Markkonschak Posted February 18, 2010 Share Posted February 18, 2010 what limits boost on any engine. say i had perfect timing and perfect afr. could someone tune a high compression motor with boost to 20 psi 15psi 10psi. if there is no detonation what makes it unsafe? would they then blow the head gasket? just a little theory question to boggle my mind. Quote Link to comment Share on other sites More sharing options...
S130Z Posted February 18, 2010 Share Posted February 18, 2010 If you have no detonation, and components to hold up against the heat, you should be able to run any boost level. I believe the main reason people have a max boost level is because they run into detonation. Look at diesels, some run upwards of 80psi of boost. Correct me if I'm wrong, but if your not close to detonating, you really have nothing to worry about. (That is if your internals can withstand the forces at specific power levels) Quote Link to comment Share on other sites More sharing options...
ozzzzz Posted February 18, 2010 Share Posted February 18, 2010 Diesels can run 200+psi with compound turbos. Diesels do not use spark plugs to ignite the fuel either. The air is compressed and then the fuel is injected.The ignition system on gas motors can also be a limiting factor, along with fuel grade. Just my 2cents. Quote Link to comment Share on other sites More sharing options...
hoov100 Posted February 19, 2010 Share Posted February 19, 2010 All tuning aside, the turbo/s is what decides the boost limit. Quote Link to comment Share on other sites More sharing options...
kolonelklink87 Posted February 19, 2010 Share Posted February 19, 2010 i think what they are saying is you set the boost limit based on your tuning results.... In your case if you're detting at say 9psi you need to pull boost before you reach the detonation prone area (not at it)... you need to tune to your engine specs, some one elses boost limit is not applicable. Other than that... the following is pure conjecture and opinion: i'd expect the main limit would be intercooling and residule engine heat - supercompressing air will make it hot and volatile so from an engineering persepctive you need to keep the temperature down as much as possible... There's bunch of complex mathmatical and experimental papers that i am not qualified to interpret (a quick journal search will turn these over). There will be a theoretical maximum derived from a relationship to the critical point of oxygen/nitrogen air mixtures... maintaining vapourised fuel will also be a massive issue at ultra high pressures... All these things could be graphed and you could decide on a value form an artbitrary engineering or theoretical perspective (the theoretical number will be higher). Basically you need to control autoignition, this gets very difficult EVEN with maximal cooling(theoretical) due to the dropping autoignition point associated with increasing pressure (increased density, molecules move closer together, less energy required to get them to "bump" into each other). futhermore.. when dealing with these kinds of pressures and temperatures the laws governing behavior of gases get a but muggy as they approach a supervolatile fluid phase. short story, there is no answer to this question that i can see.. you will run into engineering challenges WAY before you hit theoretical issues... things to consider include: *running maximal fuel pressure and injecting fuel as late as possible before ignition to prevent vapour-liquid transtion *ultra intercooling - like running liquid nitrogen heat exchangers the size of a small house &ultra engine cooling - " "^ *massively reduction the heat transfer within the intake and combustion chambers - think crazy ceramics in the CC and cylinder bore. *exotic fuels with ultra low vapour transition temperature and gas phase pressure and autoignition points... I'm thinking exotic petroleum gases maybe? ^an interesting point because you need temp to help with fuel vapourisation... but due to dropping autoignition points you will have to run the motor supercool... meaning you rely solely on mechanical pressure to vapourise fuel during injection and this will return to liquid phase almost immediately - see the first * i'm sure i can come up with some specific documented attempts... but i dont have have the time to do the readings right now I'll try to add more later or maybe someone more qualified could shed some insight on this. -pete Quote Link to comment Share on other sites More sharing options...
ozconnection Posted February 19, 2010 Share Posted February 19, 2010 i think what they are saying is you set the boost limit based on your tuning results....In your case if you're detting at say 9psi you need to pull boost before you reach the detonation prone area (not at it)... you need to tune to your engine specs, some one elses boost limit is not applicable. Other than that... the following is pure conjecture and opinion: i'd expect the main limit would be intercooling and residule engine heat - supercompressing air will make it hot and volatile so from an engineering persepctive you need to keep the temperature down as much as possible... There's bunch of complex mathmatical and experimental papers that i am not qualified to interpret (a quick journal search will turn these over). There will be a theoretical maximum derived from a relationship to the critical point of oxygen/nitrogen air mixtures... maintaining vapourised fuel will also be a massive issue at ultra high pressures... All these things could be graphed and you could decide on a value form an artbitrary engineering or theoretical perspective (the theoretical number will be higher). Basically you need to control autoignition, this gets very difficult EVEN with maximal cooling(theoretical) due to the dropping autoignition point associated with increasing pressure (increased density, molecules move closer together, less energy required to get them to "bump" into each other). futhermore.. when dealing with these kinds of pressures and temperatures the laws governing behavior of gases get a but muggy as they approach a supervolatile fluid phase. short story, there is no answer to this question that i can see.. you will run into engineering challenges WAY before you hit theoretical issues... things to consider include: *running maximal fuel pressure and injecting fuel as late as possible before ignition to prevent vapour-liquid transtion *ultra intercooling - like running liquid nitrogen heat exchangers the size of a small house &ultra engine cooling - " "^ *massively reduction the heat transfer within the intake and combustion chambers - think crazy ceramics in the CC and cylinder bore. *exotic fuels with ultra low vapour transition pressure and temperature points ^an interesting point because you need temp to help with fuel vapourisation... but due to dropping autoignition points you will have to run the motor supercool... meaning you rely solely on mechanical pressure to vapourise fuel during injection and this will return to liquid phase almost immediately - see the first * i'm sure i can come up with some specific documented attempts... but i dont have have the time to do the readings right now I'll try to add more later or maybe someone more qualified could shed some insight on this. -pete Ummmmmm, yeah what he said. Wind the boost up until something blows, then back it off a few psi. You'll find your boost limit quicker that way. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 20, 2010 Share Posted February 20, 2010 The definition is lacking to be able to answer simply. If detonation is not present, then the TURBO and it's pressure ratio/flow curve will dictate how much boost can be made. Especially if the turbo is flowing more than the engine can process. This will eventually raise the pressure in the inlet manifold to a point where the compressor experiences natural surge. If the compressor is undersized, and you don't want to overspeed it...you will reach a terminal boost, and as engine starts consuming more air, the pressure will drop as the compressor flows more air at a lower pressure as it starts its march towards stonewall... In some engines (5.0 Fords for instance) the heads will start lifting off the block due to flex at some BMEP levels. Quote Link to comment Share on other sites More sharing options...
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