Not much to add, the people here do good work.
I was told that a blown engine puts out lots of power, and a “blown” engine can be carried home in a bucket.
I believe that’s measuring the intake pressure, relative to the outside air. Naturally aspirated cars without a turbo or supercharger normally have a vacuum at the intake, because the engine is sucking air in from outside. When the gauge reads 0 psi, the turbo is pumping air in as fast as the engine can suck it, and when it’s positive, the turbo is cramming in more air than the engine could suck on its own.
Which leads me to a question… a few systems on a car are powered by engine vacuum, like the brake booster and (at least on some older cars) the cruise control. How do those systems keep working when a turbo/supercharger is installed?
Ya’ll may not know it but I prefer turbos myself.
A few months ago I installed a turbo on my Honda Civic.
Generally, Id say that SCs provide more power at low rpm and TCs provide more power at high rpm.
If you have a truck and need the extra power for towing then a SC is recommended. Unless you have a diesel truck then go with the TC.
I personally think a turbocharger is a more elegant solution. They are actually simpler machines than superchargers. They are also more easily regulated than superchargers. A turbocharged car gets almost the same MPG as a nontubocharged car while supercharged cars are notoriously bad on gas mileage.
If you have a 4 cylinder or inline 6 car, I would almost always recommend a turbo for V6 and V8s a supercharger. Although turbos work on V6s and V8s I always thought that routing both banks of exhaust to the turbo to be overly complicated and probably makes after market kits more expensive.
Did you have a specific application in mind?
Ok, another quick hijack. I remember someone once mentioning that the Honda s2000 couldn’t be turbo-ed due to the fact that it was already really tightly tuned with fairly high compression (I think that was the reason). I also remember the same person saying that one could supercharge it instead of turbocharging, and it would be ok.
Question : is this correct or totally wrong? I’m not sure now that I’m hearing that superchargers and turbochargers use different sources of power to accomplish the same thing.
Some things no-one mentioned.
First off all, the main idea behind turbochargers is that they make use of the exhaust gas energy that would otherwise be wasted. Turbos are put as close to the exhaust manifold as possible, because the gasses are still very hot there.
Thus, in theory, for a given power output turbocharged engines can have a much better fuel consumption than naturaly aspirated engines.
Superchargers are sucking off energy from the engine, so they are not so good in fuel economy.
Turbochargers also have a geometrical increase in pressure as the RPM increase. Superchargers are more linear and maybe at high RPMs the engine could suck as much air without the help of a supercharger. At high RPMs it becomes a hindrance.
Some cars had both. One that comes in mind is a group B Lancia Delta(I don’t remember the exact model). It was using the SC at low RPM, then disengaging it and engaging the TC at high RPM. Very complicated system with many failures.
Turbo lag is not a problem anymore (at least not what it used to be 20 years ago). The materials in propelers are very lightweight so they speed up in no time.
In high performance cars a misfiring (anti-lag) system is used that eliminates turbo lag completely (and making a lot of noise!!!).
Then I’ll be mistaken.
Welllll … not exactly.
For example, the P&W R-2800 series radial engine as used in the Martin B-26 and Douglas A-26 aircraft has a two speed supercharger, low blower and high blower. The supercharger is operating at all times. At altitudes below about 10000 ft. low blower is used. On takeoff the engine runs at 2600 rpm with a manifold pressure of 52 in. of mercury (just over 25 psi) which gives a lot more power out than an unsupercharged engine which is limited to a manifold pressure of whatever the atmospheric pressure is at the very most. High blower is for the purpose of maintaining engine power at higher altitudes.
A few things to consider:
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Arguments that turbos are better on gas and more efficient rest on the fact that many comparisons are between modern turbos and old-fashioned hot rod blowers. The difference in efficiency is due mostly to the high mechanical friction and high pumping losses inherent in older supercharger designs (e.g., the GMC), not the “turbo vs. supercharger” aspect.
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There is no free lunch. Exhaust power is not “free”. Power to run the turbo has to come from somewhere, so it comes out of the engine, just as with the supercharger.
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Regardless of how it is driven (exhaust driven turbos or mechanically driven superchargers), there are two basic compressors: centrifugal types (essentially fans) and positive displacement types (a.k.a. “Roots” blowers). For example, Paxton blowers are centrifugal, GMC-derived blowers are Roots. Because they have different boost curves (Roots blowers have flatter boost curves), a Roots blower vs. a centrifugal blower comparison will yield more low end power for the Roots blower (assuming maximum boost is the same). Of course, there are other factors that can interfere with this generalization, i.e., the aforementioned mechanical friction and pumping losses.
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Superchargers can be either centrifugal or Roots, but turbos are (nearly always? Never heard of a common Roots turbo) centrifugal. The end result is less low end power for turbos, sometimes aggravated by turbo lag (though less common than it used to be).
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A standard hot rod trick is increasing the size of the valves. Normally, the intake valve is larger than the exhaust; for more power, you increase them both. However, when adding a blower to a normally aspirated car, it’s a good idea to increase the size of the exhaust valve more, so that they are closer to equal.
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Mileage isn’t necessarily that much worse with a blower. Friction and pumping losses will cost you some mpg, but mileage will not grossly change unless you A) Take advantage of the blower and drive much faster, or B) Fail to retune the rest of the engine to match the blower.
Art
Ok I have a 1991 Mustang LX I plan on putting a 351W in it I would like to find which would be better for the engine TC or a SC. I noticed that the price for a SC is very high the 351W alone runs about $7,000 and i have seen SC run from $2,000 to $5,000 But what ever is best is all I care about.
Thanks Guys!
Well, your 351W ain’t exactly making a living in the upper RPMs, and it’s bread and butter is about low-end power, and it’s set up to breathe welll and be drivable at low rpm. It has limits on high RPM performance inherent in it’s design, lot limited to valves, bore/stroke ratios, etc.
Supercharger is the easy answer.
And for pure experience of people who are familiar with this motor and modifications to it, there would be a plethora of tuners who can keep a 351W with a Supercharger relatively happy.
No, there is no free lunch. But there might be a free snack, or maybe a side of fries or something.
There is some waste energy being dumped out of the exhaust. After the exhaust valve closes, there is still expansion of the gasses going on inside the pipe. This expansion is going to provide some of the energy to drive the turbine, with little cost to the engine.
If there were no waste energy being dumped out the exhaust pipe, how would a power recovery turbine make any sense? You take a turbine, let the exhaust spin it, and then apply the torque directly back into to the crankshaft using a fluid coupling. If there were no waste energy, that would be a thoroughly strupid idea. Turbo-compounding was used on the Wright 3350 aircraft engine, and recovered about 200 HP per turbine, IIRC.
So, it ain’t free, but it’s pretty cheap.
In airplanes, I was taught that when it comes to the difference between turbo- and super-chargers, besides the difference in how they’re powered, I was told that a turbo compresses only the air before it reaches the carburetor, and that a super compresses the mixture before it reaches the cylinder. I guess that only applies to engines with a carb.
That’s what they taught me in ground school…
That’s mostly wrong.
Some aircraft mechanical superchargers do compress a fuel/air mixture, usually the integrated ones on radials. Not all of them do, though. Besides, a turbocharger IS a supercharger.
Bonus Question: Can anyone name a turbine engine aircraft that has a supercharger, and why it was so equipped?
Puzzling question. Turbine engines already compress intake air so the reason for a pre-compressor compressor escapes me. It’ll be interesting to find out the answer.
Early turboprop aircraft used a mechanical supercharger driven off the engine’s accessory section to provide high pressure air for the cabin pressurization system. Modern turboprops of course use bleed air from the engines compressor section.
I wasn’t aware of it until I did an airframe inspection on a King Air 65-90. I was like, “What the heck do you mean, ‘inspect the supercharger’? It’s a PT-6!”
Cheat! Cheat! Foul Ball! Out-of-bounds, go back to the tee and hit another one!
However you are off the hook because the Merriam-Webster Collegiate gives “a device for increasing aircraft cabin air pressure” as one meaning of “supercharger.”
