The Ford Barn

scooder · 03-02-2016, 05:40 PM

Tim,
The turbo doesn't create a vacuum behind it once it's started spinning. It does a bit when you come off the loud pedal after stomping it, due to some inertia. But not when your under boost conditions. The inlet side of the turbo, the compressor under boost, of say 8lb has that same 8lb pushing against it (pressure being equal all over the area being pressurised) inturn, the exhaust side also "sees" this, due to the common shaft. So the exhaust gas has to overcome this 8lb pressure to spin the turbo.
You see, no vacuum behind to pull the exhaust gas out. A turbo works like a centrifugal supercharger (Frenzle and McCullouc (sp?) and the Paxton, to name a few) only the drive is by exhaust gas rather than belts from the crankshaft.
Under cruise conditions the turbo does turn freely, as there's no boost pressure in the inlet manifold pushing back.
And yes, the common shaft and the fact that both sides of the turbo are touching, a bunch of this heat gets sucked up by the inlet charge as it passes through the inlet manifold side of the turbo. Hence the need for intercooling.
In a blow through setup, using a (hat) on top of the carb piped to the turbo, so the whole carb is seeing boost pressure, the carb does somewhat cool the charge due to the latent heat evaporation of the fuel through the carb. This does remove a surprising amount of heat.
Hope that helps your questions.

P.S. There was an aftermarket turbo setup in the early 50's, for the flathead, it was developed by Bessia (sp? Again) not very successful, though not due to it being a turbo, it made 7lb pressure if I recall, more like money was the killer here, along with it being "new" untried and untested. I've only seen 1 pic of this, vary poor pic you can't really see what's going on under the hood.
Martin.

03-02-2016, 05:40 PM	#34
scooder Senior Member Join Date: Jul 2010 Posts: 2,597	Re: why no blowers in daily drivers? Tim, The turbo doesn't create a vacuum behind it once it's started spinning. It does a bit when you come off the loud pedal after stomping it, due to some inertia. But not when your under boost conditions. The inlet side of the turbo, the compressor under boost, of say 8lb has that same 8lb pushing against it (pressure being equal all over the area being pressurised) inturn, the exhaust side also "sees" this, due to the common shaft. So the exhaust gas has to overcome this 8lb pressure to spin the turbo. You see, no vacuum behind to pull the exhaust gas out. A turbo works like a centrifugal supercharger (Frenzle and McCullouc (sp?) and the Paxton, to name a few) only the drive is by exhaust gas rather than belts from the crankshaft. Under cruise conditions the turbo does turn freely, as there's no boost pressure in the inlet manifold pushing back. And yes, the common shaft and the fact that both sides of the turbo are touching, a bunch of this heat gets sucked up by the inlet charge as it passes through the inlet manifold side of the turbo. Hence the need for intercooling. In a blow through setup, using a (hat) on top of the carb piped to the turbo, so the whole carb is seeing boost pressure, the carb does somewhat cool the charge due to the latent heat evaporation of the fuel through the carb. This does remove a surprising amount of heat. Hope that helps your questions. P.S. There was an aftermarket turbo setup in the early 50's, for the flathead, it was developed by Bessia (sp? Again) not very successful, though not due to it being a turbo, it made 7lb pressure if I recall, more like money was the killer here, along with it being "new" untried and untested. I've only seen 1 pic of this, vary poor pic you can't really see what's going on under the hood. Martin.