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Old 12-25-2011, 03:38 PM
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7.3 Guru's, Boost question.

Arguing with my father in law on boost (don't ask he knows it all!) And on the 7.3 cruising down the road 55 to 60 mph and on level ground. The motor has no boost right? The turbo is basically free spinning. If you were to remove the turbo wheel out of the turbo the motor would still run ok just low on power,right? He thinks if the motor is running it has boost.
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Old 12-25-2011, 04:28 PM
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At 55 mph Im pushing 5-6 psi boost
But that's cause of 4.88 gears and 2100 rpm
Empty. Manual trans
My buddy with his f350 is push 2 psi cruising down the freeway unloaded
Auto Trans
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Old 12-25-2011, 04:49 PM
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My boost gauge reads zero...but I couldn't give you a true and accurate answer cause I honestly have no idea.
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Old 12-25-2011, 04:53 PM
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Typically the boost gauge will read 0. How ever there is a few psi of boost there. Just the guage may not be able to read it.
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Old 12-25-2011, 04:58 PM
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Technically you are still under load because of rolling resistance and friction that is inherent in motors, transmissions, driveshafts, diffs, axles, bearings, tires, air and anything else you can think of.
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Old 12-25-2011, 04:59 PM
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Hmm, that's sort of a tricky question.

Cruising on a flat road around 55 mph you will probably see a couple psi of boost. Does it need the boost to cruise at that speed? Not really, it's more so a result of the RPM's that you would be turning at that speed. The biggest issue if you didn't have boost would be that the PCM would fuel the engine differently and it would run like a turd. If you could tune the PCM to run on in a naturally aspirated mode then it wouldn't be such an issue. It would probably run like one of the old 7.3 IDI engines then.

Higher boost is a result of RPM and engine load. At idle you will show maybe 1 psi of boost, if that. It doesn't need boost to run though. Even revving it up in park you will only see maybe 5 psi of boost, and even then it doesn't "need" that boost to rev up. I've ran 6.0's with the turbo off and they will free rev up just like if the turbo was still on it.
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Old 12-25-2011, 05:16 PM
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Quote:
Originally Posted by justinmix View Post
Hmm, that's sort of a tricky question.

Cruising on a flat road around 55 mph you will probably see a couple psi of boost. Does it need the boost to cruise at that speed? Not really, it's more so a result of the RPM's that you would be turning at that speed. The biggest issue if you didn't have boost would be that the PCM would fuel the engine differently and it would run like a turd. If you could tune the PCM to run on in a naturally aspirated mode then it wouldn't be such an issue. It would probably run like one of the old 7.3 IDI engines then.

Higher boost is a result of RPM and engine load. At idle you will show maybe 1 psi of boost, if that. It doesn't need boost to run though. Even revving it up in park you will only see maybe 5 psi of boost, and even then it doesn't "need" that boost to rev up. I've ran 6.0's with the turbo off and they will free rev up just like if the turbo was still on it.
Good explanation, so were both right sort of speak. Our trucks would run normal without turbo IF we de-tuned the pcm. With the pcm as it is now it would over fuel and roll black smoke. And we aren't really using boost,its just reading because with the motor running its turning the turbo?
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Old 12-25-2011, 05:25 PM
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Pretty much. If you want to see how it runs without the PCM reading boost just take the hose off the MAP sensor sometime.

Yes, I would say that you really aren't using the boost under a light load condition, but it's still making some boost.

So pretty much your both somewhat right. Seeing as he's your father in law I'd just say your both right and leave it at that.....
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Old 12-25-2011, 05:32 PM
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Here's Internationals description of the air management system......

Quote:
Description

The intake and exhaust systems consist of those components that contain the flow of filtered air into the engine cylinders and exhaust gases to the atmosphere.

The turbocharger is used to increase engine power output by increasing the air supply to the engine, resulting in more uniform performance at various operating altitudes. The turbocharger incorporates an exhaust driven air compressor that allows filtered air to enter the center of the air compressor where it undergoes an increase in pressure from "atmospheric" to "boost" as it flows into the combustion chambers. After combustion, hot and expanding exhaust gases move out of the cylinders and into the turbine housing driving the turbine wheel. The turbine wheel drives the compressor wheel through a solid common shaft allowing the engine to respond directly to changing engine loads. During heavy loads, an increased flow of exhaust gas spins the turbine wheel faster causing the compressor impeller to spin in direct relation, supplying greater volumes of air (boost) into the intake manifold and cylinders. Conversely, with lighter engine loads, the flow of exhaust gas decreases as does the volume of air being compressed into the intake manifold and cylinders.
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Old 12-25-2011, 05:35 PM
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What he said /\
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