A friend of mine has a 916 with major motor problems. He wants to set up a 620 to race. He found an S4 for sale (916 motor).
Here's the question.....If he buys the S4, and puts the motor in his 916, can he buy a 620 motor and put it in the S4 chassis? The S4 has some of the things he needs already to set up a 620 for track, it's just a matter of will a 620 motor fit. I'm thinking he needs only the wire harness and motor but I'm sure that I'm not thinking of something. The header pipes may not fit but I'm not 100% about that.

Anyone know?

the s4 motor won't go into the 916 chassis as the swingarm location and location method are different.

the 620 motor will go into the s4 chassis if you cut the cross member in front of the vertical cylinder out.  he'll need new headers, complete inlet system, battery mounting box, some sort of 620 ecu plus other stuff.

exactly what I needed...thank you