do turbos kill mileage? bypass for mpg?

[NickelB NL]

Originally Posted by euromodder

Was outweighed.
The latest diesels have become very complex machines.
As a result they also have more issues.


Things have changed a bit since - especially with European diesels

Dunno if you'll ever have the chance to drive say a 2011 or 2012 BMW 3L 6-in-line "330" diesel, but that's a good example of what modern diesels can be.

Thet 3.0 td in the M550D does 385hp. And then you can even gain 25 to 30% by chiptuning.

[stillsearching]

Originally Posted by Diesel_Dave

No, I can't...but I can show you two with improved FE. The Chevy Cruze & the Dodge Dart. It comes with the option of 2 different engines: a 1.8L naturally aspirated engine and a 1.4L turbocharged engine. Both have exactly the same horsepower rating according to Chevy (138 hp):
2012 Chevy Cruze | Powertrain & Chassis | Chevrolet

fueleconomy.gov rates the NA engine at 22 mpg city & 35 highway = 27 mpg combined. The turbocharged engine is rated at 26 mpg city & 38 highway = 30 mpg combined--a 10% improvement in FE.
Compare Side-by-Side

The Dodge Dart is very similar--two engines with the same exact 160 hp power rating: 1.4L turbo & 2.0 L NA (2013 Dodge Dart | All New compact that's everything but compact | Dodge). The 1.4L turbo beats the 2.0L NA engine by 10% (Compare Side-by-Side).




Research the EPA test procedure--there's a whole lot more to it than just driving around easily in a loop.

Well thats why i'm assuming the saab LPT tech is worth emulating elsewhere... i'm just wondering if 0psi wastegate options or total bypasses were worth pursuing too.

For EPA the city is more of a struggle, but isnt the highway a steady state 65mph or 70mph now?

[oil pan 4]

You could get an over sized ricer blow off valve and use it to bypass some of the intake restriction. This is what I am doing to reduce turbo lag.
Another option might be to do an external WG in addition to the built in one.

[Diesel_Dave]

Originally Posted by stillsearching

For EPA the city is more of a struggle, but isnt the highway a steady state 65mph or 70mph now?

It's a transient test and the average speed is 48.3 mph. Here are the details:
Emission Test Cycles: EPA Highway Fuel Economy Cycle

[Big Dave]

Turbos have little effect on diesels because diesels operate at an "excess air" condition. The combustion event occurs on the surface of the fuel droplets where in a gas engine the fuel/air mixture is (more or less) uniform through the whole combustion chamber.

Otto-cyle engines are married to an air:fuel ratio. Stuff more air in and you have to add more fuel. If you don't have enough load, you'll have to throttle down and that reduces thermodynamic efficiency.

This is why direct-injection is exciting. It generates a local sufficient mixture in the combustion chamber without the thermal losses of a pre-combustion chamber. The "rich" area around the centerline of the injection pattern "blowtorches" the leaner outlying areas into combustion.

Unless you have direct injection or a pre-combustion chamber (Honda CVCC) increased vol eff means increased fuel flow.

[Firestarter]

Sorry for resurrecting this old thread. But there is so much misinformation.

Cars don't come with blow off valves. They come with bypass valves to recirculated compressed inlet air to intake to prevent compressor surge. Diesels don't have throttles so this is very difficult to do.

Turbos raise engine efficiency. The manufacturer needs to do gearing and other changes to take advantage of this. This is why all BMW's are turbo'd now.

The wastegate is to keep turbine speeds and boost in check.

On cars like the wrx. They lower compression to increase engine longevity which lowers mpg. They could keep high compression but there would be no boost or need race gas.

[oil pan 4]

Originally Posted by Firestarter

They could keep high compression but there would be no boost or need race gas.

Or they could build a diesel engine.

[serialk11r]

Originally Posted by Firestarter

Turbos raise engine efficiency. The manufacturer needs to do gearing and other changes to take advantage of this. This is why all BMW's are turbo'd now.

This is pretty iffy. The 335 and the 328 are the same engine pretty much but the 335 has lower compression and twin turbo. The 335 has poorer fuel economy. Fuel economy goes up if you decrease the engine size and then turbo to make up for the power loss, because it decreases the friction you have to deal with.

BMW engines are all Valvetronic equipped except the high performance Sxx variants. This means off load boost actually can help thermodynamic efficiency.

As people have already figured out with the best BSFC at 80% load rule, increasing power production stops increasing efficiency before the engine hits full load. A usual throttle plate controlled engine might see a slight improvement in thermodynamic efficiency from a turbo at an operating point where the throttle is nearly fully open, but the valve timing is set up so that the engine is not at maximum torque output.

[Firestarter]

Sema show mpg award went to sts turbo for having highest percentage mpg increase

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

As for the diesel ... not everyone wants a heavy diesel drive train. I love diesels, had a 750rwhp cummins. That averages 21-25 mpg (25 when stock 21 modded)

Originally Posted by serialk11r

This is pretty iffy. The 335 and the 328 are the same engine pretty much but the 335 has lower compression and twin turbo. The 335 has poorer fuel economy. Fuel economy goes up if you decrease the engine size and then turbo to make up for the power loss, because it decreases the friction you have to deal with.

BMW engines are all Valvetronic equipped except the high performance Sxx variants. This means off load boost actually can help thermodynamic efficiency.

As people have already figured out with the best BSFC at 80% load rule, increasing power production stops increasing efficiency before the engine hits full load. A usual throttle plate controlled engine might see a slight improvement in thermodynamic efficiency from a turbo at an operating point where the throttle is nearly fully open, but the valve timing is set up so that the engine is not at maximum torque output.

[Firestarter]

Also, iirc, turbos help with exhaust scavenging and help with reducing pumping loss from intake stroke. https://sites.google.com/site/shooti...ine-efficiency

Also have to look at the technology behind it.ball bearing takes less friction than journal. Comp wheel and turbine shape. Exhaust housing size etc. Just slapping one on isnt going to give you mpg.

Forgive my android writting

Originally Posted by serialk11r

This is pretty iffy. The 335 and the 328 are the same engine pretty much but the 335 has lower compression and twin turbo. The 335 has poorer fuel economy. Fuel economy goes up if you decrease the engine size and then turbo to make up for the power loss, because it decreases the friction you have to deal with.

BMW engines are all Valvetronic equipped except the high performance Sxx variants. This means off load boost actually can help thermodynamic efficiency.

As people have already figured out with the best BSFC at 80% load rule, increasing power production stops increasing efficiency before the engine hits full load. A usual throttle plate controlled engine might see a slight improvement in thermodynamic efficiency from a turbo at an operating point where the throttle is nearly fully open, but the valve timing is set up so that the engine is not at maximum torque output.