What are the advantages of polishing a crank, and of having forged pistons?
07-13-2002, 09:02 PM
#1
What are the advantages of polishing a crank, and of having forged pistons? I've always wondered but never asked. What exactly does it accomplish? Rods are polished, too, right? Why? And, what exactly is a "forged" piston, and why is it better? I'm trying to make a list of parts for a bullet proof bottom end, so I figure I'd ask questions I've had for years <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
07-13-2002, 10:56 PM
#2
TECH Fanatic
Re: What are the advantages of polishing a crank, and of having forged pistons? A few thoughts:
1."polishing" a crank. Usually the last step in crank manufacture. It improves the surface finish of the main and rod journals which may help bearing life. It doesn't add strength as such, and isn't really a mod you would do. Sometimes if bearings need changing, and the crank isn't scored or worn, just polishing it is enough.
Rods are polished along the sides of their beams (I-beam rod) to eliminate forging die or mold marks which could be the place where a fatigue crack starts. It also lightens them a bit, but every little bit helps. Modern powdered metal (PM) rods don't have much to polish off.
2. "forged" pistons are produced by forcing an aluminum slug into the rough shape of a piston under many of tons of pressure and some heat. The grain in the aluminum slug flows into the shape of the piston which increases it's strength. It also may become denser, and therefore stronger.
Most stock pistons are cast; molten aluminum is pored into a mold, cooled and removed. No grain, and the aluminum is not as densely packed together as a forging. If excess silicon is added, the aluminum is "hypeteutectic" and a little stronger, but still cast. Forged pistons usually expand more when the warm up, so they need to be fitted looser in the bores, which can result in some noise when the engine is cold.
Machining of the forging or casting is the same.
3. If you want a very strong lower end, use a forged crank (most stock are cast nodular or ductile iron). The forging should be 4340 (nickel-chrome-moly) steel, through hardened, tempered and surface hardened on the journals. A really nice one will be $900-$1200 for a last gen small block chevy; maybe more for an LS1. Good for 700 or more HP. A cheaper forging may or may not be stronger than a good stock (LS1) crank. If I was going much over 500 real flywheel Hp, I'd go for the good forging. Of course, use the forged pistons.
4. Forged, CNC machined H-beam rods (Carillo, Eagle, Arrow, etc.) should also be used of you are going for more than 500 hp. You can spend $600-$1200 there. If you feel you'll be making 800 hp regularly at 8000++ look at Arrow, but be prepared to spend $1600-2400 for very strong, but very light rods.
Probably more than you wanted to know.
"(Reliable) speed costs money" How fast do you want to go?
1."polishing" a crank. Usually the last step in crank manufacture. It improves the surface finish of the main and rod journals which may help bearing life. It doesn't add strength as such, and isn't really a mod you would do. Sometimes if bearings need changing, and the crank isn't scored or worn, just polishing it is enough.
Rods are polished along the sides of their beams (I-beam rod) to eliminate forging die or mold marks which could be the place where a fatigue crack starts. It also lightens them a bit, but every little bit helps. Modern powdered metal (PM) rods don't have much to polish off.
2. "forged" pistons are produced by forcing an aluminum slug into the rough shape of a piston under many of tons of pressure and some heat. The grain in the aluminum slug flows into the shape of the piston which increases it's strength. It also may become denser, and therefore stronger.
Most stock pistons are cast; molten aluminum is pored into a mold, cooled and removed. No grain, and the aluminum is not as densely packed together as a forging. If excess silicon is added, the aluminum is "hypeteutectic" and a little stronger, but still cast. Forged pistons usually expand more when the warm up, so they need to be fitted looser in the bores, which can result in some noise when the engine is cold.
Machining of the forging or casting is the same.
3. If you want a very strong lower end, use a forged crank (most stock are cast nodular or ductile iron). The forging should be 4340 (nickel-chrome-moly) steel, through hardened, tempered and surface hardened on the journals. A really nice one will be $900-$1200 for a last gen small block chevy; maybe more for an LS1. Good for 700 or more HP. A cheaper forging may or may not be stronger than a good stock (LS1) crank. If I was going much over 500 real flywheel Hp, I'd go for the good forging. Of course, use the forged pistons.
4. Forged, CNC machined H-beam rods (Carillo, Eagle, Arrow, etc.) should also be used of you are going for more than 500 hp. You can spend $600-$1200 there. If you feel you'll be making 800 hp regularly at 8000++ look at Arrow, but be prepared to spend $1600-2400 for very strong, but very light rods.
Probably more than you wanted to know.
"(Reliable) speed costs money" How fast do you want to go?
07-14-2002, 12:22 AM
#3
TECH Fanatic
Re: What are the advantages of polishing a crank, and of having forged pistons? Old SStroker .... Very Very well put.
And since we are talking about engine components, I would like to add that the BEST iron engine blocks are the blocks with high nickel content.
Case in point; The Turbo 3.8 Buick (GN motor/89 Turbo Trans Am)... Much higher nickel content in the iron block than a non-boosted Buick 3.8 block
Ron,
And since we are talking about engine components, I would like to add that the BEST iron engine blocks are the blocks with high nickel content.
Case in point; The Turbo 3.8 Buick (GN motor/89 Turbo Trans Am)... Much higher nickel content in the iron block than a non-boosted Buick 3.8 block
Ron,
07-14-2002, 10:47 AM
#4
TECH Fanatic
Re: What are the advantages of polishing a crank, and of having forged pistons? Thanks K&R.
Good point on the high nickel (2%) blocks. The nickel allows the iron to work harden (get harder/tougher with loading) so it increases bore life. 1% or so tin also helps the molten iron flow better into the mold. On early (non-LS1) blocks, the numbers 10(1%) or 20(2%) or both are cast on the block under the timing chain cover. Both numbers together mean 1% tin and 2% nickel; probably the best production iron block.
All the Bowtie blocks are at least that strong or stronger, which is another reason for starting with one of them.
Do you eat kimchee? It's an acquired taste, I guess.
Good point on the high nickel (2%) blocks. The nickel allows the iron to work harden (get harder/tougher with loading) so it increases bore life. 1% or so tin also helps the molten iron flow better into the mold. On early (non-LS1) blocks, the numbers 10(1%) or 20(2%) or both are cast on the block under the timing chain cover. Both numbers together mean 1% tin and 2% nickel; probably the best production iron block.
All the Bowtie blocks are at least that strong or stronger, which is another reason for starting with one of them.
Do you eat kimchee? It's an acquired taste, I guess.
07-14-2002, 02:36 PM
#6
TECH Fanatic
Re: What are the advantages of polishing a crank, and of having forged pistons? [Quote] "Do you eat kimchee? It's an acquired taste, I guess".
___________________________________________
Cant stand the stuff. I just changed my user name here 3 years ago when I transferred to Korea. Really a dumb user name if you ask me... Oh well
For those of you that dont know what kimchee is: The Koreans eat it for breakfast, lunch, and supper. Made normally from Napa cabbage that been slightly to highly fermented and flavored with LOTS and LOTS of garlic and hot pepper. There is 100s of variations of the stuff. The smell can be a little hard to handle for most Americans. Tastes pretty good when you are drunk.
Eat too much of it and it will feel like battery acid coming out of your *** when you take dump the next morning! <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" />
"Kimchee Class 101" is dismissed!
___________________________________________
Cant stand the stuff. I just changed my user name here 3 years ago when I transferred to Korea. Really a dumb user name if you ask me... Oh well
For those of you that dont know what kimchee is: The Koreans eat it for breakfast, lunch, and supper. Made normally from Napa cabbage that been slightly to highly fermented and flavored with LOTS and LOTS of garlic and hot pepper. There is 100s of variations of the stuff. The smell can be a little hard to handle for most Americans. Tastes pretty good when you are drunk.
Eat too much of it and it will feel like battery acid coming out of your *** when you take dump the next morning! <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" />
"Kimchee Class 101" is dismissed!
