Mobile Celeron 1.8

I have a laptop with Mobile Celeron 1.8. I tried dropping a Mobile Pentium 4 in it and it defaulted to 1.2GHz. I know that the Celly runs on 1.3v. Now if I took a Northwood and removed heat spreader (so it would fit in mobo), would it default to 1.5v or would it default 1.3v? I'm just about positive that just about any Norty would run default speeds at 1.3v. I wanna put a Pentium 4 in this puppy. The Mobile Celly's only have 256k L2 cache.