grumpyvette
Well-known member
"All other things equal (cam, heads, exhaust), would a 383 Chevy motor built with stock 400 rods (5.56"?) versus 6" rods perform poorer? "
in that case the shorter rod will tend to build torque earlier and peak earlier in the rpm range, but designing an engine to take advantage of the longer rod ratio will require that cam,headers,compression and parts be changed to match the rod ratio or theres not a great deal to be gained, the longer rod ratio requires the rest of the combo take advantage of the potential the longer rods, lighter piston combos, lower side loads, and better rod angles,and longer effective pressure above the piston per revolution that the longer rods potentially have, combos must be made from parts designed to match the operating perameters if effective results are expected, generally the shorter rods like a tighter LSA and slightly lower scr read below
things to look over and read
5.7" vs 6" rod piston possition vs crank degree chart
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
read the articles
http://www.hotrod.com/techarticles/82378/
http://www.grapeaperacing.com/GrapeApeRacing/tech/rodslength.cfm
http://www.geocities.com/MotorCity/Garage/1020/rods.html
http://www.victorylibrary.com/mopar/rod-tech-c.htm
http://www.stahlheaders.com/Lit_Rod%20Length.htm
http://www.airflowresearch.com/
(articles)
(The 350 Engine, Chevrolet Should Have Built)
while the gains youll see are small and mostly noticable above about 5000rpm due to the slight mechanical advantages the longer rods, lighter piston combos, lower side loads, and better rod angles, that the longer rods normally have the ADVANTAGES ARE THERE for the longer rods, and are measurable, look at the piston position vs crank angle chart again, the longer rods move away from TDC slower in relation to the crank angle allowing a longet time spent at the higher pressure part of the cylinder pressure curve, at higher rpms thois results in a very slight advantage in useable torque (useful cylinder pressure) if a matching cam timing and exhaust scavaging header is used to take full advantage of that longer pressure peak as the piston moves away from tdc all the factors must be in place before youll see a noticable advantage to the longer rods, especially the exhaust scavaging and cam timing
in that case the shorter rod will tend to build torque earlier and peak earlier in the rpm range, but designing an engine to take advantage of the longer rod ratio will require that cam,headers,compression and parts be changed to match the rod ratio or theres not a great deal to be gained, the longer rod ratio requires the rest of the combo take advantage of the potential the longer rods, lighter piston combos, lower side loads, and better rod angles,and longer effective pressure above the piston per revolution that the longer rods potentially have, combos must be made from parts designed to match the operating perameters if effective results are expected, generally the shorter rods like a tighter LSA and slightly lower scr read below
things to look over and read
5.7" vs 6" rod piston possition vs crank degree chart
http://www.iskycams.com/ART/techinfo/ncrank1.pdf
read the articles
http://www.hotrod.com/techarticles/82378/
http://www.grapeaperacing.com/GrapeApeRacing/tech/rodslength.cfm
http://www.geocities.com/MotorCity/Garage/1020/rods.html
http://www.victorylibrary.com/mopar/rod-tech-c.htm
http://www.stahlheaders.com/Lit_Rod%20Length.htm
http://www.airflowresearch.com/
(articles)
(The 350 Engine, Chevrolet Should Have Built)
while the gains youll see are small and mostly noticable above about 5000rpm due to the slight mechanical advantages the longer rods, lighter piston combos, lower side loads, and better rod angles, that the longer rods normally have the ADVANTAGES ARE THERE for the longer rods, and are measurable, look at the piston position vs crank angle chart again, the longer rods move away from TDC slower in relation to the crank angle allowing a longet time spent at the higher pressure part of the cylinder pressure curve, at higher rpms thois results in a very slight advantage in useable torque (useful cylinder pressure) if a matching cam timing and exhaust scavaging header is used to take full advantage of that longer pressure peak as the piston moves away from tdc all the factors must be in place before youll see a noticable advantage to the longer rods, especially the exhaust scavaging and cam timing