[ap72]

Ok, I know the difference and the advantages of less wear with internal balancing, my question is since the enign e I'm planning on building will never see over 6000 rpm and will rarely be over 3500 rpm should I go with an internally balanced asembly for my 383 chevy?

And while we're on the issue, a cast crank should be fine in the 4** max hp power range right? I'm building this thing mostly for low end grunt.

[ap72]

does anyone have any input?

[joseph brown]

hang in there there's a lot of talent here im sure some one will help....i have two sbc 400s ...and there both worked .30 over , flat tops , big cam and i was told that those crank's had to be external balanced ....of course i wanted to know why ...the reason i got was because of the size of the crank's web at the journal... that not enough weight could be added or taken away...and the proof was the flex plate with the big weight on it ...a long with the big front balancer...i was'nt sure one way or the other...but if chevy put it there must need it ....hopefully we will both learn something as the thread turns... good luck..jb

[TroyBoy]

For what you described about your usage I don't see a reason to internal balance your engine.You should have no problems with the cast crank either,just make sure of proper clearances as usual.

[TroyBoy]

Originally Posted by joseph brown

hang in there there's a lot of talent here im sure some one will help....i have two sbc 400s ...and there both worked .30 over , flat tops , big cam and i was told that those crank's had to be external balanced ....of course i wanted to know why ...the reason i got was because of the size of the crank's web at the journal... that not enough weight could be added or taken away...and the proof was the flex plate with the big weight on it ...a long with the big front balancer...i was'nt sure one way or the other...but if chevy put it there must need it ....hopefully we will both learn something as the thread turns... good luck..jb

Just curious as to why you were told about not int. balancing a 400 crank? Eagle sells an int. bal. forged crank for 383 and 400.

[troy-curt]

3500 RPM it should be fine. Will you be using a RPM kill switch?

You will get better all around performance and longevity if you balance all revolving parts.

Troy

[TroyBoy]

Originally Posted by troy-curt

3500 RPM it should be fine. Will you be using a RPM kill switch?

You will get better all around performance and longevity if you balance all revolving parts.

Troy

I agree with above except why you need a RPM kill switch?

[joseph brown]

Originally Posted by TroyBoy

Just curious as to why you were told about not int. balancing a 400 crank? Eagle sells an int. bal. forged crank for 383 and 400.

i was at a local speed shop and i just relied on the owner's knowledge..both engines perform.. well but i wanted torque as well as horse power..maybe my needs and use made the difference...i have more power than i expected,,at a price that was easy on the wallet...jb

[IanRiordan]

I've got over 70k miles on my ext balanced 406, I'm updating the top end with 220 cc iron heads and bigger intake so I pulled the sump for a look. The main and rod bearings are still like new and the end float is 3.6 thou like it was when new.

[johnsongrass1]

Either one is fine. The internal balance means you increase you replacement part inventory.

[joseph brown]

Balancing the rotating mass ...i get it ..always did ..how to balance.... get it....always did...what i don't get is if the big bowtie maker balanced all of the sbc's from the 265 to the 350 internally.... then comes the 400 and they balance it externally which adds a lot to the manufacturing cost ....new parts to make ..a flex plate ,a flywheel and a damper,and they did this because it was not necessary..that i don't get...can someone explain this to me..thanks jb...

[IanRiordan]

Not enough room in the crankcase for the big counterweights that most manufacturers like, same with the 454. Strokers require skilled labour to check. It all costs.

[jimdavis]

There are tens of thousands of high performance 383's on the road with externally balanced engines. The engine is still correctly balanced. You just have some of the bob weight on the damper and the flywheel instead of on the crank. There is absolutely nothing wrong with this. I was at one time involved in a project street rod that was running a 500 hp 383 with external balance. We ran it at the drags on a number of occasions turning it well into the 7,000 rpm range. The car ran low tens at 130 mph and that was 15 years ago and the same engine is still running flawlessly. So I think you needlessly concerned about the internal/external balance issue.

[joseph brown]

first thanks for the reply...ok the 383 is internally balanced,,,can you balance a 400 internally and is the bob weight heavier than that of a 383 and as always thanks jb

[jimdavis]

I believe that any externally balanced engine can be balanced internally. It is a little expensive because the mallory metal used to weight the crank is pricey. Plus the time it takes to do it can add up as well. Unless I am mistaken, a 400 crank is used with a smaller bore to make a 383 so the cranks in the two engines should be the same and can be internally balanced.