rod techs please

[wazazzle]

ok ive done all my research and i am offically confused. im piecing together a 408. i've got an eagle 4.00" cast crank in mind which is already balanced. it came from a kit using 6.250 rods. ive read other people combos and seems that most folks use 6.200 rods. then i read elsewhere folks using 6.125" and 6.250" so, which one is it 6.125" 6.250" 6.200"??? if i went with the 6.250 will it make a diff in my piston comp height? i want to put as less stress on the block as possible (yes it's stressed being stroked!) but you get the idea.. maybe its cause im a newbie to 351's and that im but please help this stupid guy out

 

[brianj5600]

It sounds like you have not bought anything yet. Why not buy a kit? Usually they are cheaper than the sum of all the parts, and hopefully someone will have already done the parts matching. I'm not sure that there is enough difference in rod lengths of the 3 to make a difference. I'm not a engine expert, but sometimes the rods can be so long that the ring package suffers, giving up any advantage gained by rod ratio. I think that the 6.125 rod ratio is better than a SBC. It seems like bench racers are more worried about rod ratio than professional engine builders.

 

[wazazzle]

anyone else know?

 

[rbohm]

yes, everytime you change the rod length, you need to change the compression height of the piston. sometimes you can get away with a small change in rod length and use the same pistons. in this case unless you have a 0 deck height(the piston is flush with the top of the block), you might be able to use the same piston with a thicker head gasket to mmake up the difference. as for rod length/stroke ratios in a 351w, you dont need to worry unless you are building a motor that will make more than 600hp. the 351w block is rather stout, and the cylinder walls dont crack like the 351c walls do. i am also planning to build a 408 based on a 351w block, and i will use the stock 351w rods, and boss 302 pistons along with 351c 2v heads.

 

[wazazzle]

i just won a bid on an eagle 4.00" crank and eagle 6.250 h-beam rods. so now i have the basis for a 408. i've been checking out kit combos and basically going to get the same pistons they list. hopefully used and cheaper. tell me if this sounds okey. either forged Mahle +.030, comp height 1.245, coated dish pistons +26cc, 65cc heads 9.1 compression. OR forged Keith Black +.030, comp height 1.240, step dish piston +25.8cc, 65cc heads 9.435 compression??? the valves on my '69 head will be swapped for larger 1.94/1.60 valves if that makes any difference. am i going in the right path? Any suggestions?