Turbo for fuel efficiency?

[acchonda]

Ok so I have been doing some reading and such for a bit now and have a basic understanding of the turbo and all that goes into it (total respect for those that have done it, and done it right!) I have run across a volvo 2.4L with a turbo and was wondering if anyone had used this turbo/a turbo to help boost fuel economy. I know that the VW Jetta with the turbo gets better MPG that the regular 2.5 liter engine. I was thinking of maybe 9 psi on a regular basis would help with fuel and make a little more power for when I felt the urge for a little umph.
I know this should go in the force induction section but I still don't have enough posts to get out of the beginner section lol (I do a lot of searching and less question asking) If someone wants to move it feel free. Thanks for the input.

[clemsoncb7]

Okay, well first of all, you can use a volvo turbo, but you will most likely need a custom manifold for it since the flange is a very small t3. I would suggest just buying the parts as a kit, it makes it much easier, I've done a couple turbo setups, and they are difficult to piece together correctly, and if you are looking for low boost, its better just to trust a kit. I shot for 500whp with my last turbo setup and boy does it get expensive... Secondly, the reason that the turbo'd jetta gets better mpg than the 2.5l is most likely because its very very low boost and .7l less displacement...
Max

[hondawonderboy]

Turbo for fuel efficiency? Yes!

Yes! It depends heavily on how the car is driven. usually a nice small turbo can be efficient. However you have to realize- hp=fuel consumption- you cannot just create matter or energy from nothing.

[NAiL05]

Yes turbos can increase gas mileage depending on how you drive, As mentioned as small turbo can benefit for you. The reason is the turbo can force more air into the combustion chamber allowing it to take up all the volume and burn. This goes for most FI applications. But yea it can give you better or worse depending on driving style and tune. Few good examples are the mazdaspeed cars that are turbocharged or the newer acura rdx or whatever with the turbo motor.

[Danronian]

The mazdaspeed protege is a bad example for this. My friend has a bone-stock one and it gets crap gas mileage (low 20s are its best) for a 4 cylinder.

Many turbos on factory cars are meant to sometimes avoid the fact that the car should have a bigger motor (i.e. a factory turbo'd 4cylinder probe instead of a v6 powered one). If this is not the case it is used for performance only. Since your accord has enough power with the motor it has, you will probably be making the motor less efficient by giving the extra fuel it needs for the turbo. Sure you could tune it to be more efficient than factory, but that would not be easy and I doubt your mileage would be better than stock.

[HondaB18]

Throttle position plays a major role. Stay out of boost and fuel consumption should be the same but when your boosting fuel consumption would increase.

[johnson]

i have my dsms and they are not fuel efficient at all!!! about 12-15 mpg..... more air = more fuel.... well thats how it is for my dsms....

[deevergote]

If you stay out of boost, you can get decent fuel economy... depending on tuning. However, that really has nothing to do with the turbo, since the turbo IS boost.

The 2.0L turbo Jettas have a 2.0L engine. The 2.5L NA Jettas have a 2.5L engine. Generally, the larger engine will use more fuel. If you pin the throttle in the turbo Jetta, you won't get good fuel economy at all!

Out of boost, you're running a small-displacement NA engine. Tuned properly, you'll get the fuel economy of a small-displacement NA engine. As soon as you see boost, the ECU dumps more fuel in to compensate for the denser intake charges. More air = more fuel is exactly right. If that didn't happen, you'd run too lean and blow your motor up!

[TheNextEpisode]

Out of boost, you're running a small-displacement NA engine. Tuned properly, you'll get the fuel economy of a small-displacement NA engine. As soon as you see boost, the ECU dumps more fuel in to compensate for the denser intake charges. More air = more fuel is exactly right. If that didn't happen, you'd run too lean and blow your motor up!

Bringing this back from the dead.

So with something like a big 16g that spools north of 3k rpm, it might be possible to squeeze out some semi-decent mpg, so long as the putt-putting remains at low rpms, correct?

I suppose the slight parasitic loss from the turbo, when not spooling, might lower power compared to stock, though.

Hmm, with a slightly built block and a big 16g or something similar, it might be possible to run get half-decent commuter mpg while simultaneously having extra horsepower on tap in the higher rpm-range.

How much damage would the non-spooling turbo provide during cruising rpms in the 2800 rpm range? Its a pretty substantial source of heat, I guess.

[d112crzy]

I suppose the slight parasitic loss from the turbo, when not spooling, might lower power compared to stock, though.

You are correct here. You lose volumetric efficiency with turbo's USUALLY. How much has to do with the size of the turbo and design of the manifold.

You CAN have great gas mileage with or without turbo. The parts of the tables out of boost are the same as any other NA engine.

[TheNextEpisode]

Got it, thanks for the confirmation.

[deevergote]

There's no parasitic loss involved with a turbo. Parasitic loss only applies when something actually takes engine power, such as a supercharger.

However, the turbo does provide a significant restriction in the exhaust stream. That can have an effect.


However, you are correct in the fact that a larger, later-spooling turbo will be much easier to keep out of boost.



When MRX went to the big meet in Nashville a few years back, he got 32mpg. He kept out of boost, and his ECU was tuned well. That's better gas mileage than most people with beat-ass CB7s get in stock form!

[bcjammerx]

I have seen many people say they can and have gotten better mpg with boost setup

but what y'all are saying is that the extra mpg prolly came from the ecu tuning? (and staying out of boost)

What about a small amount of boost coupled with little to no extra fuel being added, not enough to cause burnt valves mind you, but enough boost to gain a little extra power from the added O2 (someone said somewhere that our Honda's tend to run rich stock) won't make the mpg go down a hair...if staying out of mid to high boost?

I was searching and I kept seeing folks with boost applications talking about getting better mpg when they weren't romping on it...never got a good expl. as to why, but I'm pretty sure that while they were not experiencing massive hp gains, the way they were running slight boost gave them increased fuel economy.

[TheNextEpisode]

There's no parasitic loss involved with a turbo. Parasitic loss only applies when something actually takes engine power, such as a supercharger.

However, the turbo does provide a significant restriction in the exhaust stream. That can have an effect.

Oh haha, yeah sorry, that's what I had in mind when I phrased it poorly.


@bcjammerx, Running lean certainly will help with gas mileage, but doing that with boost alone is pretty risky. A proper ecu tune will do exactly what you're mentioning; the engine will runner leaner, but it will run leaner under the guidance of air/fuel maps that are made specifically with proper a/f ratios in mind, rather than just by introducing a little more air .

I'm pretty sure that the increased mpg that people were experiencing with the boosted applications while not spooling is a direct result from leaner tunes and/or rebuilt blocks. A 15-18 year old engine certainly won't get the mileage of a new engine, or even a non-spooling rebuilt engine.

edit: @ deev, good to hear, though, about MRX's 32 mpg. Hell, I can't squeeze anything better than 22 mpg out of my f22. I bet his boosted f22 was in much better shape than mine is currently.

[evil_demon_01]

I have seen many people say they can and have gotten better mpg with boost setup

but what y'all are saying is that the extra mpg prolly came from the ecu tuning? (and staying out of boost)

What about a small amount of boost coupled with little to no extra fuel being added, not enough to cause burnt valves mind you, but enough boost to gain a little extra power from the added O2 (someone said somewhere that our Honda's tend to run rich stock) won't make the mpg go down a hair...if staying out of mid to high boost?

I was searching and I kept seeing folks with boost applications talking about getting better mpg when they weren't romping on it...never got a good expl. as to why, but I'm pretty sure that while they were not experiencing massive hp gains, the way they were running slight boost gave them increased fuel economy.

I cant see a turbo fitted and running at, say, 2psi making an increase in fuel economy - Turbos make power, not fuel efficiency.
Tuning maps work off a rpm/load based table, so if your not in boost nothing changes - Ie if your at 3000rpm's, and 17in/hg vac, the computer will put in a set amount of fuel. It doesn't matter if you have a turbo, Cai, or full exhaust - The value is set (unless you tune it, which is where you can change the values)
If you were to try fitting a turbo and running VERY low boost, it would only make a difference when the turbo was actually boosting - ie 3/4 throttle or more, so your wasting fuel to start with rather than just cruising.
At the end of the day, better mpg comes from tuning