Here's a nice B20 Head that I reworked to provide 9.8 compression and ported the throats. This was done last year (2003) and the performance increase was readily evident. I drive this car as my only transportation and therefore clocked 16,000 miles with this head.
Same time but from a different angle. Please notice that they are not all the same height! A Volvo B20 has exhaust valves on the outside and the two middle ones. I adjusted the valves 4 times because I kept listening and could hear a difference. Each time the valve gap had narrowed...mostly #5.
A close up reveals the extent of the damage. Without hardened valve seats, the softer metal just gets banged and hammered into itself. Loss of compression is the least of the problem. Performance is terribly effected as is the heat dissipation and even the timing. The valve will close well after it is designed to close. The heat at those edges will burn the valve and the valve guides wear. Thinking more about it, If I open the gap to .020 as per the cam spec, how much am I "clearing" my little tunnel I have begun to dig??
I have the head getting new hardened seats and will provide pictures next week with the head done!
Fixed Head !!
This is a "F" head and I have reverted to SU carbs. When this is done the injector hole needs to be blocked. It can be done with a soft plug but the small hole should be blocked all the way into the throat to avoid disturbing the air flow and direction.
Intake port close up. Extreme "porting" for racing and high performance will go into the throat and cut away some of the valve guide to open up the volume and increase the velocity. This needs to be done by an expert. There's water flowing through the head and you can get too close or you might shape the chambers and not get the desired results.
This condition is only present in the exhaust valves. The intake valves are closed when the big heat goes by as the cylinder breathes out. I am very happy with the work and recommend whenever you are next busting into your engine... have this work done. The cost of the work was $350 for 4 exhaust guides, 4 hardened inserts, and one exhaust valve (it was "burnt"). The burned valve was from the valve going down the tunnel and essentially disappearing and not performing the function it for which it was designed.
The amazing thing was how well the car ran right up until I put it away for the winter. I listen very carefully to my car and have for 23 years. I really know what is right by the sound of the B20. The performance was not noticeably impaired for a road car and although I adjusted the valves 4 times in the 16,000 miles I drove in the first season since the rebuild, I cracked open the engine only to investigate the frequent valve adjustments. Why was the adjusting necessary? Bingo! I am now enlightened.