Well my grandpa races mud trucks for a living. Fastest in our area. he lets me race in the slower division with his 500hp s10 with a 377, my uncle uses his 687 hp silverado stepside 350, and my grandpa has a monster 988 hp 350! all 4 bolts. so he asked me what i was doing with my camaro and i said i was putting in a 4 bolt main block and he said why? i told him they are stronger. he quickly stated to not to. i said why? he said cuz i was gonna go get a factory 4 bolt main, get it all fixed up thinkin it could handle anything. he told me that the material factory engines are made of makes them weaker. he said that a crank shaft rotates in a circular motion and the extra 2 bolts would only help side to side, not top to bottom. he said the engine vibration will have a longer place to travel and increase chances of cracking. the example he gave was imagine a wooden dowel. a short peice would be hard to crack in half by hand but a longer piece would be a little easier, but if its made from solid aluminum, i couldnt break it regardless? well i still didnt believe him (just figured he was too old school) but he took me in the shop, and got 3 blocks out of his storage, all factory chevy blocks. 1 2 bolt and 2 4 bolt blocks. we installed a crank in them and he hooked them up to his electric shop motor, well the 4 bolt blocks caps cracked at 11,000 rpm and the other at 10,500. he brought the 2 bolt all the way up to 15,000! i wondered why the engines even made it past 8,000 rpm! he said dont think i can get a engine to run at 10,000 rpm! he said he could do that because its a empty block with no pistons, or anything in it, and no combustion going on. i was amazed. i asked him what all he had in his trucks and what they were made of! he said too much stuff i cant afford lol

 

Interesting, but we'd need at least 3 of each for it to have scientific validity.
However, most enthusiasts doing street strokers aren't going to fail either one, even with 6500 rpm and supercharging. With 400s, it's a different story. But consider that the only reason that the 4-bolt-main was invented was because of the DZ302, which in '67 was 2-bolt-main, and by '69 was 4-bolt-main. That's a large part of why everyone thinks 4-bolt-mains must be better.

 

I have spun 2 bolts all day to 650 with no issues. But they were street engines that dont see a constant 6500, just blip to it when i wanna play.

 

he told me he wasnt about to sit there and try to break his 2 bolt blocks so he just got it high enough to prove his point, he does us 4 bolts in his trucks but non of them have stock blocks or caps

 

Well, all mine now have 6 bolt main anyways

 

dam spit my Pepsi on my monitor reading this

 

what bs?

 

Dunno...

 

I think the real issue is, what will the engines be used for? I do not believe that a 2-bolt block, while strong in and of themselves, will stand sustained 6500 rpm for too long before either a bearing spins or worse. Remember the splayed main caps that Chevrolet was putting in their early performance engines? All the Hi-Po Chevy engines were 4-bolt. The splayed mains increased strength more. This holds the main caps in more than one place. It prevents the crank from exhibiting sideways force(walk) on the mains. 2-bolt main blocks lack this. While the crank can not pound up and down in the saddles(unless the bearings are shot), it can however start to deflect sideways and crack the main caps. I believe this is more of a personal preference than anything. If you want a strong block, use a 4-bolt main one. Want it even tougher? Get splayed main caps. No disrespect to your grandpa, but i think its just preference as far as blocks go. Any high performance engine built by any manufacturer throughout history has had 4-bolt mains. There is a reason for this.

 

after reading what atilla has said in previous threads i feel MUCH more comfortable with my 2 bolt ...and it may wind up being stroked next time around

 

I had 2 383s that were 2 bolts, no problems.

 

i dont think my grandpa was sayin 2 bolt is better, i think the point was with the factory material it makes no difference and is stronger in most cases but he does use 4 bolts on his race trucks, however they not made from the stock material

 

ive seen a crank come out of a 2bolt main but it was stock...
now ive seen people run arp bolts and stuff with the 2bolt and good horse power with no problems. but if its something i plan to beat on and throw a lot of power into i would like to have that extra insurance.

 

To me it's sorta like arguing over what alloy of steel I-beam to use to hold up a mailbox.

 

have him hook up a 2 bolt main with splayed caps. from what i've been reading, the 4 bolt mains from factory are weak because the bolts are straight up, splayed are at an angle and offer more strength. just curious

 

You can put splayed caps on, but it's still a waste of money on a street car. You're strengthening an area that's already strong enough.

 

Okay, but who said I wanted a street motor?

 

With regards to how many bolts are holding the mains on until you start making more than 450-500 hp all you need is something to keep the crank from falling out and hitting the ground. The caps in Chevrolet blocks are nodular iron which is pretty strong and ARP has any question of stregth covered. Most small boat (lake boat) inboard marine motors are 2 bolt blocks all that bouncing up and down in the water, and sudden load from freewheelin no problems. The idea here is to keep dirt off the crank and rods thats the real goal. The caps are what trully harness all that hp but the stregth is in the union. World Products blocks even come with the same GM style nodular iron caps. Steel caps are much stronger but they are for absolute abuse like dirt racing, nitrous blowers that kind of stuff. Thats so that the crank breaks before you split the block in two.

~Couch

 

If you're not, then why even think about using a factory block to begin with?

 

People use stock blocks at the strip all the time.

I said I was curious how it would hold up compared to the other two types of blocks. Why do these kind of threads always have to turn into some kind of debate? It makes wanting to post here difficult.

 

The point is, that for anything you could want to do in a stock block, the 2-bolt/4-bolt is going to make no distinction. When you're at the point where you need more strength, you're at the point where you're better off seriously considering an aftermarket block.

In regards to the original experiment, I wouldn't call spinning an unbalanced crankshaft alone in a block a worthwhile test.

 

That's fine, I am just curious what the result would be as I said.

 

If the caps were of similar material and similar construction, I'd expect them to crack at about the same point.

 

considering a splayed cap is not the same as a two or normal four bolt cap, i'd bet it wouldn't.

also i see no mention of the crank being balanced or unbalanced, so who's to say? again, i don't see why there is a debate about an experiment some kid and his grandfather did in his shop.

 

There really isn't one. If you want to get right down to the meat of the discussion here it's as I said before. There's no real tangable difference between having 2 bolts, or 4 bolts or 12 bolts holding your main caps in. The webbing usually goes long before the cap as the caps are nodular iron, and the block is cast iron. Not to mention if you get one particullar year, batch, casting number, and compare it to any other the weak spots are all in different places. Splayed caps are great in blocks with good webbing but there are certain blocks you can't use splayed caps in because it compromises strength. You arren't comparing constants here every different block will break in different places. Flathead fords have some pretty long strokes and spin pretty fast too, but they only have 3 main caps and you guessed it 2 bolts each. The number of bolts wont cause any more spun bearings, or broke cranks than any other. Its the block you are trying to save by adding bolts. If you tie the cap to the block with just two bolts, and build a blown injected nitro fuel car with it the webbing in the block will shatter due to the stress being in such a localized area. With two more bolts it spreads the load over a much larger area, but what we're talking about here is TONS of hp, and loads of stress/hammering. The caps are the same material and take load in the same area so they will fail under simalar stresses, but the block webbing is whats at stake. A cap under engine running loads gets stress on 45 degree planes in relation to the bolts. It's not 12 and 6 oclock it's 7:30, and 4:30. The piston comes down the hole straight which is 45 degrees to the main bolts so therefore the load is in the bottom corners of the main caps funny how thats where the heads of the bolts are also huh? Ballance has a lot to do with broken parts.

Ahem*
A crankshaft with nothing on it is way way way out of ballance. It's possible that the two bolt block in the experiment actually had weaker caps allowing flex while the 4 bolt caps couldn't give any. When you ballance a motor you have to way the assembly, and make up bob weights to hang on the throw's based on the weight of the assy. pistons, rods, rings, pins, pin clips, the theoretical oil weight that will be on the piston, and pin, bearings, big end, and small end of the rod then you gotta double the rods big end weight and add the value of everything else put that much weight in the bob weight and hang it on each rod journal. Spin it up to speed to see what needs to be corrected, and where. I have spun a naked V8 crankshaft with nothing on it on the ballancer before just wasn't thinking it was early in the morning, and I had just finished a 4 cyl. crank (those need no bob weights they ballance themselves) anyway its not pretty quite the wakeup call when a 632 BB crank jumps off the machine and into your lap if you know what i mean luckily I had the sence to turn the machine off while the crank was in the air. All v8 cranks are ballanced on a 90 degree plane that means in 1 180 degree arc they are very light, and in the other 180 degree arc they are very heavy. If this experiment was actually done it was done first of all without oil pressure which created a lot of heat in a small amount of space that would not normally be there, and seccond was done with crankshafts that weren't just out of ballance but about 5600 grams (roughly 10 pounds) out of ballance as the general bob weight of a small block chevy weighs at least 1400 grams if it's a light assy. I'd say that could really have something to do with it. In my opinion you're lucky your not wearing that crankshaft. Here's another experiment take a 10 pound weight weld a 2 foot long chain to it hang on to the chain with both hands and spin in a circle in your yard as fast as you can and see if that weight has any influence over your motion, then think you weigh 3 times what that crank does, and your not 10 pounds out of ballance spinning 10,000 rpms. Now do you see why ballance is so important?

~Couch

 

Well the materials in stock and aftermarket caps are most likely different, but aside from that they'd fail pretty similarly.

A crankshaft, on its own, with no reciprocating assembly or bobweights, is inherently unbalanced. Ask your machinist to show you one on his balancer sometime, there are massive forces throwing the thing around at even 100 RPM, let alone 10,000 RPM. It's so far from the conditions that occur inside an assembled engine that it's meaningless.

 

You pretty much just repeated what I said. You are absolutely correct, and I am a machinist. No I won't show you a naked v8 crank on my ballancer been der dun dat

~Couch

 

See, you're reading too far into things. No where did he give details on if they were balanced or not. For all you know, they put the stock internals back into these blocks that came out of them and balanced them.

 

He said they only used the crankshaft. As NAASBC355 agrees, a crankshaft on it's own can not be balanced. And by this we don't mean the process of being balanced, we mean the state of being balanced.

An imbalance of a few grams can produce a noticeable vibration. The counterweights on a 90 degree SBC crankshaft are out of balance by much more than a few grams. Centripetal force due to the imbalance also increases with the square of the rotational speed. At 10,000 RPM, a crankshaft alone, with no rods and pistons, and no bobweights to replace the mass of the rods and pistons as is done during balancing, is so far out of balance that I doubt you'd even be able to keep an engine on a stand if you were to do this test.

A crankshaft alone would be so far out of balance that I doubt that this experiment was even actually done.

 

Thats exactly what I was going to say next I really am supprised that the motor didn't end up on top of someone if this test was actually performed. I don't know how to break it down simple something like 20-30% of the total weight of a crankshaft exists to counter ballance the weight of the pistons, rings, rods, bearings, wrist pins, rod bolts, rod nuts, theoretical oil weight, so when they arren't there the crankshaft is naturally out of ballance to centerline in a 180 degree circle of up to 30%. To put it barney style if you took 20-30% of your body weight put it in one hand and tried to stand up straight you couldn't do it for long, put something the same weight in your other hand and now you can because you are ballanced. Now imagine you spin in a circle as the weights in your hands are thrown outwards you can stay pretty much in one spot. If you only had the weight in one hand you would woble all over the place. Thats the point here this test proved nothing except the complete lack of understanding of how a motor functions by what i will assume someone that doesn't exist, and by something that would phisically be near impossible to do. A naked crank at 10,000 rpms spinning in a naked block sitting on the ground wouldn't stay on the ground it would literally be hopping off the ground when the counter weights swung into the up possition. I just can't see unless you bolted it into the bed of a truck so the springs could dampen the vibration how it would be possible to even hang onto the motor that was driving the crankshaft. Spintrons spin cams to 10,000 rpms and at that speed things like the weight of a valve lock suddenly matter. The recipricating mass of a rocker arm can make the difference between holding a valve open at that speed so like 40-50 grams at a radius of an inch can hold a valve wide open with a 300 lb. spring what do you think rotating 10 pounds of iron at a radius of 3 inches would do at that speed. That would be a very very effective jack hammer. I mean you could knock the brick wall of a house down with that. When I ballance cranks I try to get it within 2 grams, thats the entire rotating assembly is rotating with an out of ballance in any radius of up to 2 grams. It's not uncommon to hang a crank in the ballancer with bob weights on it that is 150 grams out of ballance...thats WITH the bob weights on it. We spin the ballancer up to a couple hundered rpms with just 150 grams out of ballance, and you really have to watch out the ballancer gets all upset. 10,000 rpms 10 pounds 5600 grams plus.... I don't even want to be in the same neiborhood as that thing. I have had to catch cranks that come off the ballancer I don't even like thinking about the carnage that would actually occur if such an event took place.

Putting ballance aside this still leaves the question of how a set of bearings survived even a seccond at 10,000 rpms without oil pressure. Which is part two to uncrediting this "test"/waste of time. Oil doesn't just get lightly squirted on a crankshaft it gets suspended by it. It's hydrolics. Oil doesn't provide lubrication between the bearings and the crank it gives the crank something to float on like a boat. Bearings only purpose are for initial start up, and controlling the oil flow. The crank when in opperation theoretically should never come in contact with any form of metal at all there should be a bed of oil in all directions suspending the crank. So in our test here they would basically have ground their way through the cap with heat and friction that would not normally be there.

If you don't want to read this entire post basically I'm calling and delete thread

One last thing If you don't believe a 4 bolt main motor can get passed 8000 rpms then just click the link in my sig


~Couch

 

well okay then. i must have overlooked that.