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| How's a turbo and a super charger work? https://www.slantsix.org/forum/viewtopic.php?t=9047 |
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| Author: | MitchB [ Wed Apr 21, 2004 2:38 pm ] |
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OK, I'll chime in here. I don't think or claim to know that much about anything, but I'd like to tell you what I do know about turbocharging. It is a misnomer to think a turbo extracts the engergy it needs to do the work of pushing air into the engine primarily from pumping losses. Pumping losses are defined as the action of the pistons pushing the exhaust gases against the turbine wheel. Let me explain... The ideal design would derive, overwhelmingly, the majority of it's energy from the heat content in the exhaust. In a well designed system, you can measure the exhaust temp right before and right after the turbo and you will see a significant temperature drop. The turbo is using this heat content to drive the turbine wheel. This is where most of the energy transfer occurs. Of course, you will have some pumping loss, but in a well designed system, this will be minimal. So what constitutes a good design? One that places the turbo(s) as close to the exhaust ports as possible. This is where you have maximum heat. As you place the turbos farther away or downstream in the exhaust system, you use an increasingly greater amount of pumping action to drive the turbine wheel and less is derived from heat. Many years ago, Porche did testing on several of their turbo designs and found that rougly 18 percent of the energy consumed by the turbo came from pumping loss. This is documented data. This means that greater than 80 percent of the energy used to drive their turbos came from the heat content in the exhaust. I have seen many, many dyno test data from several different turbo systems all based on the Ford small block and the data supports this. Many years ago when turbocharging was a novelty, the then current designs had the exhaust traveling large distances to a turbo mounted away from the engine. This allowed the exhaust to cool considerably and with less heat content available, turbos were driven by a greater degree, proportionately, by the engine's pumping action. To 'crutch' such designs, camshafts with longer intake durations were used. Early turbo designs were designed, primarily, to use exhaust backpressure, not heat. Now let's look at turbocharging vs supercharging. Supercharging, as you know, uses a crank driven belt. All of the energy used to drive a supercharger is parasitic. When you look at dyno data, you do not see how much power the SC is consuming. In other words, the rear wheel horsepower you see includes all the driveline losses plus the power used to drive the SC. So how much power is needed to drive a SC? You would be surprised. If you take a stock 5.0 liter Ford small block and run it at 10 psi of boost (manifold pressure), it will take about 60 to 70 crankshaft horsepower to drive a supercharger with an efficiency of 85%, which is optomistically high. So what's the point? To make the equivalent crank or RWHP with a turbocharger, you need to make 50-60 horsepower less then you would with a SC. In other words, turbocharging is much easier on an engine. The main point to remember is modern, well designned turbo systems derive most of their energy from the exhaust heat and are much easier on engines than earlier, inefficient designs. Mitch 1993 Thunderbird Formerly Powerdyned 5.0 @ 11 psi Now twin turbo'd 327 stroker |
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| Author: | Middy [ Thu Apr 22, 2004 5:54 am ] |
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Wow this is a great thread! I don't have any knowledge above what has been posted. I just wanted to add that I'm really enjoying the discussion. Now to get really wacky, I've been doing a lot of reasearch on Stirling cycle engines, how about a stirling engine powered blower using the exhaust heat and engine coolant for the temperature differential?  see here, http://www.keveney.com/Vstirling.html |
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| Author: | Dartvader [ Mon Apr 26, 2004 5:49 am ] |
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Al T. AWsome is too mild a word. I know I have seen your web site before, but must have been brain dead not to respond. Everything about it is awsome: the car, the creativity, the craftsmanship, the web site, the WIFE, the friends, you name it. Congratulations! What material did you use for your inner cooler ducts? Is it steel, aluminum? Where did you obtain the material? Have you dyno's the car? How does it run. What about efficiency? Have you run MPG figures. I know your car is heavy. Is it a '58? I had a '56 Desoto which must have weighed about 5K lbs. |
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| Author: | Dartvader [ Mon Apr 26, 2004 1:00 pm ] |
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Oh yeah, that's right, Al T, your car must be a '60 if it had a slant stock. Prior to that they had the old flat head. That was a good old engine too. I had a friend with a '59 Dodge convert withthe old style Poly Head 318. He tried to rebuild the engine himself, and ruined the thing. Traded it in on a Pontiac convert in '63. Both would be neat cars to have now. Anyway, cool car! (yours I mean). |
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| Author: | Guest [ Sun May 02, 2004 5:48 pm ] |
| Post subject: | Description of operation |
How do they work. First both these devices create what is known as artificial displacement That means that if an engine was operating normally aspirated (through a standard carb etc) at sea level air presure would be 14.7 PSI. So if it was a slant six for instance with 225 cubic inches then then we would be feeding 225 cubic inches 14.7 psi at wideopen throttle. If we installed a tubocharger or supercharger and raised the pressure in the intake manifold to say double that (2x14.7psi= 29.4 psi ) then the engine would think and behave as if it was a 450 cu inch engine because it would contain that much air even though it was only a 225 cu actually. This is a bit of an oversimplification but stick with me as you will wind up understanding it. Now if we used the Turbo to produce the extra intake pressure it would almost all be there( providing the engine could handle it of course) because the turbo charger recovers power from the lost heat energy of the engine (by using exhaust gas and heat which is already wasted to drive the turbo and pressurise the intake side of the engine.) This is very efficient and is why turbos are so popular on Diesels and such(PT Cruisers even) however they have one big drawback The turbo does not always pressurize the intake , only when a heavy load is applied to the engine and exhaust temp rises sharply (Just like us , we only really sweat when we work hard) so the response is not instantaeuos , it take a slight amount of time to get there. Still with a bit of planning it is a very hard combo to beat. The supercharger however is driven from the engine crankshaft and it requires a lot of power to drive it Typically we assume that it uses 1/2 of the extra power it adds to drive it (ie if it adds 200 HP then it is probably consuming 100hp to drive it) Its advantages are it is always there and the increase in intake pressure is always there so throttle reponse is instantaneous. Both have their place . The turbo however runs or is driven on waste gas and heat that we could never use for power otherwise so it is the most efficient. Heat loss in an internal combustion engine or better put Thermal efficiency without the turbo is very poor . Much of the fuels energy is lost in the cooling system and vast amounts just flow out the tailpipe(70%plus). The turbo recovers some of this and that is why it is so popular. Hope this helps |
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| Author: | Al T [ Thu May 06, 2004 5:48 am ] |
| Post subject: | Thx Vader |
Kind words Vader . . . Just got back from an extended global business trip and haven't been reading the site. Q. What material did you use for your inner cooler ducts? Is it steel, aluminum? A. Actually both - The intercooler was from th 90 tbird application so I reused the connections and modified/extended the tubes Q. Where did you obtain the material? Local racing supply store - thin walled 3" dia., 0.060" thick ?? steel tubing - its available in straights, u's, j's, etc Q. Have you dyno's the car? Not yet - plans are to do it this summer Q. How does it run. I know your car is heavy A. Runs great, very driveable - pulls the 4000 pound car along very nicely - great torgue between 2500 - 4000 rpm Q.What about efficiency? Have you run MPG figures. around 18 - 20 mpg I'm looking forward to your stories as you get your project rolling. |
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