Turbo Boost and FE

[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)

[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).

[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.

[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.

[dkjones96]

At part throttle where it is idling the turbo isn't pressing any air into the engine. You've still got manifold vacuum like any other engine at part throttle for it to work against. By the time you've opened the throttle enough that the throttle plate isn't an issue that turbo(if sized properly) should be well into creating more than just atmospheric levels of boost.

As for the TC fix, my TCC Experiment thread in the Experiment forum describes what i've come up with. It isn't installed yet but should be this weekend.

[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_Gollum]

If you have an electronically controlled wastegate that you can program, you can program it to be wide open under cruise conditions, but this will cause severe vacuum, and might put stress on the turbo's bearings. I'm not sure it's exactly optimal.

In my experience turbos DO seem to get slightly better gas mileage than the same NA engines. I have yet to actually figure out a testable, or believable reason why. But it's not much in highway conditions, maybe 2-5%. One of the large factors in alot of engines, is that turbo version of motors run lower compression, allowing for a leaner cruise, but also turbo engines usually have different cam profiles, which affects everything.

[thisisntjared]

Originally Posted by Gollum

If you have an electronically controlled wastegate that you can program, you can program it to be wide open under cruise conditions, but this will cause severe vacuum, and might put stress on the turbo's bearings. I'm not sure it's exactly optimal.

why would you ever want to do that?