Big Block Balancing 454 vs 402

[Monte M.]

Can someone help me understand the difference in how big blocks are balanced. For example, I know a 454 is externally balanced and a 402 is internally balanced. If I am not mistaken you can even put a 454 balancer and flywheel on a 402.
The question for me is, how much does it throw off the balance of the motor and what does it typically feel like.

Is this typically at idle, or does it get much worse as the RPM's go up?

What happens when you put the 454 balancer and flywheel on a 402?

What happens when you put a 402 balancer and flywheel on a 454?

Or, What happens if you only have the 454 flywheel on the 402 set-up?

On an automatic is the flexplate going to be the same?

Are there any other balancing factors that I have forgotten about?

Any input would be appreciated. I have talked to a few people about what might happen, but they had no first hand experience.
Thanks for the help.

[Duke W.]

Re: Big Block Balancing 454 vs 402

The masses at the ends of the crankshaft or external "unbalanced" components as in the case of the 454 balance a first order rocking couple. Without proper balance to negate this couple, the engine will "rock" back and forth about the cranktrain's center of mass - once per engine revolution.

How this "feels" will depend on the engine mounts and chassis dynamic characteristics, but you would be a fool to spend money to find out.

Do it right the first time. Use properly matched components to achieve full balance of the rocking couple.

Duke

[Joe R.]

Re: Big Block Balancing 454 vs 402

Monte,

The external balance of the 454 is on the flywheel and balancer and the balance of the 402 is the crankshaft with a balanced flywheel and balancer. You cannot mix the two and expect the assembly to be balanced. Well yes, I'm sure someone could balance the mix of the two but it would take a lot of machine work or welding on weights to make it happen.

As Duke says, don't try it! You ain't gonna be happy!

JR

[Clem Z.]

Re: Big Block Balancing 454 vs 402

Can someone help me understand the difference in how big blocks are balanced. For example, I know a 454 is externally balanced and a 402 is internally balanced. If I am not mistaken you can even put a 454 balancer and flywheel on a 402.
The question for me is, how much does it throw off the balance of the motor and what does it typically feel like.

Is this typically at idle, or does it get much worse as the RPM's go up?

What happens when you put the 454 balancer and flywheel on a 402?

What happens when you put a 402 balancer and flywheel on a 454?

Or, What happens if you only have the 454 flywheel on the 402 set-up?

On an automatic is the flexplate going to be the same?

Are there any other balancing factors that I have forgotten about?

Any input would be appreciated. I have talked to a few people about what might happen, but they had no first hand experience.
Thanks for the help.

a lot of chevy fans found out the hard way when they replaced their 396,402 and 427 with 454 short blocks using their old damper and flywheel as the vibration would shake the whole car and picked up with RPMs

[Duke W.]

Re: Big Block Balancing 454 vs 402

Whenever owners restore an engine, I always recommend a precision balance, which will be better than the OE balance, and in many cases it has eliminated the "shifter buzz" that is common to vintage Corvettes.

There's nothing like a "rev forever" precision balanced engine!

Duke

[Monte M.]

Re: Big Block Balancing 454 vs 402

Thanks Guys,
but I have no idea of trying this. It just came up in conversation with a few guy sand an engine for sale. One of the guys has a big block on an engine stand. It looked to me like it was a 454 balancer like I have put on and off my car a number of times. The guy was selling the engine as a running 454, but it did not make sense to me the way it was set up.
He was trying to pass it off as a 454. I checked the casting number and that turned out to be a 402. I know there is a difference and even what the basic differences were, but I was just hoping to understand it better for my own knowledge..