External or internal balance?

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bricud

bricud

Cuda's Cuda
Joined
Jun 22, 2022
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I am in the process of building my new 408 stroker engine. Just got the block back from the machine shop and I know it is .030 over so now it is time to order the rotating assy. The question is to have it balanced or not. Since I am building from scratch, I can go either way, but I just dropped the transmission off at the shop and should tell them if the flywheel/torque converter should be weighted or not. Is internal balanced or external balanced better in general, or does it really matter, assuming you get the right combo with the rotating assy chosen.

So, I understand that if I go with a balanced rotating assy, I need a zero weighted torque converter/flywheel and harmonic balancer. If it is not balanced, I need a counterweighted converter/flywheel and harmonic balancer. Just want to make the right choice. This will be an engine rated at appx 500 hp/500 ft/lbs torque, if that matters.

Thanks,

Brian
 
Either way, its still balanced, just balanced differently.
And yes, you need to have it balanced with an all new rotating assembly. Go with the style that allows them to balance it with the least amount of Mallory metal- that stuff ain't cheap...
 
I guess I haven't heard how close the balance is on those pre balanced stroker kits. I bet they have done so many they don't balance each one individually but just make all the components the same. Just guessing.
 
If you have a choice and can afford it, I would internally balance it. It's a whole lot easier to find replacement parts. Have all the rotating parts balanced regardless if you choose internally or externally balanced system. This includes the balancer and torque converter. (or flywheel, clutch, pressure plate on a manual trans car)
 
If given a choice I'd go with internal balance. The one stroker I built I bought the induvial pieces as a "kit" was available for the options I wanted. Had my machinist balance it for me. My dad bought a Scat 408 kit that was "balanced". After he got it running that thing shook worse than some of the stock stroke motors we had in the past that we bored .030 stuck pistons and rod bolts and slapped together. He ended up taking it apart and had my machinist balance it and now it's smooth as can be. My old machinist would just take weight of 1 piston and rod and then balances the crank for that. My new machinist makes all the pistons, rods weigh the same and then balances the crank and it makes a world of difference.
 
It might be wise to verify that the pistons in whatever kit you get are compatible with the current measured .030 over diameter. My understanding is that there are different clearance tolerances for cast vs forged pistons. I think it is usually preferred to have the desired piston on hand and cut the bores to the parts, but that isn't always achievable.
 
Talk to @PROSTOCKTOM. He can fix you up with everything you need stem to stern and already balanced however you like it. That guy is top notch and has great deals. I only wish he had slant 6 stuff. lol
 
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