Ross Posted September 9, 2005 Share Posted September 9, 2005 The higher compression would increase volumetric efficiency, not thermal efficiency. Thermal efficiency would actually get worse, No, thermal efficiency will increase, by definition. This is because the thermal efficiency baisicly depends on the ratio of the hottest cycle temperature and the temperature at exhaust. Larger the compression ratio, the larger the temperture difference, the larger the thermal efficiency. Link to comment Share on other sites More sharing options...
BoostedBalls Posted September 9, 2005 Share Posted September 9, 2005 Thermal efficiency or thermal ratio? Your cylinder pressure will be higher with higher a compression ratio regardless of exhaust temperature. Thermal efficiency is a braud term. It is normally used in the context of power output compared to heat generated when discussing internal combustion engines, thermal efficiency you described is normally used in driven pumps where intake air to exhaust air ratio is important. This is a variable in total pressure density. This variable is more important to focus on regarding turbo compressor discharge. Exhaust gas temperature in a natually aspirated engine is outweighed by the importance of intake air temp and cylinder compression temp. No, thermal efficiency will increase, by definition. This is because the thermal efficiency baisicly depends on the ratio of the hottest cycle temperature and the temperature at exhaust. Larger the compression ratio, the larger the temperture difference, the larger the thermal efficiency. Link to comment Share on other sites More sharing options...
Ross Posted September 9, 2005 Share Posted September 9, 2005 You are getting mixed up. Thermal efficiency is defined for any work producing cycle as (work out)/(Heat added) where the heat added is calculated from the mass of the fuel and its heating vavlue. The thermal efficiency of the otto cycle (the cycle which the spark ignition engine approximates) can be defined as = 1-(T4/T3) where T4 is the temperature at the end of the adiabatic expansion process (exhaust) and T3 is the temperature after the isochoric heat addition (after the fuel has burned at tdc). Using the fact that (T3/T4)=(V4/V3)^(gamma-1) and V4/V3=V1/V2=compression ratio, where gamma =1.4 for air, this can be rearranged to thermal efficiency=1-(1/compressionratio^(1.4-1)) Therefore the thermal efficiency increases with the compression ratio. Sorry for the horrible incomplete proof, but its a bit tedious writing it out in words! I can send a proper proof to anyone interested in .doc format. Link to comment Share on other sites More sharing options...
calebz Posted September 9, 2005 Share Posted September 9, 2005 Are the spider intakes different for turbo and non? How about the throttlebody? Everything is pretty much the same except for the turbo has a coolant line tapped into it for the turbo .. and some of the turbo manifolds don't have an EGR.. Both very desireable things to me. Link to comment Share on other sites More sharing options...
archemitis Posted September 9, 2005 Share Posted September 9, 2005 I was only guessing in my post, if archemitis has first hand experience between the two (by the way, same aspiration on both of them???) then listen to him. ya, i have had the same carb on both engines. a 2xxk mile spfi, and a 120k mile carb block. same wagon. the carb block got less mileage, but i wasnt exactly testing under laboratory conditions. Link to comment Share on other sites More sharing options...
idosubaru Posted September 9, 2005 Author Share Posted September 9, 2005 Just curious. Are you using a spider from a turbo XT? I have one from an NA XT. WOuld trade you straight across if you're interested yes, it's from a turbo XT. i might be willing to trade. i don't know much about EA82's, so i'll wait until i pull the motor and pick up this new block this weekend and see what is what. i'm used to the ER27, there are no differences to contemplate. can you just remove the EGR without any consequences? is there a benefit to doing that? the NA manifold you have will bolt right up to any EA82 block and turbo heads just fine? that thermal efficiency talk is giving me a headache. thermodynamics is annoying. Link to comment Share on other sites More sharing options...
Ross Posted September 10, 2005 Share Posted September 10, 2005 can you just remove the EGR without any consequences? is there a benefit to doing that? yes, as long as you remove all of it and keep the solenoid in there it will be fine. No real advantage unless there is a malfunction somewhere - it just simplifies things. Link to comment Share on other sites More sharing options...
calebz Posted September 10, 2005 Share Posted September 10, 2005 yes, it's from a turbo XT. i might be willing to trade. i don't know much about EA82's, so i'll wait until i pull the motor and pick up this new block this weekend and see what is what. i'm used to the ER27, there are no differences to contemplate. can you just remove the EGR without any consequences? is there a benefit to doing that? the NA manifold you have will bolt right up to any EA82 block and turbo heads just fine? that thermal efficiency talk is giving me a headache. thermodynamics is annoying. Yes, they bolt on the same. Only difference is you will have an extra coolant line you don't need, and I will have to drill one out for the coolant line I don't have;) EGR can be removed. Even with the solenoid removed I have never gotten it to throw an EGR code. But mine has always been kinda weird about that stuff. Link to comment Share on other sites More sharing options...
idosubaru Posted September 10, 2005 Author Share Posted September 10, 2005 what is the EGR valve and why doesn't the XT6 have one? exhaust gas recirculation, i think that's what it stands for but i don't know what it does. it's connected to the intake? so if i didn't install it on mine, how would i block the hole? Link to comment Share on other sites More sharing options...
NorthWet Posted September 11, 2005 Share Posted September 11, 2005 IF the engine has an EGR valve, it should have a metal tube running from the distributor-side (driver's-side in USA) head from just below the cam-carrier up the back of the head and to a boss on the intake manifold. The valve itself looks kind of like a flattened mushroom, 2-3" in diameter. You might be able to find a threaded plug to plug the port. Regarding compression ratio, thermal efficiency, and power: In the range that we are talking about there is almost a direct correlation between increasing CR and increasing TE and power. A 10% increase in CR yields about a 10% increase in TE. If the opposite were true, the automakers would be falling all over themselves to give us low-compression engines for performance cars. CR has negligible, if any, effect on volumetric efficiency. The only argument I can see for correlation would be that more of the combustion gases would be pushed out at the end of the exhaust stroke, but that would be only about 10% more of about 1/10th of the swept volume... or about 1% total difference. Link to comment Share on other sites More sharing options...
idosubaru Posted September 11, 2005 Author Share Posted September 11, 2005 the first and only EA82 i worked on for a guy on the XT6 group had that stupid tube connected at the bottom of the drivers side head, that thing was annoying. definitley getting rid of it on mine if it has it and i don't need it. Link to comment Share on other sites More sharing options...
NorthWet Posted September 11, 2005 Share Posted September 11, 2005 ... definitley getting rid of it on mine if it has it and i don't need it. "Need" is a relative term... It is there for pollution control only; it helps reduce thermal efficiency under certain engine load conditions (mostly light cruise power) to reduce the formation of NOx. In day-to-day life, its major impact is as a maintenance item. "Modification of mandated pollution control devices is a violation..." yada yada yada. Certain versions of the EA82 do not have EGR plumbing. Go figure... Link to comment Share on other sites More sharing options...
idosubaru Posted September 11, 2005 Author Share Posted September 11, 2005 i'm not interested in polluting but i'll justify EGR removal by the fact that i'm gearing this vehicle towards optimum gas mileage so it can't be worse than what i'm putting out now with my XT6. Link to comment Share on other sites More sharing options...
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