Contour Enthusiasts Group Archives Forums Modifications Forced Induction price for power???

Originally posted by Pascal:

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Originally posted by TommyBoy:

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However lets not stray from the statment: That a turbo is not Rpm dependent!!!

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You're right. A turbo is NOT directly RPM dependant. Did you just contradict yourself?

Dahhh, I was refering to the statment someone else made

Doesn't that make any sense?

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I got a better questions, does any thing you say make sence??

Also directly or indirectly a turbo is Rpm dependent!!!
If any one can prove me wrong, I will eat dirt!!!!

As far as this thread goes, I am done discussing this, this is like beating a dead horse !!!!

Originally posted by TommyBoy:

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Originally posted by Pascal:

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Originally posted by TommyBoy:

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However lets not stray from the statment: That a turbo is not Rpm dependent!!!

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You're right. A turbo is NOT directly RPM dependant. Did you just contradict yourself?

Dahhh, I was refering to the statment someone else made

Doesn't that make any sense?

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I got a better questions, does any thing you say make sence??

Also directly or indirectly a turbo is Rpm dependent!!!
If any one can prove me wrong, I will eat dirt!!!!

As far as this thread goes, I am done discussing this, this is like beating a dead horse !!!!

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A turbo is not rpm dependant, nor is it purely exhaust gas volume dependant, it is exhaust ENERGY dependant. You can rev a turbo car while sitting still, all the way up to redline, and most cars won't make any boost at all, let lone full boost. You can also slowly creep up to redline in a given gear, and build very little (comparative to full boost) boost as well.

Exhaust energy has two main components, inertia (combination of mass and kinetic energy) and heat energy. As revs increase, the mass and kinetic energy of the exhaust can increase, but the heat energy doesn't necessarily increase much, and as most people know, the heat energy is where most of the energy to spin the turbine comes from.
So, back to the question, is a turbo rpm dependant? NO. rpm does have some effect on the turbo, but there is no direct relationship; A turbo can be at ANY rpm in its operating range at a given rpm of the engine, depending upon the conditions. Where a supercharger is mechanically coupled to the crankshaft, so that, at any given engine rpm, the supercharger will always be spinning at exactly the engine speed times whatever the effective drive ratio (assuming no belt slip) is.

So, Tommyboy, does this mean I can start calling you a dead horse?

Boost of any kind isn't directly related to RPM. Boost is more closely relate to load and total engine restriction. Full throttle and 3000 RPM holds more boost than part throttle and 3000 RPM because the load isn't the same. Reduce restriction after the boost device, boost goes down, yet HP goes up, even though the load and RPM stay the same. These hold true to either SC or turbo...

Want more boost a low RPM? Get a turbo that spools up faster (either smaller in size or just more efficient), or put a smaller pulley on the SC to spin it up faster. You can make an SC achieve max boost at 2700 RPM too if you want to. Although the boost devices are not directly related to engine RPM, they are direcly dependant on their own RPM to move air. The fan trim size and shape being equal, the turbo and SC will move the same amount of air. The SC losses power through it's drive belts and pullies, the turbo through it's exhaust restrictions. Drive either without the input tube hooked up and boy, do you know it!!!

The silly part is, everyone is hashing the exact same points here.

Originally posted by TommyBoy:

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I got a better questions, does any thing you say make sence??

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Impressive comeback! I secretly admire you...

Originally posted by TommyBoy:

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Also directly or indirectly a turbo is Rpm dependent!!!
If any one can prove me wrong, I will eat dirt!!!!

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You proved me that the engine had to run. Wow.

Originally posted by TommyBoy:

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As far as this thread goes, I am done discussing this, this is like beating a dead horse !!!!

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Right on!

Thanks for the explanation Rara.

I think a major problem that people (definitely including myself) have when debating such concepts is the inability to properly word what we are actually thinking.

It's always crystal clear when it comes from you pros, and even though some of us sometimes understand it, we can never really explain it well.

Oh well, part of not being an engineer I guess.

Originally posted by Pascal:

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Impressive comeback! I secretly admire you...

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Originally posted by bnoon:

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Boost of any kind isn't directly related to RPM. Boost is more closely relate to load and total engine restriction. Full throttle and 3000 RPM holds more boost than part throttle and 3000 RPM because the load isn't the same. Reduce restriction after the boost device, boost goes down, yet HP goes up, even though the load and RPM stay the same. These hold true to either SC or turbo...

Want more boost a low RPM? Get a turbo that spools up faster (either smaller in size or just more efficient), or put a smaller pulley on the SC to spin it up faster. You can make an SC achieve max boost at 2700 RPM too if you want to. Although the boost devices are not directly related to engine RPM, they are direcly dependant on their own RPM to move air. The fan trim size and shape being equal, the turbo and SC will move the same amount of air. The SC losses power through it's drive belts and pullies, the turbo through it's exhaust restrictions. Drive either without the input tube hooked up and boy, do you know it!!!

The silly part is, everyone is hashing the exact same points here.

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My apologies brad, I should have been using the term airflow instead of boost. But I figured that in a given scenario, boost can generally correspond to airflow enough to make the point here. Keep in mind, were have been speaking of a single, hypothetical system, not modifying the system during the time of discussion, unless otherwise noted.

As far as efficiency goes, turbo has it hands down though, a supercharger loses far more through drive losses than a turbo does through increased exhaust restriction (especially compared to a typical stock exhaust system)

as far as moving the same amount of air, yes, the trim size and compressor side shape, etc. determine the flow capabilities, but, the rpm of the "boost device" determines how much flows at a given rpm. The fact that a turbo is free to rev up to its optimal rpm well before an s/c gives the turbo a great advantage as far as torque and hp curves.
The rpm of the s/c is mechanically constrained to the rpm of the crank, so, engine rpm X drive ratio = s/c rpm at that engine rpm. You can change the drive ratio (pulley change) to increase the rpm of the s/c at a lower engine rpm, to increase low-end air delivery, while using a blow-off to limit boost pressure on the top end. Keep in mind that this spins the blower MUCH higher at the high engine rpm which increases drive losses in the s/c drive, and decreases the adiabatic efficiancy of the s/c itself (more heat in the intake charge)

Rara are you saying that the 03 Cobra and the Lightning would produce more torque and not have ANY lag if they had turbo's on them instead of roots blowers?

Originally posted by RedSVT:

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Rara are you saying that the 03 Cobra and the Lightning would produce more torque and not have ANY lag if they had turbo's on them instead of roots blowers?

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No, I should have clarified with the statement of a centrifugal blower. A positive displacement blower is a different, though similar animal, with its own pros and cons.

Boost make car go fffaaaasssssstt