[vinniekq2]

thanks Mr P-body,I thought the high RPM process wass called under balance do to the other ends being slightly lighter,,,,,,I send clutch parts not to be balanced but to ensure the factory did a decent job, I also send my flex plate/flywheel for the same reason.I do take my engine builds above 6000 RPMs,even my 434 can rev to 7k.

[zildjian4life218]

Originally Posted by Mr. P-Body

Most aftermarket forgings ARE "internal". Most castings are not. All of them can be "converted" using Mallory Metal (tungsten) as stated. Not cheap to "convert".

Many shops with a balancer have "on hand", stock 400 balancer and flexplate. We have a Pontiac flexplate that "lives" at the balance shop for this purpose.

The "bolt on" weight is popular among the 383 "crowd" because it allows the use of the "zero" flexplate or flywheel (they usually already have a 350 piece).

The clutch "cover" (pressure plate) is often attached during balancing for manual transmissions. Not used in automatic applications. With modern manufacturing techniques, this has become less an issue than it was 20 years ago.

Lastly, some "myths" about balancing. SAE "standards" are that the rotating assembly is balanced to within 1/2 of 1% of the total rotating "mass". In a 383, that amounts to about 28 grams. Most balance shops routinely balance to within 1 gram, FAR exceeding standards. The slight variations from using different "stock" balancers and flexplates/flywheels are not significant.

For higher revving engines (over 6,500), often "over-balance" is included. That's where the factor for the bob weight is changed from 50% (reciprocating) to a little higher percentage to offset the downward "thrust" under hard accelleration (engine speed, not car speed). High-end "big" engines usually have an over-balance of 4-5%.

FWIW

Jim

Awesome reply! He has an aftermarket cast crank that is externally balanced. So does he need the 400 harmonic balancer along with the flexplate?

[2old2fast]

Best reply I can give is ---check w/ the manufacturer..

dave

[bigdog7373]

Originally Posted by zildjian4life218

Awesome reply! He has an aftermarket cast crank that is externally balanced. So does he need the 400 harmonic balancer along with the flexplate?

Yes 400 flex plate and balancer. This has been said multiple times.

[68NovaSS]

Originally Posted by CNC BLOCKS NE

OHHHHH yes it does as the 5.7 rod crank uses shorter counter weights and in most cases they are extrernally balanced.

A 6 inch rod crank uses bigger or taller counter weights and can be internally balanced.

Thats why all OEM 400's with their short rods are externally balanced.

I understand that, what I was referring to was using a 5.7/6.0 rod on an aftermarket stroked crank, say 383, using the appropriate pin height pistons. The poster didn't mention using a particular crank, be it OEM or aftermarket, just the rod being used.

What I don't understand is why you say a 5.7 rod crank is usually externally balanced, case in point, a stock, internally balanced 350 Chevy uses a 5.7 rod.

[Mr. P-Body]

I've never seen any correlation between rod length and "type" of balancing. The application usually determines the type.

The flexplate or flywheel AND the balancer MUST be physically attached to the crankshaft during the process if "external". It's not uncommon to spin a crankshaft without the balancer and flexplate/flywheel if "internal". The balancer and flexplate/flywheel can be "spun" independently and checked for "zero".

Jim

[oldbogie]

Originally Posted by zildjian4life218

Awesome reply! He has an aftermarket cast crank that is externally balanced. So does he need the 400 harmonic balancer along with the flexplate?

Yes!

The aftermarket 383 stroker cranks that use external balance are made to also use the 400's damper up front and flywheel or flexplate at the rear.

Bogie

[CNC BLOCKS NE]

Originally Posted by 68NovaSS

I understand that, what I was referring to was using a 5.7/6.0 rod on an aftermarket stroked crank, say 383, using the appropriate pin height pistons. The poster didn't mention using a particular crank, be it OEM or aftermarket, just the rod being used.

What I don't understand is why you say a 5.7 rod crank is usually externally balanced, case in point, a stock, internally balanced 350 Chevy uses a 5.7 rod.

I think the OP is talking about a 3.750 stroke not a 3.480 stroke big differance between the two.

[68NovaSS]

Originally Posted by CNC BLOCKS NE

I think the OP is talking about a 3.750 stroke not a 3.480 stroke big differance between the two.

I have a 3.750 stroke aftermarket crank in my 383 blower car, with 5.7 rods, and it's internally balanced, it can go either way, no question about that. I'll assume from your post, an OEM 400 crank doesn't lend itself to internally balancing.

[CNC BLOCKS NE]

Originally Posted by 68NovaSS

I have a 3.750 stroke aftermarket crank in my 383 blower car, with 5.7 rods, and it's internally balanced, it can go either way, no question about that. I'll assume from your post, an OEM 400 crank doesn't lend itself to internally balancing.

I have internally balanced 400 cranks its very costly but it was for a cheater circle track engine.

I have seen a few 5.7 rod cranks that will internally balance but most seem to be internally.

All the strokers I build I use 6 inch rods better rod ratio, less piston hanging out of the borre at BDC, liter piston, internally balance.

[2old2fast]

Bogie , Sorry , but all aftermarket are not external/external ! Strokermotors lists 3 different scenario's- Int/Int-Int/Ext - Ext/Ext. Most,but not all 6" rod listings are Int. Most , but not all 5.7" rod listings are int..

dave

[oldbogie]

Originally Posted by 2old2fast

Bogie , Sorry , but all aftermarket are not external/external ! Strokermotors lists 3 different scenario's- Int/Int-Int/Ext - Ext/Ext. Most,but not all 6" rod listings are Int. Most , but not all 5.7" rod listings are int..

dave

Dave, I believe I used the term "that use external balance" the remainder being. "use the 400 balancer". I was not intending to discuss the effects of 6 inch rods versus 5.7 and their effect on crank balance only to clarify that the external balance 383 stroker crank is intended to use, or at least start from, the 400 damper and flywheel or flexplate.

An internal balanced 383 stroker will use the neutral balanced 350 damper and flywheel/flexplate as the best starting point. This will hold true whether the crank began life as an internally balanced with 6 inch rods or and externally balanced with 5.7 inch rods that is forced by the use of Mallory Metal to become an internally balanced crank. Which is to say that the choice of external or internal balanced damper and flywheel/flexplate needs to match the choice of external or internal balance crank.

I am not a big fan of externally balanced engines, while the crankshaft as a whole rotates on center just as it does when internally balanced; there remains a long distance between out-of-plane forces which results in bending moments along the crankshaft. Evidence of these can be seen in the main bearings when the engine is opened up you will typically see bearing shells that exhibit inconsistent wear both within the diameter and across the width. Given that the engine builder needs to understand how much of this is flexing of the crankshaft between bearing bays and how much is lack of alignment through the bearing bores.

Internal balancing eases this situation somewhat but doesn't entirely make it go away. Crankshafts do funny things which is one reason why there is so much counterweight on the ends compared to the inboard throws. Some if this is simply space related where the inboard throws don't have enough space for full counterbalance and some is the tendency of the crank to want to orbit its ends instead of just rotate them on a center. So the big counterweights are king of pulling the ends back to the plane of rotation. The center two throws usually don't have counterweights as all but depend upon their masses in opposition to achieve balance. The problem with this is that there is a lever arm distance between these throws that results is the loads being offset by that distance, this then wants to bend the crank between the number two and four main with number three being a pivot point. This is the reason why 4 bolt and cross bolted mains are found in the middle of high performance blocks. This condition can be relieved by the use of counter weights on the inboard side of throws two and three. But for a street engine this adds cost where it typically isn't necessary although the old Ford Y block crank was weighted here. The extra weight slows crankshaft acceleration so it's usually isn’t found on drag race engines. It is rather commonly found on NASCAR cup engines where constant high loading on the crank requires better bearing bay to bay balance for reduced wear on bearings and less concentrated loading into the block at this point combined with a reduced need for absolute maximum rates of crankshaft acceleration as found in drag engines. There are of course exceptions where some builders feel the aftermarket competition block and crankshaft are sufficiently strong enough to sustain these loads for the needed periods of time and they want the lighter faster to accelerate crankshaft that is more akin to what the drag racers would use.

Bogie

[PatM]

68 NovaSS and BigDog7373
Thanks for enlightening me. When I bought my parts (back 10-12 years ago) the market was more limited, and the vast majority of internal balanced 383 Stroker cranks required the 6.0 rods. This was for the reason that CNC Northeast mentioned, or at least I thought and continue to believe. The Mallory Metal is, of course, an answer for almost anything remotely within reason. But, it is very expensive. And the more you need, the more expensive it becomes. As a result of your posts I went to the Eagle and Scat sites and found a broad assortment of cranks and kits set up for internal balance with 5.7 rods. I have to presume this requires the use of their specified (or somewhat akin) pistons, to clear the counterweights.

Anyway, again, thanks for enlightening me . . And CNC Northeast -- I still agree that for an internally balanced 383 it probably makes most sense to use 6 inch rods . . but it seems there are ways to use those 5.7 inch rods now in an internally balanced 383, without the need for Mallory Metal. I'm sure you knew that already, but I (for one) feel enlightened.

PatM

[lmsport]

There can be a big difference in weight between different rods and pistons, too. Lighter parts make it easier to balance with smaller counterweights.

[PatM]

lmsport
Yeah, so true. My machinist/balancer had to remove a lot of material from the counterweights because of the very light (Lunati Streetrace, no longer available, I think) rods, pistons and pins that I selected. His comment after completing the balance was the the engine should be a "zinger", meaning quick to build up revs. . . . . I hadn't mentioned it to him, but that was exactly what the goal was. Now that I think of it, when I gave him the crankshaft and the value for the bobweights, I don't think he believed me. He asked me to bring in the parts. So I brought in one piston, one pin, spirolocks, one rod, one bearing and a ring set, all previously static balanced. I don't recall the exact bobweight (I think 1668, but I can't swear) but his calcs came out within 1 gm of the value I had given him.

Pat