I have a 1991 240sx and am wanting to start building up the engine, but i would like to know if there are any computer programs that i can do virtual builds with before i start putting money into the actual motor. I have searched thru forums and cant seem to find anything any help would be greatly appreciated.

I recommend determining how much power you plan to achieve from your motor. Then, search others around that range and also see what parts and products others are running and how its working out for them. Typically anything internal you want to stick with name brand or oem parts that are known to be reliable since once it is together, its a process to take it all back apart Hopefully this gives you some insight and also i have not heard of any virtual engine software for the KA.