There is a particular car I am interested in the 2024 Acura Integra Type S. It uses the 2.0L turbocharged 4-cylinder engine; however, it makes 320 hp with 310 lb-ft torque. It does it with 25.2 psi of boost.
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Given it’s a turbocharged DI-only engine with up to 25.2 psi of boost, how much boost is too much before the longevity of the engine is effected? Is 25.2 psi boost a lot already?
how much boost is too much before the longevity of the engine is effected?
I don't know why there should be some kind of tipping point or cliff in the boost pressure.
I think the point is simply the higher the compression in the cylinder, the more stress on the engine, starting at zero.
Also, ANY amount turbocharging automatically adds a whole bunch more parts, complexity, and points of failure
There is a limit to how much you can compress something before it basically stalls. Idk what it is, though. Jet engines can experience compressor stall if there are too many stages. There comes a point where you can't compress the air anymore, because the outside air pressure is way lower than that inside the engine. The air wants to move from high pressure to low pressure, not low pressure to high. I believe it's in the range of around 60:1. It's a part of the Brayton Cycle. We were just starting to dive into engines before the final exam in Thermodynamics. Also, the assumption of adiabatic compression breaks down after a certain point, and fuel can detonate prematurely. We see that in real engines. Jet engines compensate for this by using kerosene, which has a higher flash point than gasoline. There are intercoolers and such, but it only delays the inevitable.
@justin-shepherd
This is a bit outside of the realm of DW's question. You're talking about maximums and he's looking for a minimum.
Anyway, if you cool it, a gas can be compressed until it becomes liquid.
Above -140C (-220F) air enters supercritical phase and can compressed indefinitely. Or eventually with enough mass and gravity to overcome nuclear forces, a neutron star.
There must be pockets of gas deep in the core of the earth compressed more than 60:1.
But yes, inside an engine we are limited by materials that man is able to produce, and the ignition temperature of your fuel.
Cast iron yields in tension at about 9500 psi (655 bar).
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The mixture will heat up adiabatically (the work done by squeezing is converted to thermal energy) and conflagrate long before you reach the limits of compression.
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Given the right engine (cylinder, piston geometry and stroke, etc.), how much you can compress your mixture in the combustion chamber is primarily given by your fuel. The way the engine can control the compression ratio dynamically, is with the spark timing. It ignites the mixture when it reaches a desired compression (piston angle), which may not be 100% (though you lose some efficiency that way.)
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About 9.3:1 for 87 octane gasoline
11:1 for 92 octane gasoline
13:1 for 100LL (aviation gasoline).
25:1 for diesel.
There are also strategies to slightly elevate compression, such as "stratified charge"
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However, these things describe what happens INSIDE of the combustion chamber.
Turbocharging , and the pressures that DW asked about, happens OUTSIDE of the cylinders. Indicated boost is the pressure before it even enters the cylinder. I don't think compression provided by the turbocharger significantly contributes heating of the chamber and pre-detonation. Especially those with intercoolers, where the air charge is cooled to make it even denser. I'm going to guess that the limits of turbocharging involve: (1) the size of the engine and combustion pressures (not compression pressure) it can withstand, and (2) the pressures that all the intake gaskets/manifolds/etc are able to withstand.
jet engines are a little different since there are no pistons or turbochargers, just turbine compression stages, and all of them are output driven.
Wouldn't the capacity of the blow-off valve be a limiting factor?
Given that at sea level, the atmosphere only exerts 14.7 or so PSI on Earth, that's a pretty substantial amount of force. That's the equivalent of approximately one and a half more atmospheres on the piston. The absolute pressure on the piston is almost 40 PSI when the turbo is spooled all the way up, and that's before compression starts! That's a pretty insane amount of boost, if you ask me. Assuming compression happens adiabatically, (assuming no heat is generated during compression) and assuming an 11:1 compression ratio, you have nearly 440 PSI at peak compression. I'm not the most familiar with boosted engines, I prefer naturally aspirated ones. I like doing the math, though, lol.
Is 25.2 psi boost a lot already?
Sounds pretty high to me. I'm used to seeing 12-15 psi boost, but that's on decades-old turbocharged engines that make relatively modest output.
I am not familiar with Acura engines. However just to give you some sort of a reference point: the 2.2l engine in my 30 yo Audi Avant with 340 kkm and 275 hp is still running with its stock 31 psi of boost, and the car is still on its factory motor and turbo with no rebuilds behind.
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And guys I used to know increased the boost pressure on the same AAN engine to 34 psi and more, and still got 400+ kkm out of this setup. Not that their engine blew up after that - it is just that I lost contact...
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So IMO for a well-built engine 25 psi appears to be a rather conservative figure.
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My feeling is that the most important danger factor is not that much the turbo boost figure, but rather the torque figure. Engines seem to withstand excessive boost pressure much better than automatic transmissions can withstand excessive torque. My engine has an aftermarket chip in it, increasing the hp from the stock ca. 220 hp to 275 hp, and this chip has an additional limiter which under certain conditions artificially decreases the engine torque output to safeguard the transmission.
My, my.... how the mighty have fallen. I thought you were determined to get the final model year Lexus ES 350 with the naturally aspirated V6 before they they transitioned to the turbo 4 cylinder engine. And now you are interested in a turbocharged 4-banger Acura?
As my grandmother would have said (many years ago) "Why, it's a shame and disgrace to the whole neighborhood." 😥
Still am, but just intrigued by the new Integra Type S. Also, my current ride is a 329,000 mile 2000 Acura Integra so a soft spot for Integras.
Just teasing, but thank you for the explanation. So I guess the neighborhood's integrity is still intact. Grandma would be pleased.
Wow... 329,000 miles and 24 years old! Like an old, faithful friend.