*NOTE IF THIS IS A REPOST OR HAS ALREADY BEEN COVERED, LET ME KNOW SO I CAN HAVE THIS DELETED, THANKS*

ok i was just thinking of what rod lengths to use when going a different stroke and what not and i started playing with some figures and came up with this.

i was using values from a b18c1/5 & b18a/b & b20b/z just for references
b18c1/5:
rod length - 137.99mm = 5.42inches
stroke - 87.2mm = 3.43inches

b18a/b b20b/z:
rod lenth - 137mm = 5.39inches
stroke - 89mm = 3.5inches

now if you plug all the values into my equation from a b18a/b b20b/z or a b18c1/5 youll get 361.696mm (14.27inches). now i dont know what the number means i just know it works for my formula
rod length x 2 + stroke = 361.696mm (14.27inches)

oh and to figure out the rod length i used a little bit of math to move numbers over
1. move the stroke to the other side of the = sign.
rod length x 2 = 361.696mm (14.24inches) - stroke

2. move the 2 over by dividing the whole thing by 2
rod length = (361.696mm - stroke) / 2
*i didnt insert the value in inches because to many paratheses might get confusing*

now lets take an eagle stroker crank 95mm (3.74inches)
rod length = (361.696mm - 95mm) / 2
rod length = (266.696mm) / 2
rod length = 133.348mm

b16 rod length = 134mm
.652 of a mm difference, think itll work???

 

You need a few more factors to determine the correct rod length you need for a particular engine combo. you need deck height compression distance on the piston. The formula for figuring rod length is deck height - compression distance- half of your crank stroke. lets use a small block chevy for example. stock deck height is 9 inches and the crank stroke is 3.75 for example. The pistons your looking at buying a have a compressin distance of 1.125" what this means is from the top of the piston to the center of the wrist pin is 1.125 " so plug these numbers in to your formula. 9-1.125-1.875= 6 so the rod you are looking for is a 6" rod in this case. hope this helps

 

ok i understand exactly what you mean about the compression distance of the piston and the deck height. but i was wondering if my formula works just for the b18/b20 blocks. i dont know how to explain this properly but i used the formula for the b18a/b and b18c1/5 and it gave me the correct rod length numbers so does that mean my formula only applies to using stock compression distance pistons (honda oem/jdm) and whatever measurement of the deck height is on a b18a/b b20b/z b18c1/5? hope you understand what im trying to get at. i suck at trying to explain my methods.

 

It would be easier to find out the deck height of the block,subtract the piston compression height and half of the stroke to get the rod length(Could use piston to deck also but that is miniscule so only matters if your building an engine with extremely close tolerances).I have only browsed at your formula,but I do not think you will be able to find out the correct rod length everytime just by plugging 361.xxx in.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDMotive &raquo;</TD></TR><TR><TD CLASS="quote">I have only browsed at your formula,but I do not think you will be able to find out the correct rod length everytime just by plugging 361.xxx in.</TD></TR></TABLE>

yah the the 361.696mm is ONLY for B18a/b B20b/z B18c1/5 only because they all share the same deck height. now for a B16a or B17 the number would be 345.4mm

 

Ok...I get where youre going with that.I only looked at the top than browsed the middle briefly and saw b16a rod length at the bottom so figured it may have been for other B blocks.I guess it could be a handy way to figure rod length for specific crank/rod combo's in the b18 blocks.

 

ok i don't get any of that ... so i am curious... what's the stock rod length of a 99 b20b rod!? is it a long rod or a short rod. I think it's 89mm... but i'm not too sure. I'm tryin to figure out what it is so i can buy my eagle rods and they have totally different numbers than what i can understand. any help would be nice