do turbos kill mileage? bypass for mpg?

[JackMcCornack]

Originally Posted by Firestarter

As for the diesel ... not everyone wants a heavy diesel drive train.

One benefit of turbos is for a given amount of maximum horsepower potential, a turbo engine (whether diesel or spark) is lighter than a na engine. Thus everything from the engine mounts down to the tires can be lighter, and the complete system may end up with greater fuel efficiency even if the engine might be less efficient.

Also, regarding the additional exhaust backpressure of a turbo reducing efficiency, that is balanced to some extent by the reduction in exhaust noise. Turbo engines can get away with lesser mufflers than na engines for a given amplitude of exhaust noise. My own miniature turbo diesel sports car (32 hp Kubota) uses the turbo as its only muffler and it's never had a noise complaint (people assume it has a conventional muffler).

[Firestarter]

Originally Posted by JackMcCornack

One benefit of turbos is for a given amount of maximum horsepower potential, a turbo engine (whether diesel or spark) is lighter than a na engine. Thus everything from the engine mounts down to the tires can be lighter, and the complete system may end up with greater fuel efficiency even if the engine might be less efficient.

Also, regarding the additional exhaust backpressure of a turbo reducing efficiency, that is balanced to some extent by the reduction in exhaust noise. Turbo engines can get away with lesser mufflers than na engines for a given amplitude of exhaust noise. My own miniature turbo diesel sports car (32 hp Kubota) uses the turbo as its only muffler and it's never had a noise complaint (people assume it has a conventional muffler).

I ran my dodge strait pipe and there wasn't much of that. Exited right after front tire on the side.

A turbo setup really needs to be setup correctly otherwise it can lower efficiency as well.

But man does a s400 sound like a jetliner on takeoff when it lights under a s300. But yeah a turbo counts as a muffler in a lot of states cause the turbine does a marvelous job of breaking up sound.

[serialk11r]

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Originally Posted by Firestarter

Cams,timing, comp ratio,Afr all play into it.and all need to be adjusted accordingly to a high performance turbo motor.

BMW also switched over to a turbo 2.0l over the na n54 3.0 i6. And said the new M's will be turbocharged cause it raises efficiency which means lower emissions and higher mpg

I think you don't understand what I'm saying. A turbo does not usually increase the efficiency of the engine, if you're lucky under certain heavy load situations it will help a tiny bit. If you reduce the engine size and then turbo it, you are reducing engine efficiency most likely but the reduced engine size allows one to run the engine at higher load and thus better overall efficiency.

The biggest 2 distinctions that need to be made when talking about fuel efficiency and turbos are 1. throttle plate or fancy intake valve control system 2. electronic wastegate/bypass or not.

With a throttle plate, increasing part load efficiency is a lost cause. As long as the throttle is partially closed the turbo can't do anything because it can only blow off the pressure it builds. With a variable duration and lift system the turbo can build boost even under part load and increase efficiency because the turbo is able to "recycle" a little bit of energy from the exhaust stream (more precisely, it is the sound/shock waves/pulses that give you "free" energy).

Then there's the question of bypassing the turbine under part load, which should be done whenever the turbine efficiency drops past some point. The average turbo setup has a spring actuated wastegate that cannot do anything about this.

Air/fuel ratio and timing is going to depend on temperature and knock resistance. A relatively big cam along with turbo can potentially see higher efficiency at near maximum load, if everything is set up correctly.

[oil pan 4]

Originally Posted by serialk11r

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A turbo does not usually increase the efficiency of the engine, if you're lucky under certain heavy load situations it will help a tiny bit. If you reduce the engine size and then turbo it, you are reducing engine efficiency most likely but the reduced engine size allows one to run the engine at higher load and thus better overall efficiency.

It looks like I have picked up at least 3mpg after slapping the turbo on on my 395ci engine.
Then when I hook up the rammed air intake thats another 4% to 10% increase in FE (diesel_dave is reporting just over 4%, when I installed ram air/cold air on my non-turbo diesel setup back in 2006 it netted me closer to 10%).
I'm also not running an intercooler at the moment. No one has any rock solid numbers on hot boost versus intercooled boost but it looks like intercooling is good for at least another 5%.

Originally Posted by Firestarter

a turbo counts as a muffler in a lot of states cause the turbine does a marvelous job of breaking up sound.

This is true. I run a 3 inch down pipe into a 4 inch straight pipe and at idle its about the same noise level as when it was N/A with duel pipes and mufflers. Now its just got more of a turbo dragster sound to it.
It only starts to get loud above 9psi of boost.
In normal driving it doens't build more than 3psi.

[Firestarter]

Bro.chill.

Turbos do add mpg. Several car makers agree. 80s oil crisis saw tons of turbo vehicles.

Sts turbo has empirical evidence that adding nothing but their turbo and programming yielded the most mpg increase over any after market setup at the sema show.

They help with scavenging. Increase air density and makes the motor breathe easier when off boost.

Throttle butterfly has very little to do with overall engine efficiency. Its there to retard airflow. The maf or map sensor will tell ecu to inject fuel based off airflow. It will enrichen based off load and temperatures to prevent knock. Valvetronic motors are wide open throttle when warmed and use valve timing to retard engine performance. Reduction in vacuum in the intake tract in front of the throttle will allow the engine to breathe easier.

Big reason you don't see mpg increases in the 335 vs 328 is that they were going for performance. I bet if you drove the 335 in 6th gear everywhere it would yield more mpg over the 328 which lacks the low end torque that the 335i's tiny 1500rpm turbo delivers.

In any respect.turbos get more efficient with load and complimentary gearing would propel it much better. And give higher mpg.

I've also never heard of a company bypassing the turbine for more mpg. In off boost situations the hot side aids in exhaust scavenging and why you'd chose to negate that is beyond me. They are basically operating off wasted glass energy until they need the drive pressure to add power (boost)

All the best mpg cars out there are turbod for a reason. Bit it doesn't go without saying its not automatic. It must be done in a complimentary fashion otherwise your lowering mpg.

And since engine friction is non linear, rather exponential in regards to rpm increase. Using less rpm generally means better mpg. Turbos help lower operating rpm. Too much load will obviously be enrichened .

I don't really think you quite understand how turbochargers work fully.

Originally Posted by serialk11r

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I think you don't understand what I'm saying. A turbo does not usually increase the efficiency of the engine, if you're lucky under certain heavy load situations it will help a tiny bit. If you reduce the engine size and then turbo it, you are reducing engine efficiency most likely but the reduced engine size allows one to run the engine at higher load and thus better overall efficiency.

The biggest 2 distinctions that need to be made when talking about fuel efficiency and turbos are 1. throttle plate or fancy intake valve control system 2. electronic wastegate/bypass or not.

With a throttle plate, increasing part load efficiency is a lost cause. As long as the throttle is partially closed the turbo can't do anything because it can only blow off the pressure it builds. With a variable duration and lift system the turbo can build boost even under part load and increase efficiency because the turbo is able to "recycle" a little bit of energy from the exhaust stream (more precisely, it is the sound/shock waves/pulses that give you "free" energy).

Then there's the question of bypassing the turbine under part load, which should be done whenever the turbine efficiency drops past some point. The average turbo setup has a spring actuated wastegate that cannot do anything about this.

Air/fuel ratio and timing is going to depend on temperature and knock resistance. A relatively big cam along with turbo can potentially see higher efficiency at near maximum load, if everything is set up correctly.

[Phantom]

If a turbo will make boost depends on three things (assuming the engine is running).
1. The size of the turbo
2. The amount of exhaust gas moving
3. That the CFM being moved by the turbo is anything greater than the amount of air being consumed by the engine Naturally Aspirated.

So if the turbo being used is small it could add boost at 1000rpm even with the throttle at 1% open. It could probably do that to about 3000rpm before one of two things happen it is spinning to fast and could kill itself using a turbo for a 1.9l 4cylinder on a 6L V8. Or using the same turbo/engine set up it could be fine spinning that fast but at 3000rpm could be the point that the CFM consumed by the engine is equal to the CFM pushed by the turbo resulting in 0 boost.

If you keep the RPMs low a set up with a small turbo could work well to improve MPG. The increase would be from being able to run at a lower throttle position in a higher gear where it would have lugged the engine if it produced less power. AKA add a turbo and much taller gearing.

If you wanted to bypass the turbo get an electronic exhaust cutout QTP » Electric Exhaust Cutouts that will allow you to divert exhaust remotely and you could set up a controller to do it for you.


As for the comparison of one engine being NA and the same one being Turbo from the factory and the turbo not having better MPG most of the time there are a few reasons for it. On most of the cars the following things are different between the two (not all things will be changed but some); Pistons are different compression, a cam for turbo performance, gear ratio, VMC (vehicle motor control) programming (enrichment, timing shift points, torque converter lock speed,...), and they are built for PERFORMANCE HP/TQ.

[Firestarter]

For the most part that's what I've been saying

But even off boost turbos help a little bit as well.


So many variables to use real world comparisons between different motors and different turbos to be real evidence.

That's why I like sts cause they use the exact same vehicle just with the addition of the turbo system

Originally Posted by Phantom

If a turbo will make boost depends on three things (assuming the engine is running).
1. The size of the turbo
2. The amount of exhaust gas moving
3. That the CFM being moved by the turbo is anything greater than the amount of air being consumed by the engine Naturally Aspirated.

So if the turbo being used is small it could add boost at 1000rpm even with the throttle at 1% open. It could probably do that to about 3000rpm before one of two things happen it is spinning to fast and could kill itself using a turbo for a 1.9l 4cylinder on a 6L V8. Or using the same turbo/engine set up it could be fine spinning that fast but at 3000rpm could be the point that the CFM consumed by the engine is equal to the CFM pushed by the turbo resulting in 0 boost.

If you keep the RPMs low a set up with a small turbo could work well to improve MPG. The increase would be from being able to run at a lower throttle position in a higher gear where it would have lugged the engine if it produced less power. AKA add a turbo and much taller gearing.

If you wanted to bypass the turbo get an electronic exhaust cutout QTP » Electric Exhaust Cutouts that will allow you to divert exhaust remotely and you could set up a controller to do it for you.


As for the comparison of one engine being NA and the same one being Turbo from the factory and the turbo not having better MPG most of the time there are a few reasons for it. On most of the cars the following things are different between the two (not all things will be changed but some); Pistons are different compression, a cam for turbo performance, gear ratio, VMC (vehicle motor control) programming (enrichment, timing shift points, torque converter lock speed,...), and they are built for PERFORMANCE HP/TQ.

[serialk11r]

Originally Posted by Firestarter

I've also never heard of a company bypassing the turbine for more mpg. In off boost situations the hot side aids in exhaust scavenging and why you'd chose to negate that is beyond me. They are basically operating off wasted glass energy until they need the drive pressure to add power (boost)
...
I don't really think you quite understand how turbochargers work fully.

All I have to say to your post is, BMW and VW use electronically actuated wastegates to bypass the turbine at part load.

[Firestarter]

Originally Posted by serialk11r

All I have to say to your post is, BMW and VW use electronically actuated wastegates to bypass the turbine at part load.

Again. I don't think you understand how a turbo really works. A waste gate doesn't bypass the turbine. It bleeds off exhaust pressure to control compressor speed. Will it divert a little exhaust gases, of course. But it doesn't bypass the turbine. Just prevents drive pressure to build up which is what generates the "boost".

Sounds like they do this to make the exhaust more free flowing and not to bypass the turbo. If they did fully bypass the turbo it would become a massive intake restriction.

Variable geometry turbine turbochargers do this much better.

[oil pan 4]

Originally Posted by Firestarter

That's why I like sts cause they use the exact same vehicle just with the addition of the turbo system

I didn't need an STS system to add my turbo.
Since the turbocharger is a heat engine why would I want to remove it from its heat source?

Originally Posted by Firestarter

Variable geometry turbine turbochargers do this much better.

That is what I have and yes they do it better.