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How Balanced are you?!?

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14K views 43 replies 20 participants last post by  modaddict  
#1 · (Edited)
In recent months we have found out that many people rely on the factory balancing of brand new cranks in their engine builds. This was determined by disasembling several dozen built engines over the course of the year and noticing the cranks are untouched and not within a performance spec. or speaking with some of the people that have admitted to doing so.
In a recent production run of our crate engines I decided to put together an analysis of how well or poorly the factory crank is balanced. Without getting too technical on the ISO / SAE Tolerance formulas for balancing a crankshaft, I am going to show what the factory shoots for.

The factory USDM STi crank weight averages 20#'s
I used a 7200RPM rev limit in the formula.
At this weight and RPM the tolerance formula determines the tolerance is 3.8grams per inch.
The crankshaft correction radius is measured at 2.8".

Giving us a 1.3grams of tolerance or better....

In the photos below you will see that the factory tolerance of the four subject crankshafts are within the ISO/SAE tolerance for the factory RPM rev limit for a non-performance built engine.

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When a crankshaft is balanced for performance we use a much stricter Tolerance formula that calculates the tolerance to be no greater then .54grams at the stock RPM limit. This formula determines the factory balance of the crank out of spec. for a performance build.

Below you will find photos of the four subject crankshafts better then the .54grams tolerance.

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At AR Fab we take this formula to the next level by increasing the RPM limit at which the crank is balanced for from 7200rpm to 9500rpm which puts us to .4grams or better.

To take things a few more levels further.... all AR Fab in-house Complete builds get balanced with the flywheel, timing belt cog and harmonic balancer installed.

(BTW of the dozen or so used factory flywheels we have checked or balanced are lucky to be balanced with 5 grams...)

Below are a few photos of the processes taken to balance a crankshaft.

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Even the shop dog, SUBY, gives her paw of approval...

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More to follow!!!!

Howard
 
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#6 ·
Shop animals FTW, definitely!

I think my dog would try eating the metal shavings and using the crank as a chew toy. Sorry for hijacking......

But thats a great little tidbit of info. Keep random stuff like that coming, great stuff.
 
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#8 ·
I was there, today, when he began balancing these cranks. All I heard was "$%^&*!!! The cranks, right out of the box, need work!" :busted:


I walked over to where he was, and I was amazed at how "out of balance" some were. Unbelievable. I know OE cranks aren't "race-ready", but c'mon... You'd think they would be a little closer to spec..


Good job on the balancing, Howard:tup: I guess it's definitely worthwhile to get one from you. [cheezy plug] It pays to have the RIGHT machines to do the RIGHT jobs, in this aftermarket world.. [/cheezy plug] :D
 
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#9 ·
Are these the new crate motors with the new blocks?

<--- Loves the SFI approved crank damper
 
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#13 ·
Great work!

As always, the attention to detail makes your builds worth every penny.

<-- Very happy customer!
 
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#14 ·
Next week I will further this discussion with the balancing of the rods and pistons from the aftermarket companys.

We are going to see how well Eagle speciality , Manley and Carrillo rods are balanced from the small end to the big end and then between each other. And how each manufacturer finishes the rods for clearancing.

Howard
 
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#15 ·
AR Fab said:
Next week I will further this discussion with the balancing of the rods and pistons from the aftermarket companys.

We are going to see how well Eagle speciality , Manley and Carrillo rods are balanced from the small end to the big end and then between each other. And how each manufacturer finishes the rods for clearancing.

Howard
Click to expand...
Sweet.. Can't wait to see that, too! :wave: :tup:
 
Q
#21 ·
 
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#27 ·
Why is anyone surprised that they're only balanced to factory redline? They were never meant to rev any higher. All my stuff from flywheel forward gets balanced to 2000 rpm over intended redline to account for the occasional overrev from a spin of course, mis-shift, etc. I've also overreved twice when a tranny let go under heavy acceleration.

Cool dog Howard!
 
#29 ·
So that machine spins the crank at 9500 rpm? That crank has to be hauling *** on that machine.....
 
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#34 ·
Just an honest question for you - what's the downside to the OEM crank balancing? Everything OEM is a cost - life tradeoff. It seems to me that crank balancing would be independent of HP and only critical if RPM's were over redline (where eccentric forces increase dramatically). And what's your thought on the thousands of enthusiasts (like me) who ditched the damper for a lightweight crank pulley? (again honest question, not picking a fight here!) Are we way out of balance and risking bearing failures?
 
#35 ·
The Harmonic Balancer is not to balance the assembly. It is used to "balance" or "dampen" the Harmonic vibration caused by the twisting of the crank shaft when the compression cycle acts on the crank.

Here is another simple function of dampening or balancing harmonics...


So you have a bad ass stereo system in your car that vibrates the sheet metal causing resonance of every piece of sheet metal in the car...In order to reduce this resonance(which by the way we are trying to avoid this in the crank) is to add a material to help dampen the vibration...so DynaMat is used....its mechanical ability to reduce the resonance freq of something is by adding weight to the panel to change its resonance freq.

Back to the crank....

If you change the harmonic freq that the OEM crank shaft assembly was originally tuned for you will come to a point that the twisting of the crankshaft will start to resonate at its natural resonant freq. and the start of this is bearing failures which look like oil issues then bent cranks and if it gets that bad then broken crankshafts...

Having an aftermarket style Harmonic Balancer offers a broader range of freq. it can balance or dampen. The factory balancer is very limited and the design was never intended to spin higher then factory rpms. The LW solid Aluminum offers no harmonic balancing at all....which will ultimately reduce the life of your engine.

Back to spin "balancing"....we balance the rotating assembly so we can reduce vibration caused by being out of balance..not by the twisting force of the crank. The crankshaft is balanced within SAE or ISO spec which ultimately ends up within the parameters the factory has told the person balancing the crank shaft...these parameters are primarliy weight and rpms. Both of which, in the performance world, change from the OEM specs.

In short...

The Rotating Assembly Balancing is to reduce the vibration caused by out of balanced parts.

The crank shaft balancer is to reduce the vibration caused by the twisting of the crank.


Howard
 
#40 ·
Ryan,

I'm sorry for the confusion on the Mustang...I read someone else sig. But realized it as soon as I posted so I removed it...but you were on top of your game and caught it before I edit'd mine...which was 30 seconds later!!!

I'm in the middle of copying my balancing information off this thread and re-writing it with updates for the web-page for reference.

42K on a stock block with a GT35R.... sweeeeeeet for you...baaaaaad for me

Some people just get lucky with the engine that Subaru supplied them and have a great tune. I am sure you will find when its time to rebuild your engine will be completely worn out! LOL No rings left No coatings left on the skirts...hell you will be lucky to have valves and seats left.

Love the boat! and the Fish! I have a JetSki and a JonBoat... Now I need some time to get the two together.

Howard

AR Fabrication
AR Fabrication, 540-722-DYNO, High Performance Engine Design & Assembly in Winchester, VA
 
#42 ·
AR Fab said:
Ryan,

I'm sorry for the confusion on the Mustang...I read someone else sig. But realized it as soon as I posted so I removed it...but you were on top of your game and caught it before I edit'd mine...which was 30 seconds later!!!

I'm in the middle of copying my balancing information off this thread and re-writing it with updates for the web-page for reference.

42K on a stock block with a GT35R.... sweeeeeeet for you...baaaaaad for me

Some people just get lucky with the engine that Subaru supplied them and have a great tune. I am sure you will find when its time to rebuild your engine will be completely worn out! LOL No rings left No coatings left on the skirts...hell you will be lucky to have valves and seats left.

Love the boat! and the Fish! I have a JetSki and a JonBoat... Now I need some time to get the two together.

Howard

AR Fabrication
AR Fabrication, 540-722-DYNO, High Performance Engine Design & Assembly in Winchester, VA
Click to expand...
Yeah I'll have to assume I'll crack a ringland sooner or later. Coming from a background of working and maintaining cars.....I'd say imma bit anal when it comes to my own.

I plan on replacing the valves anyway so they can be junk and I'll be ok with it. I am hoping to reuse the seats with a fresh grind. Of course, a little measuring and inspecting will tell all.

Cam prices are coming down.......has me intrigued. This really isn't my DD anymore.

The boat is 100% fun. I'm a ******* in a past life that was born to fish.

AR Fab said:
The thread was originally a Vendor only thread...then it magically vanished!

Howard
Click to expand...
Well, it's probably best for all.

Too bad I wasn't able to read it. ;)




A real interesting thread over on Nasioc. I'd love to see your input
Flow Data? .5mm vs 1mm oversized valves and/or porting? - NASIOC

I can only imagine the parts (heads/valves/valvetrain/cams) you have in that 5500 cc'd injector fuel guzzler. :wow:
 
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#44 ·
That head package is pure secks. those ports look huge :eek: Thanks for the info.
If you have time, shoot me a PM. I understand you're busy and I also understand secrecy.

I look forward to updates on your beast.
 
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