What kills a stock rod

For instance if you have a 900gram piston on the end of a stock rod that has had the stress riser taken off with good bolts what would a safe bet to say cylinder pressure or rpm?

RPM and heavy Pistons. It's simple math.

proprer machine work can midi gate it to a point, but the simple math is going to slap you in the face sooner or later.

dfree383 wrote:RPM and heavy Pistons. It's simple math.

proprer machine work can midi gate it to a point, but the simple math is going to slap you in the face sooner or later.

I know Im riding a fine line but Im going to put a plate on my car with a small 100 or so. I have ran this engine for 5 years and it goes to 7k every pass. Im hoping to pick up some et and lower the rpm if that makes sense.

A production big block Ford rod, reciprocating at that average of 75 feet per second, won't last long with a 900 gram piston and pin before it breaks in the beam.
The rod will probably get a slight bend just under the pin end first.

^^^^^^^Please give link or explain the math associated with this. I would like to see where my combos are at. What is the high number vs RPM to avoid? etc......

Thanks in advance

rmcomprandy wrote:A production big block Ford rod, reciprocating at that average of 75 feet per second, won't last long with a 900 gram piston and pin before it breaks in the beam.
The rod will probably get a slight bend just under the pin end first.

The rpm is more of a key player in one letting go then cylinder pressure?

85bigblockfox wrote:

rmcomprandy wrote:A production big block Ford rod, reciprocating at that average of 75 feet per second, won't last long with a 900 gram piston and pin before it breaks in the beam.
The rod will probably get a slight bend just under the pin end first.

The rpm is more of a key player in one letting go then cylinder pressure?

YES ... The compressive strength is much higher than the tensile strength.

away wrote:^^^^^^^Please give link or explain the math associated with this.  I would like to see where my combos are at.  What is the high number vs RPM to avoid?  etc......

Thanks in advance

When Ford Racing originally released their 514 crate engine, it had NEW production marine rods with a bushed pin end. The red-line was 6,200 RPM, (just under 75 feet per second with that 4.300" stroke).

After almost  a 100 warranty claims from broken rods, (all broken in the beam), they went to using an Eagle H-beam rod and the problems almost totally disappeared.

rmcomprandy wrote:

85bigblockfox wrote:

rmcomprandy wrote:A production big block Ford rod, reciprocating at that average of 75 feet per second, won't last long with a 900 gram piston and pin before it breaks in the beam.
The rod will probably get a slight bend just under the pin end first.

The rpm is more of a key player in one letting go then cylinder pressure?

YES ... The compressive strength is much higher than the tensile strength.

Thanks for the advice. My pistons are 2443 trw with dove heads. I know the compression is on the high side but if I lower the rpm, you think the rods will stay happy with added pressure of nitrous? Only spraying a 100.

rmcomprandy wrote:

away wrote:^^^^^^^Please give link or explain the math associated with this.  I would like to see where my combos are at.  What is the high number vs RPM to avoid?  etc......

Thanks in advance

When Ford Racing originally released their 514 crate engine, it had NEW production marine rods with a bushed pin end. The red-line was 6,200 RPM, (just under 75 feet per second with that 4.300" stroke).

After almost  a 100 warranty claims from broken rods, (all broken in the beam), they went to using an Eagle H-beam rod and the problems almost totally disappeared.

Would you happen to have the formula for figuring rod speed?

Piston Speed

Cm = .166 x L x N
Cm is mean piston speed, in feet per minute
L is stroke, in inches
N is crankshaft speed, in RPM

That get you FPM / by 60 for FPS

dfree383 wrote:Piston Speed

Cm = .166 x L x N
Cm is mean piston speed, in feet per minute
L is stroke, in inches
N is crankshaft speed, in RPM

That get you FPM / by 60 for FPS

Thanks. So anything under 75 fps is a safe area?

85Bigblockfox, if it were me I would take it apart and change the rods, It sounds like you have a good combo and it runs well, so why take a chance on breaking a rod and destroying your engine when you can put a set of rods in it for a little money and your time, and you could do a freshen up on it while you are in there, JM2C!!!!!!

rmcomprandy wrote:

away wrote:^^^^^^^Please give link or explain the math associated with this.  I would like to see where my combos are at.  What is the high number vs RPM to avoid?  etc......

Thanks in advance

When Ford Racing originally released their 514 crate engine, it had NEW production marine rods with a bushed pin end. The red-line was 6,200 RPM, (just under 75 feet per second with that 4.300" stroke).

After almost  a 100 warranty claims from broken rods, (all broken in the beam), they went to using an Eagle H-beam rod and the problems almost totally disappeared.

Randy,
Much of this was due to AER installing ARP wave lock rod bolts. These "move" material around the bolt hole in the rod and IF ( as was the case) the cap isn't chamferred enough to compensate , the cap will not seat properly ( as I think you already told me). My 521 has a set of those rods and my "rod guy" reworked them the way you told me to , and I am using them. I will NOT be running my 521 over 4,500 rpm in my race car hauler.

butterbean wrote:85Bigblockfox, if it were me I would take it apart and change the rods, It sounds like you have a good combo and it runs well, so why take a chance on breaking a rod and destroying your engine when you can put a set of rods in it for a little money and your time, and you could do a freshen up on it while you are in there, JM2C!!!!!!

I have a set of h beams on the shelf. Engine is going in a lighter car in the winter and only have 1 more race this year. Plan is to spray 100 to it max. Car is heavy at 3400lbs been 10.91@123. Trying to get a 10.50 out of it before I swap cars.

Here is the rod killer equation. Piston weight squares for every 1,000 rpm increase.

dfree383 wrote:Piston Speed

Cm = .166 x L x N
Cm is mean piston speed, in feet per minute
L is stroke, in inches
N is crankshaft speed, in RPM

That get you FPM / by 60 for FPS

Life expectancy of oliver rods, 620 gram pistons and 90fps?

gt350hr wrote:       Here is the rod killer equation. Piston weight squares for every 1,000 rpm increase.

NO, the loading goes up geometrically so that every time you double the rpm the loading goes up 4X.

DaveMcLain wrote:

gt350hr wrote:       Here is the rod killer equation. Piston weight squares for every 1,000 rpm increase.

NO, the loading goes up geometrically so that every time you double the rpm the loading goes up 4X.

guess I went to a different school.

CA..... ya know, where everyone should do whatever they feel. Engineer, plastic surgeon, movie star............. pay your fee get your B,

gt350hr wrote:

rmcomprandy wrote:

away wrote:^^^^^^^Please give link or explain the math associated with this.  I would like to see where my combos are at.  What is the high number vs RPM to avoid?  etc......

Thanks in advance

When Ford Racing originally released their 514 crate engine, it had NEW production marine rods with a bushed pin end. The red-line was 6,200 RPM, (just under 75 feet per second with that 4.300" stroke).

After almost  a 100 warranty claims from broken rods, (all broken in the beam), they went to using an Eagle H-beam rod and the problems almost totally disappeared.

        Randy,
            Much of this was due to AER installing ARP wave lock rod bolts. These "move" material around the bolt hole in the rod and IF ( as was the case) the cap isn't chamferred enough to compensate , the cap will not seat properly ( as I think you already told me). My 521 has a set of those rods and my "rod guy" reworked them the way you told me to , and I am using them. I will NOT be running my 521 over 4,500 rpm in my race car hauler.

That was a problem in the beginning and had a lot to do with spun bearings and subsequent heat causing the rod to break at the big end ... it had nothing to do with the strength of the production marine rod or why the change to the Eagle rods, happened.

By the way, it was only at the beginning of that crate motor offering and it was less than 100 rods which didn't get a champher under the ARP rod bolt head; NOT the cap.  No champher was on the cap faces either but, that was not the cause of any breakage problems.The mistakes were caught after those. That happening was for about 19 engines, (which got one or more of those rods), and they sold hundreds of those original crate motors afterward.

85bigblockfox wrote:

butterbean wrote:85Bigblockfox, if it were me I would take it apart and change the rods, It sounds like you have a good combo and it runs well, so why take a chance on breaking a rod and destroying your engine when you can put a set of rods in it for a little money and your time, and you could do a freshen up on it while you are in there, JM2C!!!!!!

I have a set of h beams on the shelf. Engine is going in a lighter car in the winter and only have 1 more race this year. Plan is to spray 100 to it max. Car is heavy at 3400lbs been 10.91@123. Trying to get a 10.50 out of it before I swap cars.

I'm running stock rods... My combo is stock crank, rods and KB piston cast. truck #3870 with driver spray 125hp best ET 10.71 @ 126mph 6800 rpms...

kim wrote:

dfree383 wrote:Piston Speed

Cm = .166 x L x N
Cm is mean piston speed, in feet per minute
L is stroke, in inches
N is crankshaft speed, in RPM

That get you FPM / by 60 for FPS

Life expectancy of oliver rods, 620 gram pistons and 90fps?

What stroke and rpm?

Another issue with the stock rods is the big ends deform and spin the bearings.

3.9 stroke 9600 rpm.

kim wrote:3.9 stroke 9600 rpm.

your looking at a weird application..... They will outlast your valve train.....