28oz. vs. 50oz. Crankshaft and Balancing Questions?

[66P51GT]

I'm taking my rotating assembly in to be balanced next week. I have two 302 nodular cranks. One is a 68-70 28oz. crank, the other is a 50oz. from a 90 5.0. I have two SFI Steel flywheels. The 28oz. has already been resurfaced and is ready to go. The 50oz. needs resurfacing. I also have a new professional products damper with bolt in counterbalance that can be used for either.

The crank will be machined .010 .010 and will be mating a set of forged H-Beam rods and Forged Pistons. These have already been balanced with 1 gram each.

1. Is there any advantage using the 28 oz. crank over the 50 oz. crank?


2. Does the machine shop need all of the rods and pistons or just one set?


3. I have a brand new 5.0 roller block with cam bearings already installed. Do I need to worry about any machining with a brand new block?

Thanks!!!

 

[stangman67]

1. 50oz parts are cheaper and more plentiful if you need something in the future.
2.They will need the 8 rods and 8 pistons to balance correctly.
3.Only if it wasnt finished honed, which it should be.

I only wonder why you arent using a forged crank if you use the forged rods and pistons. I realize its more cash, but with that and some good quality bolts, you would have a bottom end ready for most anything.

 

[65fastback2+2]

if its a roller block, then the 50oz crank belongs in it and it will be stronger

 

[351LX]

The roller block should have a one piece rear seal.I have heard that the cranks designed for the one piece seals are different at he back than for a two piece so that might be a factor.

 

[66P51GT]

I only wonder why you arent using a forged crank if you use the forged rods and pistons. I realize its more cash, but with that and some good quality bolts, you would have a bottom end ready for most anything.

Yeah, I thought about this for a long time. But for the initial power I will be making and the research I did, the nodular is all I need for now. From what I read, the block will give out before the nodular crank anyhow. Plus I got a lot more than what I originally set out for with the forged internals and aluminum heads (neither were not in my original plan). Keep in mind that I plan to use the car primarily for Street, Autocross, and Open Track events so mid-range Torque and high RPMs are more important than peak HP.

I got a killer deal ($2,200) for the new roller block, nodular crank, roller camshaft, New Carrillo H-Beam Rods, New Speed Pro Racing Pistons and New Ported Edelbrock Performer RPM Heads. Also included in the deal was a set of ARP Main studs and ARP Head studs. The Carrillo rods are the best in the business, rated at 900HP and already come with high quality 7/16" rod bolts. It is total overkill for my motor but I couldn't pass on the deal. I'm only estimating about ~380+ at the crank. This is well within the range for the crank and block and can safely sustain high RPMs (<6,500) for extended periods of time.

As my driving skills get better I plan to grow the engine and the rest of the build with time (and $$$$). My plan is still to complete the initial build for less than $10,000 out of pocket. Forking out another $1k for a good lightweight crank and $2k for a 4-bolt block will have to wait for now. It would also dramatically change the dynamics of the car since the the bottom end could support extended periods of 7,500+ RPM and tons more HP. I'd also want to pair these components with a solid roller and a Victor or Funnel Web intake. This would make the car a terible driver on the street and I would also need to upgrade the Tranny, Brakes, and Rear end to handle the HP increase and increased speed. All of this is pie in the sky and will have to wait for Chapter 2 of the build in another decade or so LOL.

 

[allcarfan]

if its a roller block, then the 50oz crank belongs in it and it will be stronger

hmmmm, not quite. I have a late model roller block with a 28oz balanced crank.

IN order to correctly balance your engine....your machinist will need all eight pistons, all eight rods, your rings, your balancer, and your flywheel or flexplate (and the bolts).

Personally, I would not use a new block for a performance build...unless it was a B50 or an R302. The stock A50 blocks, used, have been seasoned and are considered to be a little stronger. At least, thats what most performance builders say. It looks like you are using some good parts. I would tell the machine shop to have each bore matched to its own piston so you can be sure of a good seal.

 

[66P51GT]

Performance Oil Pumps

Wrong Post

 

[66P51GT]

I would tell the machine shop to have each bore matched to its own piston so you can be sure of a good seal.

I've already checked ring tolerances and everthing is within spec. I have also mocked up the pistons in the block. I'm not really sure what this means or what the benefit is?

 

[Great68]

A 28oz balance is better for higher RPM use than 50oz.

There is no such thing as a certain balance that "belongs" to a block. It all depends on the parts you use.

Oh, and a forged crank is nice, but a stock windsor block will crack long before a good cast crank will break. (At least as far as I've seen and heard).

When I build a 331 bottom end for my car, I will use a late model roller block, but will keep it 28oz balanced. In fact, most stroker kits come already balanced for 28oz.

 

[Fostang]

If I had a choice I would go 28 oz for performance purposes. Especially when using a blower.

but my main goal is to have a Dart or A4 or R based neutral balanced in other words zero balanced.

 

[66P51GT]

Thanks for the replies. I'll stick with the 28oz crank. Magnaflux, grind, and balance and I'll be set to finally put the engine together!