Porting

You should do some porting on the head in order to help the flow.

The D1105 before 2002 has a lot of extra meat inside the ports. The later heads are much more open but can still use some work.

I like to use an air dremel with carbide tips. Remove the valves and stick them into a cardboard  sheet and number them (make sure they go back into same place).

Inspect the head carefully for any cracks or even better send it out and have it checked. Try to remove the same amount from each port on both intake and exhaust.

Remove burs and open them up but be careful not to go too far and end up in the water chamber. I also remove some around the valve stem area.

A little trick you can do for the finish polish is take a 3/8 bolt about 3 inch long and cut the head off. Next take a cutting disk and put a a cut lengthwise about an inch long. Take some emery cloth sand paper rip it in 1.5 inch strips about 3 inch long slide them into the slice you made and chuck the other end into your drill. Spin it and hold the paper it will turn into a nice circle for buffing and you can just keep changing it out to finer grit.

It would be a good idea to replace the head bolts with arp studs  Arp number 201-5002. With these you should be able to put a little more torque. 

With the higher rpm it would be a good idea to replace the stock valve springs with heavier ones as well as heavier push rods these can be found at  Zach Kerber website. 

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