Question for those that have drilled out heads

**hiss1908** · 01-15-2019, 11:00 AM

Hi. I have a 2002 250 Pro XB SN-OT430677. I’m currently looking for some 300 promax heads and have finally found a set. Only potential issue is they’ve already been shaved 30 thousandths. I was wondering if anyone could tell me what that would put my compression at as I’m not really wanting to go over 140 psi. Thanks guys.

**Jay Smith** · 01-15-2019, 11:41 AM

JSRE modifys ALL 3 liter head to any desired cc and compression numbers desired by the customer. We also put back stock OEM gasket complying Water and compression side o rings

JSRE ( Jay ) @
832 597 2603

**Jay Smith** · 01-15-2019, 12:08 PM

Last month built a modified 280 , the coustomer requested over 200 lbs cranking compression at sea level , we cut the same water side stock OEM gasketed spaghetti O ring but I’ve found the 225 X triangular compression O ring to “live” better in the O ring heads that come with a normal OEM round o rings , this is things I’ve learned cutting the O ring style heads on motors that make 225 lbs + and some on alky with heavy specific gravity numbers which is like compressing concrete with these triangular shaped OEM 225X compression side O rings the live lots better and available from Mercury or Pro Marine , good luck !

JSRE ( JAY)
832 597 2603

**hiss1908** · 01-15-2019, 06:46 PM

Thanks Jay. If I decide to shave down my XB heads I will keep you in mind. I'm trying to find out the compression numbers if the 300 promax heads shave 30 thousandths.

**Jay Smith** · 01-16-2019, 07:12 AM

The 300X heads are pretty much as tight as I’d run using pump gas , cutting them .030” and trying to run our crappy pump gas premium would be IMO risky ...

Jayb

**KIRCHNER** · 01-16-2019, 10:38 AM

DO u know the bore size on the 250? .o3o should only be a couple of cc-3-4. educated guess from 2.5 shaving. 8-10 psi.

**Jay Smith** · 01-16-2019, 12:11 PM

According to the geographic location ...After cutting litterly thousand of 2.5 heads I find most umbrellaed shaped combustion chambered head yield a loss of CC for every .010” of material you remove you will reduce the CC by .7 ( Take off 030” you reduce CC’s by 2.1 CC’s )

Good luck ,

Jay