I am currently in the process of rebuilding my engine (N14) after a seized vacuum pump caused the cam sprocket bolt to be sheared resulting in 2 bent valves. So far I have already bought a new head which I've ported slightly and fitted with Supertech valve springs and new valve seals with the plan of upgrading the camshafts down the line once the engine is broken in. From researching it seems that with the most aggressive Cat Cams (1302602) there can be issues with piston to valve clearance. It seems the most popular pistons for the N14 engine are the CP pistons, I was originally planning to stick with the stock 10.5:1 CR, but would running the 9.5:1 pistons give the necessary clearance for the more aggressive cams or do they still need to be machined further? I wanted to stick with 10.5:1 so the motor could be broken in on the stock tune and then I could swap turbos to a JMTC K04 47mm and have the car tuned for that and the additional compression ratio would produce a bit more power and help with spool. I have all of the necessary supporting mods for the larger turbo already (intercooler, exhaust, downpipe, clutch, etc.).

 

Try to see if someone else has already done the setup you're intending to put together. If not, I'd be very careful about piston clearance.

 

When choosing cams for my build, I was told by Manic that the 1302602 cam was not one of the cams he tunes for and the 1302603 was a better choice. Nothing was said about valve / piston clearance. When selecting pistons, I found an order form on CP's site that allows for cam lift. It wants all kinds of info I couldn't provide, but with a little help, you could order CP pistons that will work with Cat's wild cam. Note the attached pics --- one of my 10.5:1 after a run with 30PSI boost, the other of my 9.0:1 CP's after a crank bolt loosened. Both sizes have factory reliefs for valves. I would expect the reliefs to be deeper for the 1302602 cams.

If you plan to go no larger than a K04 turbo, 10.5:1 pistons might be OK, but 9.5:1 would be a safer choice. I suggest you talk with your tuner before buying anything else.

Note the broken cylinder wall / blown 10.5:1 piston. Had the thick head gasket installed too.


CSS installed to protect cylinder walls, but a loosened crank bolt still caused timing issues and bent valves. 9.0:1 pistons were smoothed out, re-balanced, and re-used.

 

That was the information I was after, when I was looking at the Cat Cams on the detroit tuned website I noticed it had said machining of the pistons maybe required and would not work for stock or Supertech pistons for the 1302603 cams which led me to believe that the even more aggressive ones would certainly require work on the pistons. Looking at your blown cylinder wall definitely makes me consider getting the CSS from cncwerx especially considering they're only about an hour drive away for me. As for a tuner I haven't nailed down who I'd like to go with, there is Bren tuning near me that I was looking at since I saw they can tune the N14.