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Now I am not an expert in engines, but I have a few books and I know quite a few good engine people, some of which are aircraft engine folks with extensive know how of trubines and compressors.<p>First thing one needs to understand is that <B>Hp = torque x rpm</B><br>Torque is the force an engine develops, HP is the energy it delivers in a given amount of time. And our neat gearboxes then multiply what ever force that is available through the simple (lever effect) minus friction losses.<br>So... if you have ie. 150 ft/lbs of torque and have a 13/1 gear ration, then the availabe torque at the other end would be 13x150 - (friction losses)...<p>The higher you go, the less air pressure, the less power, the less air for cooling, you lose 1% of power for every 330 feet of altitude up to 10'000 feet, above that more. The higher you go, the less oxygen per cubic feet or air.<p>The torque an engine develops depends very much upon how strong the combustion in each cyclinder is. Thus if one can reach stronger combustion forces... then torque will go right up. Of course each engine will have friction and heat losses, so that only a part of the energy consumed in form of gasoline or diesel is transformed into torque.<p><B>Two ways to increase torque...</B><br>1. More cubic inches for the engine<br>2. Find a way to squeze in more air into a smaller engine<p><B>Feeding more air into an engine:</B><br>A turbocharger is a turbine driven by exhaust gases, that drives a compressor that increases the pressure in the air intake system, where gasoline is added before it enters the cylinders (can be port injection, carburator, direct injection or a combination). When ever you compress air, it heats up. This is why modern cars use an intercooler (charge cooler) to reduce the temperature of the charged air to level where it will not cause early detonation in gasoline engines. (Diesel engines work using a controlled detonation, so for them hot charge air is less of an issue). Detaonation is a problem on gasoline engines because the compressed air fuel mixture will be compressed some more during the compression cycle of the engine. Thus most Turbo engines have compression rations in the 6:1 to 10:1 range, while modern non Turbo gasoline engines would range in the 9:1 to 14:1 range.<p>When compressed air is cooled in the intercooler, its volumetric density is increased, which means that there now is more oxygen in the same volume. It now enters the cylinder through the admisson port, where gasoline is added, which will also act as a coolant of the charged air. Thus, one solution to avoid detonation and to cool the charged air is to run the engine with a rich mix (a relative high level of gasoline in the air-gas mixture). By definition this is not a good way to obtain a fuel efficient engine. Thus using a large or multiple intercoolers is the best way to obtain good efficiency. However, you want to avoid that the intercooler installation is so large that it acts a pressure reservoir that takes too long to empty through the turbo bypass valve.<p><br><B>Engine installation:</B><br>Next most important thing on a turbo car is the engine installation. Because of the fact that intercoolers require a lot of space, many installations, either don't increase the size of the engine cooling system or they install too small intercoolers, or they end up with both, which will require that the engine runs a lot under rich mix in city driving or under hard driving. A perfect example would be the Porsche Cayenne Turbo... where Porsche has already increased the efficiency of the intercoolers twice (along with an increase in torque and Hp), but is unable to resolve the problem of the too small cooling system which forces the engine into rich mix nearly all the time. Note that the Subaru WRX and STI installations are also not what one could call a good installation.<p>Fact is turbo engines require extra cooling, as they deliver more power for their weight, they also require internal modifications, to avoid heat build ups in some areas. Typically on high pressure turbo engines you will find, sodium filled exhaust valves, oil jets that cool the pistons from underneath, or full alloy construction which avoids many of the heat build up problems.<p>The other mistake that is popular is to use multiple turbochargers and run em next to each other, for example two smaller turbochargers, one for each engine bank. While this might reduce turbo lag... it also creates it own share of problems, as the engine will newer have quite the same charge pressure on each bank, which results in asymmetric loads and down the road more engine break downs. This is why Maserati and Audi have killed their Twin Turbo V6 engines, along with many Japanese manufacturers. This solution is great for racing... but not good for mass production where you have warranty claims down the road. This is why the new GM/SAAB V6 Turbo engine fitted in the 9-3... has one larger turbo feed by both cylinder banks, not two small ones.<p>So by definition, in order to make a car that is fuel efficient while using a gasoline powered turbo engine you need to select en engine small enough to leave the room needed for the cooling system which will be larger then for a non turbo engine, enough room for the intercoolers and enough room for some air flow. Volvo, SAAB, VW and Renault seem to have the most experience in this field. The installation is the Hirsch Performance 300Hp<br>SAAB 9-5 Aero is probably one of the best... (modded it will generate 40Hp extra and burn 7% less fuel) with a full SAAB 3Y warranty in Europe. What you will find in Volvos is also rather good stuff.<p><B>The turbocharger:</B><br>Most modern turbochargers are relative simple radial constructions. Most use an oil film for the axis, few use bearings. Some newer turbos use vanes to offer a better efficiency at lower RPM, (mainly Diesel Engines which have lower temperature exhaust gases)... from a technical point of view anything out there is some form of cheap junk if you compare it to what could be done using jet engine grade compressor and turbine technology. There is a simple reason for this... would you pay $50'000.- for a turbo replacement ? Neither would I! But cheap junk or not... these cheapo turbo's work pretty well these days and can last many 100'000 of miles if properly cared after. As a note here, Mitsubishi seems do spend quite some R&D to advance the car turbo technology using higher quality light alloys in some of their turbos like used in the Lancer EVO9.<p>So to sum things up, a good turbo installation requires large intercoolers, a large cooling system, a non cramped engine bay for air flow and if possible an engine that avoids head build ups, and a good turbocharger.<p><B>Heat, altitude and gasoline octane:</B><br>As mentioned before, too hot charged air can lead to detonation. Thus for hot conditions, turbo engines require higher octane levels then non turbo engines as hot air during hot summer days gets very hot from the turbocharging. With altitude, if the engine ECU and turbocharger can compensate somewhat of fully for altitude, more boost then at sea level will be generated, which also means higher charged air temperatures. Again high octane gasoline is required. Now if the gasoline is lower octane (ie.US91) then the engine will have to switch to rich mix and it will have to reduce boost to avoid detonation on hot days or at higher altitudes. Don't forget that lower air density at altitude reduces the efficiency of the intercooler. Now... the only engine that is capable of compensating fully for altitude, heat and less ambient oxygen is the SAAB B235 engine, as fitted in the SAAB 9-5 Aero. It can do this because it can measure the combustion while it goes on, measuring the electric voltage generated during combustion over its spark plugs. Thus it can determine the mount of O2 that was burned and it can increase its base boost by up to 40% to compensate for altitude up to 10'000 feet and heat. A large turbocharger makes this possible. But, for it to work you must use high octane gasoline to avoid detonation. BMW is now also going in this direction. Regular Bosch ECU systems, don't measure combustion but measure the remains of the combustion in the exhaust system. Now this works well but makes it harder to compensate fully for altitude, but they will fully compensate up to 5'000 feet.<p><B>ECU upgrades, larger intercoolers, tricks to increase power:</B><br>Compared to non turbo gasoline engines, increasing the power of turbo engine is less costly, easier and quicker.<br>1. A simple ECU update that mobilizes engine reserves.<br>2. Larger or more efficient intercoolers along with an ECU update.<br>3. Cold air intake.<br>4. Better air filter to have quicker turbo spool up.<br>5. (2) plus a larger turbocharger.<br>6. Water sprays on the intercoolers (which works best if the water evaporates).<br>7. For the nasty... (6) use alcohol-water (1A to 9W) instead, has a lower evaporation point... remind<br>you there is a fire hazard with alcohol.<br>8. A better BPV... bypass valve for higher boost levels.<p>For details... ask the other board members... many know much more then I do when it comes to mod you car... when I need to mod my engine, I have it done by competent people. But it is always good to understand the basic concepts behind the turbo engine. And there are many thing I left out above... because it would get too long...<p>P.S. Now you know why I have a good lough each time I see a Porsche Cayenne Turbo... and some poor fellow paid for that stuff... <IMG NAME="icon" SRC="http://www.vwvortex.com/zeroforum_graphics/screwy.gif" BORDER="0"><p>Regards,<br>Coolknight
 

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Re: Quick overview of the Turbo concept. (Coolknight)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Coolknight</b> »</i></TD></TR><TR><TD CLASS="quote"><br>First thing one needs to understand is that <B>Hp = torque x rpm</B><br></TD></TR></TABLE><p>One minor correction: HP = (TQ x RPM)/5,250<p>Regards,<p>Derek
 

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Re: Quick overview of the Turbo concept. (bb vign)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>bb vign</b> »</i></TD></TR><TR><TD CLASS="quote">One minor correction: HP = (TQ x RPM)/5,250</TD></TR></TABLE><p>The original equation was correct in that no units of measure were specified.<p>The 5250 constant is when SAE units, HP and ft.lbs. are used. That number varies for kW, Nm and other Euro-popular unitary systems.
 

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Re: Quick overview of the Turbo concept. (JimLill)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>JimLill</b> »</i></TD></TR><TR><TD CLASS="quote"><p>The original equation was correct in that no units of measure were specified.<p>The 5250 constant is when SAE units, HP and ft.lbs. are used. That number varies for kW, Nm and other Euro-popular unitary systems.</TD></TR></TABLE><p>Good point Jim - thanks for the clarification!<p>Regards,<p>Derek
 

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Re: Quick overview of the Turbo concept. (Coolknight)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Coolknight</b> »</i></TD></TR><TR><TD CLASS="quote"><br><B>Two ways to increase torque...</B><br>1. More cubic inches for the engine<br>2. Find a way to squeze in more air into a smaller engine<br></TD></TR></TABLE><p>To expand on what you said, Coolknight, It may help people to understand this a bit better by thinking of an engine as an "air pump". More specifically a "combustable gas" or "combustible mix" pump. The more combustable air/fuel mixture you can push through in a given time, the more output the engine will make, generally speaking. <p>More cubes = more volume per stroke = more combustion mix pumped through per measure of time.<p>Compression = more density of your combustion mix = more specific volume of mix is pumped through per measure of time.<p>Nitrous = more available oxygen in a given volume means the mix will be able to grab and burn more fuel per given volume. Hence the reason you fit larger injectors and / or fuel pump with nitrous.<p>More revs = more volume pumped through in a given period of time = more HP. Not practical / cost effective for a street car, which uses torque for performance more than horsepower.
 

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Re: Quick overview of the Turbo concept. (Coolknight)

A great read . . . thanks for the time & effort you took to prepare this post.<p> - Mark
 

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Re: Quick overview of the Turbo concept. (Coolknight)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Coolknight</b> »</i></TD></TR><TR><TD CLASS="quote"><p>So to sum things up, a good turbo installation requires large intercoolers, a large cooling system, a non cramped engine bay for air flow and if possible an engine that avoids head build ups, and a good turbocharger.<p></TD></TR></TABLE><p>So would you consider the R a "good turbo installation"? I know the intercooler and intakes are considered to be too small by most, but how about the rest of the engine?<p>Nice write-up BTW. <IMG NAME="icon" SRC="http://********************/smile/emthup.gif" BORDER="0"> <BR><BR>
<i>Modified by I Roll at 12:33 PM 6-14-2006</i>
 

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Re: Quick overview of the Turbo concept. (Coolknight)

Coolknight, I really enjoyed your note and the responses that the others provided. One question that I have had reading about the R and the turbo system it uses on the Forum is the repeated statement (that I am sure is true) that as temp goes up the R’s performance goes down relative to its normally aspirated competition--BMWs, Audis and the like. This seemed counter intuitive to me because the turbocharger in the R would continue to provide boosted air to the engine while the normally aspirated engine would be limited to intake pressure equal to just about ambient pressure. If you take a 100 degree F. day at sea level at a barometric pressure of 29.92 and a due point of 60 degrees F., the density altitude would be about 2800 feet, meaning that a normally aspirated engine would be operating as if it were at nearly 3000 feet while the turbocharged engine would be still be boosted well above ambient. Is the problem that the air temperature entering the turbocharger at 100 degrees F. results in higher temperature boosted air out of the intercooler to the point that, in order to protect the engine from detonation, the ECU has to act to protect the engine by reducing power output? I know that a turbocharged aircraft engine will continue to make its rated power as it climbs (to some given attitude) while a normally aspirated engine will continuously lose power from ground up. I am sure that I am missing something simple.
 

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Re: Quick overview of the Turbo concept. (Shipmate)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Shipmate</b> »</i></TD></TR><TR><TD CLASS="quote"> Is the problem that the air temperature entering the turbocharger at 100 degrees F. results in higher temperature boosted air out of the intercooler to the point that, in order to protect the engine from detonation, the ECU has to act to protect the engine by reducing power output? </TD></TR></TABLE><p>Ding, ding, ding, ding, ding! We have a winner! You answered your own question correctly, so you aren't missing anything on that end. <p>Rember that boyle's law states that (P1*V1)/T1 = (P2*V2)/T2. In other words, there is no free lunch. If you increase the pressure of the intake air from one side of the turbo to the other, the temp is going to increase in order to keep the gas following the law. <p>So the heat of the intake air comes from both the physical heat of the turbo (driven by exhaust gas) as well as the heat of the pressurization process. And in order to avoid detonation, the ignition timing must be changed, resulting in a loss of power. <p>The function of the intercooler is to reduce the IAT after it has been pressurized. However, our intercoolers are not sufficient to prevent this from happening at higher ambient air temperatures. A higher (cooling) capacity intercooler, mounted out front of the radiator (max cool airflow) greatly helps out here.
 

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Re: Quick overview of the Turbo concept. (needsdecaf)

O.K. But what about the normally aspirated engine. The horsepower and torque available from a normally aspirated engine are dependent upon the density of the air, the lower density (higher altitude) due to higher temp. means there is less oxygen and less power. Is it that the higher temperature just ultimately effects the R’s turbocharged installation due to ECU adjustments even with boost more than the loss of horsepower that the non-turbocharged engine suffers?
 

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Re: Quick overview of the Turbo concept. (Shipmate)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Shipmate</b> »</i></TD></TR><TR><TD CLASS="quote">O.K. But what about the normally aspirated engine. The horsepower and torque available from a normally aspirated engine are dependent upon the density of the air, the lower density (higher altitude) due to higher temp. means there is less oxygen and less power. Is it that the higher temperature just ultimately effects the R’s turbocharged installation due to ECU adjustments even with boost more than the loss of horsepower that the non-turbocharged engine suffers? </TD></TR></TABLE><p>I keep re-reading your post and your previous post and I'm not sure how you're equating higher altitude with higher temperature air. Remember, the HP and Torque of any engine is dependant on the oxygen density that the engine sees (i.e. AFTER turbo in a forced induction car). Let's compare some scenarios. Assume that all factors except the ones discussed (i.e. gearing, launch, tires, torque and hp peaks, etc.) are equal. <p>300 HP R vs. 300 HP Naturally aspirated car, sea level, 60 degrees. Tie. <p>300 HP R. vs 300 HP Naturally aspirated car, sea level, 100 degrees. The R loses due to reasons discussed above.<p>300 HP R. vs. 300 HP Naturally aspirated car, 5,000 ft above MSl, 60 degrees. R wins hands down, the N/A car feels like a sprinter with asthma. <p>300 HP R. vs. 300 HP Naturally aspirated car, 5,000 ft above MSl, 100 degrees. Both the R and the N/A car are losing power now, the R due to the heat and the N/A car due to the altitude. I'm not going to do the calcs to see who's ahead. <p>That's why turbos rule at high altitudes. They do not feel the reduced oxygen density in the air due to the forced induction.
 

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Re: Quick overview of the Turbo concept. (needsdecaf)

Sorry if I am not making myself clear (which isn’t surprising). A normally aspirated car will develop less horsepower and less torque at high temperatures because high temperature, like added moisture, will result in a higher density altitude. Air density is affected by the air pressure, temperature and humidity. The density of the air is reduced by decreased air pressure, increased temperatures and increased moisture. A reduction in air density reduces the engine horsepower. A turbocharger will, to some extent I think, make up for this, assuming no ECU corrections for engine protection. The non-turbocharged engine will only produce whatever horsepower the air pressure will allow. So a 300 hp non-turbocharged engine (rated at some standard temperature/pressure which will be well below 100 degrees F.-- standard Atmosphere conditions use, I think, 59 degrees F) will not make 300 hp at 100 degrees, all else being equal. All that being said, however, it may be that the reduction in hp for the non-turbocharged engine is not as great as the reduction in hp due to the ECU.
 

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Re: Quick overview of the Turbo concept. (Shipmate)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Shipmate</b> »</i></TD></TR><TR><TD CLASS="quote"> All that being said, however, it may be that the reduction in hp for the non-turbocharged engine is not as great as the reduction in hp due to the ECU. </TD></TR></TABLE><p>I think you are right. I have not run the numbers, but it seems like it should be correct.<br>
 

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Re: Quick overview of the Turbo concept. (Coolknight)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Coolknight</b> »</i></TD></TR><TR><TD CLASS="quote">P.S. Now you know why I have a good lough each time I see a Porsche Cayenne Turbo... and some poor fellow paid for that stuff... <IMG NAME="icon" SRC="http://www.vwvortex.com/zeroforum_graphics/screwy.gif" BORDER="0"><br></TD></TR></TABLE><p>Sorry, I must have missed something, but I didn't quite get the reason from the above read. <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/confused.gif" BORDER="0">
 

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Re: Quick overview of the Turbo concept. (needsdecaf)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>needsdecaf</b> »</i></TD></TR><TR><TD CLASS="quote"><p>I think you are right. I have not run the numbers, but it seems like it should be correct.<br></TD></TR></TABLE><br>Turbochargers were initially developed for piston-driven fighter aircraft. The goal was to reduce/elimate power loss with altitude. You'd have to admit this is a bigger issue for aircraft! The benefit comes mainly from the way turbos work, not from the ECU.<p>What you would see if you had the proper instumentation is that turbo shaft speed rises as ambient air density falls due to the reduction in required pumping power, thereby mitigating the intake manifold density loss that normally comes with altitude. This natural characteristic of turbos -- plus sophisticated engine control schemes that factor-in barometric pressure changes -- means that turbo engine hardly lose any power as you head west out of Denver toward your favorite ski resort. The locals know this from experience, for sure. <p>The person selecting the turbo needs to take the shaft speed effect into account to avoid turbo overspeed at high altitude. It's known as "altitude reserve".
 

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Re: Quick overview of the Turbo concept. (Dyno)

Dyno, <p>I think that I understand what you are saying as to how a turbocharger works: as air density decreases the turbo has to turn faster (work harder) to pump enough of the now thin air to keep the boost where it is supposed to be and a limiting factor is the maximum shaft speed of the turbocharger. Once that is reached the maximum amount of boost available is going to decrease with a further decrease in density altitude. But how does that effect the R’s loss of performance relative to a normally aspirate engine in high temperature situations. Is it shaft speed limitation, is it the inability of the intercooler to deal with the high temperature in conjunction with ECU intervention to prevent detonation or a combination of both or are there other factors involved? <p>I found a good website that discusses density altitude and its effect on engine performance as well as such things as corrections to make to a dyno to understand how an engine is performing relative to standard conditions. Its wahiduddin.net/calc/calc_hp_dp.htm. Looking at this stuff seems to suggest that at sea level just increasing temperature may not have a very large effect on a normally aspirated engine. But that does not, in and of itself, explain why it has such an apparent effect on the R. <br>
 

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Re: Quick overview of the Turbo concept. (Shipmate)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Shipmate</b> »</i></TD></TR><TR><TD CLASS="quote"> as air density decreases the turbo has to turn faster (work harder) to pump enough of the now thin air to keep the boost where it is supposed to be </TD></TR></TABLE><p>You almost have it, but missed a key point...<p>As the air density decreases the turbo spins faster <U><I>all by itself</I>. </U>. Early turbocharged engines, like the aircraft engines I mentioned didn't have an ECU. In fact, they didn't even have wastegates. As density decreased and altitude increased, the shaft spins faster due to reduced resistance, thereby counter-acting the density loss in the manifold (at least partially).<p>The addition of an ECU, mass airflow sensor, and a wastegate mean that this natural tendency can be further optimized.<p>You are correct to say that once the max shaft speed limit has been reached, you need to do something, like limiting boost and suffering a loss of power if you go higher.
 

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Re: Quick overview of the Turbo concept. (Shipmate)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Shipmate</b> »</i></TD></TR><TR><TD CLASS="quote">seems to suggest that at sea level just increasing temperature may not have a very large effect on a normally aspirated engine. But that does not, in and of itself, explain why it has such an apparent effect on the R. <br></TD></TR></TABLE><br>I did not go to that site, but there are two main reasons why engines lose power as air temperature goes up...<p>1. Air density, and therefore oxygen content, goes down<p>2. The engine can experience knock. <p>The Volvo engineers have designed and calibrated our engines to run very close to knock (they've gone as far as possible with boost, timing, and compression ratio) to maximize performance. The timings and boost levels they've selected assume that air temps are "nominal". When ambient air temps air high, or if the underhood components become heat-soaked, the basic timings and boost levels would push the engine over the edge into knock.<p>Rather than let that happen, they've equipped the engine with knock senors. If incipient knock is detected by the ECU, timing is retarded and boost is reduced to reduce the threat of damage. This results in a power loss.<p>So, it's really the #2 item on the list that's killing the performance on a hot day. The website you mention may only consider the #1 item, which is small by comparison.
 

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Re: Quick overview of the Turbo concept. (JimLill)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>JimLill</b> »</i></TD></TR><TR><TD CLASS="quote">The original equation was correct in that no units of measure were specified.<p>The 5250 constant is when SAE units, HP and ft.lbs. are used. That number varies for kW, Nm and other Euro-popular unitary systems.</TD></TR></TABLE><br>Not to futher split hairs, but with "HP" and not simply "P" on the left side of the equation he is talking about horespower not simply power. The generic equation without any units would be:<p>Power = Torque x RPM
 

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Re: Quick overview of the Turbo concept. (Coolknight)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Coolknight</b> »</i></TD></TR><TR><TD CLASS="quote">P.S. Now you know why I have a good lough each time I see a Porsche Cayenne Turbo... and some poor fellow paid for that stuff... <IMG NAME="icon" SRC="http://www.vwvortex.com/zeroforum_graphics/screwy.gif" BORDER="0"><br></TD></TR></TABLE><p>Sorry, I must have missed something, but I didn't quite get the reason from the above read. <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/confused.gif" BORDER="0">
 
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