I have a 400 sbc bored 40 over. All the machine shop work is done except I have purchesd new pistons. My problem is the connecting rods. A couple of them look a little suspect and I don't want to chance using them and regret it later. I have tried and tried to find a set of reasonbly priced 5.565" rods that the 400 comes with. But have had no luck. I have read that it is possible to use a different rod such as the 6". Any thoughts on this?

You can use 5.565", 5.7" or 6" rods in a 400.
All you need to do is buy the appropriate pistons for whatever rod length you choose.
May also require some block clearancing for the 6" rod.

I just checked the pistons that I bought a while back. Speed Pro, and it says in the specs that clearance is .0015 with 5.7" rods. I should be ok with the 5.7's

that's the piston to cylinder wall clearance, unrelated to rod length or piston compression height. If you're new to this I'd run the 5.7" h-beam rods from SCAT or Eagle. Call them and mention it's a 400, ask if they have a model that works better with 3.75 stroke engines. Apparently the pistons you already have are for a 5.7 rod. You might want to double check that, make sure before ordering rods.

Yep, I agree, overall, especially for a street/performance engine the 5.7 rods are the better choice. If it is a serious race engine, then of course the 6.0 rods would be the better choice. With the stock length 5.565 rods, the rod angles become somewhat severe, and that severity is reduced with the 5.7, and even more so with the 6.0in rods. BUT, with the 6in rods (FOR A DAILY STREET ENGINE) you end up with a really short piston which will rock more in the cylinders. Also, with a 6.0in rod, the wrist pin hole is into the oil ring groove-----------------I DO NOT LIKE THAT AT ALL ON A STREET ENGINE!!!!!!!!!!! Therefore, I feel the 5.7in rod is the optimum choice for a street engine (SB400). Also, EVERY piston maker that I'm aware of now makes pistons for a SB400 with 5.7 rods, and today those pistons are just about as cheap as a 350 piston, especially hypereutectic pistons------------------which I really perfer for a street engine. :D

you are right...the pistons are meant for the 5.7" rod. I double checked.
Thanks for the help. Greatly appreciated.

GM made a heck of a bunch of short-rod 400 engines through the years and my hopped up, strong-arm 406 has them in it too!!

pdq67

went with Scat H beam rods. large journal of course for the 400 crank. Now I have everything ready for assembly...

make yer move doood! have it done and the car driveable by spring.

Gonna swap it out as soon as the chill leaves the air. Gonna pull out that meager little 283 out of my 66 chevelle and store it away. The 400 will be a much better fit for that car.