Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
John M McIntosh wrote: Well they use to also suck gasoline when you had carburettors, you need to control the fuel and air mixture to ensure best milage/combustion cycle. This gets at the point that there are actually *two* types of vacuum available on many gasoline engines: manifold vacuum and carburator vacuum. Manifold vacuum is created by the restriction of the throttle plate. It's highest when the throttle is closed, and drops to nearly 0 when the throttle is open. This is what powers your vacuum brake booster and all that other stuff that diesels have to have a vacuum pump to run. Carburator vacuum is caused by the Bernoulli effect. As air moves through the restricted area at the carburator throat it speeds up, creating a pressure drop. This helps atomize the gasoline in the carb. Carburator vacuum is related to the velocity of air going through the carb throat, so it's greatest at full throttle and high engine speeds. For that reason it's tapped off to control distributor advance, in many cars.
Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
I'd kind of wondered on the specifics of this myself. I *think* I might be starting to get a better handle on it now... So, what I'm hearing is basically that on a gas engine with a throttle plate, when the cylinders are drawing in air, the throttle plate is a restriction which is what creates vacuum. Whereas with a diesel, there is no throttle plate and therefore no restriction (at least not much of one) so we have no vacuum. I would assume that technically speaking there must be *some* vacuum as air is getting sucked in, but without the restriction, probably not enough to be of any use. And of course this is mostly null and void on turbo/supercharged vehicles when producing boost as at that point the intake is under a positive pressure situation. Am I more or less on the right track here? Thanks! Levi On 10/25/05, David Brodbeck [EMAIL PROTECTED] wrote: John M McIntosh wrote: Well they use to also suck gasoline when you had carburettors, you need to control the fuel and air mixture to ensure best milage/combustion cycle. This gets at the point that there are actually *two* types of vacuum available on many gasoline engines: manifold vacuum and carburator vacuum. Manifold vacuum is created by the restriction of the throttle plate. It's highest when the throttle is closed, and drops to nearly 0 when the throttle is open. This is what powers your vacuum brake booster and all that other stuff that diesels have to have a vacuum pump to run. Carburator vacuum is caused by the Bernoulli effect. As air moves through the restricted area at the carburator throat it speeds up, creating a pressure drop. This helps atomize the gasoline in the carb. Carburator vacuum is related to the velocity of air going through the carb throat, so it's greatest at full throttle and high engine speeds. For that reason it's tapped off to control distributor advance, in many cars. ___ For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://striplin.net/mailman/listinfo/mercedes_striplin.net
Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
You have pretty much got it. Regards, Trampas -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Levi Smith Sent: Wednesday, October 26, 2005 7:38 AM To: Mercedes mailing list Subject: Re: [MBZ] why does a gas engine create vacuum and a diesel does not? I'd kind of wondered on the specifics of this myself. I *think* I might be starting to get a better handle on it now... So, what I'm hearing is basically that on a gas engine with a throttle plate, when the cylinders are drawing in air, the throttle plate is a restriction which is what creates vacuum. Whereas with a diesel, there is no throttle plate and therefore no restriction (at least not much of one) so we have no vacuum. I would assume that technically speaking there must be *some* vacuum as air is getting sucked in, but without the restriction, probably not enough to be of any use. And of course this is mostly null and void on turbo/supercharged vehicles when producing boost as at that point the intake is under a positive pressure situation. Am I more or less on the right track here? Thanks! Levi On 10/25/05, David Brodbeck [EMAIL PROTECTED] wrote: John M McIntosh wrote: Well they use to also suck gasoline when you had carburettors, you need to control the fuel and air mixture to ensure best milage/combustion cycle. This gets at the point that there are actually *two* types of vacuum available on many gasoline engines: manifold vacuum and carburator vacuum. Manifold vacuum is created by the restriction of the throttle plate. It's highest when the throttle is closed, and drops to nearly 0 when the throttle is open. This is what powers your vacuum brake booster and all that other stuff that diesels have to have a vacuum pump to run. Carburator vacuum is caused by the Bernoulli effect. As air moves through the restricted area at the carburator throat it speeds up, creating a pressure drop. This helps atomize the gasoline in the carb. Carburator vacuum is related to the velocity of air going through the carb throat, so it's greatest at full throttle and high engine speeds. For that reason it's tapped off to control distributor advance, in many cars. ___ For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://striplin.net/mailman/listinfo/mercedes_striplin.net ___ For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://striplin.net/mailman/listinfo/mercedes_striplin.net
Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
Bzzzt - wrong. The same volume flowing through a smaller area in the same time span requires higher speed. Higher speed produces lower pressure. The fuel is literally sucked out of the carburator porportionaly to the speed of the air - more vacuum (lower manifold pressure)=faster air through the ventury=lower pressure=more fuel sprayed into the air=more power. Posibly a minor point - the low pressure area is just behind the narrowest part of the venturi, so yes, there would be an increase of pressure as th air is squezzed into the smaller area, then a decrease as it expands on the other side. However, it is the lowered pressure that sucks the fuel from the jets -- -- On 10/26/05, Mike Canfield [EMAIL PROTECTED] wrote: Are you sure you are not referring to the Venturi principle? When a large volume of material is made to fit through a smaller diameter hole(such as the venturi in a carb) the pressure INCREASES. The increases airflow and turbulence atomize the gasoline as it comes out of either the injector in a TBI or the jet in a carb. Mike -- OK Don, KD5NRO Norman, OK '87 300SDL, '81 240D, '78 450SLC The FSM created the Diesel Benz http://www.venganza.org/
Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
I stand correctedThat makes more sense. Mike - Original Message - From: OK Don [EMAIL PROTECTED] To: Mercedes mailing list [EMAIL PROTECTED] Sent: Wednesday, October 26, 2005 9:13 AM Subject: Re: [MBZ] why does a gas engine create vacuum and a diesel does not? Bzzzt - wrong. The same volume flowing through a smaller area in the same time span requires higher speed. Higher speed produces lower pressure. The fuel is literally sucked out of the carburator porportionaly to the speed of the air - more vacuum (lower manifold pressure)=faster air through the ventury=lower pressure=more fuel sprayed into the air=more power. Posibly a minor point - the low pressure area is just behind the narrowest part of the venturi, so yes, there would be an increase of pressure as th air is squezzed into the smaller area, then a decrease as it expands on the other side. However, it is the lowered pressure that sucks the fuel from the jets -- -- On 10/26/05, Mike Canfield [EMAIL PROTECTED] wrote: Are you sure you are not referring to the Venturi principle? When a large volume of material is made to fit through a smaller diameter hole(such as the venturi in a carb) the pressure INCREASES. The increases airflow and turbulence atomize the gasoline as it comes out of either the injector in a TBI or the jet in a carb. Mike -- OK Don, KD5NRO Norman, OK '87 300SDL, '81 240D, '78 450SLC The FSM created the Diesel Benz http://www.venganza.org/ ___ For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://striplin.net/mailman/listinfo/mercedes_striplin.net
[MBZ] why does a gas engine create vacuum and a diesel does not?
? Thanks, Christopher McCann, Squier Park, Kansas City, Missouri -1987 300TD, 150K miles, Rotkäppchen (Little Red Riding Hood) -1985 300SD, 209K miles, Wulf (http://www.pictureblogger.com/My-1985-Mercedes-Benz-300SD) -1976 240D, ManyK miles, AKP-Wagen (Alternativen Kraftstoffs Prüfenlastwagen = Alternative Fuel Test Vehicle) running WVO/WMO/LO/CO/WATF/WGL/WBF/DA/MS/lard/gas/kero/D2 mix (do not attempt this unless you are willing to sacrifice your IP, injectors, pre-chambers, etc.) -1971 Case 222 Hydrive, 12HP Kohler, 38 deck, Snowcaster, One Banger __ Yahoo! FareChase: Search multiple travel sites in one click. http://farechase.yahoo.com
Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
The gas engine has a throttle plate to close off the intake tract and produce vacuum as the engine tries to suck air past the throttle. Some of the MBZ turbo engines can produce a fair bit of vacuum when the turbine isn't producing boost. There is a thread on buymbparts.com forum in which a 603 turbo engine was sucking the intercooler hose shut and choking itself. I hadn't expected that level of vacuum until I read about it.
Re: [MBZ] why does a gas engine create vacuum and a diesel does not?
Well they use to also suck gasoline when you had carburettors, you need to control the fuel and air mixture to ensure best milage/combustion cycle. On 25-Oct-05, at 10:30 AM, Mitch Haley wrote: The gas engine has a throttle plate to close off the intake tract and produce vacuum as the engine tries to suck air past the throttle. Some of the MBZ turbo engines can produce a fair bit of vacuum when the turbine isn't producing boost. There is a thread on buymbparts.com forum in which a 603 turbo engine was sucking the intercooler hose shut and choking itself. I hadn't expected that level of vacuum until I read about it. ___ For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://striplin.net/mailman/listinfo/mercedes_striplin.net
