Say an engine makes 500hp on the dot at 100kpa N/A. In a perfect world, with the same compression ratio, same fuel, same everything, does doubling the atmospheric pressure by running 14.7 psi mean you will roughly make 1000 hp?

 

I understand this is not possible because you would have to change the compression ratio, fuel, and other things so in real life the hp will not be doubled.

 

theres SO many variables... but i understand what u mean.. with my 416 ls3 i plan on runnin 16lbs or so to around double my hp.. but every turbo is very different as well. but typically that boost will double your hp give or take id say up to 100hp.. also on my bone stock ls1 made 290 at the wheels theu an auto.. then made 565wheel with everything same except for a t7575 on 12psi. so i imagine around 15 lbs i should make right around 600 which is double the hp..

 

yes... in theory.... the horsepower will double at 2 atmosphere

 

Interesting topic. Take for example if you took a small like 60mm turbo and threw it on a 6.0L. If it could even reach 14.7psi, the turbo would not be able to flow enough air to double the engines HP, but however if you took a 91mm turbo @14.7psi, it definitely should be able to double the hp. So I personally think that the statement should not hold true.

I think it helps to analyze the ideal gas law equation.

PV=nRT

If we set the pressure to 14.7psi, and considering that the volume of an engine is fixed the left side becomes a constant. So you get:

constant = nRT

and since R is a constant also, you can divide that across and just get

constant = nT

This helps me understand the difference between the two examples I stated up top. If both pressures are the same, then the only two things that can differ are temperature and the amount of air molecules in the motor. So for example, the 60mm would definitely put out more heat, and thus the "n" value will drop, resulting in literally less air into the motor. Whereas, comparatively, the larger turbo will have less heat in the charge and a greater "n" value. Does that help?

Summary: HP is not related to the pressure value, it is related to the n value, which is moles of oxygen.

 

I'm by no means an expert on this stuff but that would have to be based on the fact that the engine had 100% VE correct but in theory yes it should.

 

My question is does the compression affect the equation of doubling hp under certain amount of boost?

Basically Im at 10:5 CR which is a tad higher than the average build with a billet S480/96. By having higher compression enables you to run less boost. So instead of achieving 14.7psi in order to double the hp of my car, could 12lbs be the doubling point for me? Or does higher compression motors double their hp at a lower boost rating? Trying to learn more.....

 

Yes, if everything is sized and matched correctly it "should" make 2x the power you get at WOT at atmosphere (zero psi boost).

Theory test ruling out most variables, take a turbo car and set wastegate to atmosphere (0psi) then dyno it for massive disappointment. Then turn on the boost to 14.7psi and your hp should double. You can probably test it with a blower car too with a bypass.

Busted a boost hose on my STI and it wouldn't build any boost on the drive home, felt like a 3500# civic.

 

In a perfect world yes, it will double.

There are dozens of variables, though. For it to double, IATs would have to be equal as well as intake velocity, backpressure, etc.

You have IATs, backpressure (effects power as pumping losses), timing (you'll run less timing in boost), and a few other small variables working against you.

However you do have intake velocities working in your favor. It would even be possible to gain a little extra power from boost since the pressure differential on opposing sides of the intake valve are greater in a boosted combo, increasing intake velocities allowing both better fuel atomization and causing the heads themselves to be slightly less restrictive. Unless your N/A setup suffered from these problems, though, you likely won't be able to outweigh the downsides of backpressure and IATs.

 

Compressor effecincy and the major affect the Turbine have on VE are the two big players here

 

Doesn't parasitic loss play into this equation ?
Blowers or turbos use power to make power .... There has to be an effect on the net increase.

 

Im no expert....but Gayle Banks is perhaps the #1 turbo genius on planet earth.

He says a turbo system on a V8 engine......and only on a V8 engine......will MORE THAN DOUBLE its N/A horsepower with 15 psi of boost.....with a properly matched engine combo.

He has an article as to how that happens on his website.

.

 

The only parasitic loss from a turbo is related to pumping losses from backpressure. This is far far less loss than a supercharger being mechanically driven by the crank.

 

Gayle Banks article about 15psi MORE THAN doubling N/A horsepower......

http://www.bankspower.com/techarticl...Facts-of-Life-

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That's because actual pressure on most production NA engines will NEVER be 14.7 psi aboslute. For emission and noise reasons it will all ways be lower. This is why putting a freer flowing intake can often net you power gains. What you are actually doing is increasing the absolute manifold pressure and thus air density in the intake manifold.

Au summing you have a super efficient setup you could in theory make more than a 100% power increase.

 

This calculator show that it doubles, even at 80% VE

https://racingcalcs.com/psi-boost-fo...et-calculator/

 

Nice 5 year thread bump.

 

I am always curious why people are averse to someone adding to a thread that is older

Its only bumping a thread, if your intent is to drive the topic back to the top of the thread list and is usually done by the OP I don’t have a problem with someone bumping a thread if they have not received the input they desire.

I Googled a question which led me to this forum, which had lots of opinions, but didn’t seem to have a clear cut answer. I found that answer elsewhere and took the time to return to this thread and link that information for the benefit of all forum members

Why you are offended is beyond me

 

I don't get why people care when old threads are bumped either, especially when they are still relevant. Plus its really easy to do on this forum layout with endless scrolling.

That said there's a youtube video floating around of a SBE 5.3 swapped 240, they start the dyno with the charge pipe off essentially NA making ~300hp, then raise the boost and show the numbers along the way up to 1000whp.