351w Stroker - 28oz vs 50oz

[JWMcCrary]

In the process of reworking my stroker (395) and switching from a non roller to a roller block. Plan is/was to use the rotating assembly I have with new bearings and rings. The roller block is at the machine shop but I haven't taken them the rotating assembly as the current engine is still together. Right now they are hot tanking and pressure testing to make sure the block is good and then proceed from there. The machine shop, which was highly recommended to me, doesn't like the fact that my rotating assembly was balanced to 50oz rather than the normal 28oz for all 351w engines. He says now is the time to correct something that should have never been, says 28oz is much better on the life of the engine, journals 2 & 4, especially a stroker. This will add another $300+ for a cast crankshaft and then another $150 for flexplate and balancer. Every nickel counts and adds up but I agree if necessary this is surely the time for it. The current engine was built in 2005, I didn't know anything about strokers and was told 50oz was better, geez. It's lasted 15 years and still running, just blowby and a little smoke which is due to dust and dirt I'm sure.

Long question short - Which is better and why?

 

[DirtDonk]

I've never heard that one is "better" than the other. Ever.
Doesn't mean it can't be true. Just that I've never seen written, or heard of anyone saying that.
It was my understanding that Ford simply wanted to put more of the balance out at the ends, to gain more internal clearance in the smaller 302 block. Is that not correct? The 351/5.8 was never changed because it wasn't needed in the larger block.

And if 28oz is better, then why not 0 balance like many strokers are?
Would that not be the most stable in high-performance situations theoretically?

The biggest change Ford made that did effect longevity for the longer stroke 351 was changing from the 302 firing order (15426378) camshaft to the 351 firing order (13726548) camshaft. To reduce a small harmonic they detected only in the 351's original testing.
Hopefully your modern roller shaft is going to be that way, if your existing cam wasn't already?

I would think the only negative would be to any future owners not familiar with your engine having been changed. But since selling it is not on the immediate horizon it doesn't sound like, then that's a moot point. And something you can deal with down the road.

Hopefully someone here knows for sure, because while I'd hate to spend extra money for something I don't see as having any benefit, I'd hate for you to go through all this trouble and not change something for the better when you had the chance.
I just don't see why a perfectly good running engine needs a new flywheel and damper, or modifications to those parts, plus a new crank, or new mods to that part, when it's been working fine all these years.

What about the manufacturer of the stroker parts? What about the original builder? If they're still accessible, what do they have to say about it?
Very curious how this turns out.

Paul

 

[DirtDonk]

A side question for later would be, what do the rod bearings and main bearings look like in the old engine when you take it apart.
That might indicate some internal stress not detected over the life of the engine.

paul

 

[Broncobowsher]

If this were a flat out race motor, get the 28 or 0 balance crank.
Of course you would be building a 408 and not using stock rods and 302 pistons.

You are building an economy stroker. The 50 oz-in will be just fine. And will work with the Explorer crank damper without modification.

Yes, the engine builder wants to build the perfect engine, but this is going to be a close enough. Just from the nature of the build there is no need to go with the better engine balance.

 

[Timmy390]

The more the imbalance the more rotational weight you have to swing around Correct?

Tim

 

[hucklburry rev2]

I always thought they went to 50oz imbalance because it was cheaper to do and they could. I just assumed that.

I am no expert, always assumed zero imbalance was the best, and the external balances would be harder on bearings and stuff

Honestly though if you are setup for 50oz already, I wouldn't sweat it and ask the shop to just run what you brung and not change from the 50oz, although they are most probably correct on it being better, I don't think it matters below 6000rpm right?

 

[spap]

My understanding which is limited is that the 50oz take more drilling into the crank to get the balance and the 28oz takes less, so the theory is the 50oz is weaker. But like what was said under 6000 rpm I wonder if it matters. If you do look and A 50oz crank vs a 28 oz crank the 50 oz it is drilled a lot more. That’s why I thought the stroker kits usually come in 28oz balance
You can google it and people explain better than I could

 

[Quick & Dirty]

Ford went to the 50 oz-in balance to make the crank lighter, and therefore total engine weight lower.

Internal balance is best for the engine, but that requires custom parts. 28 oz-in is better than 50 oz-in. Both 28 and 50 oz-in parts are readily available, so that's a wash.

I'd suggest leaving it at the 50 oz-in it already has unless it's being pushed for high rpm and hp.

Here is the difference in the crank counterweights between 5.0 and 302. The lighter crank has to carry the harmonics through the journals to the external counterweights, so it is under more stress.

 

[73azbronco]

I've learned through the years if yourt going to change the balance, just drop dime and buy a rotating assembly you want with the balance you want. Now, no issue correcting imbalances when they balance it, but change it that much up or down? Probably not a good idea.

50 oz is fine if thats what it is. How did it get that way BTW?

 

[JWMcCrary]

Thanks for all the replies. Got the answer I was hoping for. This engine has always run very well and still does, it just smokes a little so I'm taking this opportunity to redo it while some other major work is being done to the Bronco. It was built by me using a machine shop near where I was working at the time in 2005. And at the time I didn't understand the whole process of strokers, although I thought I did. I ended up with a very high compression engine but it still performed well not just ever really setup right. I've had a custom roller cam designed by Jones Cams for this rotating assembly and cylinder head combo that it currently has. For some reason the machine shop thought 50 oz was an upgrade and did it without me instructing them during the balancing. I didn't know any different. Oh well, that's where I'm at.
The machine shop I'm using now told me to pay attention to #2 & #4 when I disassemble the engine, if those bearings look worse than the others then they recommend a new crankshaft, otherwise use what I have. I'm going to have them check the crank, rods, pistons, etc, and reassemble the rotating assembly with new bearings and rings, using the roller block, and then hand back to me.

Here's a few pics of the current engine from march 2005, you can tell that crank was drilled to remove weight.

 

[nvrstuk]

... I'm with saving money... from the cam goals you were looking at rpm isnt what you wanted so keep the 50oz, keep the rpms down and you should easily get 150k out of your mains. But I would definitely check main brg and crank journal wear on what you pulled out then make your decision.

I spec neutral balance in all the strokers I work with, but that's from building from the ground up.

 

[Yeller]

And twice I'm posting in one of JW's threads and not blowing holes in his budget, I got nothin to contribute but smiles

 

[JWMcCrary]

And twice I'm posting in one of JW's threads and not blowing holes in his budget, I got nothin to contribute but smiles

Got to love the smiles.....;D