Hey guys, I just got a call from my machine shop that my '74 400 block is crack free and cleaned up with a 0.020" overbore.

I am building the 405 for my little 280z car. It will weigh about 2800-3000lbs after the roll cage installation (without myself, another 300lbs). The rear has 3.69:1 gears w/posi. The car can fit a max tire diameter of 26", so I'll be running a 26/10.5/15 slick.

I have been flipping through the JE/SRP catalog and noticed the small price difference between pistons for 5.7" and 6.0" rods.

Plus there is no price difference for the 5.7" or 6.0" SCAT H-beams I have been looking to buy. Same goes for the SCAT 4340 forged cranks for either 5.7+ rods (ext balance) and the cranks for 6.0 rods only (int balance).

Personally, going with a 6.0 seems the way to go if for only the reason of int balancing the motor. Not to mention better rod angle, longer dwell, etc.

The only down side with using 6.0" rods I can see is the pistons have the oil rail support. I have heard that they are not recommmended for any type of forced induction. Although I am not turbocharging this motor, I might hit the motor from time to time with a 100-150 shot of nitrous if I can't get into the high 10's with all motor.

Is this true?

Engine Specs as planned:

-SBC 400, 2 bolt block, 0.020" overbore (4.145"). The three center mains are being machined for billet steel splayed main caps
-ARP main studs will be used on all inter holes.
-Dart aluminum Pro 1 215cc heads w/2.05/1.65" SS valves
-Lunati Solid Flat Tappet Cam: .550/.550" lift, 283/283 adv dur, 255/255dur@0.050", 108 LSA (ground on a small base circle)
-SCAT 4340 Forged Steel 3.75" stroke w/400 mains
-SCAT 5.7" or 6.0" 4340 H-Beam rods
-SRP Forged Pistons, 10.5-11.0:1 compression
-Edelbrock Victor Jr. or Super Victor Intake Manifold
-Holley 750 cfm double pumper (tuned and choke horn milled off)
-1.75" Primary S&S Headers
-TH350 w/3000-3500 tight ATI, Trans-Specialities, or Coan converter


Thanks guys!!

Cable,

What compression and stroke? Will it be internal or external balanced?

Performance-wise you will see little-to-no difference when it comes to .3" of rod length. I never "want" a particular length... just whatever fits.

If you are dead set on a certain rod length then you should tune the rest of your engine (valvetrain espeically) to match... otherwise It would be like choosing a single plane manifold because you heard it produced more HP but you still kept your stock heads...

All the rod lengths have their pros and cons... I'd pick what would be most reliable in your engine.

If it helps, from what I've been told, shorter rods produce more torque and longer rods produce more HP... but the difference is really small.

Originally posted by JOHN WILSON:
Cable,

What compression and stroke? Will it be internal or external balanced? Hey John, I edited the post and added the planned combo.

If end up using the 5.7" rod, it will be externally balanced.

If I go with a 6.0", it will be internally balanced.

Of course I'd prefer internal balanced, but not at a greater cost of something else (parts).

I'd go for the 6". You'll be able to run a lighter piston that will more than offset the addt'l weight of the longer rod along with being able to internal balance without mallory.

Originally posted by JOHN WILSON:
I'd go for the 6". You'll be able to run a lighter piston that will more than offset the addt'l weight of the longer rod along with being able to internal balance without mallory. What about the 6.0" rod pistons living with a 100-150 shot of nitrous?

Shouldn't be an issue. My JE's had plenty of crown thickness with a 6" rod and flat top. 18dg pistons with short compression heights tend to get a little more sensitive to "big" doses of nitrous (100-150 shot would not be considered big) because of valve relief placement and proximity of the top ring land. But, before committing to a piston, call the manufacturer and run it by them.

If the bore and stroke are the same why do you get more or less torque with the longer rod?

I would think maybe a little more of both with the curve moved to the left a little with the longer rod. Is that right?

Are you sure on that external balance on a 4340 crank for 5.7 rods? My crank is a 4340 Eagle in my 383 and it was internally balanced with 5.7's, no mallory.

http://www.chevelles.com/forum/ultimatebb.php/topic/9/18288.html

Sure you want those 6" rods?

If it runs as good as Johns does,,,I wouldnt be afraid of 6" rods :D

Originally posted by Schurkey:
http://www.chevelles.com/forum/ultimatebb.php/topic/9/18288.html

Sure you want those 6" rods? KB's?? I am not suprised......

Originally posted by Schurkey:
http://www.chevelles.com/forum/ultimatebb.php/topic/9/18288.html

Sure you want those 6" rods? =

My opinion, go with the 6" rod.
The above link only applies to one brand of piston that I know of.
All the forged stuff like SRP, JE, etc. use a support rail that is spring steel & stronger than the piston itself & is just not an issue.
I have used these rails in everything from a 496 in a motor home on propane that has over 80,000 miles on it to a number of 496's runnin around on the street, some makin' reasonable power to a LOT of 383's, 400's & 427 small blocks with no problems what so ever.
You can also use a 5.850 rod if the support rail is a concern to you.
Most 5.7 rod combos are on the edge at best regarding internal balancing.
I have rebalanced a couple of the supposed 5.7 internal combos & had to add tungsten to get them where I wanted them.
Not saying it can't be done with 5.7 rods, just saying it's a little iffy & tungsten is expensive to install ;)

As for power & rod length,,, it is a non issue here

If it helps I'm going to quote the SA design book on how to build big inch chevy small blocks "We have witnessed short rod length that tend to push the piston harder against the cylinder wall as evidenced by larger wear patterns in the cylinder's otherwise virgin cross-hatch" .....a shorter
"rod will tend to push the piston harder into the thrust side of the block. This creates additional side load , friction, and wear." pg 37. It seems to me that the 6 inch rod would be the better choice as long as you have the correct pistons with the correct compression height. I am in the middle of building my first stroked small block and have found quite a lot of info out of this book and think that the 20 bucks I spent on it may have prevented me from making one or more costly mistakes. Good Luck!