Longer rods reduce the angle and therefore allow more revs and power throughout the entire rev range.
NZ Toranaman dont take this personally, your post is just happened to be the one I decided to reply on.
Dont trouble yourselves on worrying about this or that rod length, build what you can using the most obtainable parts, the angularity difference is only very slight, unless you make a big change. Plus a longer rod pulls away from TDC a fair amount slower than a short rod. Next time you fellas build a 202 with your long rod set up #1 cyl with the long rod combo and # 6 cyl with the short rod combo, set up a dial indicator on both and rotate the crankshaft and record the thou readings of piston movement every 2 degrees. You will note the longer rod climbs to TDC faster and the shorter rod in the last .005" catches it up and the on the way down the bore (the part that matters most on the intake cycle) will out accelerate the long rod all the way till approx 73-75 degrees bbdc (the fastest point of piston travel in the bore at which point they become even again. The situation is reversed at the swing around from bdc albeit the fastest point of piston travel then occurs @ 73-75 degrees btdc.
Point 1 is a shorter rod pulls harder on the intake port and therefore signals the carb better for down low torque and throttle response.
Point 2 is look at the RPM you use each day you drive around and end up a Maccas, is it 7000 and above?
If your talking a smallish cube like a 202 circuit engine and say a 12 turn track, the shorter rod motor will out accelerate the longer rod motor every time the foot goes down, and lets assume the car's weight gears tyres cams etc are all the same. I know what I'd rather have.
If its a NASCAR and you've got the motor parked up on 8500-9500 rpm then by all means put a long rod in it.
By the way yes the piston becomes lighter with a longer rod, but the down side is the rod is heavier and last time I checked Aluminium was lighter than steel. Food for thought.
Your money on those longer possibly cutom rods and custom shorter pistons just may be better spent elsewhere in your car.
Edited by Allports, 18 April 2009 - 01:09 AM.
View Garage
