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Old 02-16-2007, 06:52 PM   #1
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Default Somethin to chew on

Here is somethin i have been wondering, and i dont remember reading about it in maximum boost... What is the limit as far as psi goes of the ammount of boost you can shove in an inturnal combustion engine before is is inefficent? and stops making power? Assuming of course you could get enuff fuel in with the air to keep a good AF ratio.


Anyone know?
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Old 02-16-2007, 07:47 PM   #2
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I dont know if there would be a limit, assuming temperatures and fueling is not an issue. The point would come where timing would have to be retarded too far to make more power, the turbo cannot spin efficently enough, or engine parts would break from the stress, but I dont think theoritically there would be a limit

oh ya, when F1 allowed turbocharging, some cars were running close to 70psi if that means anything to ya
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Old 02-16-2007, 07:51 PM   #3
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yeah, i've seen a supra running ~63 psi putting out over 2kHP so hell i don't know about that one.
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Old 02-16-2007, 07:59 PM   #4
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Old 02-16-2007, 08:02 PM   #5
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That's funny that you bring up that link, my questions in that thread never did get answered. Anyone else have answers to my questions there?
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Old 02-16-2007, 08:14 PM   #6
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yeah it is abuot seat restraints. good catch. Also the other is way expensive,
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Old 02-16-2007, 08:58 PM   #7
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It stops making power when it blows.

You´re limited by:
-Fuel
-Cooling
-Detonation
-Turbo efficiency / flow capacity

Yoy solve those three issues, let´s say standalone with 4000cc injectors, infinite cooling capacity, 300 octane fuel and a gigantic turbo, it would stop making power when the rod bends, the ringlands fail, the piston blows or the block cracks.
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Old 02-16-2007, 09:18 PM   #8
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And psi is just a measurement of the engine's resistance to flow. So... increase the flow and the boost needed for a given power will lower, I'm simplifying it but I think that helps get the point across.

Take any motor and boost it, after that work the heads over and get some cams capable of making power at double the stock power peak and a bottom end capable of surviving there. Now find another turbo that can efficiently make the same boost pressure on the new set up and the horsepower will be greatly increased.

Look at the performance diesel guys, they are running well into the 100s as far as boost goes.

Metallurgy is the limiting factory really.
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Old 02-16-2007, 09:38 PM   #9
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Hmmmm... this does sound like one for Corky. But I'll say something stupid just for a laugh.

Suppose you had infinitely strong engine internals and unlimited cooling... there's gotta be some theoretical upper limit.

Does it have anything to do with the fact that you can't compress a liquid? You could dump 49.5cc of fuel into a 50cc combustion chamber and then boost as needed to get a nice A/F... but it wouldn't fire. Somewhere prior to that you simply couldn't atomize it. Some sort of fuel saturation. Am I even close?
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Old 02-16-2007, 10:28 PM   #10
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that is why we bolt on turbos
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Old 02-16-2007, 10:50 PM   #11
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I don't know if there is a boost limit, but there has to be an ultimate compression limit. At some point the A/F mixture will be compressed to the point where it becomes a liquid, at that point it would either stall or break the engine, no matter how strong it is made.
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Old 02-16-2007, 11:00 PM   #12
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good point

ok im doing the math now ...

hmm thats interesting

ok got it. The number you are looking for is 147.67psi. Cant go any higher than that sorry to say.
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Old 02-17-2007, 12:23 AM   #13
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i thought this one would get some intrest.. Thanx for all the NHRA facts
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Old 02-17-2007, 04:24 AM   #14
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Quote:
Originally Posted by Kurt Rohmer View Post
is that 147psi for the miata motor? or is it the compression charge of a single piston regardless of engine? and what kind of fuel are you using to solve for your equations? different fuels offer different stoichiometric values for a given quantity of mix... so which did you use? nitro, gas, alky, blue gas, blend?
lol it was a joke, i just made that number up.
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Old 02-17-2007, 11:36 AM   #15
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hmmm could you compress the mixture so much you can extract zero point energy from it? now that would be power.
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Old 02-17-2007, 11:39 AM   #16
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back in the days when I had my Starion, there was a guy pushing 54psi, yes fifty-four, on his car for drag racing. Thats pretty retardedly high.
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Old 02-17-2007, 11:55 AM   #17
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some diesel trucks have been known to run over 150 psi.. (think I saw 230 or so on a drag racing semi).
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Old 02-17-2007, 12:33 PM   #18
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well you are right to a point the higherthe compression the less movemet allowed in the substance hence going to liquid and then solid. or just skipping liquid all together. Gas is where the matter uses most of its energy in kenetic motion of the molecules. And occurs at lower pressure reading more easily or higher temps. So if you either create a serius - vaccuum or cold enviroment then the molecules will calm down.
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Old 02-17-2007, 12:56 PM   #19
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diesel motors depending on the build can easy run 100s of psi. Specially competition drag semis
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Old 02-17-2007, 02:37 PM   #20
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Having experienced a 9000 RPM launch with 38psi through a 74mm turbo on a Supra with cams and head work I cannot even fathom how absolutely terrifying a Top Fuel car would be. 6 times the power and half the weight...
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