Does a turbo have to work harder when towing?

[mjoekingz28]

Originally Posted By: Jetronic
the compressed air isn't free. The backpressure before the turbine is higher than the boost provided by the compressor. Increased backpressure = more pumping losses.



Thanks for stating that. They were getting a bit off track saying it was 'free'.

 

[turboseize]

Originally Posted By: HosteenJorje
More weight, more fuel consumption, more hot exhaust gasses going through the turbo. What do you think?


That is exactly what the engine was made for. Warm her up gently before demanding either boost or high rpm (or any combination thereof) and let her cool down afterwards before switching her off. That is all.

 

[roadrunner1]

Originally Posted By: mjoekingz28
Originally Posted By: Jetronic
the compressed air isn't free. The backpressure before the turbine is higher than the boost provided by the compressor. Increased backpressure = more pumping losses.



Thanks for stating that. They were getting a bit off track saying it was 'free'.


The compressed air is "free" as it takes waste (exhaust) and turns it into something beneficial (compressed air).

Turbochargers have been in use since the 1930's, they aren't some new fandangled device that someone just invented. Anytime one can take something that would otherwise be dumped, thrown away, or otherwise not used and take that energy and re-use it for something else is "free". An engine isn't "taxed" by adding a turbocharger in the exhaust as the exhaust would just exit the tailpipe anyways. The added fuel used is directly related to the person running the throttle, yes with added boost you would have more available horsepower which means more fuel, but you have more available horsepower because of the added boost.

 

[Quattro Pete]

Originally Posted By: roadrunner1
An engine isn't "taxed" by adding a turbocharger in the exhaust as the exhaust would just exit the tailpipe anyways.


http://www.thesaabsite.com/faqs/FAQ--tur...le).html?id=489

Quote:
One cause of the inefficiency comes from the fact that the power to spin the turbine is not free. Having a turbine in the exhaust flow increases the restriction in the exhaust. This means that on the exhaust stroke, the engine has to push against a higher back-pressure. This subtracts a little bit of power from the cylinders that are firing at the same time

 

[y_p_w]

Originally Posted By: roadrunner1
Originally Posted By: mjoekingz28
Originally Posted By: Jetronic
the compressed air isn't free. The backpressure before the turbine is higher than the boost provided by the compressor. Increased backpressure = more pumping losses.



Thanks for stating that. They were getting a bit off track saying it was 'free'.


The compressed air is "free" as it takes waste (exhaust) and turns it into something beneficial (compressed air).

Turbochargers have been in use since the 1930's, they aren't some new fandangled device that someone just invented. Anytime one can take something that would otherwise be dumped, thrown away, or otherwise not used and take that energy and re-use it for something else is "free". An engine isn't "taxed" by adding a turbocharger in the exhaust as the exhaust would just exit the tailpipe anyways. The added fuel used is directly related to the person running the throttle, yes with added boost you would have more available horsepower which means more fuel, but you have more available horsepower because of the added boost.

It's still putting a restriction on the exhaust, so it's not exactly free. It's not quite as free as waste heat being used by the heater core to heat the interior. But yeah, the exhaust has to go somewhere.

Turbochargers have been around before 1910, but the first ones were simply lab prototypes. The first practical turbochargers were used on aircraft engines during WWI, but General Electric made the first really successful turbos. They hired someone who was an expert in steam/gas turbines for power generation, and that translated pretty well to developing turbos. GE's expertise in turbines eventually translated to jet engines. This training film goes over some of the history, and also has the famous 1918 photo of GE taking their turbocharged engine for testing at the top of Pikes Peak.

 

[KrisZ]

Go for a run and while running, every time you exhale put a balloon in your mouth. You're breathing anyway so free energy right? You should not have any problems running the same distance and posting the same time.

 

[y_p_w]

Originally Posted By: KrisZ
Go for a run and while running, every time you exhale put a balloon in your mouth. You're breathing anyway so free energy right? You should not have any problems running the same distance and posting the same time.

Not sure how that exactly ties into how a turbocharger works, since that breathing in happens separately than breathing out. A turbo forms a continuous loop of exhaust feeding the turbine feeing the engine, etc. Also - human breathing is far different than engine breathing. In my experience, force feeding air into my lungs is kind of a self-defeating proposition. I tried drying my face with one of those hand driers, and I frankly had a difficult time breathing.

But yeah - having that restriction is going to cost something. It may cost a bit of the power generated by the engine, but it's certainly cheaper than the power taken by an engine-driven supercharger. That's a parasitic load on the engine, just like an alternator, A/C pump, water pump, or PS pump.

 

[Jetronic]

I don't think it's much less for the same boost level, actually. Except the loss in the brive belt and the internal friction in the supercharger. But the biggest dierence is that the supercharger boosts if you need it or not, and the turbo only if there's enough exhaust gas available. At low loads the supercharger will be far less economic.

 

[mjoekingz28]

Good point y_p_w, I remember hanging my head out of my Uncle's third gen Camaro and couldn't breathe at all very well. Must be some kind of aviation weather phenomenon of low or high pressure areas. I really don't know, but kind of had a fear for those people skydiving as it seems they would be gasping for air the entire way down.



I guess the way to find out if turbos hinder airflow is to see if the lag is the turbo bogging down the engine or is the lag just what the engine has to offer before the turbo begins its work.

 

[y_p_w]

Originally Posted By: mjoekingz28
I guess the way to find out if turbos hinder airflow is to see if the lag is the turbo bogging down the engine or is the lag just what the engine has to offer before the turbo begins its work.

There's got to be a lot more that creates a less powerful engine until the turbo kicks in. They're often lower displacement, low compression (to deal with boost), and there's still the exhaust restriction due to the turbo. Of course those issues go away once the boost is available.

I thought that goosing the accelerator at a stop will bring the boost pressure up. I don't have a boost gauge on my car though, so I haven't been able to test that out.

 

[roadrunner1]

Originally Posted By: y_p_w
Originally Posted By: mjoekingz28
I guess the way to find out if turbos hinder airflow is to see if the lag is the turbo bogging down the engine or is the lag just what the engine has to offer before the turbo begins its work.

There's got to be a lot more that creates a less powerful engine until the turbo kicks in. They're often lower displacement, low compression (to deal with boost), and there's still the exhaust restriction due to the turbo. Of course those issues go away once the boost is available.

I thought that goosing the accelerator at a stop will bring the boost pressure up. I don't have a boost gauge on my car though, so I haven't been able to test that out.


A turbo isn't bogging an engine down on take off, older generation turbochargers took a moment to spool. This has been overcome by VVT, basically shutting the veins upon take-off then feathering them out to control an over-boost.

A turbo is such a minute restriction in the exhaust flow compared to a muffler or cat, its placement as close to the exhaust manifold(s) as possible is to increase efficiency. At one time we had a twin turbo 6V-92 marine that came from Detroit Diesel with turbo blankets to hold the heat against the turbochargers to increase efficiency, and these weren't liquid cooled chargers.

All a turbo is in the exhaust stream is a fan, turning another fan, swirling the exhaust flow as it passes through.

 

[Srt20]

Yeah, heat is good for turbos. We wrapped my buds turbo on his 2 stroke twin cylinder 800cc engine. We also did not use an intercooler, to maximize throttle response. The turbo has almost no lag, or at least no noticeable lag. It is a fantastic setup. Boost is a good thing.

I will say, I lost an intercooler boot on my old diesel truck. I was pulling a modest load, maybe 6k lbs and going up hill. It was a heavily fueled truck. I lost a lot of power and it smoked like a locomotive from the 1800s. On a diesel, to much fuel spikes EGTs. Well it was so heavily fueled, and without boost, at WOT the EGTs actually went down. So much fuel was putting the fire out. Or I should say, not letting the fire happen. That truck regularly hit 45psi of boost. It took a bit to find a good system to keep the boots on.