Getting low end from a centri ?

[Burkey]

Who said 12 psi at 3000 RPM. Who said 12 psi at 3000 RPM I thought it Was 4000 to 3000 RPMs sooner And was just used as an example

Nobody but that’s the point of the exercise is it not?
The OP was asking how he would increase the “bottom end” on his 15-17 car, presumably to a level where it can compete with a TVS or Whipple in that region.
Given that 10-12psi (12 if you really want it to go) is a fairly accepted norm for 93 octane, you’d want the thing to be making somewhere in that vicinity to be in the hunt (without allowing for the slight efficiency advantage of the Centri of course).
We can argue the semantics of what constitutes “bottom end” of course, but if redline is 8k, I’d suggest that 4-6k is mid-range, with anything under 4k falling into “bottom end”.

Some clarity from the OP regarding his vehicle and his goals might be more helpful for all concerned.

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[engineermike]

The parasitic loss is almost nothing on a open centrifugal just inhaling and exhaling. no piping just venting to atmosphere. Because it is not compressing the air. It also does not increase in temperature. Also because it is not compressing the air.

You do realize that the air vented through a “wastegate” is actually compressed first right? You’re paying the horsepower tax for the wasted air when it passes through the compressor and is pressurized. It’s over 200 deg due to being compressed to the 10 psi. It will maintain the same 200 deg when it exits the “wastegate”.

But just for arguments sake let’s say you’re right since a pro chargers parasitic lost at 10 pounds of boost is 7-8% let’s add 30% and now we are at a whopping 2% more loss But a gain of 10% more power. What is the problem?

It takes 100-150 hp to drive a compressor making 10 psi boost at 80 lb/min. Increasing flow 30% to account for a “wastegate” will require at least an extra 30-40 hp to drive, more if it falls to a lower efficiency (likely). You can see it in the graph you posted because when making the same boost, the non-wastegated combo makes more power from the same boost.

The attached curves (credit: Emerson Automation) demonstrate exactly what’s going on. [It’s almost eery how well the example graph fits our situation.]

Curves N2 represent a conventional setup without a wastegate. N3 is spinning faster but the control point is at the same pressure. The bottom graph shows that N3 takes more power to turn even at the same pressure. Also note that as you reduce discharge pressure the compressor drive power actually goes up not down as you might expect. This is due to rising mass flow and rapidly dropping efficiency.

 

[Jackson1320]

Nobody but that’s the point of the exercise is it not?
The OP was asking how he would increase the “bottom end” on his 15-17 car, presumably to a level where it can compete with a TVS or Whipple in that region.
Given that 10-12psi (12 if you really want it to go) is a fairly accepted norm for 93 octane, you’d want the thing to be making somewhere in that vicinity to be in the hunt (without allowing for the slight efficiency advantage of the Centri of course).
We can argue the semantics of what constitutes “bottom end” of course, but if redline is 8k, I’d suggest that 4-6k is mid-range, with anything under 4k falling into “bottom end”.

Some clarity from the OP regarding his vehicle and his goals might be more helpful for all concerned.

Ok. I understand now. I don’t see any centrifugal making 12psi boost at 3000rpm even a f1x. Now 4000rpm maybe, with a f1x and some aggressive pulleys and you can get close. 4500rpm is doable.

 

[Jackson1320]

You do realize that the air vented through a “wastegate” is actually compressed first right? You’re paying the horsepower tax for the wasted air when it passes through the compressor and is pressurized. It’s over 200 deg due to being compressed to the 10 psi. It will maintain the same 200 deg when it exits the “wastegate”.
It takes 100-150 hp to drive a compressor making 10 psi boost at 80 lb/min. Increasing flow 30% to account for a “wastegate” will require at least an extra 30-40 hp to drive, more if it falls to a lower efficiency (likely). You can see it in the graph you posted because when making the same boost, the non-wastegated combo makes more power from the same boost.

The attached curves (credit: Emerson Automation) demonstrate exactly what’s going on. [It’s almost eery how well the example graph fits our situation.]

Curves N2 represent a conventional setup without a wastegate. N3 is spinning faster but the control point is at the same pressure. The bottom graph shows that N3 takes more power to turn even at the same pressure. Also note that as you reduce discharge pressure the compressor drive power actually goes up not down as you might expect. This is due to rising mass flow and rapidly dropping efficiency.

ok first I did not say the waistgate I said no piping at all. In the centrifugal and out that’s all nothing else. It will not heat up because it is not compressing the air. The air only gets hotter with pressure.
So if you compress the air to 10lbs you get 200deg temps. (agreed)

Now if you are moving more air but at the same pressure you still get 200deg.
Second. what exactly are we arguing about? Will a torque booster=more parasitic loss. Yes of course, but you are going to still come out ahead as the gains out weight the loss.
the p1x is well within its Efficiency running a torque booster setup at 10psi. I’m not saying pulley it for 50lbs and gate it at 10.
Come on man your assuming someone is going to throw some sh!t together without doing there homework. You have to setup your torque booster to give you the best efficiency not go balls out. You acting like it’s a worse case scenario. If you setup your torque booster correct you will experience the benefits. Do it wrong and yes you will fu@k yourself. But a correctly setup torque booster will make more boost/power in the mid range.
this is a test done by dragzine on procharger. To find out what amount of hp is lost at a given boost. It is way less than the 100-150 you Suggested

https://www.dragzine.com/news/lose-power-to-make-power-procharger-parasitic-loss-testing/

 

[engineermike]

Second. what exactly are we arguing about? Will a torque booster=more parasitic loss. Yes of course, but you are going to still come out ahead as the gains out weight the loss. the p1x is well within its Efficiency running a torque booster setup at 10psi. I’m not saying pulley it for 50lbs and gate it at 10.

Im simply saying that it’s not all pluses with the “wastegate”, that boost for boost it will make less power and torque than one that’s not. You’re introducing what amounts to a boost leak and spinning the blower faster to compensate for it. It’s like installing a smaller cam; you sacrifice top-end power to gain torque in the lower rpm range. If the supercharger drive were something like a cvt that could reduce the ratio at high rpm, it would be different.

this is a test done by dragzine on procharger. To find out what amount of hp is lost at a given boost. It is way less than the 100-150 you Suggested

It’s rather convenient that they left the mass flow out of that test. You can’t compare the compressor drive power if you don’t know the flow rate, as I’ve stated many times before! I can assure you that procharger isn’t breaking any laws of thermodynamics.

 

[80FoxCoupe]

Centri compresses air in the volute, so even without piping the power needed to drive the compressor should be the same.

 

[illtal]

No. Because it’s not compressing the air anymore. It’s getting the same amount of boost pressure. moving air is not heating it up. compressing it does

But you still would have a higher impeller speed which should still raise the IAT. Is that a correct assumption. Are we not moving around the compressor map by speeding the impeller up?

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