blowing up small blocks

[redflash]

I would like to approach a thought, that will probably cause bombs to go off, just my thoughts.
pred 212's and other small motors can be hot rodded. We remove governers, stock exhaust, and intake modifications. We add cams, compression, rods, and flywheels all in an effort to pump up hp.... And sometimes "kaboom" because we "cross the line". The solution seems to be to restrict the rpm......a little bit. and yet to extract as much spin as possible short of "Kaboom"..
I have always taken a conservative approach... as follows my 212 has custom exhaust.....free flow intake... medium cam...18 lb valve springs.
I have removed the governer...the low oil sensor...stock throttle linkage......AND NO billett ROD OR FLYWHEEL. I have though retained the stock Carb with larger jet.
Now what I believed I have accomplished is......18 lb valve springs can float, ( therefore no over rev), The restricted carb cannot deliver enough flow to again "over rev".
So no need for expensive billett rod or flywheel ...voila And I fear no "Kaboom"
Again, I'm not racing or competing, I just want the strongest "FUN" motor I can have at a reasonable cost. Comment ?

Da Flash

 

[7thofa2nd]

Well, you sound like me... your approach matches mine exactly.

 

[madprofessor]

I like your method of using valve float to prevent overrevving, both by only up-jetting the stock carb and by using somewhat conservative upgrade valve springs. It's just too close to the fatal line for my own risk-averse approach.
I had no fear or guilt sending off a 212 hemi (in a scratch-built minibike) that I hotrodded up to about 12 hp., with the stock rod and cast iron flywheel, and full governor delete. It was sold to a fellow in Ohio that bought it and paid for the shipping, and I haven't lost a single night's sleep over it. That's because I sent it to him with the stock 10.8# valve springs still in it.
The valves are absolutely sure to float before reaching 6K rpm with those stock springs, more likely before 5.5K rpm.. There's no concern that the cast iron flywheel will shatter at that kind of rpm and kill or maim someone. The 18# springs you put in would in my opinion allow the flywheel to spin up past the point of danger to humans and other animals.
I've got 22# springs in my current 212, with an ARC over-length rod, PVL flywheel, and Superman .265 cam. This setup was chosen by my performance guy up in N.C., and he said he expects 7.2K rpm from the engine with my stock carb. See where I get worried about the 18# springs?

 

[Functional Artist]

"There was no Earth shattering kaboom!" "What happened to my Earth shattering kaboom?"

JK
I like your thought-thru conservative approach

 

[Denny]

A conservative engine is always going to last longer than a radical one. Just look at GM, Chrysler and Ford in the 60s. They prove it out. The turd in the punchbowl nobody talks about is when you change the piston, rod and flywheel you should balance the rotating assembly. Harmonics and crank flex are two reasons I can think of doing it. But reliability would be the real reason for doing it.
Oil windage is the next big problem. Knife edging would help solve some of this along with some type of crank scraper. When we have to start dealing with full pressure oiling systems then this will be a real nightmare.
So in summary I think the crank flopping around like a wet noodle at 7k with all kinds of strange vibrations going on concerns me more.

 

[Denny]

Mad, I hope this does not make you want to tun to the nearest beach to drown your self to get away from the nightmares of an unbalanced engine. Instead try to wrap your head around it.

 

[madprofessor]

the crank flopping around like a wet noodle at 7k with all kinds of strange vibrations going on

Okay, now I'm really concerned, that's a scary way to describe things. I know my PVL flywheel comes balanced for 17K rpm, but I've only made an assumption about the ARC rod being well balanced, and no thought at all about an aftermarket cam's balance. Just how important is the absence of a V8's harmonic balancer or some such thing on these small displacement engines we talk about?

 

[panchothedog]

You ask for comments. It seems to be economics vs saftey. I think you're betting pretty hard that those valves WIII float. Two factors to consider,
" medium cam ". Cams have 3 important numbers. Lift, duration, and lobe separation . All 3 can affect max rpm, with duration probably being the most important. The second factor, and I will admit I have nothing to offer on this,
is at what rpm do the flywheel explode or the rod either break or siez? Also when these failures happen is it at a consistent rpm from engine to engine. I have seen some very poor examples of Chinese steel, honey combed and differences in coloration, like something was poured into the slurry mix to make it go farther. Personally I am much more afraid of the flywheel than the rod, but since everything I build I put my grandkids in its a no brainer for me. Saftey wins.

 

[Denny]

You don’t balance camshafts. Only high rpm assemblies. Which would be your crankshaft, but you need the rod and piston on it to do so. If the engine is externally balanced you need the flywheel also.

 

[Denny]

A harmonic (or frequency) balancer is needed to do just like it says. Remove the harmonic vibrations from the crankshaft. See these engines were never meant for high speed operation. They were made to spin at a max 4000 rpm for their whole lives. So we must live with the engines short comings. But balancing and knife edging a crank is something we can do something about. Which will prolong bearing and crankshaft life. I do believe harmonics do play a part in flywheel failures, crank and rod failures in addition to rpm.

 

[madprofessor]

I understand how windage can become a huge problem for splash lube systems, but to get that "splash" it seems a billy club would do more good than a knife. What exactly would you modify to "knife-edge a crankshaft", the rod's splash arm? With the ARC rods there's a "scoop" instead of just a stick at the end of the splash arm, with the drilled passage to force oil into the bearing. Would a knife-edge affect the performance of that?
Mental picture's fading, not getting enough imagination in there to feed it...............

 

[karl]

Comment ?

The title says blowing up small blocks, yet I see no pictures of destruction. What gives?

 

[panchothedog]

Blowing up small blocks is on a very small scale somewhat akin to using
nucular wepons. Something we all try very hard to avoid. If you do happen to grenade one or come across any good pictures of the aftermath please post them. It would work as good reinforcement for us all. It would probably also cause an uptick in ARC sales.

 

[Denny]

I understand how windage can become a huge problem for splash lube systems, but to get that "splash" it seems a billy club would do more good than a knife. What exactly would you modify to "knife-edge a crankshaft", the rod's splash arm? With the ARC rods there's a "scoop" instead of just a stick at the end of the splash arm, with the drilled passage to force oil into the bearing. Would a knife-edge affect the performance of that?
Mental picture's fading, not getting enough imagination in there to feed it...............

Knife edging a crank, basically you are cleaning up and recontouring the counterweights to cut through the oil cleanly. See as the counter weights hit the oil instead of a blunt power robbing end it is streamlined to slice through the oil. It has many benefits. Reducing windage in the crank case is one of them.

 

[madprofessor]

counterweights to cut through the oil cleanly

I need to see a something in real video or scale drawing to understand just how deep a crank's counterweights dip toward the oil surface, never really thought about a huge hunk of steel slapping at a lake of oil at 7.2K times per minute. They don't actually hit that normally, so is it only when the splashing or windage is raising the surface up to the counterweights that they become a problem?
How much contouring of a counterweight could be done without ruining even the OEM balance of the motor? Is it just a given that finer modding of a motor like that will automatically require a machine shop-level-grade rebalancing of the whole rotating assembly?
Please overlook the ignorance, I really want to learn these things, and maybe some others here want to know it too.

 

[Denny]

I don’t know of any videos off hand. In school I did see a movie (high speed camera) of a crankshaft spinning in oil. I was surprised to see how much a crank shaft flexes and how oil gets whipped around and airated. Knife edging cranks on race engines has been around since cars started racing. One other benefit is longer oil lubrication life. Oil becomes less slippery the longer it is used. One reason is because the molecules of the oil get sheared by the spinning crankshaft counter weights. There may be some video on YouTube or something of the flex in a fuel car crank. You would have to look it up.

 

[65ShelbyClone]

Comment ?

They aren't new ideas. They are also not reliable because valve springs and carburetion cannot prevent engine overspeed under all conditions.

Engine failure is a statistical probability that increases exponentially with power and RPM, but it's not something that can likely be quantified by the average person unless you want to buy hundreds of identical engines and run them to failure at various power levels under tightly controlled conditions. A sample size of one or even several does not prove that everyone will have the same results.

How much contouring of a counterweight could be done without ruining even the OEM balance of the motor?

They're not balanced from the factory and already tend to be too light. Taking material off the counterweights won't ruin anything the factory does; it just makes a bad balance worse. They have to be slugged with heavy metal to get it right. I think nearly all the cranks you're likely to find have crossdrilled rod journals in order to improve the balance without having to do that.

 

[madprofessor]

Curiosity has me by the short ones now, I'll have to hunt something up. Not really wondering about the flex of a crank, cracked sidecovers' bearing points tells me all about that. I'm going to hunt some crankshaft-knife-edging.