GT5 vs GT5-a
Intake 32mm vs 40mm (exhaust matched)
Piston: Same
Head: Same
Bolts: Same
Ports: havent checked but likely the same
Literally the only difference between the GT5 and GT5a is the 5a allows a larger intake. The wider bolt spacing will allow you to port larger and get less restriction. With our motors, you'll want a full 1" port (with matching manifold, stock is 1/2" I.D.). The intake and exhaust are pre-matched from factory and honestly the only difference between the two is the intake port. I've been exchanging parts between the two motors for two years now. HOWEVER, the Type D motors (Dax, speeddemon, etc. basically any non-grubee motor) have ports that are 1mm lower (restricting), a connecting rod 5mm shorter than the grubee, the piston wrist pin sits 5mm lower than the grubee (21mm compression height for the grubee vs. 26mm for the Type D). The heads are identical as well. There are no Type D motors with 40mm intake spacing to my knowledge but I havent looked into it, the higher ports in the grubee motors makes for more power anyway. A GT-5a jug on a dax balanced low end, RT carb, voodoo pipe, and a Puch hi head could easily make for a cheap powerful little bike for about $190 (not including shipping)