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Have tried multiple combinations of 2.1 and even 2.0 with OS valves. The 2.1 will provide some intake advantage over the original 2 liter on port size. Valve size is the same for both exhaust and intake but the 2.1 and 2.3 liter have a larger port casting. It would be easy to rework your original cylinder head to increase the size of the intake ports but the 2.1 would need some porting and relieving, as well. The end result should be a port close to size of it's valve seat and since the valves are the same size, the 2 liter and 2.1/2.3 liter would be the same port size. A port that is any larger than it's valve and you will defeat low end. A larger intake valve from the 1994 and up 9000 also seemed to have an ill effect on my low end as well as the total removal of the valve port ramping on the 2 liter heads.
Make sure that the shop gives the head a full 3 or 5 angle seat and flow the valves.
With my 1990 SPG, more benefit came from preparing the exhaust ports, valves and manifold. Lag nearly fell to an all time low.
Still have an SD cylinder head on the engine which was an upgraded original 2 liter head that came with the car and the difference in port size was obvious.
Don't feel that you need to run out and buy a 2.1 liter cylinder head and and work with the 2 liter head as most of your work will be the disassembly, cleaning, and valve work. Have the shop port and quickly polish but make it a point that the finish isn't critical as most shops will spend lots of time making the ports look pretty. Your largest flow gains will come from the removal of large obstructions (guide boss, etc.) Have them do a nice valve job and call it a day.
I saved a little money by having SD send the head without the valves fitted and did the installation myself. The valves were numbered and ready to go into place.
Good luck but most of all have fun!
posted by 152.163.201....
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