i was just at the phathead web site phatheadracing.com and i took a look at the 04 cr mod article and it makes this product sound like it could be a very good thing has any one had personal experiance or heard anything about it.
As bruce said, this is not a very good performance mod. Usually, a good tuner will make head modification along with porting to get the kind of powerband you asked for. I have tried on a stock cr125 to increase compression by just shaving the head and the results were not very good. I personnaly think you would spend more money than you should on the phathead. Porting from a good tuner is a better choice. For the fuel requirements, you probably will have to see for yourself if you hear detonation noises. It may also depend on the kind of fuel you buy in the first place. Around here the only fuel I found suitable to 2-strokes is the ultramar premium. Almost every other have winter additives that will cause detonation. Petro canada being the worst.
I have the phathead set up, it was worth the $$$. I have a higher comp for more power, and then a low end insert, very big improvement over stock. Also, when I am done w/ it, I can sell it on Ebay and have the other stock head to put on. Some people don't like cut heads for race gas, etc,,,,
I have a phathead on my 2000 yz125. I first put on a pc pipe and gained a little mid and top and lost a little low end. I was running race gas already so on a whim I bought a phathead. The difference was unbelevable. The motor gained power everywhere.This bike is just as fast as my ktm 144. as far as running race gas it depends on which dome you put in the head.I would recomend 100% in most of the higher compression domes. These heads also have bigger passages for water so your bike runs cooler plus you get 2 domes so you can use one with pump gas.
Freestyle they gave me one dome just slightly higher than stock that can be used with pump gas. The other one was one step higher and thats the one I used. if you look on their website they have 2 recomended domes and when you order you can change to different ones. I just took the 2 they recomended for my bike.
what they give you is a standerd ( pumpgas) and a 1 step up (racegass). You could try the 1step up with 50/50. otherwise if your not willing to use race gas the standerd dome wont give you any more power. So if you want more power your going to need race gas I know it costs alot but for me its worth the extra money.