Gridrunner on the C64 is deliberately slow. With the following simple patch we can tune it to be twice as fast, and to my taste, even more enjoyable to play.
diff --git a/src/c64/gridrunner.asm b/src/c64/gridrunner.asm
index ec22f51..f91d146 100644
--- a/src/c64/gridrunner.asm
+++ b/src/c64/gridrunner.asm
@@ -924,7 +924,7 @@ DrawBullet
BEQ b84FD
b84FC RTS
-b84FD LDA #$18
+b84FD LDA #$08
STA bulletAndLaserFrameRate
JSR MaybePlayBulletSound
LDA currentBulletYPosition
@@ -1494,7 +1494,7 @@ DrawDroids
BEQ b88CE
b88CD RTS
-b88CE LDA #$80
+b88CE LDA #$40
STA droidFrameRate
JSR UpdateDroidsRemaining
LDA noOfDroidSquadsCurrentLevel
To see it in action go to:
https://www.youtube.com/watch?v=1a3ogaWaxMM