I am looking at buying a forged rotating assembly and I am looking for some advice on what to balance at the same time. For example, should I have the flexplate and clutch pressure plate balanced along with it?

Also, is the difference in wieght of a forged assembly really worth much power? Is this a major advantage, or is the major advantage the strength?

Thanks in advance

 

I don't know hom much of a weight savings are involved in forged components. Any variation in the density of steel across different compositions is minimal. Any weight savings come from journals being drilled and a better design. However, any minimal weight savings is desired because of the dynamics forces of twisting the motor to 6500+rpm. The increase in strength is what you're looking at when you go forged.

Good luck w/ your build.

Later,


Steve.

 

If you take your crank by itself to get it balanced the shop will tell you to go home.

In order to balance a rot.assly. you need everything that will be attached to the crankshaft. Pistons, rods, crank, flywheel/flexplate, and balancer, not to mention the amount of oil that everything holds on it gets balanced, .04g or something like that I believe.

Weight savings from forged or billet components only comes if the superior strength is taken advantage of. If something is stronger there doesnt have to be as much material to keep the same strength. The reason you wont see cast superlight crankshafts, only forged ones. There is no, or negligable difference in weight between a base cast and a base forged crank.

IE:
Scat 9000 cast 3.48 crank 51lbs
Scat 4340 forged 3.48 crank 51lbs
Scat 4340 lightweight 3.48 48lbs
Scat 4340 superlightweight 44lbs

 

I personally have my engines balanced with just the internals, and internally balanced. Then I have the accessories balanced separate. This way in the future i can change the damper, flex, flywheel or clutch and still be spot on.
Spend the extra money and get your assembly internally balanced its worth it.
Like other stated you are buying 4340 forged for strength not weight.

 

go get the crank balanced then wiegh your pistons with rods and match wieght the piston rod assembly so they all wiegh the same then if you want send the flywheel out and get it balanced as far as the harmonic goes by a new one then every thing is good have some fun with it

 

First do you want it internally balanced meaning you need a neutral balanced flywheel/flexplate? Or…. Do you want to use stock components which have added weight on the outside for overall balance which is called external balancing?

The advantage of external balancing is that you don’t have to have your stock components rebalanced to neutral. Most people building high hp combinations internally balance everything and neutral balance their flywheel/flex plate.

Flexplates are for automatics… flywheels are for six speeds and you will for sure need the “whatever” if you’re externally balancing and most builders prefer to check the “whatever” even for neutral balancing just to make sure there are no other issues. Most don’t need your pressure plate but some will even check it.

The material your rotating assembly is comprised of has nothing to do with how much power you’re going to make….. rather how well it will hold up to the power you're making. Apples to apples there is not much difference in either’s weight unless you want a lighter assembly in which you will pay the price of more expensive forged components.

If you’re not going absolutely stupid hog wild…. a cast crank, cast rods and hypereutectic pistons are fine. If you’re going for higher hp, higher rpm and/or want to use nitrous, you’re better off with the forged stuff. There are however, some pretty awesome combinations running cheap cast cranks/cast rods and loving it. Some sitting in the junk yard also because they should have been forged..

 

Every so often you might see a reworked cast crank that might be considered "lightweight" to "superlightweight". Strength isn't compromised if only the material that isn't adding much to the strength is removed. Of course selecting that material is the trick. Reshaping a cast crank to the shape of a "lightweight" forged piece is a good start.

If a cast crank is strong enough to support high hp, and some are, using lightweight reciprocating parts and significant lightening of the cast crank might be a reasonable method, especially if aftermarket forged cranks aren't readily available or are VERY pricey.

There are some old cast cranks, like some Pontiac cranks, and even some newer ones, which are candidates.

 

[QUOTE=Denny McLain]First do you want it internally balanced meaning you need a neutral balanced flywheel/flexplate? Or…. Do you want to use stock components which have added weight on the outside for overall balance which is called external balancing?

The advantage of external balancing is that you don’t have to have your stock components rebalanced to neutral. Most people building high hp combinations internally balance everything and neutral balance their flywheel/flex plate.[quote]

Not sure if i understand this,i just had a 383 built,that was internally balanced and i used the stock flywheel,balancer.It took some mallory to get it right,the only reason i ask is because from reading this statement if you use stock parts its externally bal.??

 

Whenever you change any internal component of the rotating assembly, it should all be rebalanced. As mentioned above, you need to take just about everything in for them to balance it properly.

If it's an internally balanced engine then the balancer and flexplate/flywheel don't need to be taken in since those are already neutrally balanced. Any externally balanced engine, 400 SBC, 454 BBC etc needs the balancer and flexplate/flywheel since there are counterweights on each that the crankshaft needs for balance.

When we say everything needs to be taken we mean everything.

Crankshaft
Con rods
Pistons
Rings
Rod bearings
Wrist pins

Technically only one set of rings, one wrist pin and one set of rod bearings are needed so they can get the weight from them. Even the weight of the rings or rod bearings can make a big difference in the balance.

Lightweight components such as con rods and pistons only reduce the amount of rotating mass. Unfortunately weight needs to be added to the crank to offset the reduced weight from the lightweight parts but it's a better trade off. The weight on the crankshaft spinning around isn't as bad as the weight connected to the crankshaft. They'll use what's called Mallory weight which is very heavy to add weight to the throws. Mallory metal is also very expensive.

You can get externally balanced engine converted to internally balanced but that's a lot of expensive Mallory metal required to do it.

For the most part, a typical street engine that rarely sees above 5000 rpm will be fine if it's assembled unbalanced. When you start to really spin the engine high up, it's a good investment to get it all balanced. My BBC's shift point is around 7000 rpm. Lots of expensive internal parts. I don't want a failure because of balance weight. 4340 steel crank, lightweight forged pistons and aluminum rods help cut the weight down.

 

In a broad sense any time you balance an engine it's done internally but if you used a stock flywheel which has a weight cast into it for balance, it's considered externally balanced.

You can use "stock" parts and have the flywheel either drilled or machined to remove the weight making the flywheel neutral in balance. (Much like balancing a tire) This is what is called internal balanced even though both are done by adding removing weight from the crankshaft.

 

Thanks for all the input, and yes, I have a flywheel (duh!)

The internal rotating assembly will be balanced together. Although I haven't looked at it in while I think the flywheel and clutch pressure plate are not neutral on a stock LT1. I was thinking it would be a good idea to have the flywheel and clutch balanced along with it. But in this case I would expect the internals are balanced neutral, then the flywheel and clutch are balanced "externally" meaning brought into balance with the rotating assembly by modifying them "externally".

What about the LT1 balancer? How does it fit into this equation?

The question about the added power came from something I heard an engine builder say a while back about the lighter forged assembly spinning up faster resulting in more power to the wheels. Makes sense in general. I went with it and bought an aluminum clutch pressure plate. I don't know if it will help much but it is quite a bit lighter. It probably matters more to the components that spin farther from the axis of rotation like the pistons and rods and the clutch too.