MustangWorks.com : Ford Forums - View Single Post - Long rod 306??? 400 sbc crank and chevy rods.

Shaggy · 08-19-2003, 08:17 AM

Choose to believe or not, but my experience having been lucky enough to witness an actual dyno test of 3 motor all identical except for rod length, cough they were Chevy's but the theory is the same cough, all three motors dynoed within 10hp and ft/lbs of each other at the crank with no accessory. The only think that was noticed was while they produced the same power and relative power curves the curve it self would shift either up or down a little bit, a little bit being less then 500 rpm, but you could lay all three graphs on top of each other and they would basically all lay on top of each other if you shifted the rpm +/- the slight shift in rpm. Me personally after seeing that no longer subscribes to the theory of long rods being better... especially since the long rod shifted the rpm up without a any real power gain. Well personally I would rather make same power a little lower on the rev scale and keep my motor altogether a little longer since revs will kill your bottom end as fast as changing you oil will. Now I don't thing that the slight shift up in the revs would promote that much faster wear but if you are spending the money and are putting something to together that compared to stock will have accelerated wear anyway, why put it together with just one more thing that will cause faster wear (the slight shift in RPM's being higher).Now that all that has been said the three motors were not extreme examples of rod lengths but were common lengths used by allot of people when doing there Chevy's IE the long rod motor was a 6" rod vs. the stock 5.7 and If I remember correctly the shorter was a 5.4 just because if they were going to test the rod length theory they had to put something to together with short rods.

When he tells you it has a 400 SBC crank is he sure it is not a 400 ford crank? That was actually a popular swap before all the after market crank manufacturers started making new stroker cranks. The 400 ford crank has enough meat in it that it could be offset ground in a variety of different lengths and to the Chevy or Chrysler rod bearings and ford main bearing sizes. The 377 kit that is sold to this day by many vendors is based on a 400 crank with stock throws, Chrysler rods and Chevrolet pistons in the 9.5 deck block.

08-19-2003, 08:17 AM	#23
Shaggy Registered Member Join Date: Feb 1999 Location: Houston,TX Posts: 466	Choose to believe or not, but my experience having been lucky enough to witness an actual dyno test of 3 motor all identical except for rod length, cough they were Chevy's but the theory is the same cough, all three motors dynoed within 10hp and ft/lbs of each other at the crank with no accessory. The only think that was noticed was while they produced the same power and relative power curves the curve it self would shift either up or down a little bit, a little bit being less then 500 rpm, but you could lay all three graphs on top of each other and they would basically all lay on top of each other if you shifted the rpm +/- the slight shift in rpm. Me personally after seeing that no longer subscribes to the theory of long rods being better... especially since the long rod shifted the rpm up without a any real power gain. Well personally I would rather make same power a little lower on the rev scale and keep my motor altogether a little longer since revs will kill your bottom end as fast as changing you oil will. Now I don't thing that the slight shift up in the revs would promote that much faster wear but if you are spending the money and are putting something to together that compared to stock will have accelerated wear anyway, why put it together with just one more thing that will cause faster wear (the slight shift in RPM's being higher).Now that all that has been said the three motors were not extreme examples of rod lengths but were common lengths used by allot of people when doing there Chevy's IE the long rod motor was a 6" rod vs. the stock 5.7 and If I remember correctly the shorter was a 5.4 just because if they were going to test the rod length theory they had to put something to together with short rods. When he tells you it has a 400 SBC crank is he sure it is not a 400 ford crank? That was actually a popular swap before all the after market crank manufacturers started making new stroker cranks. The 400 ford crank has enough meat in it that it could be offset ground in a variety of different lengths and to the Chevy or Chrysler rod bearings and ford main bearing sizes. The 377 kit that is sold to this day by many vendors is based on a 400 crank with stock throws, Chrysler rods and Chevrolet pistons in the 9.5 deck block. __________________ A good plan, violently executed now, is better than a perfect plan next week. George S. Patton, General (1885-1945)