 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / July 2005Super charged vs. standard engine?
I am considering a Mini-Cooper and wondering what the pros and cons are regarding these two engine types. Of course I know the fundamental things, like lower gas mileage, more horse power with the super charge engine. What about maintenance, engine life, repairs, etc.,. I don't have any experience to draw on so any technical advice would be appreciated. -Larry As with a turbocharged car that extra power isn't free. It does come at the cost of much lower mpg and higher engine wear if you have to be the first across the intersection all the time. But those generalizations apply to a normally aspirated engine too. OTOH if you drive like most other drivers and stay with the flow of traffic I don't think you will notice a big difference in milage and added engine wear will be negligible. A supercharger, like a turbocharger will eventually wear out and have to be replaced. But you can say that about several other automotive accessories too. So if you need (or want) the extra power that comes from a supercharger then go for it. Both of my cars have turbochargers, and I find the the added power to be very helpful at times. I would drive both the standard and supercharged version of the Cooper and base a decision on what seems to work the best for you and whether it is worth thre extra $$. The supercharger probably comes as a part of a package, so you will be getting (and paying for) several other goodies as well. The Cooper is a very attractive car in either configuration imho. Thanks for your insight. I gather from your remarks that having a super charged engine does not add any significant maintenance factor or should I say reliability problems over a standard engine. I will test drive both versions when I get an opportunity but just wanted a heads up from the technical group and not rely on dealer sales staff. -Larry > As with a turbocharged car that extra power isn't free. It does come > at the cost of much lower mpg and higher engine wear if you have to be [quoted text clipped - 17 lines] > > The Cooper is a very attractive car in either configuration imho. > Thanks for your insight. I gather from your remarks that having a super > charged engine does not add any significant maintenance factor or should I > say reliability problems over a standard engine. With any kind of forced induction, bearings going south are probably the most common failure. They can go bad prematurely if they overheat and/or there's oil contamination/wear/starvation. Pay attention to engine oil. Oil lubricates and (partially) cools the bearings. Regular changes using a high quality oil should reduce the chance of oil related failure, such as blocked oil passages, corrosion, abrasive, etc. I believe Mini only recommends high performance synthetic oils. Replacing a worn supercharger is probably less than rebuilding an engine. Even so - most of the newer ones are supposed to be more reliable than in years past; most newer superchargers are also water cooled which reduces bearing overheating. Take good care of it with regular oil changes, and it'll take good care of you. > I will test drive both versions when I get an opportunity but just wanted a > heads up from the technical group and not rely on dealer sales staff. > -Larry Have fun. > Thanks for your insight. I gather from your remarks that having a super > charged engine does not add any significant maintenance factor or should I > say reliability problems over a standard engine. You are welcome. Those Coopers just look like they would be a lot of fun to drive. I took an Austin Mini from London to Penzance and return once, and it was a blast. The sensation of speed was amplified in that tiny car that was just inches off the ground. As long as you keep the maintenance up you should not have any problems, but that goes for any engine. A supercharger or turbocharger does essentially the same thing and both result in more power for the car without changing the physical size of the powerplant much. At one time both type of compressor had reliability and performance problems, but those days are way behind now. Both are reliable accessories. As someone else noted the turbo runs in engine oil, so just be perform regular oil changes and use synthetic. I've always changed oil every 3,000 to 3,500 miles no matter the car, and I've used synthetic in my cars since 1996. I see the difference at 200,000 miles when the engine still runs smoothly, gets good milage and when you look down into the oil gallery there is no evidence of sludging. Frequent oil changes are a cheap alternative to a prematurely wornout engine. >As someone else noted the turbo runs in engine oil, so just be perform >regular oil changes and use synthetic. I've always changed oil every [quoted text clipped - 3 lines] >oil gallery there is no evidence of sludging. Frequent oil changes are >a cheap alternative to a prematurely wornout engine. Synthetic is not needed to get long life out of a turbo. I had a Dodge Omni GLH turbo. I sold the car with 153k miles on it without touching the turbo. I used whatever brand name oil was on sale and changed it every 3k miles. I also let the car idle for a minute or so before I shut it down. That the core was water cooled also helped. ---------------- Alex really enjoyed my 96 Pontiac Bonne V6 traded it at 120K miles and it was still running like new very strong - lots of torque admit that I sold it before the supercharger failed fearing the $2k repair cost I believe it was an Eaton s.c. in it. Pretty neat, a low profile screw type air pump. > As with a turbocharged car that extra power isn't free. It does come > at the cost of much lower mpg and higher engine wear if you have to be [quoted text clipped - 17 lines] > > The Cooper is a very attractive car in either configuration imho. > As with a turbocharged car that extra power isn't free. It does come > at the cost of much lower mpg and higher engine wear if you have to be [quoted text clipped - 3 lines] > think you will notice a big difference in milage and added engine wear > will be negligible. A supercharged car can actually save a bit of gas in normal driving. An engine is not efficient at low throttle settings. In fact, it would be most efficient at wide open if it were not for power enrichment programming to aid drivability. If we have two engines, one with large displacement giving a certain horsepower, and another that is smaller, but turbocharged, then in normal driving at partial power- say ordinary street driving, the turbocharged car is running at a higher percentage of throttle, and hence a little more efficient. This is the same rationale that makes hybrids so efficient. Use a small engine and run it at a higher percentage of its power capability. Also, especially in a series hybrid, the IC engine does not need power enrichment because the electric motor does not create drivability problems. > > As with a turbocharged car that extra power isn't free. It does come > > at the cost of much lower mpg and higher engine wear if you have to be [quoted text clipped - 8 lines] > most efficient at wide open if it were not for power enrichment > programming to aid drivability. I thought a supercharger was demand based, i.e. not running at light throttle openings > If we have two engines, one with large displacement giving a certain > horsepower, and another that is smaller, but turbocharged, then in > normal driving at partial power- say ordinary street driving, the > turbocharged car is running at a higher percentage of throttle, and > hence a little more efficient. Efficient as measured by mpg? > This is the same rationale that makes hybrids so efficient. Use a small > engine and run it at a higher percentage of its power capability. Also, > especially in a series hybrid, the IC engine does not need power > enrichment because the electric motor does not create drivability problems. >I thought a supercharger was demand based, i.e. not running at light >throttle openings No, that more accurately describes a turbocharger. Until you get enough exhaust gas flow, it is basically doing nothing. To get more exhaust gas flow, you need to step on the throtle some more. ----------------- Alex > >I thought a supercharger was demand based, i.e. not running at light > >throttle openings [quoted text clipped - 5 lines] > ----------------- > Alex I didn't think superchargers were running full time, but were brought into use by a clutch. > I didn't think superchargers were running full time, but were brought > into use by a clutch. Not necessarily. >I didn't think superchargers were running full time, but were brought >into use by a clutch. It is possible to do it that way, Mel Gibson's car in 'Mad Max' comes to mind, but most do not have a clutch. They are 'on' all the time. ------------ Alex > >I didn't think superchargers were running full time, but were brought > >into use by a clutch. > > It is possible to do it that way, Mel Gibson's car in 'Mad Max' comes to mind, > but most do not have a clutch. They are 'on' all the time. I call bullshit on that one, wasn't the "mad max" blower a GMC x-71 or similar? That would be a positive displacement (Rootes) type blower, if the drive were disengaged the engine wouldn't run at all unless some kind of bypass were provided. Looks cool as heck on film though :) nate > I call bullshit on that one, wasn't the "mad max" blower a GMC x-71 or > similar? That would be a positive displacement (Rootes) type blower, [quoted text clipped - 4 lines] > > nate I think you are right, Nate. It was a GMC type, with Hollywood drive. >>I didn't think superchargers were running full time, but were brought >>into use by a clutch. > >It is possible to do it that way, Mel Gibson's car in 'Mad Max' comes to mind, >but most do not have a clutch. They are 'on' all the time. Useless trivia: Robbie Coltrane (Haggrid in the Harry Potter films) is a gearhead. He made a documentary out of buying a 1949 (?) Cadillac in California and driving it across the US to the port of New York to ship it to his home in the UK. He also hosted an interesting miniseries called Robbie Coltrane's planes and automobiles. Each episode looked at a breakthrough in motive systems. The ones that I can recall are the gas turbine, the diesel engine, the two stroke engine, the V8, and the supercharger. The episode on the supercharger looked at automotive racing in the 1920's and aeroengines of WWII. Both of these situations involved competition between the british and the germans. Daimler-Benz introduced supercharging to auto racing with an on-demand system that only began supplying boost near WOT. A british racer (whose name eludes me) got tired of being smoked for a couple of races and convinced his sponsor to pay for mounting a paxton blower on his bentley. The engine was not built up to take the strain of the boost, so he did not finish the next race. Score one for british pride, anyways, as the germans had to keep running their supercharger to keep up, and their engine failed first, allowing a normally aspirated bentley to take the win. People say that all a supercharger does is cram more fuel/air mixture into the cylinder, but that is a very simplistic and inaccurate description, as it leaves important stuff out. What it does it make the engine behave like a larger displacement engine, with a higher ratio. So a 2 litre engine with an 8:1 compression ration, and 7 psi of boost, will behave as a 3 litre engine with a 12:1 compression ratio. Unfortunately, the similarity ends at top dead center. The 2 litre supercharged engine only expands the air charge by a factor of 8, not 12, so it is as if the exhaust valve of the larger, higher compression engine opened after the piston had only gone two thirds of the downward stroke. This explains why supercharging reduces the efficiency of an engine, as it increases the power. Turbocharging is more efficient than an accessory driven super charger, because it uses the power that is expelled out of the exhaust (by effectively openning the valve before BDC) to drive the compressor. >People say that all a supercharger does is cram more fuel/air mixture >into the cylinder, but that is a very simplistic and inaccurate description, >as it leaves important stuff out. That's all it does. It is a simple device. ---------------- Alex >>People say that all a supercharger does is cram more fuel/air mixture >>into the cylinder, but that is a very simplistic and inaccurate description, [quoted text clipped - 3 lines] > ---------------- > Alex Let's talk about the air. Ratio-wise the fuel is a small fraction, and the charger does not ordinarily affect the fuel distribution since it is usually but not always added AFTER the charger. A non-supercharged engine is technically called a normally aspirated engine, from the medical term aspiration for breathing. Even if the pressure in the cylinder dropped to absolute pressure of zero the maximum pressure difference driving air into cylinder would be 14.7 pounds. At high rpm this is not enough pressure to fill cylinder. Even if it did, the weight of the air would be the weight of that displacement volume of air. Supercharging compresses air to a higher pressure and density. The higher pressure does a better job of filling the cylinder quickly. Even more important, however, if we double the pressure of the air being crammed into the cylinder (and if we intercool it to prevent too high a temperature rise) the density of the charge in the cylinder will be doubled. Now, the weight of fuel in the charge must be proportional to the wieght of the air (NOT the volume). If we double the weight of air in the cylinder, double the fuel weight and double the energy content is in the charge to be ignited. The reason for intercoolers is to prevent the air from getting too hot. Since density is INVERSELY proportional to temperature (on the absolute scale) an increase in temp reduces the density and hence weight of the charge. BTW, compressing air raises its temp, and it IS possible to raise the air temp so high in a high pressure supercharger that the temp reaches the ignition temp of the fuel/air mix- bad situation. This was a problem with early P-38s in WW2. >>I thought a supercharger was demand based, i.e. not running at light >>throttle openings [quoted text clipped - 5 lines] > ----------------- > Alex Centrifugal gear driven superchargers also had very little boost at low rpm. Positive displacement ones such as Roots and the GMC style gave boost at all rpm. There were also some engine driven chargers that had a complicated drive mechanism that did respond to throttle position in terms of speed of charger. These were for street machines. I think there was a clutch that either kicked in, or speeded up the blower speed on higher throttle openings. > >>I thought a supercharger was demand based, i.e. not running at light > >>throttle openings [quoted text clipped - 15 lines] > that either kicked in, or speeded up the blower speed on higher throttle > openings. The old centrifugal McCullochs (later Paxton) used a variable ratio drive pulley. http://www.vs57.com/ nate > I am considering a Mini-Cooper and wondering what the pros and cons are > regarding these two engine types. Of course I know the fundamental things, > like lower gas mileage, more horse power with the super charge engine. What > about maintenance, engine life, repairs, etc.,. I don't have any experience > to draw on so any technical advice would be appreciated. A mini is a car to buy because you love the great style and/or go-cart like handling. Buy it because you are passionate about it. Um, cuz' last I checked the reliability for mini coopers did not have great relatively. Both S and regular. http://autos.yahoo.com/newcars/mini_cooper_convertible_2005/15801/style_reliabil ity.html http://autos.yahoo.com/newcars/mini_cooper_convertible_2005/15800/style_reliabil ity.html http://autos.msn.com/research/vip/Reliability.aspx?year=2005&make=MINI&model=Coo per&trimid=-1 http://www.epinions.com/auto_Make-MINI_Manufacturer Brian- Thanks for the URLs they provided some interesting reading. I have got to make a call into the dealer in Scottsdale and set up an appointment for test driving. Not too many dealers in the state of Arizona and probably not a buyers market:-) -Larry w on so any technical advice would be appreciated. > A mini is a car to buy because you love the great style and/or go-cart > like handling. Buy it because you are passionate about it. [quoted text clipped - 9 lines] > ooper&trimid=-1 > http://www.epinions.com/auto_Make-MINI_Manufacturer
|
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.