Time bomb?
 

I have been running a 125 shot of NOS on a 100000 mile engine for a while now, and she's running strong a little smoke between power shifts. Nothing major just enough to stand out from the croud. I'm wondering if its worth while to swap valve springs and push rods (and related ie; stem seals ect.) or wait till I can afford a full rebuild.
Any one know of the first part(s) prone to brake down on NOS driven engines?

i have a stock motored mustang with almost 300,000 on her now. I have been shooting a 150 shot down her throat for 5 years, and she loves every minute of it!..... No worries drive on!!!!

Just dont over rev it or bump the limiter and you will be fine. Pssst put the 150 jets in!

might as well drive it till ya kill it if you're doing a rebuild anyways

Only problem with driving it until you blow it is if you send a rod through the block. Then you'll be finding a new block as well. If you're going to go that route, just find a new block now and start doing the work and enjoy the current engine until the new one is ready.