Originally Posted by 03 tls nc

Both blocks are the same. The only difference in the oil pumps is the pressure valve and spring, the J32A2 parts can be purchased for around $20. The coolant crossover manifold is different but can be made to work. The EGR valves are different and must correspond to the appropriate ECU. Of course the crank, rods and pistons are different. J35A3 has forged crank and rods but they are not comparable to after market forged rods but still better than cast (J32A2 has forged crank only). The heads are the same castings and use the same valve seats even thought the J32 uses a 1mm larger intake vale (with a valve job the smaller valve will flow more, due to less shrouding). Lost motion assemblies were updated for the 03 J32. The cams and springs are different (J32 springs are considerably stronger). The intake of the J35 utilizes are 1" spacer between the upper and lower runners and the upper intake is the same between the two with the exception of the longer trumpets used on the J35 (produces more torque below peak). The TBs are the same with the exception of the MAP sensors and the corresponding MAP sensor must be used with the correct TB (both use the same plug).

If forced induction is in your future use the J35A3. Clean up the casting marks in the intake tract but do not increase the size and enjoy the lower static compression and cams with less over lap. (upgrade the oil pressure spring and valve for good measure)

For some NA fun on the cheap start with J35A3 use J32A2 cams and springs, port from the J35A3 IM to the valves, valve job and mill the head. (.010" is approximately equal to 0.25:1 static compression with J35 rotating assembly). I milled mine to 0.030" with no valve clearance issues and an estimated 10.75:1 static compression (no issues achieving correct mechanical timing with 0.030" milled). I also upgraded the oil pressure spring and valve in the bottom of the oil pump.

Assuming that even if you don't separate the heads and run the long block as is replacing all exterior seals and gaskets only makes good since. Since you have to pull the pan to replace the the gaskets behind the oil pump and pickup, removing one allen plug and dropping the J32A2 oil pressure spring and valve in place is some really cheap insurance.