Lightened Rods

[veeracer98]

Anyone seen rods lightened this way? Dont know if this is ok or not. I know someone (not me) went to a lot of work.

[Stumpthumper]

GCR: C (vee) 5.C.6: Connecticut rods with bolts and small end bushing minimum weight = 425.0 grams ...
GCR: C (vee) 5.D.5: Where minumum weights are specified, any lightening is permissible provided the original part complied with thedemensional restrictions set forth.

It's legal if it's at least 425 grams.

[problemchild]

Anyone seen rods lightened this way? Dont know if this is ok or not. I know someone (not me) went to a lot of work.

Please explain what you mean by "this way". Thanks

[Steve Davis]

All of the 'meat' of the structure on the big end is GONE. I've never seen it done quite that thoroughly and I would NOT recommend using them. I doubt seriously that there is enough structure left to keep them from elongating (and blowing your your engine) at anything higher than, maybe 5500 RPM if that.
YMMV,
Steve

[veeracer98]

Thanks for the input. I'll throw them on the ever growing scrap pile.

[Steve Davis]

I use the local metal recycling center .. they actually PAY ME for scrap metal .. not much, but better than having to PAY SOMEONE ELSE to get rid of it
Steve

[BLS]

The ribs on the bottom end are gone. Cheapest way to remove weight and probably thinking it is the best place to reduce rotating mass.

Both idea's are faulty. I wouldn't use them.

[EACIII]

The ribs on the bottom end are gone. Cheapest way to remove weight and probably thinking it is the best place to reduce rotating mass.

Both idea's are faulty. I wouldn't use them.

Exactly, the place to remove weight is the little end. It stops and goes the other direction twice on each stroke. The big end just keeps going around in a circle.

Ed

[Stumpthumper]

Just thinking outloud here, aren't all the major forces on the opposite side of this area? Intake stroke would have a little, but that's about it.

[Daryl DeArman]

delete. Duplicate

[Daryl DeArman]

That heavy turd piston decelerating as it approaches TDC at high rpm is putting a tremendous load on the con-rod cap and rod bolts.


That said, if those rods are of legal weight I'd use 'em just to see what kind of gains can be had (if any). If they fail the damage isn't exactly prohibitively expensive.

[R. Pare]

That said, if those rods are of legal weight I'd use 'em just to see what kind of gains can be had (if any). If they fail the damage isn't exactly prohibitively expensive.

Other than maybe needing a new block and crankshaft......

[Daryl DeArman]

Other than maybe needing a new block and crankshaft......

Cheap.

Both can be had from a reputable engine builder for about the price of a set of tires. Ruining a really good cylinder head and a dnf would be my only reservations.

[Hardingfv32]

1) Why did VW provide ribs on the rod cap that was only going to see 4000 rpm? Did they know something that some Vee engine builders have failed to recognize.

2) Investing in a set of Crower rods is one of the best things you can do to improve engine reliability.

Brian

[Daryl DeArman]

1) Why did VW provide ribs on the rod cap that was only going to see 4000 rpm? Did they know something that some Vee engine builders have failed to recognize.

Because they wanted those engines to last 100x longer than any competitive FV racer anticipates getting. Therefore there are a number of comprises made in longevity when chasing performance.

[provamo]

maybe i should READ the rules

[Daryl DeArman]

1. Connecting rods with bolts and small end bushing minimum weight = 425.0 grams. Crower part#SP93280B is allowed as a direct replacement connecting rod but must meet the same minimumweight requirement as the OEM part.
   

[BLS]

"Because they wanted those engines to last 100x longer than..."

4000rpm occasionally Vs 6500 all the time. Very significant difference from one to the other.

[Daryl DeArman]

"Because they wanted those engines to last 100x longer than..."

4000rpm occasionally Vs 6500 all the time. Very significant difference from one to the other.

Yes. Absolutely. As is 35 hours TBO and 3500 hours. As is 40hp vs 65. I get it. While the probability of failure may be much higher than many are willing to stomach, nothing ventured; nothing gained. Only the end user can decide if they are willing to take such risk.

[BLS]

Sure, it's up to the individual to determine the risk. IMO, it's not worth it. Those rods were most likely done by someone that had little knowledge of what they were doing.

[Daryl DeArman]

Sure, it's up to the individual to determine the risk. IMO, it's not worth it. Those rods were most likely done by someone that had little knowledge of what they were doing.

Or somebody who felt the caps were 3x as strong as they needed to be and was willing to sacrifice quite a bit of strength there to see how it played out. . .

[Marty Nygard]

The pictured rods look like what we used to use in our 948 HP Sprite engines. Worked great to over 9000 rpm as long as you were willing to replace rod bearings every two race weekends (ya gotta love oil dripping on your face!).
Marty

[BLS]

Or somebody who felt the caps were 3x as strong as they needed to be and was willing to sacrifice quite a bit of strength there to see how it played out. . .

There is quite a bit of information available on lightening rods. Perhaps someone wished to start from scratch and prove what is known to be false.

More likely they did not know what they were doing. Show me some pictures of a rod built by any of the V engine builders that looks like that and I'll rethink my evaluation.

Anything is possible. Some things are more likely than others.

[Hardingfv32]

Show me some pictures of a rod built by any of the V engine builders that looks like that and I'll rethink my evaluation.

Vee engine builders used trial an error to get where they are on rod lightening. Even with that said there is really no way to know what caused a rod to fail. How do you tell a lubrication failure from a rod that actually broke all on its own? Maybe a lubrication failure develops while the rod is physically deforming but not breaking (ovaled big end).

If you want to know what a FV rod should look like, then check out the Crower rod. It was developed using FEA, structural element analysis. It tells you exactly where to allocate your material and in what shape. They are also surface treated to reduce stress, which is something the FV engine builders do not do.

Brian

[Daryl DeArman]

There is quite a bit of information available on lightening rods. Perhaps someone wished to start from scratch and prove what is known to be false.

More likely they did not know what they were doing. Show me some pictures of a rod built by any of the V engine builders that looks like that and I'll rethink my evaluation.

Anything is possible. Some things are more likely than others.

Sometimes people too close to the trees can't see the forest. Professional engine builders aren't concerned with getting you that last .05% HP if their engine is going to go kablooey in what the market determines is too short of time period.

FV engines make 16-17HP per cylinder. A maximum piston velocity of around 24m/s. Mean piston speed under 15m/s. A piston weight under 12 ounces. Doesn't require near as much rod as we think until we demand they last tens or fifty-ish hours.

[BLS]

"if their engine is going to go kablooey"

You're making my point.

[BLS]

Vee engine builders used trial an error to get where they are on rod lightening. Even with that said there is really no way to know what caused a rod to fail. How do you tell a lubrication failure from a rod that actually broke all on its own? Maybe a lubrication failure develops while the rod is physically deforming but not breaking (ovaled big end).

If you want to know what a FV rod should look like, then check out the Crower rod. It was developed using FEA, structural element analysis. It tells you exactly where to allocate your material and in what shape. They are also surface treated to reduce stress, which is something the FV engine builders do not do.

Brian

Every Crower rod I look at has substantial ribs on the crankshaft end. As I recall the VW rod also has it, but I don't see a picture or listing in their catalog.

[Hardingfv32]

Google Crower SP93280B and go to the Crower page.

Brian

[Daryl DeArman]

"if their engine is going to go kablooey"

You're making my point.

I never once argued that the life of those rods would not be shortened over a stock or even typical FV engine. Not once.

[BLS]

Google Crower SP93280B and go to the Crower page.

Brian

Thanks Brian. Found them that way.

[BLS]

I never once argued that the life of those rods would not be shortened over a stock or even typical FV engine. Not once.

Didn't suggest you had, Daryl.

My opinion is different from yours - you suggested using them to see what they would do - I suggest don't waste your time because they do not match any known rod builders methods of lightening and balancing rods.

[Daryl DeArman]

Every Crower rod I look at has substantial ribs on the crankshaft end. As I recall the VW rod also has it, but I don't see a picture or listing in their catalog.

The stock 1600 rod does not have such ribs.

*** to clarify by "such ribs", I am speaking to your descriptor as "substantial". Neither the Crower FV or stock 1600 rods have what I would call substantial ribs.

[BLS]

The stock 1600 rod does not have such ribs.

*** to clarify by "such ribs", I am speaking to your descriptor as "substantial". Neither the Crower FV or stock 1600 rods have what I would call substantial ribs.

Substantial being in the eye of the beholder...

With Brian's help I found the picture of the Crower VW rod. It has a single rib that I would classify as substantial when measured against the pictured rods from the original poster. Those rods appear to have all the ribs removed. They look perfectly flat and smooth.

With that I'll let sleeping dogs...

[mmi16]

https://www.youtube.com/watch?v=-DXX...s392JVX3eflrCs