Saturn71

Hi everyone. This is my first new thread(outside of the newbie forum) and I wanted to get some opinions about the ease and feasibility of internally balancing a 455 with aftermarket(in this case SCAT) H beam rods and forged pistons. I haven’t purchased pistons yet, but the options I have been able to research(both 2618 and 4032) range anywhere from 550 grams each to nearly 600 grams. The bare block is at the machine shop right now being checked, but will more than likely be bored .040 over stock.

I have both a N crankshaft as well as an Eagle 4.25” crankshaft. My intent was to use the Eagle crankshaft for the build, but was recently wondering if its lower weight(relative to the N crankshaft) would hurt me in pursuit of internally balancing the engine. I’ve been slowly building up parts over the past 10 years in preparation for this build, so I’m definitely not made of money. However, I’m of the mindset that you do it once and do it right. A damper/balancer and flex plate have not yet been purchased. Has anyone else had experience internally balancing a similar rotating assembly? If so, how much Malory may I be looking at to achieve this?

This build will be primarily street, but I do occasionally touch 6000 rpm in spirited driving. End goals for power are 500HP and north of that.

Thanks!

fleming442

You'll have to check it to see what it needs. ATI makes a good damper, and Scat has one with a removable counterweight. Flywheels and flexplates are available.
I am running an internal balance, offset ground 425 crank. The Eagle 4.5" needed too much weight.

BillK

Eagle can tell you the target bobweight for the crank. It might even be in the catalog. The lower overall weight really does not mean much as far as balancing. Anything is possible if you are willing to spend the money I balanced a 455 not that long ago. Illl have to see what the bobweight was.

Saturn71

Good call on the bobweight! Eagles published target bobweight for this crankshaft is 2425 grams.

oddball

Gotta sketch together the combo you would have and see how much heavy metal it would need. Your friendly local machinist can help you figure that out. Then decide if you want to spend that much.
I'm not convinced that it's super-worthwhile to internally balance. ATI makes both neutral and external balance versions of the Olds balancer. if you want to use theirs. They are super nice, but also a PITA - they hit the water pump, you need a custom timing mark, probably have to replace the timing cover bolts with something lower profile, and the timing shells are only available for neutral balancers.
If the crank is designed for internal then that's the way to go. If it's designed for external, then there's not necessarily a ton of benefit converting it.

BillK

According to the Eagle catalog I have, that crankshaft is "factory" balance which would mean external. I have some notes on the Olds flexplate and damper "unbalance" amounts and it looks like it would take at least 2 if not 3 pieces of Heavy metal in each end of the crank to make it internal balance. Probably not economically worth it.

The bobweight on the last 455 I balanced was 2528 grams which is pretty heavy. It had stock rods and Sealed Power forged pistons.

Saturn71

I really appreciate the input from everyone! I’m still waiting to hear back from the machine shop on the block. Once I know what pistons I will be working with, I’ll see what the machine shop says regarding balancing options.

I'm just trying to get out ahead of the game on this build while at the same time trying not to blow money on parts I won’t use.

I’ve been building up funds and parts for this build for many years. But now that it’s started, waiting is the hard part. But I’m guessing most here have experienced the same thing. It’s time to cool my jets and do things right, even though it may take a little longer than I’d like.

cutlassefi

Wow! Most everyone danced around his question. I guess because most didn’t have an answer.
Normally they take 2 slugs each in the front and rear.
And yes the fact that the crank is lighter DOES help, BECAUSE they took most of that weight out of the rod throws, they’re all drilled. Stock N cranks aren’t.
Whenever possible, ALWAYS balance it internally. There are lots of advantages to doing it that way. Maybe someone here can tell you what those advantages are.😎
And you know you need to use a different rod bearing with the Eagle crank right?
Jason, ATI makes both internal and external shells, just sayin.

cutlassefi

But that’s based on an external balance.

Saturn71

Thank you Mark for educating me!! I didn’t know that the Eagle 4.25 crankshaft required special rod bearings. What rod bearings do you recommend for that crankshaft?

BillK

I am not sure if that is true on the 4.250" crank. The 2020 catalog says ".092 radiuses so standard bearings can be used" You could call Eagle and ask them to be 100% sure. The 4.500" crank has Chevy rod bearing size so it obviously needs a different bearing.

As far as balancing goes I think I said the same thing as Mark in reply #6 I will disagree with needing to internal balance in most street applications. How many millions of externally balanced Olds engines are running for hundreds of thousands of miles with no problems. Same with Chevy, Ford etc. If you are building a 7000 rpm race piece and its in your budget then yes internal is better. But I am not sure if I would be doing that with a cast steel crank anyway

Just my opinion,

fleming442

I think it's worth the money, regardless of end use.

cutlassefi

^^^^^^ And there are other reasons for internally balancing it as well. Anyone?

CB542HXN. The Eagle recommendation isn’t correct. The radius will normally just touch a P bearing. Plus their sizing normally runs on the high side. So having the extra clearance in the HXN bearing is a plus as well.

oddball

Well, @#$%@#. The ATI guy that answered the phone a few years ago said they would only make them for the neutral dampers. Didn't make any sense to me (seems like the shells are the same), but hey.

cutlassefi

In addition they make an integral AEM style trigger wheel for them as well.

fleming442

The simple physics of moving the counterweight closer to the imbalance sold me.

cutlassefi

👍

fleming442

AND, when you couple it with a light rotating assembly, it revs obscenely quick 😁

CANADIANOLDS

explain to me the part about the rod throws NOT being drilled on the 455 factory crank but are drilled on the Eagle?

cutlassefi

All four are drilled on the Eagle cranks. I’ve only ever seen 1 455 crank out of dozens and dozens that were drilled on all four. A vast majority are only drilled on the end ones.