Quick Question - Brian Crower Stroker Kit

cofo11

10psi is 10psi as the measurement is not taken at the turbo but out of the downstream system, (ie intake pipes and manifold). Now a larger turbo will make a higher boost number and will be running at a much lower percentage of capacity than a smaller turbo at a given boost number. That's where the benefits are derived.

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Chuck33079

You have to take flow into consideration. 10psi out of a large turbo is a lot more cfm than the same psi out of a small turbo.

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2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

cofo11

No, it is not. A larger turbo has the potential to flow more cfm and will be using a smaller percentage of its flow potential at the same PSI than a smaller turbo would, but 10 PSI is 10 PSI. If the downstream tubes are larger it would take more volume of air to create 10 lbs of pressure but you would still only have 10 PSI.

PSI is a function of pressure, not volume. The reason it is called FORCED Induction is that you are forcing air into the motor at a rate exceeding what the motor pulls on its own. You can have an unlimited volume (vented to the atmosphere right off of the manifold) of air available and (assuming a correctly designed intake ie no flow restriction) will still only pull in what the motor pulls through its intakes. When you add FI you are utilizing the pressure (PSI bar etc) the device creates to force more air into the motor. Thus 10PSI of air entering the same intake manifold will always be the same 10 PSI of air no matter the size of the pump. The only way to get more air into the motor is to increase the pounds per inch.


What you are describing with the "more cfm" of the larger compressor is pushing more volume into the same space thus raising the PSI of the system.

Chuck33079

Ok. So when I look at compressor maps showing flow for different sized turbos showing dramatically different cfm at the same PR, what am I missing?

Like in the following: Compressor maps - examples and explanation

__________________
2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

cofo11

You're confusing the difference in flow and PSI and what each means in terms of getting more air into the motor. If PSI is kept the same the motor could not care less about an increase in flow because without the increase in PSI it is not going to see an increase in the amount of air entering it.

Again, a larger compressor can create higher pressure levels but when run at the same pressure level as a smaller compressor its only advantage is that it is running at a lower percentage of maximum output.

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cofo11

You're missing the fact that you are confusing flow rate and PSI and what each means to the motor. CFM coming out of the compressor has nothing to do with the PSI (the amount of air) entering the motor. The motor can only naturally accept (Naturally Aspirated) so much air. Forced Induction does what it says forces more air into the motor using a generated pressure difference (PSI, bar, etc.) CFM only comes into play if the compressor cannot flow high enough to make the desired PSI.

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