I finally have my car running! I need help setting the timing on it. I noticed that the spark plug holes/location are slightly different between my NA s4 housing and the replacement s5 turbo housing. Does this mean the stock s4NA pulley marks will no longer be accurate for timing with the S5 housing? How do i solve this issue? Do i need to physically look for the seal on the L and T holes and mark my pulley? Do i need to advance the timing in order to use the S4 pulley marks?

 

TDC is a relationship of the crank taking the rotor to its maximum displacement position

this has nothing to do with spark location, and at any rate neither housing has both plugs equidistant from the housing waist position

the crank pulley will still be displaying TDC
the ecu program however has optimised ignition timing for the other spark plug locations
but the swap has been done many times with no problems
and fuel burn rates are often different to back when designed
and so many report a slight increase in performance when running the later engine with early ecu

 

great so I don't have anything to worry about setting stock timing on my streetported NA using 2 s5 housing? Why is it catastrophic to mix rotor housing from different series if timing doesn't matter on housing differences?

 

because the spark plugs are in different places.

when the spark plug fires, timing, is different from WHERE the spark plug fires, plug location.

perhaps it is better to say that when you physically move the spark plug, you do want slightly different ignition timing.