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Old 01-11-2006, 07:04 PM
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Rod Length Confusion, Short or Long???

Ok, Im building up a 400 chevy, and Ive heard never use the "short" 5.565 in rod, it will not produce the low end torque a longer rod does. Then I hear "A short connecting rod achieves this right angle condition sooner than a long rod. Therefore from a "time" perspective, a short rod would always be the choice for maximum torque." And I hear that its all a bunch of bull and it doesnt matter. And that a short rod will wear the bores down faster. And that I wont notice rod lenght...First time builder...street engine...forget it. Can someone shead some light on this? Should I stick with 5.56 or get some 5.7s? Thanks!
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Old 01-11-2006, 07:10 PM
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The preferred connecting rod to use with a 400 is the 5.7 rod.

Connecting rod length and it's benefits have been overblown for a long time. Particularly concerning street engines. We can all thank Smokey Yunick for the phrase "use as long a rod as you can get to fit."

This is not the case, and if the short 400 rods are so bad, why did so many 400 small blocks last so long?

The truth is, the short rod works pretty well, and if money is tight, I wouldn't waste my time trying to spend money putting longer rods in the engine.

Money would be better spent elsewhere on things like chrome or uv lights.

Brian
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Old 01-11-2006, 07:26 PM
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If you need a second opinion, I agree with Brian.

Isky site, just scroll down to rod ratios:

http://www.iskycams.com/techtips.php#2005


If I might risk paraphrasing old Smokey...... based on what he actually said to us..........

longer rods are better because they flop back and forth less so they have less forces trying to break them.
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Old 01-11-2006, 07:37 PM
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If it's for a street engine, run what you can afford. Only your wallet will know for sure, the "Butt Dyno" won't be able to tell the difference.
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Old 01-11-2006, 07:40 PM
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Interesting article...sounds like 5-7HP gain isnt worth my time for adding new 5.7s in a 400.....And I Qestions the "longer rods are better because they flop back and forth less so they have less forces trying to break them" thinking in my mind....it would seem like a shorter rod is harder to brake....think of it like a really long ruler..easy to break in half...then think of a short ruler...harder to break. Im sure im missing manythings to it and it is not that simple, but it seems logical and I wonder.
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Old 01-11-2006, 07:45 PM
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Quote:
Originally Posted by Warrant
Interesting article...sounds like 5-7HP gain isnt worth my time for adding new 5.7s in a 400.....And I Qestions the "longer rods are better because they flop back and forth less so they have less forces trying to break them" thinking in my mind....it would seem like a shorter rod is harder to brake....think of it like a really long ruler..easy to break in half...then think of a short ruler...harder to break. Im sure im missing manythings to it and it is not that simple, but it seems logical and I wonder.


Think of whip lash. A shorter rod changes a greater angle to the cylinder centerline twice every revolution. Times that by 6000+ rpm..... it is not much, but neither is the 5 horse power gained above 8000 rpm by a longer rod.
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Old 01-11-2006, 07:49 PM
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I see, So they will be no significant advantage to a street drving engine with a longer rod (5.56 -> 5.7) and I will never tell, even if I really romp on it and make alot of power (This will be my first Buildup and I dont want to screw anything up)
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Old 01-11-2006, 08:13 PM
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Here's an interesting rod comparison by Rick Draganowski:

http://www.rustpuppy.org/rodstudy.htm
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Old 01-11-2006, 08:37 PM
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here's another quote from reher-morrison. you can find the whole article on their website:

We also wanted to point out some of the common myths and misconceptions about high-performance motors. For example, I've seen dozens of magazine articles on supposedly "magic" connecting rod ratios. If you believe these stories, you would think that the ratio of the connecting rod length to the crankshaft stroke is vitally important to performance. Well, in my view, the most important thing about a connecting rod is whether or not the bolts are torqued!

If I had to make a list of the ten most important specifications in a racing engine, connecting rod length would rank about fiftieth. Back in the days when Buddy Morrison and I built dozens of small-block Modified motors, we earnestly believed that an engine needed a 1.9:1 rod/stroke ratio. Today every Pro Stock team uses blocks with super-short deck heights, and we couldn't care less about the rod ratio. A short deck height improves the alignment between the intake manifold runners and the cylinder head intake ports, and helps to stabilize the valvetrain. These are much more important considerations than the rod-to-stroke ratio. There's no magic - a rod's function is to connect the piston to the crankshaft. Period.
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Old 01-11-2006, 09:36 PM
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Quote:
Originally Posted by Warrant
I see, So they will be no significant advantage to a street drving engine with a longer rod (5.56 -> 5.7) and I will never tell, even if I really romp on it and make alot of power (This will be my first Buildup and I dont want to screw anything up)


http://www.rustpuppy.org/rodstudy.htm
This link is great! Thanks.

I think the consensus is that if you already have rods, run what you have.

If you NEED to buy rods, buy long ones.
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Old 01-11-2006, 09:41 PM
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there is one other option. i'll give you a part number for some con rods you can get. if they don't work in your motor, then you can send them to me!!!!


(i'll get my new parts for my engine somehow!!!)
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Old 01-12-2006, 02:30 PM
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I still believe in using a shorter rod in street enignes if you have to buy them- reason being the piston will have less time spent near TDC which will allow lower octane (negligeble in all honesty though) as well as provide a better angle throughout most of the power stroke between the piston and the crank. It does usually ad to the piston's weight, thus loosing a few hp at the top, but a longer skirt is also produced- which in effect saves cylinder walls and if you're looking at a low rpm torque monster allows for 4 rings instead of 3.

Its all pretty negligible really, but hey, if you have to buy them you might as well pick up the free advantages.
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