I am looking at getting a MPS, so i can switch back to stock if needed.
with intake, high flo cat would i be ok to run a 3.4 pulley?

also, instead of changing the belt can i change a tensioner pulley?
which one and what size should i switch to?

Without a scantool to determine KR, the 3.5 may be the safer choice for you, and may net more power than the 3.4 SC pulley. It varies from car to car.

As far as the belt vs. idler pulley is concerned, from what I've seen, the first step down will be ok on the stock belt and larger idler. When you start to go smaller, you'll need the shorter belt.

if you are wanted to go back to the stock pulley, then dont get a MPS, get a normal press on... with the MPS you have to get a special removal tool and such...

if you want to get a MPS and then be able to put a 3.8 MPS pulley back on, thats what you would want... but nobody does that...

would auto xray be able to scan for KR. my friends dad has one
be he said i would need a laptop to check for KR..

i would like to get a 3.4 just so i can get that little bit more outta her.

:?:

www.google.com

Find the model of his XRay and double check it. Most of the time it'* a GM Enhanced parameter.

We unfortunately don't have enough information from what you have posted about the tool to know if it would or not.