Reciprocating weight tests ?

[Tom68]

Any links to any dyno tests of reciprocating weight along with the potential reduction in rotating weight for balance ?

If it's dyno results, it would have to be with the load held for a period of time, otherwise mathematical.

[Geoff2]

Not sure what you are asking. D. Vizard had a lengthy piece in PHR magazine on few years back. One test was when lighter wheels were fitted to a Mustang, it et'd quicker.

[Tom68]

Not sure what you are asking. D. Vizard had a lengthy piece in PHR magazine on few years back. One test was when lighter wheels were fitted to a Mustang, it et'd quicker.

Reciprocating not rotating, i.e. lightweight pistons and rods, the lower rotating weight is a bonus that has several of its own advantages.

[mag2555]

There was a issue of engine masters that came out between 2012 and 2014 if I recall correctly that covered the balance question in depth.

One of the eye opening things for me out of that article in terms of reducing the load on the main bearings was the placement/ phasing of the counter weight on the crank.

Getting these placements right would reduce the loads by thousands of pounds.

Later today I will post the pages from this article that cover this.

[Stan Weiss]

Any links to any dyno tests of reciprocating weight along with the potential reduction in rotating weight for balance ?

If it's dyno results, it would have to be with the load held for a period of time, otherwise mathematical.

I don't have the math to do reciprocating weight changes, I do have some math to do rotational weight changes and you will see no difference with the load held for a period of time. The greater the acceleration rate the greater the difference you will see.

This is from testing that David Vizard did.

Stan

David_Vizard_Flywheel_MOI_Test.gif

[juuhanaa]

One of the eye opening things for me out of that article in terms of reducing the load on the main bearings was the placement/ phasing of the counter weight on the crank.

Hmmm i know sometimes a less aerodynamic car can actually be faster but i wonder how they did that crank and i look forward to reading about it.

IMG_0287.JPG

-juhana

[rebelrouser]

Dan Begle Technical Sales Engineer at MAHLE gave an excellent presentation at PRI about bearings, harmonics, engine, balance and related topics at 2022 PRI show. Could not find a video of it but it was a good explanation of these forces in an engine. Maybe somebody with better computer skills could find it. https://pri2022.mapyourshow.com/8_0/ses ... eduleid=99

[panic]

I've yet to see a conventional engine in which the CW directly opposes (in the same radial path) the rod journal, so there always be some rocking couple.

[Stan Weiss]

Reciprocating not rotating, i.e. lightweight pistons and rods, the lower rotating weight is a bonus that has several of its own advantages.

I know when doing load calculations, that the big end of the rod is rotational weight and only the small end of the rod is reciprocating weight.

Stan

[panic]

I have doubts about the method used to separate reciprocating weight from rotating weight.
The usual is to suspend the rod at one end horizontally, with the other end on a scale, then reverse. Obviously if the total of both doesn't match the entire rod the routine was flawed.
The center of gravity is not the dividing line between types of motion: it's exactly midway between the pin end center and big end center.
Another anomaly: the rod eye above the pin and the big end below the journal are moving in directions opposite to the beam at some point.
Since the big end is always much heavier than the small end, the center of gravity will only begin to locate at the geometric center (50% of the center to center distance) in a rod of infinite length; shorter rods will tend to have more bias between the C-of-G and geometric center. Therefore, the absolute length of the rod (as well as the rod ratio) has an effect on balance.

[In-Tech]

I have doubts about the method used to separate reciprocating weight from rotating weight.
The usual is to suspend the rod at one end horizontally, with the other end on a scale, then reverse. Obviously if the total of both doesn't match the entire rod the routine was flawed.
The center of gravity is not the dividing line between types of motion: it's exactly midway between the pin end center and big end center.
Another anomaly: the rod eye above the pin and the big end below the journal are moving in directions opposite to the beam at some point.
Since the big end is always much heavier than the small end, the center of gravity will only begin to locate at the geometric center (50% of the center to center distance) in a rod of infinite length; shorter rods will tend to have more bias between the C-of-G and geometric center. Therefore, the absolute length of the rod (as well as the rod ratio) has an effect on balance.

Yes, and why it's ok to "overbalance" in high rpm high hp applications. Or, it just doesn't matter as long as all the parts weigh the same and the crank CW's are close enough. Jon Schmidt?????

[af2]

Not sure what you are asking. D. Vizard had a lengthy piece in PHR magazine on few years back. One test was when lighter wheels were fitted to a Mustang, it et'd quicker.

Reciprocating not rotating, i.e. lightweight pistons and rods, the lower rotating weight is a bonus that has several of its own advantages.

Only when you are coming out of a corner...

[juuhanaa]

Was it DV who said that one change is rarely enough? I think it comes down to what were trying to achieve, whether its rear tire grip or whatever.

Tom, how much timing and/or cranking pressure can you put on a SBC or Ford?



-juhana

[Stan Weiss]

I believe if when doing the crank load calculations and one doesn't have the big end and small end weights the general rule is 1/3 of rod weight is small end weight and 2/3 rod weight is big end weight.

Stan

[PackardV8]

Not sure what you are asking. D. Vizard had a lengthy piece in PHR magazine on few years back. One test was when lighter wheels were fitted to a Mustang, it et'd quicker.

Reciprocating not rotating, i.e. lightweight pistons and rods, the lower rotating weight is a bonus that has several of its own advantages.

Only when you are coming out of a corner...

Agree, lightweight recip/rotating components don't make power, but they are their own reward as relates to connecting rod and rod bearing durability and holding the power together at higher RPM and longer hours. Today's NASCAR pistons weigh enough less that the engines will live 500 miles at 9000 RPM. Back in the bad old days of heavy pistons, car owners/crew chiefs would use a tell-tale tach, because they knew more than 6,500 wouldn't finish the race.

A bit of trivia, word went around among drivers to keep a little magnet in the pocket if one needed to pull back the tell-tale needle. If a crew chief had a win-or-blow driver, then the tach needle had to be aluminum.