I've measured an R1 5 port GT engine;
exhaust port = 184 degrees
transfer ports = 126 degrees
29 degrees blow-down.
- Chrome was still present in top of all liner ports and the piston did not appear to have any signs of modification via decking, and no liner shim was present.
- The exhaust port plus sub exhaust ports width was the full width of the bore, a lot of overlap to transfer ports.
- No sub port induction at TDC, port closed.
- Crank 220 duration, closing at 70. Note - The crankshaft (DLC coated) open and close sides had been ground upon exposing steel prior to me receiving this engine so cant say if its OS timing or aftermarket. I suspect the latter.
- Bowl volume in head = 0.15cc, angled squish, dished piston.
I have not yet measured a 2104 to compare, but figured someone else may have and can use my numbers as a reference. I have measured NR Mito GT5/17 and Mephisto GT5 also, they both have higher transfer and exhaust port numbers.
As you can see by the numbers above, its not as low timed as a buggy engine but not as high strung as many on road engines. 184 degrees exhaust with 29 blow-down, coupled with the bowl volume all point to being built for more torque - which makes sense for a 3.5kg GT.