway spooling except when the wastegate opens and air is not sent to the turbo. this means that even though a motor may not have the turbo up to producing max psi, it is still spooling that turbo and feeding the motor more air than it would prior to having the turbo.

now how does that help fuel economy? more air means more gas, but it also means more power and at a lower rpm. somebody else had mentioned it earlier but i will say it again: this helps with pumping losses. the topic is similar to that of WOT shifting.

of course if your driving up into boost and not shifting earlier enough for fuel economy, you will naturally be getting much worse mpg.

essentially forced induction broadens the possibilities for FE

[DRW]

Originally Posted by thisisntjared

a turbo is alway spooling except when the wastegate opens and air is not sent to the turbo.

Could you clarify this statement? Something doesn't seem quite right.

[thisisntjared]

Originally Posted by DRW

Could you clarify this statement? Something doesn't seem quite right.

ah my bad

when a motor is running the turbo is always spooling except when the wastegate opens(and of course when there is 0 throttle).

when the wastegate opens, not all the air is not sent to the turbo because the turbo is fully spooled. what i mean by this is that all exhaust gases are pushing the turbo until it is either fully spooled, or the exhaust gases cannot cause it to accelerate any more. in the later case, where the wastegate is still shut, the motor is still using the exhaust gases to help the motor breathe. its still not positive pressure but yea, hal pretty much already said this.

[GasSavers_Hal9000]

What he means is that the turbo impellers are always spinning and producing some level of positive pressure in the intake system. As long as exhaust if flowing through the turbo housing, the impellers just about have to be turning.

When people talk about a turbo "spooling up" they're describing one of several things because the term has too much of a catchall meaning. The most important meaning for this discussion is when the turbo comes into it's efficient operating range and begins producing large enough quantities of pressure to affect performance... But even when a turbo isn't spooled up (like when cruising on the highway for example) it's still idling so to speak. When this is happening, the turbo only produces a small amount of pressure. That won't affect performance substantially, but what it does do is alleviate the need to the engine to suck air into the engine on it's own (like a vacuum pump). The turbo pushes the air in instead. This can make a difference in the VE and FE of the engine.

[theholycow]

Originally Posted by Hal9000

But even when a turbo isn't spooled up (like when cruising on the highway for example) it's still idling so to speak. When this is happening, the turbo only produces a small amount of pressure. That won't affect performance substantially, but what it does do is alleviate the need to the engine to suck air into the engine on it's own (like a vacuum pump). The turbo pushes the air in instead. This can make a difference in the VE and FE of the engine.

I don't understand how this could help FE. The energy isn't free; it's not recovered waste energy, the engine has to push the exhaust out to turn the turbo, right?