Supercharger vs Turbo MPG ?

[LoCo]

Hey everyone.

**SKIP THIS PART IF NOT INTERESTED IN BACKGROUND OF QUESTION**
I think the phase of a tuner car like any other here is reaching the more more more HP part, where people will start building motors when more and more companies offer engine build parts (pistons, rods, bearings, cranks, block sleeves etc) and stupidity will rule for a while with "who's got 800hp", then slowly - like again any other car, there will be a select few, who will try to maximize the efficient output of a tuner car. Getting the best of all worlds out of it in terms of power delivery, driveability, mileage and comfort.

I'm that guy too.

**TLDR

Now after seeing successful boost applications taking place more and more, whats the more functional one? For peak power - obviously turbo as always, but overall?

How does the supercharger affect mileage when driving around 80-90mph cruise (yes I'm from Europe, where that is normal and you don't get arrested for driving to work at 110mph). I know turbo won't affect it much off boost or can even improve it at times. Does the SC do the same? Which would be a more desirable product for a daily driven car that competes in auto-x and trackdays often for you?


*Answers we do not need in this topic as they are already known:
- under boost and WOT, the MPG goes to hell, we know that
- "if you have a lead foot" - read previous answer
- "superchargers spool earlier and turbos later but more peak power"
- SCFTW!!! // TURBOFTWOMG!$)!

I'm looking to start a discussion that might aid someone that would be on the verge of choosing one or the other for an overall performing car, hence any info provided should be argumented. And keep in mind that the main goal of this thread is still comparing the MPG of the SC vs Turbo while justifying what each one does.

Let's get the ball rolling?

[sw20kosh]

Neither. Both will decrease mpg. Will you notice it in a DD environment? Probably not.

You don't buy a turbo or supercharger kit if you are worried about maxing mpg.

[Turbowned]

Depends entirely on your driving habits and the type of turbo or supercharger used. In other words, moar gas pedal and moar boost equals worse MPG.

[Mild2Wild]

The form of forced induction that is making more power at your cruising rpm will get worse mpg.

[FR-S Matt]

I've seen Turbos actually increase MPG in cars that are cruising at ~70 mph with low boost at lower rpms. I think this is what the OP is aiming for. If there was any MPG to gain, I think a turbo would do it since it just feeds off of the exhaust compared to the SC which will always require extra work of the engine.

Much of a difference? Probably not. At 80-90 mph, you won't even get good gas mileage NA.

If I could pick, Turbo would be the route to go for a chance at better gas mileage in the 60-70 mph range cruising on the highway. There's also a difference between boost levels and turbos on these cars so it will depend on the setup and tuning done.

[diss7]

Power means more fuel, means less MPG. But you're talking on the whole, not just WOT. Considering the supercharger is always taking effort from the engine to turn it, this will reduce cruise MPG. A turbo doesn't feed from off the engine, it feeds off exhaust gas.

I agree with FR-S Matt's comments above.

[TyperRspec789]

I got 26mpg on my 93octane 8psi setup. With "normal" driving, which means 10mph above speed limits and a few ride alongs to have forum members experience the ride. Again, it all depends on your driving habits.

e85 on the other hand... Let's just put it this way- I have 2-4 five gallon jugs in the trunk when I drive out of town.

[Celica00]

I feel like this thread will erupt into a war based on opinion and personal experience and not facts.

[jamesm]

All else equal, the turbo wins. With a supercharger, boost maps to rpm. The engine spins a given speed, it makes a certain amount of boost. With PD superchargers, it should be the same regardless of rpm, just always making boost. So, you get better power on tip in than with a turbo, because the boost is right there. No lag. Great feeling, but you're always boosting, burning the extra fuel necessary.

With a turbo, boost is load dependent. If you sit in neutral and rev the car, you will build little if any boost. Being that highway driving usually involves very little load, it's quite easy to avoid boosting at all. You're driving an NA car, for all intents and purposes. Win.

[A5D5TRYR]

Originally Posted by jamesm

All else equal, the turbo wins. With a supercharger, boost maps to rpm. The engine spins a given speed, it makes a certain amount of boost. With PD superchargers, it should be the same regardless of rpm, just always making boost. So, you get better power on tip in than with a turbo, because the boost is right there. No lag. Great feeling, but you're always boosting, burning the extra fuel necessary.

With a turbo, boost is load dependent. If you sit in neutral and rev the car, you will build little if any boost. Being that highway driving usually involves very little load, it's quite easy to avoid boosting at all. You're driving an NA car, for all intents and purposes. Win.

Just to clarify, although the compressor spins with RPM for an SC, it doesn't burn the same amount of fuel as WOT. It would however have the load of compressing the air and I have a feeling that is what you mean. But beyond the load of the compressor it wouldn't burn any additional gas over being NA.

Like others have said, for most applications I think a turbo will result in better cruising mileage. However, if you're looking to autocross or take it to the track the difference in cruising mileage between the two probably isn't going to be enough to override your desire for how you want the car to drive when you're driving on the track. Mind you, I think properly set up either one is going to be a blast.

[Adeets]

Neither, the only reason people are seeing an increase in mpg with a turbo is the tune that comes with it. If your looking for MPG the tune is what matters, or you can coat your engine with ceramic and that will also increase your HP and MPG, because its keeping heat where it should be and keeping the areas around it cooler... Btw heat is energy being zapped away from your engine.

So best MPG = NA tune+ ceramic coatings.

Turbos do not increase mpg, company's using undersized displacement engines on a car and adding a turbo to make up for the lack of displacement increases mpg.

[Adeets]

Btw @LoCo NA +tune should be a choice.

[nonicname]

there's not accurate way of answering this question, a lot depends on the amount of boost and/or how fast boost kicks in.
a tiny turbo that makes full boost at 2k rpm will burn more gas than a turbo that makes full boost at 4k rpm simply because you are more likely to always be around 2k rpm. there's a ton more scenarios.

if you care about hurting MPG don't add FI to the car.

[200hp/tonne]

All things equal, you mostly need the same power at the wheels to maintain the same speed. I.e. you will consume the same mass of air and same mass of fuel. In FI application, some device will be pushing air into the intake manifold through the throttle body, which ultimately decides mass of air entering the engine. So in FI compared to NA you will have less throttle pedal input for maintaining same speed. In SC, there will be a power draw from shaft to spin the SC and compress air while a TC would do that from exhaust energy so if to maintain 80 mph you need 20% pedal NA, you would need maybe 15% for SC and 10% for a TC application.

All this assumes that the fuel map air fuel ratio has not been tuned to be different than NA for cruising, which a good tuner would know.