Got a 400 SB that I'm fix'n to freash'n up. Currently I'm running the stock rods. I've heard alot about power increase by using the 5.7 rods. Most tech articals I've read say the short rod builds more torque. Whats the scoop?

I'm look'n for low end to mid range power, 3500 rpm and below. I'm running 9:1 cr, Crane H272 cam, 486 heads (2.02/160) LT-1 factory manifold, 795 cfm Q-jet in a 68 to current 4X4. 

If you're really looking for off-idle to 3,500rpm, my suggestion would be to stick with the rods the factory gave you.  Save the money spent on other rods, and take a friend out to dinner and a show.

On the other hand, if you're looking for additional suds (coupled with additional rpms) out of that 400, by all means step up to a longer rod.  There are several advantages...  1) the piston slows down near TDC, providing for more efficient combustion; 2) less side-to-side stress on the piston during its up-and-down travel in the cylinder (longer rod = less angle in relation to the crank).

400s can be made into a nice thumper.

Don't forget, to go to the 5.7 rods, you'll need a set of pistons to go with it, do to wrist pin location.  

Go with the 5.7's. You'll have a wider torque curve and your engine will run cooler.

To join the chorus, longer is better if you have the financial resources for the rods and matching pistons by all means go this route. The longer rod reduces angularity of the rod between the crank and piston, this reduces side thrust on the piston which allows more of the generated power to go into the crank rather than overcoming friction between the piston and cylinder wall. The piston moves the pin toward the ring pack which reduces piston rocking about the pin which frees up some more power.

Folks like to talk about longer dwell times at the dead centers of a long rod engine and how that helps breathing and combustion characteristics, all of which is true. In addition to that characteristic, a long rod tends to reduce shock loading to the crank and rod thru the TDC/BDC periods which aids in extending the life, or permits space for greater power loading, of these elements before structural limits are met. The long rod also spreads these loads into a longer period of time which reduces vibration on the crank, lessening the oscillating torsional load (twisting) that the counterweights and damper have to contend with.

All-in-all long rods are a good move.

Pistons, since you'll need pistons let me suggest the you look for either flat tops with no more than 2 valve reliefs (like Speed Pro), or if you must have a dish go with a "D" dish. The "D" dish and the flat top keeps a flat piston surface against the head's quench/squish deck; this greatly improves both turbulence and quench. The high turbulence improves completeness of the burn so you get the most power from the fuel, this also results in the least emissions. The flat piston surface to flat head surface hold "end-burn" gas temps down so you get the benefit of maximum mechanical resistance to detonation (mechanical octane). This is where power gets made and is the engineering basis behind Vortec and Fastburn heads annnnnd it's free 'cause it's all in the shapes and one piston crown and head shape is about the same cost as anyother shape, so why not do it right.

Bogie

I completely agree... longer rods (to the point of optimal rod/stroke ratio) are the way to go if you're looking for a measureable performance increase.

I suggested that NDL2 stay with the standard rods because he stated he was looking for power up to 3,500rpm.  I believe that a gain - if any over the production rods at that rpm range - will not be worth the cost of longer rods and new slugs.

Peace. 

A more modern combustion chamber of the World heads would be a significant improvement over the 486s. Especially since the 486s have run quite a while with unleaded fuel. If the guides are gone, the seats are probably in similar condition. By the time you invest in new guides and hard seat inserts, new seals, springs and valves you've spent a lot
(if not most) of money toward a new set of heads, be they World, or Proline, or whatever. The new SR Torquer is a lot of bang for the buck as are GM Vortecs.

I wouldn't be afraid of Al. heads, except the GM L-98/ZZ3&4, the aftermarket and GMPP stuff have pretty thick decks, in some cases a 1/2 inch, which gives the head a good solid base against the gasket. The L-98 Corvette/ZZ3&4 head is a thin wall aluminum casting that could get you into trouble with slender dimension between cylinder walls of the 400 block.

I haven't worked out chamber ccs for the compression ratio your looking for, but I'll share concept data with you. I like either a flat top piston or a "D" dish (not talking pop-ups for racing level compression over 10 to 1) for a street vehicle. These shapes give two things; 1) better mixture turbulence as the piston closes on TDC, this speeds the burn which surprisingly reduces detionation tendencies and gets more energy out of the fuel by driving to a more complete burn. 2) The quench is more effective when you can keep the closing distance of the piston to the chamber quench step around .060 to .090 inch. This maintains a high ratio of surface area to volume which pulls excess heat out of the end burn, reducing temps and again helping subdue detonation tendencies. These add up to more power, better efficiency, lower emissions, and greater resistance to detonation and preignition.

I would use the piston volume data as described above + you need the piston crown to block head deck distance and the gasket thickness to calculate the combustion chamber volume for the desired compression ratio. Then select your cylinder head with the right volume and shape to maximize these efficiencies. Remember that an aluminum head will allow .5 to 1.0 more compression ratio compared with cast iron using the same octane rated fuel. The thicker the head's gasket deck reduces the effect of compression ratio difference between aluminum and cast iron as the thicker the deck becomes, the more time it takes to transfer heat through it. Thickness also affects cast iron heat transfet rates, I say that as a comment on theory, as some aftermarket heads can be pretty thick when they are intended for racing so be carefull about cast iron racing heads for a street engine as you can't generate enough heat to make them work right while driving in traffic.

Bogie

  I have a 400 with a scat 3.75 crank and scat 6" stroker rods This is a great combination, if you can afford it.  Of course you will have to use a special stroker piston, but Keith Black offers one that is fiarly inexpensive for this combo.  Mine has the 18cc dish.  With the right heads you can run anywhere from 8.5 to 10.5 to one with this combo.  I have Dart Pro1 heads cut down to 68cc and the combination gives me 9.5 to one.  The engine has gobs of torque 500 ft lbs.  and 480 HP  It is in a 77 Camaro with 3.42 gears and I have problems gettin the car to hook with street tires.  But either way, with the 5.7" or the 6" rods, you are going to have to buy new pistons.

Smokey Yunick belives the long rods are the way to go.  While increasing dwell time at top dead center for better combustion and also decreasing side load on the cylinder walls for longer life!

What do you about the 492 head? I was mistaken about having 486. Had to go dig through all my notes. These heads are set up with 2.02/1.60 stainless valve, no hardened seats, 64cc chambers. They have been "pocket ported". Heads and manifold have been matched ported (gasket). How well do these heads flow? I haven't seen any numbers on the 492.  

492's are very good "old school" performance heads, proabably a bit better than 462s which they are related to.

The same old problem arises with the old camel hump heads, while very good and pretty sturdy, they are not quite the power producers that Vortec's, Fastburns and more modern factory and aftermarket heads are.

A little porting especially in the pocket and guide area helps 'em breath better. The chamber from the spark plug hole around to where the chamber becomes tangent to the cylinder wall side of the chamber can be relieved a bit which greatly helps getting the intake charge into the cylinder. I recommend you read "How to build & Modify Chevrolet Small- Block V-8 Cylinder Heads" by David Vizard. It's an excellent read and throughly addresses the needs of these heads.

The "old school" heads will still be a little light on efficiency compared to post 87 designs because they lack the "beak" projecting from the quench/squish deck between the valves. This not only helps with burn characteristics, but also aids in keeping the incoming mixture from being sucked out the exhaust during overlap. This helps build cylinder pressure which increases power, reduces unburnt HC emissions, and improves fuel mileage. Also, the newer combustion chambers move the spark plug toward the exhaust valve and in toward the center of the chamber. This provides a more consistent ignition of the mixture, and reduces burn time by upwards of 25 percent. The later improvement reduces the need for too much ignition lead which can result in spikey pressures and temperatures. This leads to a reduction of end burn temps which reduces detonation and thus allows higher compression without producing NOx emissions while preserving the virtues of high compression; mainly more power and greater efficiency.

But it largley goes back to economics, if the 492s need seat inserts, guides, valves, springs, etc.; it might be no more expensive to replace them with up-to-date designs. If they don't need a major rebuild, it might be more economical to stay with them, as they are pretty good.

Bogie