I hear people say that the best set up motor wise is and 86 bottom end and an 89 top end. Is the 89 rod longer to get a longer stroke? I have a big bore kit now ( 302cc LA Sleeve ) which makes great power but i would like to make a longer stroke motor . I have a 40,000 mm spacer plate which came with the big bore kit but i have an 86 crank which means i have to run the 86 piston. The piston hieght is good and i run 185lb of compression but want just a little more if you know what i mean. If i put and 89 rod on the 86 crank (which i have an 89 piston already ) will this give me the height for the spacer to create more volume giving more power?

 

40,000mm? do you know how much that is?

 

What do you mean ? How thick the spacer plate is in SAE ?

 

i believe the short rod yields a 1.74 R/S ratio, 1.75 being ideal.

 

Switching to the 89 rod & piston won't change your stroke. the stroke on the 86 crank,rod & piston is the same as the 89
crank,rod & piston. It's just that the connecting rod on the 89 is 5mm is longer. And the 89's piston has the wrist pin set
5mm higher. so that the piston will sit 5mm lower. Giving you the same stroke as a 89. If you put a 89 piston on a 86 crank,
You wouldn't have much compression and the skirt would hit the crank. But if you ran a 86 piston on a 89 crank with a spacer
plate. That would give you more crank case volume. Which would in turn give you a smoother powerband. But that still doesn't
change the stroke. To change the stroke you have to get a crank that actualy throws the rod down farther. That's how you
change the stroke. Correct me if I'm wrong anyone. I'm by no means a know it all.