Nissan 370Z Forum - View Single Post

wstar · 01-21-2013, 09:23 AM

Well, I'm sure we will see pulley-attributed failure, eventually, if the threads aren't out there already waiting to be found. Some will be installation issues, and some will be choosing the easy target when the real cause of engine failure hasn't been accurately determined and they want a scapegoat. Separating out the true pulley-induced failures over the internet would be difficult in itself.

My engine's at ~34K miles now, with over 2K of that as track miles. I've had Stillen's 20% underdrive pulley on for most of the engine's life, and not had any issues so far as I can tell. I think it's probably reasonable to assume, although certainly not proven, that altering the weight there could at least wear out some bearings faster, as mentioned above. Does it make a 5% difference or more? No idea. If anyone's done the engineering study to figure that out, you'd think it would be the pulley mfgs.

I also question why people never bitch about swapping in lightweight flywheels as much as they bitch about this mod. The flywheel would be at least as important in terms of balance (but maybe not so much damping), and is far more difficult (and critical) to balance correctly when manufactured.

If you're on the fence (not because the data's on the fence, but because nobody here really has conclusive information), my gut feeling is that even if you believe the worst, it's probably even safer on a 7AT car than a 6MT car, as the 7AT has the crankshaft coupled to the Torque Convertor, which probably acts as a huge fluid damper most of the time anyways.

The most-legitimate reason I've seen to fear this mod so far is what GTM documented and others have verified (and makes basic sense): these Al pulleys will often weld themselves to the crankshaft over time. Dissimilar metals and heat and a tight fit and constant rotational torque, etc. If you ever want to take that pulley off again (e.g. to do some engine-internals work... or I think it also has to come off to replace the oil pump) or plan to go FI (which probably ups the harmonics risks and makes it pointless to worry about little things like pulleys), you need to be aware that removing the Al pulley could be very very difficult and require some serious heat and torque.

01-21-2013, 09:23 AM	#57 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	Well, I'm sure we will see pulley-attributed failure, eventually, if the threads aren't out there already waiting to be found. Some will be installation issues, and some will be choosing the easy target when the real cause of engine failure hasn't been accurately determined and they want a scapegoat. Separating out the true pulley-induced failures over the internet would be difficult in itself. My engine's at ~34K miles now, with over 2K of that as track miles. I've had Stillen's 20% underdrive pulley on for most of the engine's life, and not had any issues so far as I can tell. I think it's probably reasonable to assume, although certainly not proven, that altering the weight there could at least wear out some bearings faster, as mentioned above. Does it make a 5% difference or more? No idea. If anyone's done the engineering study to figure that out, you'd think it would be the pulley mfgs. I also question why people never bitch about swapping in lightweight flywheels as much as they bitch about this mod. The flywheel would be at least as important in terms of balance (but maybe not so much damping), and is far more difficult (and critical) to balance correctly when manufactured. If you're on the fence (not because the data's on the fence, but because nobody here really has conclusive information), my gut feeling is that even if you believe the worst, it's probably even safer on a 7AT car than a 6MT car, as the 7AT has the crankshaft coupled to the Torque Convertor, which probably acts as a huge fluid damper most of the time anyways. The most-legitimate reason I've seen to fear this mod so far is what GTM documented and others have verified (and makes basic sense): these Al pulleys will often weld themselves to the crankshaft over time. Dissimilar metals and heat and a tight fit and constant rotational torque, etc. If you ever want to take that pulley off again (e.g. to do some engine-internals work... or I think it also has to come off to replace the oil pump) or plan to go FI (which probably ups the harmonics risks and makes it pointless to worry about little things like pulleys), you need to be aware that removing the Al pulley could be very very difficult and require some serious heat and torque. __________________ 7AT Track Car! Journal thread / Car setup details Last edited by wstar; 01-21-2013 at 09:28 AM.