wastegate with centri blower?
Originally Posted by engineermike
It's not going to pick up 4 psi boost anywhere. As Skunkworks eluded to earlier. . .
If the base case boost curve is:
1000 2000 3000 4000 5000 6000 7000
1.4__2.9__4.3__5.7__7.1__8.6__10.0
Then you pulley up, the boost curve is:
1000 2000 3000 4000 5000 6000 7000
2.0__4.0__6.0__8.0__10.0_12.0_14.0
Now, you add a restrictor to bring the boost back down to 10 peak:
1000 2000 3000 4000 5000 6000 7000
1.9__3.7__5.3__6.7__8.0__9.1__10.0
Comparing the final boost curve to the base case, you retain 10 psi peak, which is the original goal, but get more boost in the midrange. The boost gain at 5000 rpm is only .9 psi and at 6000 rpm is only .5 psi. There will be inefficiency losses at these points also, though not quite as much as the 15 hp loss at peak. The net change will be a slight increase in the 2000 - 5000 rpm range (<1 psi worth) and a loss of 15 at peak.
Mike
If the base case boost curve is:
1000 2000 3000 4000 5000 6000 7000
1.4__2.9__4.3__5.7__7.1__8.6__10.0
Then you pulley up, the boost curve is:
1000 2000 3000 4000 5000 6000 7000
2.0__4.0__6.0__8.0__10.0_12.0_14.0
Now, you add a restrictor to bring the boost back down to 10 peak:
1000 2000 3000 4000 5000 6000 7000
1.9__3.7__5.3__6.7__8.0__9.1__10.0
Comparing the final boost curve to the base case, you retain 10 psi peak, which is the original goal, but get more boost in the midrange. The boost gain at 5000 rpm is only .9 psi and at 6000 rpm is only .5 psi. There will be inefficiency losses at these points also, though not quite as much as the 15 hp loss at peak. The net change will be a slight increase in the 2000 - 5000 rpm range (<1 psi worth) and a loss of 15 at peak.
Mike
So if thats the case then a wastegate is better than a restrictor since it doesnt really come into play until 10psi. A wastegate might waste even more power than a restrictor at that point, but the area under the curve would be alot greater under 6K RPM.
Staging Lane
Joined: Jul 2005
Posts: 83
Likes: 0
Originally Posted by LSs1Power
So if thats the case then a wastegate is better than a restrictor since it doesnt really come into play until 10psi. A wastegate might waste even more power than a restrictor at that point, but the area under the curve would be alot greater under 6K RPM.
Here is low pressure boost curve (Boost bash Part 1):
Here is higher pressure boost curve (Boost bash Part 2):
Here is Z06 dyno:
My point is disk will increase low RPM flow better then pressure and this is reported by people saying car feels quicker at low RPM. As far as bleeding boost you will make your parasitic loading explode and it's not worth it because you loose so much and then never mind belt problems.
I can run numbers but can tell you it will be ugly. Look at first graph it's fairly accurate and can post more examples.
Mike
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Posts: 2,153
Likes: 3
You guys are killin' me with all these Thermo permeataions and commutations. Here's a summary of the old and new calculations:
Base case of 10 psi boost and 70 lb/min. IAT is 202 deg F and it takes 52 hp to drive the supercharger.
Pulley up to 14 psi then add an outlet restrictor to get back down to 10 psi. IAT is 211 deg F and it takes 67.3 hp to drive the supercharger.
Pulley up to 14 psi then add an inlet restrictor to get back down to 10 psi. IAT is 211 deg F and it takes 65.2 hp to drive the supercharger.
Pulley up to 14 psi then use a BOV to bleed off excess boost and get back to 10 psi. IAT is still 211 deg F (by sheer coincidence) and it takes 63.9 hp to drive the supercharger. This at first seems like the best, but let me caution you that this particular method may lose significantly more depending on how quickly the efficiency falls off at the end of the curve, and how close to the end of the curve you are running. I'm sure kp's setup would lose alot more than this since he's already running near choke flow. If I had done this same set of calculations assuming 80 lb/min, then this method would have lost the most power by far.
Mike
Base case of 10 psi boost and 70 lb/min. IAT is 202 deg F and it takes 52 hp to drive the supercharger.
Pulley up to 14 psi then add an outlet restrictor to get back down to 10 psi. IAT is 211 deg F and it takes 67.3 hp to drive the supercharger.
Pulley up to 14 psi then add an inlet restrictor to get back down to 10 psi. IAT is 211 deg F and it takes 65.2 hp to drive the supercharger.
Pulley up to 14 psi then use a BOV to bleed off excess boost and get back to 10 psi. IAT is still 211 deg F (by sheer coincidence) and it takes 63.9 hp to drive the supercharger. This at first seems like the best, but let me caution you that this particular method may lose significantly more depending on how quickly the efficiency falls off at the end of the curve, and how close to the end of the curve you are running. I'm sure kp's setup would lose alot more than this since he's already running near choke flow. If I had done this same set of calculations assuming 80 lb/min, then this method would have lost the most power by far.
Mike
Mike, in your 1st case above, the IAT at 10psi doesn't seem to sync well with the IAT after adding another 4# of boost. Are you calculating this with an intercooler in the system - if so it makes more sense.
I'm glad some people are chiming in with data that supports my earlier point - you are not going to ever get the boost curve of a positive displacement blower with a centri. They are 2 different animals with advantages & disadvantages each. I hear people on the street all the time now that believe it's all a matter of pulley change and you'll be more like a Whipple.
Jim
My Site: http://home.mindspring.com/~jim_fisk/id1.html
I'm glad some people are chiming in with data that supports my earlier point - you are not going to ever get the boost curve of a positive displacement blower with a centri. They are 2 different animals with advantages & disadvantages each. I hear people on the street all the time now that believe it's all a matter of pulley change and you'll be more like a Whipple.
Jim
My Site: http://home.mindspring.com/~jim_fisk/id1.html
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Originally Posted by DeltaT
Mike, in your 1st case above, the IAT at 10psi doesn't seem to sync well with the IAT after adding another 4# of boost. Are you calculating this with an intercooler in the system - if so it makes more sense.
BTW, I like your car.
Mike
blower, boost, calculated, centri, centrifugal, cfm, charged, control, f1a, lowest, mustang, procharger, race, spinning, supercharger, traction, wastegate
