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Old 12-17-2014, 05:38 PM   #1
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Turbo gas engine braking question

I drove big rigs for thirteen years, so I don't need a bunch of info about diesel engine brakes.

Does turbo charging a gas engine provide any help to conventional engine braking?
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Old 12-17-2014, 06:18 PM   #2
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About the same.
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Old 12-17-2014, 08:23 PM   #3
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If you know about diesel engine braking, then you should know the answer is yes. Compressing air above 1ATM on an engine that is not injecting fuel to provide power will make it work harder to compress that much more air, making it compress slower, and slow the engine.

Now, it's not actual Jacobs braking, of course, but just plain engine braking provided by the inherent design of an internal combustion/compression engine.
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Old 12-17-2014, 08:29 PM   #4
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Good question ,I don't know which gas direct injected engines do not have a throttle plate ,but the ones that don't will not have a lot of engine braking.

Anybody know about the Ford Ecoboost?

I don't use gas so not really involved
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Old 12-17-2014, 11:05 PM   #5
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Quote:
Originally Posted by jesilvas View Post
If you know about diesel engine braking, then you should know the answer is yes. Compressing air above 1ATM on an engine that is not injecting fuel to provide power will make it work harder to compress that much more air, making it compress slower, and slow the engine.
I suspected as much, but sought confirmation.

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Originally Posted by hone eagle View Post
Good question ,I don't know which gas direct injected engines do not have a throttle plate ,but the ones that don't will not have a lot of engine braking.
I'm curious about the usefulness of a throttle plate for engine braking with a turbo gas engine. Engine braking without a turbo depends on vacuum, but a turbo engine would need the higher manifold pressure to do any good.

I'd rather ask here than ask a sales person. I guess I may have to test drive an EcoBoost model to find out, but would rather understand how it works on top of having it work.
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Old 12-18-2014, 02:36 AM   #6
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This is Autoshop 101...
...A turbo has no impact on engine braking with a gas engine.

When the throttle valve is closed on a gas engine, any boost left in the intake path is released through a bleed valve...the intake manifold and combustion chamber vacuum increases and engine braking takes place.

There is no throttle valve on a Diesel, so an exhaust brake or similar device is needed to create/increase engine braking, or the engine braking would be limited to that at start-up...which is easily overcome by the starter.

The big difference between gas and Diesel engines is ignition, but because Diesels use compression to spark the fuel vs. an electric spark, there is no need in a Diesel for the throttle valve...just add more fuel and the Diesel will run faster.

Gas engines are more finicky on the fuel/air mix, so engine speed is controlled by the balance of air (controlled by the throttle valve) and fuel (controlled by the carb or injection system).

Because of these differences, Diesel's with engine braking devices can far exceed the braking forces that can be created in a gas engine.

And by the way...
Ford's eco-boost engines are simply a 2 turbo set-up. There is a main turbo for the bulk of the RPM range -PLUS- a small turbo in-line to help prevent "turbo lag" found in most conventional turbo systems. Ford is also using electronic controlled variable fin technology in the turbos to improve effect. But this has no impact on engine braking.

Hope that makes sense.

Safe travels
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Old 12-18-2014, 04:44 AM   #7
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All true -turbo(s) has nothing to do with engine braking
But some of the new GDI engines have NO throttle plate,also they are tiny.
Even if they have a throttle they are still handicapped by the lack of displacement.
It is a valid question
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Old 12-18-2014, 07:39 AM   #8
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The Ford Eco-Boost V-6 uses two turbo's of the same size, one turbo on each of the exhaust manifolds. They are small compared to turbos used in past years, like on Chrysler 4 cylinder cars and mini vans. The smaller turbos allow them to spool up faster and the pair of them feed enough air into the engine at higher RPM's. The auxiliary braking is more from the transmission being forced to down shift a gear or two than from back pressure caused by the engine. It is not a exhaust brake.


I have drove diesel power trucks with both Jake brakes and exhaust brakes and the gas engine's braking is not as great. It still makes a big difference over just using the regular brakes. Can also notice a big difference between the Eco-Boost V-6 and the Ford V-10 with the tow haul mode on. I had the V-6 Eco-Boost in a F-150 and now the V-10 in a class A. So I can say there is a difference. Miss this feature on the company work trucks.
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Old 12-18-2014, 02:07 PM   #9
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I live and will be working on the west coast. I've been trying to convince myself that a gas engined TV will be just fine, as I am hoping to avoid the normally higher price of diesel fuel and was hoping to enjoy some better MPGs with the EcoBoost engine when not towing. However, my experience and research into TVs is pushing me towards a diesel engine, and with that engine brakes become available.

Now all I have to do is pick a brand. Like that's easy to do.

Ford has what anyone could consider a great engine with their PowerStroke, and there are plenty of used 250s in my area. Dodge has the Cummins and there are plenty of used RAM2500s in my area, but not as many as the Fords. I never hear anything good, or bad, about Chevy anymore, which means the they are simply unpopular in the 250/2500 range for some unquantifiable reason, they are awful, or they are great and simply fly under the radar.

I guess I have to start another thread just for the brands discussion. can't wait to see what kind of "information" I will get from that.
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Old 12-18-2014, 08:38 PM   #10
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I think the ecoboost runs ok on regular but should have mid or premium to achieve the MPG and HP as advertised. Though I have yet to hear from anyone that gets close to the MPG on the sticker.

I know my 6.7 Cummins gets better mpg than my neighbors 3.5 ecoboost... by a lot and we have the same drive to work. So I pay 25% more than regular for diesel, but I go 25% farther per gallon. I have 100% more torque and a bigger fuel tank.

As to the exhaust brake, a turbo does nothing for you if there is a throttle plate (gas) and no variable turbo geometry to close the turbo. So you need a jake brake or exhaust brake or variable geo turbo.

Where the efficiency is gained from a throttle free design is the LACK of engine braking. Being able to coast with little or no engine braking is as much of an advantage as a powerful engine brake.
BUT, many diesels (due to emissions) do have a throttle to redirect gasses through the EGR, which is not only inefficient, but horrible for your engine. These systems are not only bad for the life of the engine, but rob power and throttle response and efficiency.
I do not know of a gas turbo that is as good as a diesel in both engine-braking free operation and being able to employ serious exhaust/turbo braking on-call.
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Old 12-18-2014, 10:09 PM   #11
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As an owner of a brand new MB C400 I can say that engine breaking by turbo gasser is same or better as the naturally aspirated one. Turbo 6 is quite amazing, with tons of low-to-midrange torque followed by great top end power. It combines the best from both worlds, turbo diesel and gas. I am looking forward to to get the same mill in my next TV (ML400) at some point. ML250 blutec is just puny for towing, a rare disappointment from Mercedes
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Old 12-19-2014, 10:19 AM   #12
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My son traded a Hemi for an EcoBoost. He misses the power and mileage he got with the 1500 Ram.
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Old 12-19-2014, 11:46 AM   #13
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My son traded a Hemi for an EcoBoost. He misses the power and mileage he got with the 1500 Ram.
Kind of a hard comparison. What "Hemi" was it? What was the transmission and rear axle ratios of the Dodge and what is the Ford now?
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Old 12-19-2014, 03:21 PM   #14
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Quote:
Originally Posted by Scarab0088 View Post
This is Autoshop 101...
...A turbo has no impact on engine braking with a gas engine.

When the throttle valve is closed on a gas engine, any boost left in the intake path is released through a bleed valve...the intake manifold and combustion chamber vacuum increases and engine braking takes place.

There is no throttle valve on a Diesel, so an exhaust brake or similar device is needed to create/increase engine braking, or the engine braking would be limited to that at start-up...which is easily overcome by the starter.

The big difference between gas and Diesel engines is ignition, but because Diesels use compression to spark the fuel vs. an electric spark, there is no need in a Diesel for the throttle valve...just add more fuel and the Diesel will run faster.

Gas engines are more finicky on the fuel/air mix, so engine speed is controlled by the balance of air (controlled by the throttle valve) and fuel (controlled by the carb or injection system).

Because of these differences, Diesel's with engine braking devices can far exceed the braking forces that can be created in a gas engine.

And by the way...
Ford's eco-boost engines are simply a 2 turbo set-up. There is a main turbo for the bulk of the RPM range -PLUS- a small turbo in-line to help prevent "turbo lag" found in most conventional turbo systems. Ford is also using electronic controlled variable fin technology in the turbos to improve effect. But this has no impact on engine braking.

Hope that makes sense.

Safe travels
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