my father in law is building my motor, and although he hasn't gotten to the motor to check the cam to rod clearance yet, i was hoping someone else has a 400 running a 6" rod on a stock 3.75 stroke crank. did you have any problems? the cam is a custom solid roller w/236-240 duration @.050, .510 lift and 110 lobe seperation. the pistons are forged mahle that were made for a 6.125 rod. and he has them .005 in the hole! should run well!

 

as a rule cap screw rods give a lot more clearance as does running a small base circle cam. the length of the rod has little to do with gaining or not gaining clearance since the stroke is the same and the rod moves the same amount. where the longer rod would factor in is sticking the piston out of the hole. you need to dummy the parts up and check clearance one every hole before you assemble it for good.

 

My math puts the piston .145 in the hole. If those pistons are at a deck height of .020 (factory) and were for a 6.125 rod, putting them on a 6" rod would add .125 to that. You may want to read this paper on Quench and what happens with excessive quench area and detonation. Here's a quote: "A running quench height in excess of .060" will forfeit the benefits of the quench head design and can cause severe detonation."
http://speedomotive.com/Building%20Tips.htm

EDIT: Didn't realize the block had been decked.
Disregard.

 

I'm using 6" Eagle SIR rods along with the stock cast crank. Two of the rods/bolts were shaved slightly and I'm using a .900 base circle cam. I want to say #6 and 2 are the two rods that come close to the cam lobe but I'm not positive. Either way a small amount of grinding is necessary.

www.geocities.com/dzperf

 

Even if the block is decked it still doesn't add up.

 

i was there when he plastic gauged the main and rod bearings, and we measured how far down the piston was in the cylinder. cam out to .039 on one side and .026 on the other. so the deck was squared and now the pistons sit .005 in the hole. i read the part number for the pistons and they were made for 4.155 bore and 6.125 rods. mahle doesn't make pistons for a 6." rod. but it works. he said we would most likely have to grind on a rod bolt. they are arp bolts. i see what you're saying about the difference in deck height though, unless these were in fact made for 6" rods??

 

Mahle lists their pistons by compression height IIRC, not by stroke and rod length. What's the part number?

 

i don't recall. the pistons are at his shop. but i looked at a jegs catalog and matched the part number and it stated 6.125 rod. well either way, i know they sit .005 in the whole. but, i guess my ?'s was answered. that he should be able to only notch the rod bolts to get enough clearance. i was just curious the see if anyone else needed an off base cirlce cam to run the 6" rod. i have heard of this, but usually with a bigger stroke crank. i trust him, he's got his own mechanic shop, however he mostly does fords. just needed that extra input. thanks

 

im using a 6" H-Beam rod with a 3.8" stroke and it did NOT clear my cam, cam was big tho 264/272 w/ .649/.649 lift w/ a 1.6 ratio rocker arm. Had to get a small base cam. You might be good with a smaller cam and a 3.75" stroke tho. Just tellin you what did not work on mine.

 

well hopefully he'll build it soon and find out. when he does, i'll respond with the results. thanks for all the input!!!