Lz9 rotating assembly weights

[Shaun41178(2)]

Seeing as the lz4 pistons are the same as the 9, the same goes obviously. I didn't weigh an lz4 rod yet

Lz9 rod 630g
Big end. 471g
Lz9 piston with rings and pin 592g
Lz9 pin 149 grams
Lz9 piston with rings 444g
Reciprocating weight = 751g

Pauter rods 655g
Big end 464g
JE piston with rings and pin 536
JE pin 104g
JE piston and rings 432
Reciprocating weight = 727g

The Pauter rods is only 20 grams more than a stocker. But the pistons are 56 grams lighter. What will this do for the balancing? Obviously it will be off. I'll have to do some research. But 36 grams total lighter doesn't seem like a hell of a lot.

Last shop said since I was using the lighter je pistons, the weight was was close enough where I didn't need to have it balanced but 60 grams seems like a decent amount. Maybe they just didn't want to bother will balancing it?

Reading says you can go lighter a certain amount of the bobweight without any ill effects.

So maybe these will essentially be close enough to be a straight drop in. Which will add to the simplicity of the whole thing.

[pmbrunelle]

Lz9 rod 630g

Pauter rods 655g

To work this out, you need to weigh the big end of the connecting rod separately from the small end.

[Shaun41178(2)]

Yea I got the big end weight of the Pauter which they provided but no way to measure myself the stocker.

I'll have to take it in.

[pmbrunelle]

You can balance the stock rod on a razor blade to find the location of the centre of gravity.

Knowing the total weight (which you have), and the CG location, you can work out the big and small end weights.

[The Dark Side of Will]

I've seen both a 50% recip factor and 40% recip factor listed for 60 degree V6's. I would intuitively think that the split crank throws would make it different than balancing a V8, but I don't have data to back it up.

[SappySE107]

You can balance the stock rod on a razor blade to find the location of the centre of gravity.

Knowing the total weight (which you have), and the CG location, you can work out the big and small end weights.

Is that something people do? Is there a math formula for it? This is my math alternative;)

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I've seen both a 50% recip factor and 40% recip factor listed for 60 degree V6's. I would intuitively think that the split crank throws would make it different than balancing a V8, but I don't have data to back it up.

You can find the balance info and more in the power manual.

https://gafiero.akroncdnr.com/docs/60V6Pwr.pdf

[Series8217]

This is my math alternative;)

This is the way.

[pmbrunelle]

Is that something people do?

No, not really. The swingarm jig for the scale is the standard way in automotive rebuilding/repair.

In the OEM world, I'm guessing that the CG location given by the CAD software is close enough to reality.

Is there a math formula for it?

Yes, the math is straightforward. There are two simultaneous equations to be solved:
Big_end_weight + Small_end_weight = Total_weight
Big_end_weight * Big_end_to_balance_point_distance = Small_end_weight * Small_end_to_balance_point_distance

********************************************************************************

My idea is a simple, no equipment required way for Shaun to make a preliminary evaluation. He can then decide if the method is good enough for his purposes.

[SappySE107]

Id love to see you balance a connecting rod on a razor blade.

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Got it as close as I could, came up with 128.5mm SE 75.5mm BE. 204mm OAL. That makes it a 37/63 weight split, but the weight based on measurements is not even in the ballpark compared to the math. Unless you have a better formula, this way doesn't look legit to me.

[pmbrunelle]

The CG of the rod is above the razor blade, so it's a naturally unstable configuration that will want to tip over to one side.

What weights did you measure by direct measurement?

I'm not sure what the issue is, but static equilibrium equations are pretty legit.

I'll review this tomorrow when I'm not sleepy.

[pmbrunelle]

I think I see the issue.

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You need to measure the distances with respect to the center of the holes, not to the extremities of the rod.

Just like when you are using the measuring jig and balance, the rod is supported by the hole centers.

[SappySE107]

Makes sense to measure from the center of the bores, but really difficult to do. I thought balancing a connecting rod on a razor blade was difficult.

[pmbrunelle]

Sometimes, it's hard to directly measure to the centre of a hole. However, you can measure to the edge of a hole, and then (by measuring the hole's diameter) add the radius to come up with the dimension to the centre of the hole.

Pretty much 99% of holes in technical drawings are dimensioned to their centres. Metrology departments are used to this.

[Shaun41178(2)]

To work this out, you need to weigh the big end of the connecting rod separately from the small end.

I edited the original post to include big end weight. It appears the Pauter rod is lighter on the big end too. By about 7 grams

So the big end is lighter than stock but overall heavier. But the pistons and pin are lighter than stock.

Difference in reciprocating weights is 24 grams which is less than an ounce

[The Dark Side of Will]

You know how to calculate a bobweight. What's the bobweight difference?

[Shaun41178(2)]

It's within 2%. It's gonna be overbalanced by 1.6%. It's t cjnically a drop in setup. To rev over 7k I'd recommend a balance but to 6k it' should be good.

[Shaun41178(2)]

Expensive proposition but I wanted to get the info in writing so I don't forget about it.

Ls9 Ti rod info.

Wrist Pin Dia. 0.984
Weight 452-482g
Length. 5.99
Big end dia. 2.225

Lz9 has pin dia of .945 and a big end of 2.375. So the ls9 small end can be bushed I would assume, and maybe the big end bored out or a larger bearing installed? I am also unsure of the width on the ls9 rod

[Shaun41178(2)]

Ls7 also uses a Ti rod but it's listed at 6.067. Weight is similar to ls9 rod.

With a 3.9 crank, ls7 rod, you would need a compression height of about 1.1. And whattaya know. It exists! Several dishes exist. I found a 16cc which is about 11.7 CR and a 26cc dish for about a 10.2 CR.

600 for forged pistons
https://www.summitracing.com/parts/sum- ... /chevrolet

[eHoward]

If you go used, you probably could find a set of Ti rods, on a budget. This one is $1,250:

https://www.ebay.com/itm/266472618709?m ... media=COPY

[Jalisurr]

If you go used, you probably could find a set of Ti rods, on a budget. This one is $1,250:

https://www.ebay.com/itm/266472618709?m ... media=COPY

I would be very cautious about used LS7 rods. They have an anti-friction coating on them from the factory that wears off naturally over time and usage, and once gone they start shedding titanium flakes which quickly destroy the engine. Ask me how I know, and what happened to my previous C6 Z06 time attack car...

There used to be some places that were re-coating rods, but I don't know if that's still an option.