My 1999 Honda Civic EX has a forged steel crankshaft and connecting rods. That may be a big factor in how smooth and easy revving the engine is, and how well it is doing at 179,000+ miles.
Who still puts forged crankshafts in engines? Which engines?
How important is it for smoothness, longevity, overall quality feel of the engine?
You won’t feel the difference in driving a car with a forged crank if the engines are otherwise identical. A forged crank is used if you want more horsepower or rpm than a cast crank will tolerate. Sometimes a forged crank is used when a passenger car engine design is used in a truck or marine use because of higher sustained loads on an engine. Chrysler used it’s 225 cu in slant six in moving vans but gave it a forged crank and rods.
I was thinking the same, as far as difference in feel. I wouldn’t think forged crankshafts would offer huge reliability advantages in normal commuter car driving either, but I could be wrong. Crankshaft failure in a daily driver has got to be rare. But I could be wrong. Forged connecting rods, those are nice. Maybe Honda was thinking ahead and new the Fast and Furious types were going to use nitrous!
Steel weighs about 0.278 lb per cubic inch whether it’s cast or forged. Really I think we should call forged parts swaged parts. The forge is the furnace that the blacksmith uses to heat the work. A swage is a tool used to give that red hot part a certain shape, similar to a mold.
“Easy revving” usually comes from a light flywheel.
I put a quarter of a million miles on a '91 Geo Metro with a 1 liter 3 cylinder engine. It wasn’t the crankshaft that wore out.
The crankshaft is not the achille’s heel that determines engine life in modern engines that aren’t abused at the race track.
It’s not
Most engines that feature forced induction will have a forged crank, as will many higher performance N/A engines. Diesels almost always have them.
Smoothness? Doesn’t matter
Longevity? A forged crank is stronger than a cast one, if you used a cast crank in an application where a forged one would be needed (high output engines or engines that are under a constantly heavy load) Then the forged crank would be more reliable.
Overall quality feel of the engine? No difference at all, you can’t tell if an engine has a forged crankshaft just by driving the vehicle.
I sold my '98 Civic to a friend with about 100k miles on it. A year later, she put a rod through the crankcase “passing a semi on the interstate.”
;-]
Compression ratio, torque demand and the layout of the crankshaft have seemed to be the critical reasons for using a forged rather than cast crankshaft. In line 6 cylinder engines and 90* V-6 engines with stepped rod throws forged steel would seem more critical while V-8 and 60* V-6 engines put less stress on their cranks.
The only broken crankshaft that I have ever dealt with was on a Ford Ranger. It was a 2.9L V-6 and the crankshaft broke just ahead of the rear main bearing and the break was at such a angle that the truck could be driven if carefully eased away from a stop. With a manual transmission the crank would jump at the break if pushed even moderately. No one had a clue what would cause such a failure other than a faulty casting but the truck was several years old with nearly 100,000 miles on it when the failure occurred.
A few years ago the group here chatted at length about how crankshafts are manufactured. OP might find that thread (below) interesting to read through. I found the experts here and their discussions on the subject very interesting. My plan is that when I finally need to retire either my truck and Corolla, I’ll retain the crankshafts and install them in my living quarters as a reminder of all the fun places they took me.
Smoothness in a crankshaft is about balance rather than processing of the material of which it’s made.
Smoothness as regards connecting rods has to do with stroke and weight.
Connecting rods are what’s known as “reciprocating masses”. They change direction and go up and down thousands of times a minute. The heavier they are is the more inertia that needs to be stopped and have its direction reversed… thousands of times a minute. Ideally a connecting rod needs to be as lights as possible while still being strong enough to hold together. And, in a mass-produced family car, still be affordable.
Stroke (which is controlled by the crankshaft) is also a factor in connecting rods. The longer the distance that the reciprocating masses (rods & pistons) need to travel at speed is the greater the difficulty in turning them around.