Not sure of the real plans here to help out with my recommendation yet without asking a few questions.
Is the goal for the springs for lowering or better track performance?
Other mods may be needed from personal experience to maintain drivability and handling without uneven tire wear and poor alignment. Consider wear on axle half shafts as a regular item dealt with by lowered cars. Also not having the ability to adjust alignment with stock parts means looking into adjustables like those from AAD.
Is the pulley option listed for short or long term power increase? (with a suitable tune of course)
Changing lower gives an opportunity to pin crank which is always a solid recommendation.
You mention the 9% which is the IWI model, in my experience I was advised to go with 10% ATI as a better part overall.
Have not heard of anyone having a 9% pulley fail so to speak so it may be a moot point but I trusted the shop that sells both to advise me of their opinion.
It is a good bit of work for both installs and you give no indication of the speed shop you will be working with on the project. Taking the blower snout off to swap upper pulley is doable as shown from many owners, you have to ask yourself if you will ever want to change the ring and increase boost and blower spin or just get one set UP and stay with it. If that latter is your case, then if you go with upper, I advise getting a Hellraiser or another clutched version like the one from Satera. The one from ST does offer options of clutched hub and swappable rings. I have heard of no feedback on their install or use personally.
Have a very frank discussion with a few shops to discuss your achievable goals (power and budget driven very often) and then go with who you seem to trust for their advice.
Thank you for the reply and the questions!!
The goal for the springs is to get the car to transfer weight better and lower 60’ times. I am not looking at lowering spring, both the ones I’m looking at are drag springs. I do understand that it could end up lowering the car slightly in the rear. From what I have read these 2 sling options are not hurting the drivability for most on the street, and the weight transfer seems better in most reviews.
The pulley, either upper or lower, will be done by my own 2 hands. I am more than able and capable of doing any work on this car on my own. Not planning on going to a shop to have it done. The upper is a Griptec, I know it’s been said to use clutched, while others argue it’s not needed. That debate has been had on this forum for years. The Lower is a IW one. I haven’t read a bad thing about it and it requires less cutting than the ATI. Either way a lower will probably go on(either an OD or an ATI stock size) and the crank will be pinned. I haven’t heard of the ST pulley yet. That’s a new one to me. Will look into them.
The goal with the pulley is a slight bump in HP and boost. I don’t want to do a ton and don’t plan on making this a fully built car. Being in a M6 would just like to have a little more pep.
