Thinking of sleeving my B18 block with Darton MID 84mm's and was told I can go up to 86mm all-motor. Would like to know how more HP I will gain by moving from 84mm to 85mm and from 84mm to 86mm

This will be a daily driver so if I shouldn't go past 84mm, let me know.

Thanks!

 

Just recompute your new displacement for your new bore, divide by old displacement and you will get a <u>very</u> rough estimate.

 

Please help me with this computation...

 

You won't gain very much displacement by going from 84 to 86 mm. Less than 5%. You won't gain much power with such a small increase IMO.

 

rule of thumb is 5whp per mm, assuming same compression, airflow etc. thats a rough guesstimate.

 

of course the bigger displacement, there will be some % of increase in power gains.

But I would look at reliability more in this situation more than anything. Personally I only recommend 84mm to our customers for a true daily driven car. The more extreme Daily cars are in the 85mm bore. 86mm will work, but considering the freeway driving, hot temperatures in certain areas, etc. make the 86mm not the best decision to go with?

I would stick with 84mm just because of the reliability factor.

 

10% increase in displacement will yield more than a 10% increase in torque gains.

 

Going from an 84 mm bore to an 86 mm bore gives ~95 cc's more displacement. Not worth it, IMO.

 

Thanks for all the replies. Given the daily driver factor, I will stay at 84mm. Pistons are also easier to source and since my head is 81mm staying at 84mm makes more sense

 

From what I've heard, you'll have problems with h/g sealing issues at 86MM. 84MM will be your best bet.