[PontiacJim1959]

Originally Posted by JLMounce

What happens to a factory rod that is over rpm'd? does it break at the cap, snap/bend down the center or does it break at the pin?

Answering that, might help answer the question based on the parts that are in the engine.

In many cases, the g-forces pull hard enough on the rod bolts that it causes the main cap to pull in/collapse at the parting line enough that the edge of the cap acts as a scraper and scrapes the oil off the journal and you are now left with a rod bearing having no oil and the rest is history. So it is not generally a fail of the rod itself, but the effects of rod bolt stretch.

Some will counter this problem by inserting thin shims between the cap/main rod section, and then resize the rod so when the rod bolts do stretch, there is a little cushion built in when the cap sides pull in at the parting line, they don't wipe the journal of its oil.

[Stan Weiss]

Originally Posted by steve25

Seeing as I don’t know the strength difference , nor the weight difference between stock 455 components and yours which can make a big difference in loading with a small change in weight, here’s how things look with stock factory weight Rods, pistons and wrist pins when comparing a 400 to a 455, so all I can do is look at the difference that stroke makes.

At 1000 rpm a 400/ 3.750” stroke motor has a maximum ft per min piston speed of 1020 and at 6000 rpm this goes up to 6120 ft per min.

Yup, at 6000 rpm the piston in a 400 has traveled over 1.5 miles in 1 minute!

A 455 @ 1000 rpm with its 4.210” stroke has a speed of 1156 ft per min, or 13.3% greater then a 3.750” stroke.

Now here’s the Rod busting numbers in terms of the G force loads at the moment when the crank yanks the piston from TDC.

The 400 has a load of 68.34 G at 1000 rpm.

The 455 at 1000 rpm is loading the Rod with 78.8 Gs , or 14 percent more!

At 6000 rpm these G force numbers are a full 36 times higher!!!

If you want to look at this as pounds of force trying to snap the Rod in two, then at 6000 rpm the Rod in a 455 is experiencing 7818 lbs of force trying to take it apart!!

I tend to picture two 3900 lb cars hanging off the small end of a cast iron factory rod in terms of that number.

Even at 5500 rpm the Rod in a 455 is experiencing a G force load of 2383.

The pounds of force at TDC at 5500 rpm is still a amazing 6569!

For you 400 fans, at 6000 rpm the pounds of force are only 211 more then a 455 at 5500 rpm,

A motor geared stiffer to make better usage of how it’s built to go drag racing , and as such rev’s faster produces near the same increase in loads as would stroking it.

This is another overlooked consideration that people over look when they ventilate a bock!

Steve,
What piston and rod weights or you using in your G's calculations?

While your max piston speed numbers are correct I think most here were talking mean (average) piston speed fpm.

Stan

[mgarblik]

The Boss Bird nitro engine had a bob weight of 2419 grams.
Highest piston speed we ever ran was 8288 Mean piston speed and 13,018 max piston speed. All the internal parts stayed attached, aluminum BME rods. This was on a runaway engine with the loss of high gear.

Typical piston speed was 5950 mean piston speed and 9346 maximum piston speed. Never had a piston speed or rod related failure in 10 years of running this combination. You do have to run good parts, that's a given.

[steve25]

Stan I am not home till tomorrow to check my numbers for sure for you but I recall a stock reciprocating weight of 1255 .

The mean piston speed of a 400 @ 1000 rpm of 620,and of a 455@ 1000 rpm of 700.

[Vengeance Race Engines]

Originally Posted by PunchT37

What would one consider a safe max piston speed for a 4.21 stroke 455 engine with 4340 rods and a ross full float piston?


How much would be a safe continuous speed?


Let`s say one has the cam and heads to get there.

Parts are not rated for specific piston speeds. Too many variables. Once you know stroke and the rpm it will be run at for max power, you choose parts that are capable of handling it, and design the parameters to help them live. Parts can handle more than you think. Manufacturers rate their parts on a very conservative scale.

I will add that from what I have seen, there is a correlation to piston speed in regards to max power, and where these engines like to operate for max power. Anything more, it often just becomes an unreliable grenade/ or simply starts to lose it's ability to make power per cubic inch at higher piston speeds. It's just not something i let de-ter me from building milder combinations with a lot of stroke.

Regardless of piston speed, if a part wants to break, it will, and won't care how much you spent on it.

[PunchT37]

Originally Posted by Vengeance Race Engines

Parts are not rated for specific piston speeds. Too many variables. Once you know stroke and the rpm it will be run at for max power, you choose parts that are capable of handling it, and design the parameters to help them live. Parts can handle more than you think. Manufacturers rate their parts on a very conservative scale.

I will add that from what I have seen, there is a correlation to piston speed in regards to max power, and where these engines like to operate for max power. Anything more, it often just becomes an unreliable grenade/ or simply starts to lose it's ability to make power per cubic inch at higher piston speeds. It's just not something i let de-ter me from building milder combinations with a lot of stroke.

Regardless of piston speed, if a part wants to break, it will, and won't care how much you spent on it.

That`s why I started this thread. I saw a vid that pretty much stated that 4000 fps piston speed was used across the board to determine the redline of an engine. He gave out a formula to get piston speed and that was that.


I knew that, at least, parts selection would punch a hole in that statement.

[Vengeance Race Engines]

Originally Posted by PunchT37

That`s why I started this thread. I saw a vid that pretty much stated that 4000 fps piston speed was used across the board to determine the redline of an engine. He gave out a formula to get piston speed and that was that.


I knew that, at least, parts selection would punch a hole in that statement.

A big hole... and i was actually referring to fpm.

[PunchT37]

Originally Posted by Vengeance Race Engines

A big hole... and i was actually referring to fpm.

FPS? my bad.

[4zpeed]

Originally Posted by Vengeance Race Engines

Parts are not rated for specific piston speeds. Too many variables. Once you know stroke and the rpm it will be run at for max power, you choose parts that are capable of handling it, and design the parameters to help them live. Parts can handle more than you think. Manufacturers rate their parts on a very conservative scale.

I will add that from what I have seen, there is a correlation to piston speed in regards to max power, and where these engines like to operate for max power. Anything more, it often just becomes an unreliable grenade/ or simply starts to lose it's ability to make power per cubic inch at higher piston speeds. It's just not something i let de-ter me from building milder combinations with a lot of stroke.

Regardless of piston speed, if a part wants to break, it will, and won't care how much you spent on it.

Agreed, although most I observe building these strokers are not building them with the mentality of a mild combination in mind, hence the stroke in the first place.

Not trying to criticize but trying to run things on the ragged edge and building a reliable street engine doesn't mesh well, therefore at the root of the problem.



Frank

[steve25]

Also whole lot of Crankshaft failures can be traced not to the actual maximum load in kilonewtons that they are dealing with, but from the flexing induced from the condition of the massive loading of full throttle and high rpm and all of that cylinder pressure produced, and then the unloading when getting off the throttle at high rpm and now that amount of crank flexing is not there.

[Steve C.]

"... I observe building these strokers are not building them with the mentality of a mild combination in mind, hence the stroke in the first place."

Presuming the 4.250" stroke I might suggest the availability, thus the popularity, for it's use in a upgrade or replacement in many builds. High performance or not. The 6.8 rod length it was designed for in it's initial development many yeas ago is a plus.

Edit: My comment is regarding the increase over a 4.210" stroke.

.

[Vengeance Race Engines]

Originally Posted by 4zpeed

Agreed, although most I observe building these strokers are not building them with the mentality of a mild combination in mind, hence the stroke in the first place.u

Not trying to criticize but trying to run things on the ragged edge and building a reliable street engine doesn't mesh well, therefore at the root of the problem.



Frank

Didn't say anything about running mild engines on the ragged edge. My point was to show that like anything, the more power you make, the less reliable it becomes, however there is a fine line in the middle where both can be had, to an extent. But to say even mild engines CAN'T run at higher piston speeds without breaking is false. I am talking piston speed in general. NOT just from big stroke applications. How it is achieved matters where reliability is concerned. If the engine is designed correctly, and the right parts are chosen, it will be more reliable than you think.

Originally Posted by steve25

Also whole lot of Crankshaft failures can be traced not to the actual maximum load in kilonewtons that they are dealing with, but from the flexing induced from the condition of the massive loading of full throttle and high rpm and all of that cylinder pressure produced, and then the unloading when getting off the throttle at high rpm and now that amount of crank flexing is not there.

That's a lot of fancy words to describe why a part would fail, however parts break for many reasons beyond our control. Mostly due to not running the right parts for the application from the start, and using bare minimum stuff with hopes of getting away with it. It's usually not IF, but WHEN it fails.

[Vengeance Race Engines]

Originally Posted by Steve C.

"... I observe building these strokers are not building them with the mentality of a mild combination in mind, hence the stroke in the first place."

Presuming the 4.250" stroke I might suggest the availability, thus the popularity, for it's use in a upgrade or replacement in many builds. High performance or not. The 6.8 rod length it was designed for in it's initial development many yeas ago is a plus.

Edit: My comment is regarding the increase over a 4.210" stroke.

.

I think if people step outside the box of the Pontiac world and venture into what other engines do all day long with no issue, regarding myths and limitations they put on themselves due to said myths, they will realize the true potential a Pontiac, or any engine can achieve.

[4zpeed]

Originally Posted by Vengeance Race Engines

Didn't say anything about running mild engines on the ragged edge. My point was to show that like anything, the more power you make, the less reliable it becomes, however there is a fine line in the middle where both can be had, to an extent. But to say even mild engines CAN'T run at higher piston speeds without breaking is false. I am talking piston speed in general. NOT just from big stroke applications. How it is achieved matters where reliability is concerned. If the engine is designed correctly, and the right parts are chosen, it will be more reliable than you think.

I think Steve C. made a very good point in that as far as availability, there just wasn't and still isn't allot out there for us Pontiac guys.

I didn't say you said people are running them on the edge, I said that, in terms of a street engine, not something meant for the track.

I'm sure a stroker can run at higher speeds, but at a greater cost, and for what, I believe in using the shortest rod you can, that's all.

I get up into the 6k's reliably, all day with factory rods and lighter pistons just cause I can, and it doesn't cost me an arm an a leg.

Edit - Not knocking the strokers, just saying, with the forces created, it takes money, a quality build and knowing the intended use.



Frank

[Steve C.]

I'm going with the longer rod

https://www.enginebuildermag.com/201...ng-rod-ratios/

Related to piston side loading....

Taken in part from Jim Butler comments, Q&A section, PE magazine March/April 1997:

They built two engines for Rodney's '82 T/A street car. Both engines had 455 blocks. One was filled and the other wasn't. The filled block ran 10 to 15 degrees cooler than the unfilled block. It was reported upon tear-down and inspection, the cylinder walls on the unfilled block were seen to be scratched and scored from excess friction. When measured with a dial bore guage, it was found to be out of round. The filled block was smooth and bore round. He confirmed you do not lose significant coolant capacity by filling the block. However, the difference in the amount of friction is much improved.


.

[mgarblik]

Originally Posted by Vengeance Race Engines

I think if people step outside the box of the Pontiac world and venture into what other engines do all day long with no issue, regarding myths and limitations they put on themselves due to said myths, they will realize the true potential a Pontiac, or any engine can achieve.

That was the main reason I posted the Boss Bird piston speeds in the street section. If you believe all the urban legends and ALL the things a Pontiac CAN'T do, your Pontiac engine will perform accordingly.

[4zpeed]

Originally Posted by Steve C.

I'm going with the longer rod
https://www.enginebuildermag.com/201...ng-rod-ratios/

Oh shut up Steve...



Frank

PS. I'm gonna go read this an I'll be right back.



Edit - 1st of all thanks for that link, I always enjoy learning and trying to figure out the method behind the madness, I do have a better perspective on rod length.

OK, so what really surprised me was the side loading, I would have thought that a longer rod would have more just from the way it enters and exits the cylinder.

If you look at the you tube video from the earlier link posted, it sure seems to me like the angle would create more force with a longer rod, am I missing summin?

All other things seam to make sense, and I liked the information, but with all the torque our Poncho's make naturally, I think I'll stay where I am with my thoughts.

https://blog.k1technologies.com/stok...ngle-explained

[Vengeance Race Engines]

Originally Posted by mgarblik

That was the main reason I posted the Boss Bird piston speeds in the street section. If you believe all the urban legends and ALL the things a Pontiac CAN'T do, your Pontiac engine will perform accordingly.

Exactly. The world is a lot bigger when you view it from outside the box. Pontiac is just a brand name, nothing more, nothing less. The math doesn't change because of it.

[4zpeed]

Seems some are quick to assume they have a unique view with a magic answer, while offering nothing but what's known or been mentioned previously.

I don't see any Pontiac myths about limitations, I see calculations and facts, physics and the build itself will determine the performance and reliability.

The knowledge of someones piston speed from a race car is valuable information and appreciated, but may not appropriately correlate to the OP street car.

There are builders that will let someone spend $$$$$ when it's not needed, not to mention possibly having to resize "new" rods or turn a "new" crank.

Appears the consensus is it depends on the quality of the build, parts used and intended usage, which is no more or no less, what is initially suggested,

in addition to calculations posted by Steve showing forces multiplying as the weight increases, with an addition of performance and also additional stroke.

My takeaway from the last link FWIW...
"As a general rule, large bore, short stroke engines are high revving, high power engines good for road racing and circle track applications. Pro Stock racers also like this combination for drag racing as do NASCAR engine builders. Small bore, large stroke engines, on the other hand, are better for low RPM torque, street performance, towing and pulling, but have limited RPM potential".



Frank