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Old 03-23-2012, 09:10 PM
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stroke and rod ratio combinations:

NOTE: Let's keep the discussion pertaining specifically to the small block chevy for now.

What would be better and why? A shorter stroke crank, say 3.48-3.60" with a longer rod---say 6". OR a long crank---4" with a shorter rod--5". Or is it possible to have a long crank AND long rod?

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Old 03-23-2012, 09:26 PM
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Rod length is almost irrelevant. Go for ask the stroke you can and a rod that allows a decent ring package.
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Old 03-24-2012, 01:27 AM
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I personally like the longest stroke I can afford and the shortest rod I can afford, so in an SBC the 400 rod is 5.565", then you have 5.7", 5.850, and 6.00".

To figure out what you can use.

9.025" block deck ht = Stroke / 2 + rod length + CHT Piston

With a 4" stroke and a 5.7 rod you need a 1.325" piston ht to make 9.025 = Standard chevy block deck HT

2" + 5.7"rod + 1.325cht = 9.025BDH

If you add .300 to the rod for a 6" rod you have to either take .300" out of the Piston CHT or take 1/2 of that .150" out of the crank size to get it all to fit.

2" + 6.0"rod + 1.025"cht = 9.025BDH

If you go too short on the piston the rings go down into the pin and need expensive spacer rings. $200 set for rings, regular non-spacer ring $50-$100.

Bottom line 4" stroke with 5.7 rod is easy to get a piston for and rings are cheap.

The bigger the stroke the more grinding...

You better be careful on the cam cause you will need a .900" base circle even if you buy stroker rods, cause the rods will hit the cam. It even happens with stock rods on 383 stroker if the cam is above .500" lift and advanced any.

If you don't buy a small base circle cam you will have to grind the pi$$ out of the rods and that ain't fun or good for the rods.
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Old 03-24-2012, 09:55 AM
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stroke and rod combos

There is an interesting article to read on that goes into detail about different rod and stroke.
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Old 03-24-2012, 08:58 PM
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cdminter59, that was a great article very informational. but it contradicts a little bit with what raceman14 is saying. personally i like a longer rod and stroke for a few reasons, one being what was stated in the article above is sidewall pressure, the shorter rod the higher the angle on the wrist pin so you get more force on the bottom side of the cylinder causing oval shaped ware over time. another advantage i have read about in other articles on the subject is the actual time at tdc and bdc, a longer rod will stay at bdc and tdc for longer giving you more air in during intake stroke, longer burn at start of power stroke and with a good exaust and lobe sep a good transfer of exaust out and air in during the exaust/intake stroke.
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