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After pulling my head off and apart, I found that my valve guides were excessively worn. The valve could move in place a good 2-3 mm resulting in it not seating well, thus the low compression. Carbon also built up on the valve seat which didn't help with seat either. 20 new guides, 20 new lifters, 3-angle valve job, port match and polish, and rebuild in the process...here are my thoughts.
I am unsure of the similarities between the 7A and 3B/ABY as far as head castings. What I do know is that the 7A head can use a LOT of massaging. I was quite amazed at the casting process, or the lack of uniformity within. I didn't perform a radical port as this is a stock engine, and I have intentions of selling it. I only port matched and polished the exhaust ports. There are about a dozen casting flaws I could find in each intake port; obvious flaws that would obviously restrict flow. The sides of the ports appear round, but under investigation they may be the furthest thing from round. More off when measured, the flat sides on the intake ports aren't even of similar measurement. The smallest at 1mm, the largest at clost to 3mm. I worked those out and just buy hand you can feel the difference. There was only maybe 1mm difference between the gasket and the head...I was impressed. My last BMW as close to 2.5mm difference in some places.
The exhaust side was the worst though. There was a clear 1.5-2mm of difference between the gaskets and head. This was a good bit to be pulled off the head for a street port. The port is noticably larger...just to be port matched. Furthermore the exhaust port is 1.5" at exit, but 3/8" inside the exhaust port, the port is only 1.35". That meant I had to match .15" just to make the inside even, plus remove another 1.5-2mm to make the exhaust port matched. There is also a very sharp edge right at the exhaust port entry. This smooth showed and incredible difference. The exhaust gasses needed to make nearly a 90 degree turn right after the exhaust valves open.
To sum it all up, there is a lot that can be had from the 7A head. I am hoping for an easy 200hp at the flywheel. Seeing what I have done on other heads I wouldn't doubt this. I have before flowbench testing, and am going to get post flow bench on just a port match. I could have easily taken a lot more out. I wasn't even CLOSE to a water jacket...probably 3-4mm at the closest point now. I think a lot of the guys looking for easy power and smoother power, I would address your head. This head is clearly a production head and not a 'worked' head as in my BMW's.
Let me know your opinions!
Wes
I am unsure of the similarities between the 7A and 3B/ABY as far as head castings. What I do know is that the 7A head can use a LOT of massaging. I was quite amazed at the casting process, or the lack of uniformity within. I didn't perform a radical port as this is a stock engine, and I have intentions of selling it. I only port matched and polished the exhaust ports. There are about a dozen casting flaws I could find in each intake port; obvious flaws that would obviously restrict flow. The sides of the ports appear round, but under investigation they may be the furthest thing from round. More off when measured, the flat sides on the intake ports aren't even of similar measurement. The smallest at 1mm, the largest at clost to 3mm. I worked those out and just buy hand you can feel the difference. There was only maybe 1mm difference between the gasket and the head...I was impressed. My last BMW as close to 2.5mm difference in some places.
The exhaust side was the worst though. There was a clear 1.5-2mm of difference between the gaskets and head. This was a good bit to be pulled off the head for a street port. The port is noticably larger...just to be port matched. Furthermore the exhaust port is 1.5" at exit, but 3/8" inside the exhaust port, the port is only 1.35". That meant I had to match .15" just to make the inside even, plus remove another 1.5-2mm to make the exhaust port matched. There is also a very sharp edge right at the exhaust port entry. This smooth showed and incredible difference. The exhaust gasses needed to make nearly a 90 degree turn right after the exhaust valves open.
To sum it all up, there is a lot that can be had from the 7A head. I am hoping for an easy 200hp at the flywheel. Seeing what I have done on other heads I wouldn't doubt this. I have before flowbench testing, and am going to get post flow bench on just a port match. I could have easily taken a lot more out. I wasn't even CLOSE to a water jacket...probably 3-4mm at the closest point now. I think a lot of the guys looking for easy power and smoother power, I would address your head. This head is clearly a production head and not a 'worked' head as in my BMW's.
Let me know your opinions!
Wes