I am already half way done with my winter build by completing my head, now I am in the process in finishing the bottom end. however i am in debate about staying in the 81mm range or boring it out to 84mm or 85mm. My question, what is the pros and cons of the bigger bore block and the 81mm block? torque? high end? I have seen many big bore engines producing 220+ WHP along with 81-81.5mm engines producing almost the same WHP. If they both produce almost the same WHP what will be the difference within the two engines?
TIA

 

You can't bore a stock 81 mm block out to 84 mm. You have to re-sleeve a block to get 84+ mm.


Modified by mar778c at 6:27 PM 10/5/2008

 

Bigger is always better, as Torque matters. I would bore your engine to 84.5mm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mar778c &raquo;</TD></TR><TR><TD CLASS="quote">You can't bore a stock 81 mm block out to 84 mm. You have to re-sleeve a block to get 84+ mm.</TD></TR></TABLE>
I should of stated I already know that when I mentioned boring the block to 84mm or 85mm.

If i stay in the 81mm bore I would most likely bore it .25 or .5

any other inputs?

 

In an NA build, there's no replacement for displacement

 

the only real reason in boring an 81mm to like an 81.5 isnt for power wise its for a clean cylinder if ur gonna bore it sleeve it to an 85mm or get a b20 block.

 

will a higher compression ratio on a 81mm bore have any advantage over the bigger bore? also for those who have sleeves and bigger pistons, do you have any issues on the 81mm head? did you bore it out? I have read that boring out the head will lose compression, so will a higher dome piston fix that problem?