The calculator you used for our discussion counted the stroke twice, one down and one up. Each stroke is a discreet event as the piston stops between them. While the piston obviously must travel both directions it should be factored over a single event. I knew what you did earlier, but I just didn't want to get into it. You also used a stroke of 3.5 when the stroke of a standard 350 is 3.48, but you pointed that out earlier.

Do you determine parts selection from piston speed? I have never met anybody in my extensive performance career that did. Nor have I seen a catalog or talked to a manufactuer that verbalized it as a criteria. Common sense prevails there. Certainly 6000 rpm in a 350 isn't out of the realm for durability with a cast piston, hell LS1, LS2, LS7's are upwards of that now with longer strokes from the factory.

Ok, I'm really done with this thread now, I promise.

 

Well, Engine Anilizer Pro, Lockeeds Pro Stock program, and several on line calculators will tell ya the same thing as far as piston speed.
If you have come up with a new formula,you might want to share it and show us the error of our ways.


You saying they are ALL wrong,don't think so!!!!


No I use piston speed for other things and it comes into play with making HP. I'm with Bret,blowers are for people who cant build HP. As I DO NOT use anything but FORGED pistons it is NOT a concern. The hyper-u-crap-tic are junk and I won't build another engine with them.

I just started my extensive engine building career about 40 years ago so I am probably still a rookie.
Use your common sence then and build with the hyper-u-crap-tic,I don't care.Make um live too.
As far as LS1's go they are back to the dealer quite often with piston problems.

 

I don't know about other brands of hypereutectic pistons, but Keith Blacks work great. I've run the same set since 1998 and my car has seen a lot of street miles and runs 11.30's at 120MPH in a 3,400 lb. street car. I routinely shift at 7,000 to 7,200 and have gone as high as 7,500 RPM. When I freshened up the motor last year the pistons looked brand new. A friend ran KB's in his 468 with a 250 shot in a '68 Camaro. Car ran 11.60's on the motor and 10.30's on the bottle. He had more than 100 passes on the motor without any problems. Until a friend convinced him to run a 400 shot.

It's a given that forged are stronger than HE pistons. However, I doubt this piston failed simply because it was hypereutectic.

 

Actually, that's exactly why it failed.

Look, there's nothing wrong with Hypereutectic pistons, but you have to understand that there are ways that different materials behave based on their composition.



Let me give you an analogy...

You have a brick and a 2x4.

In both cases, you can put each of them on the ground and drive a fully loaded dump truck up on top of them.

Now take a ball peen hammer and give each one a light to medium tap. The brick is a metaphor for the hyper and the 2x4 for the forged.

See what I'm saying...?

 

Mean (average) piston speed is calculated form this formula: PS = stroke (inches) x rpm /6 and has the units of ft/min

To derive it: in one crank revolution the piston travels the length of the stroke twice, as you said. With a 3.48 stroke, that's (3.48 x 2) or 6.96 inches or (6.96/12) or .58 ft. If it does this 7000 times/minute (rpm), it travels (.58 ft x 7000 rev/min) or 4060 ft/min.

In the formula the "6" comes from multiplying the stroke by 2 and dividing by 12 to convert inches to feet. If you used a 3.50 stroke it would be 4083.3 ft/min.

How about choosing the strength of parts based upon the loads they get applied to them in service? The largest loads on a piston and rod are inertia or acceleration loads especially at TDC where the piston is trying to come out of the top of the block and the rod/pin forces are all applied to the bottom of the pin bore effectively putting the piston in tension with it own mass causing the forces.

At 7000 with a 3.48 stroke and 6.00 rod, that's about 3120 gs. and of course 4060 ft/min PS. A 4.00 stroke would give 3710 gs and 4667 ft/min. More piston speed = more gs = more forces all at the same rpm.

From Newton: F=Ma. My conclusion is that PS along with piston mass (weight) might be a very good criteria for determining parts selection. Piston gs would be better, but the average piston catalog and tech rep are NOT talking to the guy who calculates piston gs during his engine design. The average Swinging Richard is a buyer, not a designer nor an engineer. More's the pity.

When it comes to very high rpm engines, like 19000 F1's, piston g's exceed 10,000. Yes the PS are still reasonable (around 5000 ft/min) but with everyone hovering around the same max bore (98mm),and attendent stroke (39.7mm), increasing rpm to get more power means more PS and more gs. What it really means is trying to shave a few grams of mass out of the F1 piston without weakening it to help minimize the amount of load increase. You can read the same thing for 9700 Cup engines and 10K ProStock engines.

My $.02

 

It's not because they are hypers.... it's because something wasn't working right. I like the idea that a lock slipped out and caused the pin to come out, that makes the most sense to me. It sure as **** isin't the material. The LS1 can make 500rwhp on a hyper piston (stock bottom end)

Dude, I love ya but hyper pistons and PM rods aren't bad because they are younger than you!

Bret

 

The one i'd heard to use in place of just mean piston speed is piston acceleration. Which takes into account connecting rod length as well as stroke to give you the maximum acceleration the piston sees. It's something like RPM^2*Stroke*(1+(1/(2*(RodLength/Stroke))/2180)) and it gives you the result in feet per second squared

 

Using 1racerdude's logic. The block cyclinder wall failed because it is crappy cast iron and not forged.

 

LOL, and double humps are the best head back then and now.

 

One thing the dude has is experience. That's the good part of age!

IMHO if i'm putting a aftermarket hyper piston in a motor it's going to be a KB.

Bret

 

Yep, that's the piston gs I was talking about. One g = ~32.2 ft/sec^2 so multiply the gs I mentioned by 32.2 to get actual piston acceleraton. (3120 x 32.2 =100,464 ft/sec^2). My rounding 1g to 32.2 gives about 0.43% error. Sorry I wasn't more clear.

 

Every body in the world can use them,but I won't put them in my lawn mower. They are junk for a preformance build IMO.
I won't change my mine either.


LOL, and double humps are the best head back then and now

IHI,
I can STILL make 600FWHP with a set of angled plug 302 heads and they are cast iron.So don't be knocking something ya don't know about.


Using 1racerdude's logic. The block cyclinder wall failed because it is crappy cast iron and not forged.

Z28sorr
Never said the block failed don't believe it was the cause.

The STRONG blocks these days are CG=compacted graphite so keep up on things.

One thing the dude has is experience. That's the good part of age

Bret,
Bitten once, lack of knowledge,bitten twice my stupidity. Just doesn't happen twice.
Have seen more than one set of LS1 PM rods hung out the side of the block.

 

Before this gets too far out of hand...

First, based on the pics and limited info that was provided in the initial post, at this point any attempts at explaining what actually happened to this engine is purely speculation. Let's keep that in mind before we begin tearing eachother's heads off.

Second, some valid points have been made on both sides of the "hyper vs. forged" argument. Even still, having a vast working knowledge of metallurgy, it's effects on the mechanical properties of each metal, the effect of piston speed, etc., doesn't begin to explain the human element involved here. This engine was merely idling when the failure occured: because of this, we can safely assume that whether a forged or hyper piston had been used, neither one would have been remotely close to it's mechanical limits.

Achem's Razor: "The simplest answer tends to be the correct one."

Since the piston was perfectly within the boundaries of it's mechanical operating limits when the failure happened, what do we have left to blame?

Human error maybe? (Ducks for cover.)

 

Experience without understanding is useless.

Nice side step. You aren't telling us that you have never rebuilt an engine using stock Chevy replacement pistons.

 

IMO it was hurt before it came apart. It just decided to come apart ideling.