I did some looking but didn't find the info I wanted. I am assuming that a forged crank is superior to a cast in the strength catagory. What I want to know is, looking at a 327, which is better; a small or large journal crank?
A lot of 327's had steel cranks in the higher hp versions. They are a great set up for a street or race motor. I don't think you would ever know the difference between a cast and forged crank once the motor is together. Steel cranks offer bragging rights just like camel hump 2.02 heads do. I have no idea what the large journal or small journal does for you. I would like to know also.
Small journal obviously has a little less meat and is pretty much stuch as 2 boly main, but looses less power through bearing drag, but big has a stronger block around the webbing, and the ability to put in 4 bolt main caps
Small journal cranks have less bearing speed. Creates less oil drag. At the journal. Small journal 327 forged cranks were the hot setup back in the day. Ask "grumpy" jenkins. Large journal forged 327 cranks are very rare. I have seen three or four in forty years of engine building.
That is one of those questions that probably has no real answer. If you ask 10 top engine builders that same question you would probably come up with a 50/50 split. Both sides having good arguements for their view. I honestly think unless you are building an ultimate engine where a percent of HP gained is considered a worth while investment in time and money. I asked this a long time ago and that is what I learned. If what you have is good..........use it.
First lets ask where did cast cranks come from? They were developed by Mickey Thompson in the sixties for making none stressed Stroker cranks. There is an article on it in the 1963 Hot Rod annual. Because of the way a forged crank is made by twisting a piece of steel around to form the rough core Mickey explored making cranks by casting and the OEM industry took hold of the idea . Nothing has been the same since. They are not weak. I have used them several times . For years even during the pro stock wars 351 Clevlands only were avialable with a cast crank. In Mopars we have only cast cranks for the 360. Also the new 5.7 hemi is cast. Mopar 400 was cast only as was the Chevy 400. Much too much is made of the cast forged thing. Unless you are building a 500+ hp small block or a 600+ BB block dont even think about it. Small journal? The bearing speed thing previously mentioned it well put and true. Some serious racers grind their cranks to use Honda bearings believe it or not. I dont think it is a serous consideration for anyone but a pro racer. Thousands of SBC chevies have been built and raced with small journal cranks. I lived back in those days and they were not noted for having bearing or crank problems. Use what you find I would say. Don
Small journal forged 327 cranks can be broken in a street driven car. I have proven that; but you do have to work at it.
probably depends if you have a small or large journal block? I prefer the crank to fit the block. Oh...seriously....interesting that chevy made the journals larger about the same time they increased the stroke to three and a half inches in the small block. And also about the same time they went to cast cranks. Wonder if either has anything to do with it?
We just built a small journal 327 that had the bearings knocked out of it, junked the crank, and the line bores measured perfect. Very unusual for a sbc, I line honed 4 of them in the last 2 days. The 350 one piece seal blocks, or Hencho blocks as I call them (hencho en mexico) are horrible for the line bores being out of whack and the metal is soft so they hone out really quick. The 327 we built (after I finally found a crank) made 345 hp on the dyno with a comp thumpr cam, edelbrock performer intake, holley 600 and factory 1966 heads with no port work. Not too bad for a 9.5:1 327 John
Engine designers like to have a large overlap between the rod and main journals. As the stroke increases, the bearing journal diameters also increase to keep this "overlap" area as large as possible to maintain stiffness and keep crank harmonics to a minimum. Bearing speed is one of the limiting factors.
Actually, you can get spacer bearings for running a small crank in a 350 block, like the 301 i'm building, and nothing wrong with turning a large journal down to fit in a small journal block
Yeah, Ford Y blocks had cast crankshafts right from the start, so that punches a hole in the M/T theory.
440 roadrunner. I gave you the reference and the exact book. Maybe he didnt invent them but he certainly produced them for high perfomance use. BTW I dont deal in theories. I am going to check on your Y block thing tomorrow. If it is true I wasnt aware of it. I know where there are 2 right now. The main point is that I see people wanting always a forged crank when there is no way on earth they are making an engine that could ever hurt a cast crank. Don
Don, Yep! on your cast vs. forged point. It is true that most Y blocks have cast cranks. '61-'64 292HD engines have the forged C1TE truck crank; this engine was used in the medium duty trucks. Robert Stevenson, the head of the Y block design team, stated in his SAE presentation that using the cast crank allowed them to use a total of eight counterweights since they weren't limited by the forging process. According to one source, FoMoCo developed the foundry processes, determined the correct iron alloy, and pioneered the cast crankshaft in the flathead for 1934. Perhaps one of the flathead guys like Bruce can confirm this. I've heard the M/T story a number of times, and always interpreted it that he took the concept of cast crankshafts and developed it for aftermarket stroker cranks, due to the relatively common failures resulting from welding journals. Back to the original topic, cast crankshafts will hold up very well under most use. I do have the opinion that Ford designed their cast cranks better than GM, as a general rule. I couldn't say as to the quality of Mopar castings from personal experience, other than that the 360 cranks seem to be respectable pieces. If I wanted to build the easiest-to-find-parts 327 SBC, I'd simply use a 350 two-piece seal block, and a dirt-cheap, common, 307 crank, with 327 pistons of choice. 327 cranks, even small journal, seem to have a bit of a premium price..the glamour, I suppose. Bearing speed is a ridiculously overrated topic...just like rod/stroke ratio....unless you are running NASCAR-type applications. Many Ford engines have too-large bearing diameters by the standards of some people...and yet they work just fine. All this is just spittin' into the wind unless the original poster states what he actually intends to DO with this engine.
________________________________________________________________ That, unfortunately is a question to which I don't think you will find an absolute answer. I asked that question to a bunch of engine builders and racers over the years, and there was no clear benefit either way, small or large. A forged steel crank is preferred, but for medium duty or daily driver a cast crank is fine. Look at it like car insurance, you can drive without it, but if you have a problem, you have a major problem. Never forget this..... EVERYTHING breaks.......best you can do is hedge your bet. Good luck
Generally speaking forged is stronger than cast and larger journals are stronger than smaller. However... Much of a cranks strength is depends on the radius between the counterweight side and the journal surface. The strongest cranks have large radii that require narrowed bearings. Smaller journal cranks have less frictional losses. The relative "bearing speed" is slower on the smaller journals. It's interesting to note that some of the most powerful normally aspirated drag engines are now using 1.880 inch diameter rod journals. That is even smaller than you are asking about. Hope that helps.
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