Help me understand Turbo diesel Theory - Page 5 - PeachParts Mercedes-Benz Forum

dannym · #61 08-03-2005, 12:15 PM

I was just thinking.....watch out, doing that again

Anyway just thinking that a N/A engine would get more horsepower if the cam was designed for overlap. That's called the "Ram Effect" where the intake valve opens a little early allowing the velocity of the exhaust gas to actually draw in the fuel/air mixture from the intake.
Of course the EPA doesn't allow this. OK all at once THANK YOU EPA!!

About the back pressure. That would almost have to be designed into the system to keep the exhaust valve temperatures down. You wouldn't want to be melting down your valves now would you?
Is that why higher boost pressures would need an intercooler?

And lastly, if an N/A engine doesn't suck how does it build manifold vacuum?

Danny

boneheaddoctor · #62 08-03-2005, 12:50 PM

Quote:

Originally Posted by dannym

I was just thinking.....watch out, doing that again

Anyway just thinking that a N/A engine would get more horsepower if the cam was designed for overlap. That's called the "Ram Effect" where the intake valve opens a little early allowing the velocity of the exhaust gas to actually draw in the fuel/air mixture from the intake.
Of course the EPA doesn't allow this. OK all at once THANK YOU EPA!!

About the back pressure. That would almost have to be designed into the system to keep the exhaust valve temperatures down. You wouldn't want to be melting down your valves now would you?
Is that why higher boost pressures would need an intercooler?

And lastly, if an N/A engine doesn't suck how does it build manifold vacuum?

Danny

The reason you need intercoolers at higher boost levels has to do with charge heating....feel the tank on your aircompressor that has bee in heavy use and runing constantly...its hot right? same thing off a turbocharger...anything above 9psi and the charge heating is a bigger detriminte than the lag from the piping and the restriction of the intercooler.

TonyFromWestOz · #63 08-05-2005, 09:17 AM

Quote:

Originally Posted by P.E.Haiges

Bonehead,

SNIP

That's why Diesel engines only compress air up until the point the fuel is injected.

P E H

Diesels compress the air up until TDC. This has no bearing on when the fuel is injected.
In fact, most diesels inject before TDC, which means that the air is still being compressed (until TDC)!

TonyFromWestOz · #64 08-05-2005, 09:23 AM

Quote:

Originally Posted by dannym

SNIP
And lastly, if an N/A engine doesn't suck how does it build manifold vacuum?

Danny

As we are discussing this on a DIESEL forum, the answer to this is that Diesels should not build manifold vacuum. If they do, then they need to have the air cleaner element replaced. NA diesels should have air at (or very close to) atmospheric pressure.

t walgamuth · #65 08-05-2005, 07:11 PM

on a gas engine is caused by thngs like carbon getting hot enough in the combustion chamber to ignite the mixture before the spark does it. (that is why it is called preignition). this is destructive to the engine and can melt pistons etc. the ingnition by the spark is a controlled ignition which is friendly to the engine.

running on after the iginition is shut off is also a type of spontanious ignition from carbon building up and being hot enough to cause it to ignite the gas air mixture.

these terms are not much known today because the computer controlled fuel injection pretty much makes it all a thing of the past except for in collector cars.

the fuel injection we enjoy today is a direct result of laws relating to pollution and mileage. when those laws were introduced int he seventies they were cursed by anyone driving american iron. the europeans embraced fuel injeciton much faster and as a result the saabs, volvos bmws and others were sweet driving cars when some of the merican cars would barely run.

tom w

Hit Man X · #66 08-05-2005, 07:30 PM

Quote:

Originally Posted by dannym

And lastly, if an N/A engine doesn't suck how does it build manifold vacuum?

Danny

The manifold is almost shut... it's regulated via a throttle body or bodies. As you approach higher throttle manifold vac drops.

DieselAddict · #67 08-05-2005, 08:15 PM

The fuel mileage of NA vs. turbo diesels is something that I've been wondering about lately. I looked up the fuel economies of 96-99 E300D's and they're nearly identical. Also I'm not sure if the idea that a turbo increases fuel economy by allowing the driver to accelerate to a given speed faster holds much water. Sure you spend less time with the pedal down, but you're also using more fuel while the pedal is down. My 240D gets significantly better mileage than my 300D turbo and I usually accelerate with the pedal to the floor, unlike in the 300D. Of course it's a smaller engine so it may not be a good comparison, but it does suggest to me that slower acceleration may lead to better fuel economy.

One thing I've never understood completely is why it's ok for diesel engines to have excess air in the combustion chamber while in gasoline engines this would cause a lean condition which is bad for the engine. Why is that so?

MB-Owner-in-ind · #68 08-05-2005, 08:16 PM

Quote:

Originally Posted by Hit Man X

The manifold is almost shut... it's regulated via a throttle body or bodies. As you approach higher throttle manifold vac drops.

HUH?????????

Hit Man X · #69 08-05-2005, 08:27 PM

Quote:

Originally Posted by MB-Owner-in-ind

HUH?????????

On a gas vehicle, they pull let's say 16" of vac at idle... as you increase toward 100% WOT that vac drops to 12" then 6", etc.

Diesels have no throttle body, it's an open manifold. Gas motors use a throttle body to regulate airflow into the intake thus vac too.

Make more sense?

dannym · #70 08-05-2005, 08:31 PM

Makes sense to me but the gas or N/A engine still sucks..

Better watch out Tony doesn't like "gas" talk in the diesel forum!

Danny

t walgamuth · #71 08-05-2005, 11:33 PM

comments:
1. on a gasser a lean condition would not be a problem if not making power, but perhaps that much control is a problem to achieve.
2. of course accelerating faster uses more fuel. work times speed equals energy. same work done faster uses more energy.
3. just thought of another reason na can use less fuel. a 240 is quite a bit lighter than a 300 turbo. so around town less mass to accelerate and not doing it too fast either.

tom w

Gurkha · #72 08-05-2005, 11:57 PM

Quote:

Originally Posted by DieselAddict

The fuel mileage of NA vs. turbo diesels is something that I've been wondering about lately. I looked up the fuel economies of 96-99 E300D's and they're nearly identical. Also I'm not sure if the idea that a turbo increases fuel economy by allowing the driver to accelerate to a given speed faster holds much water. Sure you spend less time with the pedal down, but you're also using more fuel while the pedal is down. My 240D gets significantly better mileage than my 300D turbo and I usually accelerate with the pedal to the floor, unlike in the 300D. Of course it's a smaller engine so it may not be a good comparison, but it does suggest to me that slower acceleration may lead to better fuel economy.

One thing I've never understood completely is why it's ok for diesel engines to have excess air in the combustion chamber while in gasoline engines this would cause a lean condition which is bad for the engine. Why is that so?

Having used both N/A OM616 as well as turbo OM 616 on the same vehicle, my results were pretty interesting, around town, I would get the same MPG, but in highway, I gained over 4mpg with the turbo, less throttle was needed to keep up the speed.

Hit Man X · #73 08-06-2005, 02:50 AM

Quote:

Originally Posted by dannym

Makes sense to me but the gas or N/A engine still sucks..

Better watch out Tony doesn't like "gas" talk in the diesel forum!

Danny

It's all in the understanding of theory!

t walgamuth · #74 08-06-2005, 08:10 AM

did the cars carry the same gear ratios in the rear end? and the same in the transmission? and were they in comparable running condition?

tom w

Gurkha · #75 08-06-2005, 08:55 AM

Same vehicle with same powertrain, just different engine. The driving conditions and route were the same too.

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