Will turbo increase gas mileage?

[LouisMartel]

What are the pros and cons of adding a turbo to 3800 motor? (excuse me not a true car guy) Just wondering if it will better my gas mileage.

[haro1225]

Pros, moar power, nicer exhaust note, faster car, turbo noises, boost.
Cons, it will make fuel mileage worse, takes more fuel to make boost. It’s quite a bit of work if you’re doing it yourself, will be expensive if you pay someone to do it, then you’ll need someone to tune it, and your transmission might not like you very much anymore. And who turbos a bonneville anyway? Sheesh. (Just kidding).

All that being said, it’s a good way to go faster and surprise unsuspecting ricers. And you should totally do it. If I still had a bonneville I would totally slap a turbske on it while drinking Mountain Dew.

[Jfridge92]

If I still had a bonneville I would totally slap a turbske on it while drinking Mountain Dew.

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[96 SSEi]

HOW you use your right foot will affect it most!

[RJolly87]

So, if a person is not on boost at cruise, it would not use less fuel than a supercharged engine that has the added drag of the supercharger on it?

[96 SSEi]

I have been running for about 400 klm with charger belt off and I only see 1mpg difference at most - I believe its all in the driving style: without the boost, you tend to drive like granny from a stop.

[bs009]

The supercharger does of course have a parasitic draw, removing the belt should help free the engine up during low load conditions, but a stationary rotor pack makes for a pretty poor intake manifold design.
One of the biggest reasons the NA 3800 motors get such good gas mileage is because they have a lot higher of a compression ratio than the supercharged motors.



For a turbo though, as mentioned before it's more likely that you'd use more fuel with a turbo and there's a couple of other main reasons I can think of as to why you would.

1. To make more power your motor will require more fuel. Basically air+fuel = power, so to make more power you'll need more air and fuel. the turbo supplies the air part of the equation.

2. Any time you are making boost pressure the motor needs to see a lower Air/Fuel ratio to help prevent knock. So not only are you using more fuel to make more power, you also need to push the fuel in disproportionately to keep the motor from being damaged.

3. Also a lot of people talk about turbos as giving you free power without any restriction or loss at all and I think that's the biggest misconception with turbos these days. with the turbo there the engine needs to work against it to get it spinning to produce boost pressure so there is some loss there that no one likes to talk about. It's not as significant as the draw from a supercharger, but it still exists.
Because of this I think it's likely that given two of the exact same motor (one with a turbo and one without) while cruising the motor without the turbo would get slightly better mileage than the turbo motor, though it would be slower in a race.

I think the only reason why turbos have a reputation these days as being more fuel efficient is because they allow manufacturers to use smaller motors that are more fuel efficient during cruising when the turbo isn't making pressure. The turbos can then allow those small motors to produce the same amount of power as a much larger motor once they do produce boost pressure into the intake manifold. They will use more fuel at a specific power level though than a naturally aspirated motor at that same power level though because of the difference in Air/Fuel ratio.

[MattStrike]

Combustion engines are only 30% efficient to begin with, anything that can harness some of that 70% wasted heat energy improves the overall efficiency of the 'system'. It's easy to forget that the turbo is powered from wasted heat energy.

Your efforts are better directed at increasing volumetric efficiency (ie, intake and cam/valve work), and making custom long-tube headers for scavenging. Turbos are easy to make power with, but there are a lot of other little variables that need to change that most likely mean you won't see an increase in mpg with just a turbo.