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Discussion Starter #1
Does a car "come on to boost" as a factor of WOT, or is boost purely RPM dependent. I understand the difference between the different types of boosters. I'm a little suprised with my own Z06 to see that the ALKY system doesn't come on at RPM's progressively, but does come on at WOT progressively. I have a Vortech SC.

I kinda thought it (ALKY) would start coming on at 3 to 4K and increase from there. This happens only at WOT.

Can anyone enlighten me?
 

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From my understanding these are the general characteristics:

Boost produced by centrifugal compressors is RPM dependent. The boost builds up in an exponential fashion so maximum boost is not reached until RPMs get up in the proper range.

All turbochargers are centrifugal pumps driven by exhaust gasses. I don't see how they could be effectively designed any other way. Turbochargers are thus dependent on RPMs but throttle also has some effect because you have more gases to drive the turbine.

Superchargers on the other hand are belt driven and have two major pump types - centrifugal and positive displacement. Throttle doesn't have much effect on the boost produced by either type of supercharger (outside of a bypass valve activation) since the speed that they're turning is in a direct ratio with engine RPM. The centrifugal pump supercharger produces boost similarly to a turbocharger. Boost produced by positive displacement superchargers is mostly independent of RPM in that the SC will make very close to the maximum boost across a wide operating range.

You said you have a Vortech SC so I'm assuming its a centrifugal pump. The WOT dependence you see isn't much different from the WOT dependence of an NA engine. The SC is making the same amount of boost at that RPM, you're just not all of the air get into the cylinders at part throttle. Thus less fuel is burned and less power is made.

If anything I've said isn't quite right, feel free to correct me.
 

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I was under the impression that the injection kits (alkly)
had a variable controller that was set to when the boost RPM range was reached. Say 3800 rpms is when boost starts to force its way into the motor and the controller starts with the injection. Im no expert just what ive read.
 

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Effective boost on setup with BOV should be considered. I can with about 1/4-1/2 throttle run the rpms up to 5500 rpm or so and the needle on the boost gauge will stay on the vacuum side. If I punch it boost comes on around 2200-2500 and maxes out at the some where near the top of the rpm range. The BOV doesn't really fully close without the WOT condition. So yes, boost on a centrifigual S/C is rpm dependent, but effective boost (power to the rear wheels) is a function of WOT. Just a humble newbie to S/C's Opinion.
 

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Discussion Starter #5
Zrod said:
Effective boost on setup with BOV should be considered. I can with about 1/4-1/2 throttle run the rpms up to 5500 rpm or so and the needle on the boost gauge will stay on the vacuum side. If I punch it boost comes on around 2200-2500 and maxes out at the some where near the top of the rpm range. The BOV doesn't really fully close without the WOT condition. So yes, boost on a centrifigual S/C is rpm dependent, but effective boost (power to the rear wheels) is a function of WOT. Just a humble newbie to S/C's Opinion.
Zrod, I don't have a boost gauge but your description seems to be exactly what I'm experiencing. I can run up the rpms and didn't see the alky coming on. At WOT, it progressively comes on just like it's supposed to. I have a controller that monitors boost to bring on the ALKY spray. I didn't realize the BOV didn't fully close unless you were at WOT.

Makes sense now!! Thaks to all who chimed in here! :thumb:
 

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If they closed at part throttle, you would get WOT acceleration, without being at WOT, which would cause a few problems ala Audi 5000!!!!!!
 

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Discussion Starter #7
Pakisho said:
If they closed at part throttle, you would get WOT acceleration, without being at WOT, which would cause a few problems ala Audi 5000!!!!!!
Thanks Pakisho. I got the gist from Zrod, but I appreciate your participation. :guiness:

Roger
 
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