naschbac
Sep 13th, 2011, 09:19 PM
I have a 2005 210hp JCW w/ about 38,000 miles on it. I love it. I'm looking to do something to get a little more power out of it, or more specifically to move the powerband down in the RPM range a little. It drives me crazy how the car doesn't really pull hard until you're up in 3rd gear and running over 3k RPM. Not crazy enough to spend big $$$ on it, but enough to see if there are some low-cost improvements available.
So I've been thinking about going with a 17% S/C pulley from Alta. They still make these, they're just not on their current website. The problem with this is that it's irreversible. Once I pull that JCW pulley off the S/C there's pretty much no going back. Short of swapping out the whole supercharger it's not likely to ever go back to stock.
This leads me to looking into an oversized crank pulley (+2 or +3 %). The obvious problem here is the lack of dampening, but this is also an issue I'm trying to understand... so bear with me.
According to the article at motoringfile.com about the MCS Powertrain this is the reason stated for the dampener:
The basic engine for the Mini One and the Mini Cooper is fitted with a conventional torsional vibration damper at the front end of the crankshaft. Calculations and measurements showed that the addition of the supercharger with its relatively high moment of inertia was resulting in excessive torsional vibration at about 1600 rpm. This solution was unacceptable both acoustically and in terms of component strength.
The torsional vibration damper used on the Mini Cooper S engine therefore has the belt pulley additionally isolated elastically from the secondary mass, with belt drive vibration damping. Vibration amplitudes are significantly reduced by the isolated belt pulley. However, the decisive factor is that the most marked resonance is shifted into a zone below idle speed and is therefore outside the engine’s operating range,
This indicates two key facts. At least as they're reported here. First, is that the reason for the dampener on the MCS and JCW cars has to do with the crank interaction with the S/C somewhere around the 1600 RPM mark on the motor, or at ~3300 RPM mark on the S/C. Second, that the function of the dampener is to move the problematic vibration down the RPM range to below idle to an RPM mark that the engine basically never operates at. There are several things I don't understand about this description at all, but here's the big one...
The implication is that the problem isn't the crank, it's the feedback on the crank from the accessories (specifically the S/C). However, a rubber belt is an exceptionally crappy tool for vibration transmission, so it's really hard to understand how such consistent vibration (that it can be isolated to the 1600 RPM band) is making it's way all the way from the S/C to the crank. Doubly so when you consider the nature of the rubber belt, the distance that it has to travel, the sprung belt tensioner, and the other accessories that it pulls through it seems like there's a whole lot of noise in that system to produce all sorts of other random vibration effects. By the description in that motoringfile.com document, you should be able to also dampen the pulley of any of the accessories to change the transmission of vibration to the crank.
There's a lot about this makes no sense to me. Can anyone clarify before I move my questioning further ahead?
So I've been thinking about going with a 17% S/C pulley from Alta. They still make these, they're just not on their current website. The problem with this is that it's irreversible. Once I pull that JCW pulley off the S/C there's pretty much no going back. Short of swapping out the whole supercharger it's not likely to ever go back to stock.
This leads me to looking into an oversized crank pulley (+2 or +3 %). The obvious problem here is the lack of dampening, but this is also an issue I'm trying to understand... so bear with me.
According to the article at motoringfile.com about the MCS Powertrain this is the reason stated for the dampener:
The basic engine for the Mini One and the Mini Cooper is fitted with a conventional torsional vibration damper at the front end of the crankshaft. Calculations and measurements showed that the addition of the supercharger with its relatively high moment of inertia was resulting in excessive torsional vibration at about 1600 rpm. This solution was unacceptable both acoustically and in terms of component strength.
The torsional vibration damper used on the Mini Cooper S engine therefore has the belt pulley additionally isolated elastically from the secondary mass, with belt drive vibration damping. Vibration amplitudes are significantly reduced by the isolated belt pulley. However, the decisive factor is that the most marked resonance is shifted into a zone below idle speed and is therefore outside the engine’s operating range,
This indicates two key facts. At least as they're reported here. First, is that the reason for the dampener on the MCS and JCW cars has to do with the crank interaction with the S/C somewhere around the 1600 RPM mark on the motor, or at ~3300 RPM mark on the S/C. Second, that the function of the dampener is to move the problematic vibration down the RPM range to below idle to an RPM mark that the engine basically never operates at. There are several things I don't understand about this description at all, but here's the big one...
The implication is that the problem isn't the crank, it's the feedback on the crank from the accessories (specifically the S/C). However, a rubber belt is an exceptionally crappy tool for vibration transmission, so it's really hard to understand how such consistent vibration (that it can be isolated to the 1600 RPM band) is making it's way all the way from the S/C to the crank. Doubly so when you consider the nature of the rubber belt, the distance that it has to travel, the sprung belt tensioner, and the other accessories that it pulls through it seems like there's a whole lot of noise in that system to produce all sorts of other random vibration effects. By the description in that motoringfile.com document, you should be able to also dampen the pulley of any of the accessories to change the transmission of vibration to the crank.
There's a lot about this makes no sense to me. Can anyone clarify before I move my questioning further ahead?