Is this strictly a cost thing or what ? Are forged alu pistons and forged crank a waste of money or what , just a gimmick to add cost ? I've only had 2 cranks go bad on me , both in a truck 360 1977 brand new , went in 10,000 miles and the rebuild lasted 20,000 miles , both cranks were cast .
A lot of people here are often advising to use cast crank and pistons ,
- Thread starter jerry6
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I "think" the cast makes for a lighter rotating assembly. I would think a forged crank would be stronger. That is what I will be using when I put my 360 together.
OldmanRick
Well-Known Member
I think intended use, rpm range and the possibility of adding boost/nos down the road really dictates what to use. A N/A cast engine with good machining should go 5500/6000 on occasion and still last a good long time on the street. More R's and hammering on it you really gotta go forged imo.
Forged metals are stronger than cast. And, in the case of stock pistons, forged pistons are usually lighter too. I know the set that I put in my 318 were.
Forged pistons are more resistant to detonation and better with forced induction/nitro set ups than cast or hypers. You also don't have to worry as much about piston speed as with hypers. Basically, they're a tougher piston.
Forged cranks can take higher horsepower and torque ratings than cast. As far as them lasting longer, well, if cracks were what ended the cast cranks life than maybe. I don't see the bearing surfaces lasting any longer. But, they'll still take more abuse than a cast crank.
As far as whether to use them or not, it really depends on the build. If you're building a mild or even moderate engine they aren't necessary. If you're not planning a ton of track time, they probably aren't necessary. And of course the forged stuff is more expensive, so if you're not venturing out over 400 hp, its an added expense that you probably don't need. On the other hand, if you're planning on beating the crap out of your engine, forged parts are good piece of mind.
Forged pistons are more resistant to detonation and better with forced induction/nitro set ups than cast or hypers. You also don't have to worry as much about piston speed as with hypers. Basically, they're a tougher piston.
Forged cranks can take higher horsepower and torque ratings than cast. As far as them lasting longer, well, if cracks were what ended the cast cranks life than maybe. I don't see the bearing surfaces lasting any longer. But, they'll still take more abuse than a cast crank.
As far as whether to use them or not, it really depends on the build. If you're building a mild or even moderate engine they aren't necessary. If you're not planning a ton of track time, they probably aren't necessary. And of course the forged stuff is more expensive, so if you're not venturing out over 400 hp, its an added expense that you probably don't need. On the other hand, if you're planning on beating the crap out of your engine, forged parts are good piece of mind.
360 cast crank are very strong, both for everyday use or drag racing. For Pistons, unless I was doing something really cheap i would at least use hyperuetic pistons. KB107 seems to be the piston of choice.
I have spun 360 cranks up to 7500 rpm and never had a problem with them...and that was with a heavy trw piston....
I have spun 360 cranks up to 7500 rpm and never had a problem with them...and that was with a heavy trw piston....
cannucky
The Guy With No Birthday
If your going much above 500hp look at a forged crank but there's a couple of builders on here that use the light weight alloy Scat 9000 cast cranks in motors making more than 500 hp with no issues , they even say you can spray another 150hp to them if you like but I haven't personally tested this point yet .
breakstuff
Well-Known Member
Its a fancy cast piston with a higher silicon content. Stronger than cast but more brittle.
http://en.wikipedia.org/wiki/Hypereutectic_piston
"A hypereutectic piston is an internal combustion engine piston cast using a hypereutectic alloythat is, a metallic alloy which has a composition beyond the eutectic point. Hypereutectic pistons are made of an aluminum alloy which has much more silicon present than is soluble in aluminum at the operating temperature. Hypereutectic aluminum has a lower coefficient of thermal expansion, which allows engine designers to specify much tighter tolerances."
From Wikipedia
I always seen,been told Hyper's are a 1/2 way point between stock cast, and forged pistons.Lighter then Cast, less durable and cheaper then Forged.
Stock 360 cranks will handle 550-600hp and turn 7500+ with the right stuff attached to them.
KB107's going the same... 7800 and in the high 500, low 600 hp range.
If a truck ate 2 cranks in 30K, I'd bet the root issue of what caused the damage wasn't discovered.
Sometimes people don't need the absolute, top whack parts for their build, but, they spend the money anyways. Some even complain about why the stuff cost so much which is ironic.
KB107's going the same... 7800 and in the high 500, low 600 hp range.
If a truck ate 2 cranks in 30K, I'd bet the root issue of what caused the damage wasn't discovered.
Sometimes people don't need the absolute, top whack parts for their build, but, they spend the money anyways. Some even complain about why the stuff cost so much which is ironic.
According to Dodge the root cause was my lead foot , back 40years or so when I was 16 , even when 30 I had a lead foot , 200 miles at 5000 rpm was just to much for those 360's . The 440 six pac replacement with forged parts lasted 100,000 miles before I sold it . Back then the fines were nothing , and no points .
Those 360's turning 7800 , those are street or race that are torn down every 3 weeks or 75 passes ? That or the machining and balancing today are 100 times better than back in the day
OldmanRick
Well-Known Member
Jerry, when i responded earlier i think i was thinking the same thing as far as use. A average performance street engine that you could drive everyday and put 50k or more on.
Just to comment further, if im going to all the expense of building a engine that really makes power in the 7500+ range i'm certainly not gonna save a few bucks and use a cast crank, or even a stock forged one for that matter. JMO.
dustinmoran91
Well-Known Member
i think it comes down to how well its balanced, how well your tolerances are set, rotating weight, and if its N/A or forced induction. they use cast pistons in racing all the time BUT they have their timing and fuel set perfect to prevent detonation. forged pistons are the choice for high horsepower engines using nitrous and turbos because of the resistance to heat and detonation being able to melt them. cast pistons can handle a lot of abuse but the detonation kills them, and like was said earlier, if building a high horsepower engine its cheap insurance to buy the forged stuff from the start. hypereutectic pistons don't see much action in the turbo and nitrous crowd because of the tighter tolerances making them more likely to seize up when they get hot from the power adder. as far as the crank shaft goes, i dont know much about them lol
Okay , thanks guys , off the the Legends of Racing at Mont Tremblant , a weekend of good ole horse power with open header CAN-AM , Trans-Am ,and Indy F-1 cars from the past . Last time had no ear protection and my ears hurt from the noise . Ear plugs this year .
Best comment here.
Planned use was never stated. For most street guys a forged crank, especially a 360, is an unnecessary expense. Even a 4" arm doesn't need a forged unit in most cases. Pistons, same deal.
No, the 7800 rpm engine was not torn down every 3 weeks. It had turned 7800 on occasion, wasn't the norm. Most of the time it was in the 7200 range. The crank went into a daily driver and still runs today. It went 5 years and about 400 runs before it was pulled apart for good. It was inspected on a yearly basis and most of the time the bearings were put right back in service. Forged cranks for 360's just weren't reasonably priced for a long time.
Machining and tolerance control now is better than it was in the 70's especially from the OEM's.
OldmanRick
Well-Known Member
Screamin' F1 and roarin' Big Block CAN-AM engines.......Now that's cool.
Have fun, Rick
Mostly a cost thing from my point of view since most here are street bound and have no need to spend large on parts for the power they want to make.
Your short lived engine and rebuild on it points (for me at least) to two things. CRAP workmen ship and/or abusive driving.
If this were a race car question and the car was deadacated (sp?) race car, 'd be advising forged parts and maybe even race blocks. Considering stock parts can propel an A body for years in the 11 second range without problems, why go forged?
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