Quote:
Originally Posted by TransAm 474
Tom Molnar is a very sharp individual ... here is a lengthy read of the conversation we had when we were purshasing his rods for our 1800hp Procharger application ...
Tom Molnar ....
"Below is what I tell people when they ask about how much power a rod can take.
Regarding HP ratings, we are asked this question very often but there is no easy way to honestly answer it because NO ONE HAS EVER BROKEN A ROD (or a crank) from horsepower. While there are a lot of people who rate rods by power, these ratings are simply a fake number that they provide to sell their product. I have been designing rods for over 37 years and I can tell you that NO ONE can honestly tell you at a certain power level the rods will break. First off, the load on the connecting rod in an engine making 800 HP with a 3.250" stroke is completely different than the load on one making 800 HP in an engine with 4.000" stroke. In most cases the people who are giving out these numbers are reading from a script, giving you a quick answer so they can get your money and go on to the next caller. These horsepower “ratings” come from the misconception that power goes up from higher and higher cylinder pressure pushing on the piston which then pushes on the rods. The fact is, maximum cylinder pressure pushing on the piston takes place at peak torque then goes down as RPM continues upward past this point. The reason HP continues to go up past peak torque even though the push on the rod does not is due to more power pulses per minute. HP is a calculated number based on torque and RPM not due to force on the parts. Torque is work done, HP is work done over TIME so with more pulses per minute, the HP number goes up even though the push on the rods does not. Next, if you ever see a broken rod and look at it closely, you will see it is not crushed but actually pulled in two. This high tension pulling load takes place at top dead center of the exhaust stroke when the piston changes direction and is due to the weight of the piston trying to go through the cylinder head and the crank pulling it back down. You are not making any power on the exhaust stroke. The heavier the piston, the higher the RPM and the longer the stroke, the higher this pulling load will be. Also if you ever see a dyno sheet you will see the power peaks then falls off but connecting rods will normally break at high RPM when the engine is making less than peak power. If power broke the rod, it would break at the peak not when it is making less power. Also in most cases the rod will break at the end of the straight away or the end of the quarter mile when the throttle is suddenly closed. Since you are not making more power with a closed throttle, I challenge anyone who rates rods by power to explain this to me and where they came up with their rating. In all of the years I have been doing this, I have not found anyone who has been able to explain where they came up with their numbers. The simple answer to your question about our rods, we have people who are making more than 1,000 HP with our standard weight rods and over 1,800 HP with our PWR ADR™ rods but I am not aware of anyone who has broken one, so if there really was such a maximum power number, we have no idea what it is because no one has reached it yet. One major difference between us and the other people selling rods is we provide honest information rather than quick, get your money type of answers. The bottom line is, if someone tries to sell you rods based on any kind of "rating", be very skeptical because they either simply do not understand the loads and forces on the parts they are selling or are telling you something that is not true so they can get your hard earned money."
|
Thanks for posting that. That long talk I had with Tom almost made me wish I rocked a smart phone and recorded it. So much high end, hard won information on a very interesting subject to so many of us comes at you fast, its hard to take it all in at once.
I did not know that some Pro Stock guys are going with steel rods. There is a tiny bit of power to be had and in that world that is enough to win.
His explanation of rod breakage was also very interesting. What happens first in a engine blow up, breaking it all down was fascinating.
Turns out, a lot of the time the pin rips out of the piston first and people blame to rod.
Tom is a very interesting guy and calls customers, potential customers back without any BS.
Can not ask anymore then that.