Hey guys. Long time Forum member, first time engine builder here.
My SB406ci ballanced rotating assembly came with 6.0 piston rods. What are the differences/advantages/disadvantages of these vrs a 5.7 rod? Compression? stroke? what??? I did notice that there were many more piston choices and lower compression piston choices with the stock SB400 5.7 rod. All info appreciated....
Thanks
Eddie

 

Wow...I found some very interestring reading here.
http://victorylibrary.com/mopar/rod-tech-c.htm
Eddie

 

A stock 400 rod is 5.565 and going to the 6 inch rod will take friction out of the cylinders as there is less anglulatoin and on most 6 inch rod assemblys they can be internaly balanced not having to buy costly balancers and flywheels and on most pistons used with 6 inch rods require a spacer ring as Mahle pistons use a smaller and tighter ring package not requiring a spacer ring.

And the longer rod does not change the stroke any the crank determains the stroke and the longer tends to make the piston dwell at TDC longer then the short rods.

Any of the 383s we build we have always used the 6 inch rod and it seems to be better all the way around.

Hope I have been of some help to you. GOOD LUCK

 

Yes, you have been informative and helpfull Blockman...thank you. I'm sure I'll be asking a ton of stupid questions during this build, but I wanna do it right.
Eddie

 

Different rod lengths do not affect the stroke of the engine or the compression ratio. The 5.7" rod is ALMOST the universal SBC rod, but as previously mentioned the 400 rod is unique in several ways, including it's 5.565" length. My recommendation would be a LOT more studying before trying to build that first engine.

RACE ON!!!

 

Just my 2 cents here Ed but if u bought a balanced rotating set with 6" rods ur already better off than with the 5.7 and all the research has been done for u. U can read more and it won't hurt but it looks like ur already there. I would prefer the longer rod in any engine. And all numbers crunching, parts search has been taken care of for u. Now there are some longer rods availible or should i say adaptable but i don't think u want to go there as 1st timer (well even a 3rd or 4th time builder). For an example D. Vizard says the difference in torque/pwr between 5.7' and 6" rods is only 1/2% (2.5hp on 500hp eng).
I would worry more now on selecting a cam to match ur heads and c.r. or selecting heads to match ur cam and c.r..
1 thing longer rods do is increase the dwell time at TDC and can breath well enough for max mid-range torque with a little less overlap - allowing a wider LSA thats friendlier on the street. Longer rod engines also tolerate higher compression better with low octane fuels. And i still have an rag article on a sb Chevy combo with a 1.91 rod/stroke ratio making 11:1c.r. running on 83 octane. I don't expect u to try this with ur 406" using 6" rods but with 91 octane u should be able to run well over 10:1c.r. with aluminum heads. Quench hieght plays in here to so read over the nearby posts for that (covered well enough there).

Congrats on a bitch'n 406.
cardo0

 

Here is a link on a engine we built for a customer last summer as its a 383 not a 406 and a 6 inch rod was used in the engine. This may be of some help here.

http://www.chevelles.com/forums/showthread.php?t=106715

 

There will be more choices simply because there is not room for many heights with a long rod. The compression height has to be so small that they can only do so much until durability is compromised. That said, generally a longer rod will enable you to run sustained RPMs that are higher than the short counterparts. This is due to the less severe angle inside the engine that does not bind it up as much. Our engine runs a tall deck with a 6.125 rod with a 4" stroke for that reason. So your 6 inch is better for high output, but stinks a little for piston options.

 

Thanks for all the replies guys.
The machined deck surface of the race prepped short block I bought two months ago was severly damaged (beyond repair) by Roadway Trucking Co durring shipment. I was refunded full purchase price + shipping, so I recently bought another standard bore 400 block. (picked it up this time ) It's going into the machine shop soon so I'm studying up on what I have, and what I'll need, for the kind of motor I want. More questions to come!!
Eddie