A plate holder and quality automotive two sided tape will run you less than $10 at autozone... 5-10 min to install it...
SF off yer back
Yer undersized stock intercooler will thank you as well.
Annnd... dental floss and goo-gone will get rid of it if you want to ditch it later on.
Did you do the license plate zip tie thing before, after, or at the same time as the Solo install?
I'm not tracking how an exhaust swap would cause detonation. Am I missing something?
Now... Blocking 50+% of the intercooloer opening does seem a viable culprit.
Try the plate fix and see what happens with the detonation?
Heck, just cut it off and drive it for a little while? 4 zip strips is a pretty cheap price to see if that was the cause.
Edit: I feel your pain. It was an AF wide thing with SF.
I finally stuck on the cheapy plate holder because I got tired of explaining/arguing that where I had it in the windshield was ok as long as it was secured. (I used tape, the CA statute says "affixed no lower than X" off of the ground")
There's only so much grief I will give SF... ESPECIALLY in the only Sky on base, and one of 2 black ones in the local area
Besides, I like the guys that keep us safe. (shrugs)