4 Jaw Chuck ....... Please respond

4 Jaw Chuck **** You say that stroke makes no difference in the reving ability of a motor. I can accept that since you seem to know what you're talking about. You're saying it will do absolutly no good to put a large journal 327 crank in a 350 4 bolt block......matter fact the way you talk it will actually lose power as opposed to just sticking with a stock 350 crank. But let me ask you this...Have you ever heard of anyone turning a 350 crank down to small journal size and using oversized bearings or spacers? Would that make the 350 rev like a 327? Or would that weaken the crank too much? It just seems that a small journal 350 would be awsum if it would work. <img src="graemlins/mwink.gif" border="0" alt="[mwink]" />

If you respond, thanks. If you dont I will stalk you and bug you until you do <img src="graemlins/boxing.gif" border="0" alt="[boxing]" /> ...LOL...just kidding man. Later, S10

[ August 10, 2002: Message edited by: HotRodS10 ]</p>


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Turning down a large journal crank and making a small journal crank out of it is very easy. The problem usually lies in the fact that castings are porous and the further into the casting you go the more porous it gets, also the grain sizes become larger which leads to a weaker crank. You can think of castings as a loaf of bread, once it is baked the air becomes entrained and only the skin is smooth (typically crankshafts will have a skin about 0.060" thick). Grain growth is very undesirable from a strength standpoint and leads to uncontrolled brittle fracture.

Forgings are a different story, the forging process squashes out the air and could be compared by thinking of the bread as being dough that has dried. This makes a dense structure with pancake shaped grains and is very strong and more flexible. The flexibility comes from the laminar arrangement of the grains. Of course you can usually grind forgings more than you could grind a casting but a forging also has a skin and it is much thinner due to the nature of the process....blah blah blah.....it's a long story.

As far as drag and journal diameters go...forget about it unless you are interested in turning 10 000 rpm, you will never notice if the engine has a large journal or small journal. The difference is mostly academic and relates to critical speed loading of high speed bearings and you don't even come close at typical V8 rpm's

Now if you are racing formula 1....that's a different story, those engines can turn up to 20 000 rpm before coming apart. There is considerable interest in development of the air-foil bearing. Basically there is no lubricant and the journal floats on a cushion of air, they are used in small gas turbines and are self aligning and self cooling. Here's a link;

<a href="http://www.grc.nasa.gov/WWW/PAO/PAIS/fs14grc.htm" target="_blank">http://www.grc.nasa.gov/WWW/PAO/PAIS/fs14grc.htm</a>

Cool hey! Anyway the idea has been around for decades but no one has figured out how to adapt it to an automobile engine yet.

Hope this answers your question.

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bore vs stroke
The point in the rpm range where peak torque and horsepower develop are dictated by how the displacement is built. As stroke increases, the lower in the rpm range peak hp and torque occur. In addition, a longer stroke engine produces more peak torque and less peak hp...on the flipside...lower torque at low rpm. Maybe a thought for heavier cars.

[ August 10, 2002: Message edited by: windmaster ]</p>

The technology of hydrodynamic bearings as used in auto engines in facinating. In fact, oil pressure on your gauge has nothing to do with how well the bearings work, it just assures the oil is there when needed. At the point of interface of the journal and bearing, the pressure on the oil is thousands of psi and the oil layer is only a few molecules thick. Bearing design (as is all mechanical design) is a compromise between friction loss, strenght, load carrying capacity, etc. All of those parameters are mutually exclusive and the designer must reach a happy medium for the application he is designing for. Grocery getter is totally different from a 6000hp top fueller. Neither woud survive with the others engine.

4 Jaw Chuck **** You say that stroke makes no difference in the reving ability of a motor. I can accept that since you seem to know what you're talking about. You're saying it will do absolutly no good to put a large journal 327 crank in a 350 4 bolt block......matter fact the way you talk it will actually lose power as opposed to just sticking with a stock 350 crank. But let me ask you this...Have you ever heard of anyone turning a 350 crank down to small journal size and using oversized bearings or spacers? Would that make the 350 rev like a 327? Or would that weaken the crank too much? It just seems that a small journal 350 would be awsum if it would work. <img src="graemlins/mwink.gif" border="0" alt="[mwink]" />

I couldn't find where 4 Jaw Chuck said anything about stroke making no difference in the reving ability of an engine and if he had, I would have a hard time listening to anything he had to say. Note: that is not the case and 4 Jaw chuck made several good points.
An engine with a longer stroke does not like to rev as high because because of piston speed. At a given engine speed say 6,000 rpm's the piston in an engine with a longer stroke has to travel a greater distance than a piston in an engine with a shorter stroke, so the piston has to travel faster to make up for the added stroke. At these greater piston speeds the piston endures great amounts of G Forces and a piston will try to rip itself apart. If money is no object then there is more horsepower to be made at high rpm's, however, horsepower is just a number that is calculated from torque and rpm's. It's torque that get's you down a track. The cars that I've had the most fun in are cars with engines that made lots of torque like my trans am with a 400 small block chevy, that probably wouldn't turn 6,000 rpm but it made gobs of torque right off idle and all the way to 5,000. A shorter stroke crank would make it rev higher but if you shorten the stroke you are loosing valuable cubic inches which make that great torque.
Smaller diameter crank journals and rod journals would mean less friction but as 4JC said forget about it unless you're turning 10,000 rpm...that's Nascar rpm range and they use the absolute best parts money can buy then change them out after every race. The shorter stroke allows higher rpm's the small diameter bearing journals allows for less power robbing friction for those that are looking for every possible edge over the competition.
I have heard about people putting a 327 crank in a 400 block using thicker bearings or bearing spacers which would be simular to a NASCAR bore and stroke combination.

hope this helps and i'm not out of line here

Lou

This thread is over 6yrs old.

still a good read

You know what they say...."Can't beat the classics"..........

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Ontario Rodders

though, reading it on a lazy sunday arvo.

Geez you know your old when they start digging posts out of the past on ya.