Overbore

[Projekt]

since the rb26's is 86 mm wide does that mean you can overbore a rb20 to this width? also, a related question: are the rod and piston dimensions the same between all the RBs?

[meggala]

no you cant bore an rb20 out to 86 mm 82 is the limit and rod sizes are differentmeggala

[Projekt]

sorry to ask but why can't you bore it out? different water passages?

[meggala]

teh block is differentyou can fit an rb26 crank and rod in though makes it around 2.4http://www.meggala.com/rb24.html

[Projekt]

yeah i've read that and it's quite vague. what about the block is different? does anyone have comparison pictures?

[meggala]

the bore size is different 78 v 86

[Projekt]

yeah i know, but if it's an RB block the length would be the same and therefore either bore could occur. maybe i just don't understand the differences between the two. i know you shouldn't overbore any motor 8mm but if the block had versions of it that came like that from the factory why not?

[meggala]

cause the blocks are different the rb 25 and 26 block are very similar the 20's are very different even though they look slimilar at a glance

[Projekt]

GAH! not what i need! i just want photos of the blocks.

[93RPS13]

it definatly cant just go to meggala site

[themadscientist]

while the exterior dimensions or the 25 and 20 are the same the cylinders are smaller within. You will bore them into nonexistence. there are a few differences in the water passages nothing a dremel couldn't correct!

[Nismo_Freak]

Problem being you get the combustion too close to the water passage and cooling becomes extremely difficult. Headgaskets blow constantly, etc.

Also note that the head's combustion chamber will need to accomodate the extra 8mm of overbore.