North American Turbocoupe Organization



freewheeling?
phil88tbird Offline
Member
#1
i think i read in here sometime ago that the turbo will not build boost if not in gear... is this true? on auto and manual? if so... why?
and can it be fooled to build when no load is on the engine? not saying i would do it just curious... don't know alot about turbo engines this being my first one
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Matt S Offline
Posting Freak
#2
Yes that is true. There just isn't enough load (exhaust gasses) to spin up the turbo. Auto is a little different because the motor is under a load when in gear so you can build boost with your foot on the brake keeping you from moving. Not suggested for the A4LD. If the cat is plugged or timing is way off you can build boost in neutral but will notice a marked power decrease.

I have seen people who race talk about "2 step" and other things that way retard timing, or shut down spark for a couple cylinders. I don't know much about it, but I guess that this allows the motor to pump more air/exhaust whithout over-revving. This way they can build boost and flip a switch, or whatever their system is, so the car runs fine off the line when the lights go green.
Sold it Sad*
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phil88tbird Offline
Member
#3
okay. well not to sound like an idiot.. . but how is there more exhaust gasses at any given RPM when the engine is under load? i mean wouldn't you think that 4000 RPM is 400 RPM?
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phil88tbird Offline
Member
#4
sorry i meant 4000RPM is 4000RPM with or without a load?
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Pete D Offline
Administrator
#5
Think about how far the throttle is open to make 4000 at no load vs 4000 trying to accelerate the car rapidly.
Pete Dunham


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Joe F Offline
Posting Freak
#6
Think of "under load" as "making HP". When your engine is freewheeling, it doesn't take much HP to spin it; 10 or less, maybe (just a guess).

Now when the engine is moving the iron, it must produce "serious" HP to do so. Like Pete said, gas pedal pressure. Further depressed, more gas, more air, etc.

Clearer?
JR's Place - My '87 Turbocoupe
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moneypit Offline
Member
#7
Also you must keep in mind the fact that the turbine is not in fact driven by the exhaust gasses, but rather the heat contained therein. The more load you have on the engine, the more energy is requied and therefore produced from combustion. The vast majority of the energy released during combustion is lost in the form of heat. So really a turbo is an energy recovery device... kinda...
'88 TurboCoupe, '01 Impala, '83 Crown Vic, '95 Jeep Cherokee, 63.5 Galaxie Fastback, '57 Studebaker President... So many cars, so little time.
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Robert Camp Offline
Posting Freak
#8
So if I were to separate the turbine from the exhaust manifold and put a water jacket around the manifold and one around the turbine and pump the hot liquid from the the manifold jacket to the turbine, it would work? Just put heat into the turbine.
Robert Camp
'86 Medium Regatta Blue TC, 5-speed, original owner.
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phil88tbird Offline
Member
#9
well robert i imagine that is taking it a little tooo literally, i guess it just still does not make since totally to me, cause the cumbustion chamber stays the same size at all times thus at any given RPM it is giving off the same amount of exhaust gasses whether under load or not right?
also if i am in nuetral and rev to 4000 RPM or i am driving down the road and i am at 4000 RPM (granted i would have to be deeper into the peddle when i am driving ) amount of air and fuel ingested by each cylinder is the same correct? or am i wrong on that?
so if the same amount of air and fuel is being burnt then in theory the same amount of exhaust energy is being expelled right? (keep in mind i am using a theoretical non tubo engine, yes i know a turbo crams more air into a cylinder)
or am i just being completely stupid here?
i am not trying to argue any points here just trying to get a better grasp on turbo charged engines.
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57fan Offline
Member
#10
A former Mechanic School instructor stated years ago that the turbo actually is moved to create boost by the "Expanding Exhaust Gases". Under no load the gases are not expanding when they exit the cylinder. When the RPM increases more fuel is burnt and the exhaust gases do not have enough time to completly burn in the cylinder before the exhaust valve opens, they continue to burn / expand in the exhaust manifold and into the turbo. thus causing the turbo to spin up and create boost. Its a simple concept when you get down to it.


As stated above, most heat energy from engines goes out the exhaust pipe.


On a different note, when you get your home carpet professionaly cleaned, most good companies use a cleaning unit that heats the water up via engine exhaust gases (heat exchanger). Saves money and it get the water hotter than a electric heater and cheaper than a gun burner. If we could just harness all that wasted energy out our tail pipes we would all be better off.
87 Turbo, 5 spd, full loaded with sun roof.
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