http://www.magnusmotorsports.com/eng...et_Crankshafts

I assumed these harmonics were just part of the inline 4 cylinder design, so why didn't Mitsubishi "reengineer the crankshaft" when designing the 4G63 Engine to remove these harmonics as it would have saved manufacturing costs and mass from the rotating system.......?

And to those who say, well that was like 20 years ago......the new Evo motors still feature balance shafts, correct ?

 

Yes of course the EVO's 4G63 still has balance shafts. However, just about everyone who builds them, removes the balance shafts. I think I may in the future as well.

 

Balance your rotating assembly and you don't need balance shafts. Guess it would of cost mitsu more to balance the whole rotating assembly than just putting the 2 balance shafts in, or wouldn't of done the job enough for picky evo drivers.

I have no balance shafts in my motor but the rotating assembly is balanced. Thing spins great with not a bit of increase in vibration.

 

Magnus is talking absolute rubbish.

You can engineer a crankshaft to better deal with harmonics that arise from motion of the the reciprocating and rotating assembly as a whole (not of the crank shaft itself).
You can reduce flexibility and/or increase strength of a crankshaft and reduce bending or torsional vibrations of the crankshaft itself.

But you cannot "remove" harmonics entirely in an inline 4 that does not have balance shafts.

 

Those that consider removing the balance shaft should drive and spend some time in a car that does not have one.
Do not go by someone else subjective feel.
while the vibration may not be very harsh it does add quite a bit more resonance in the vehicle and if it's your daily driver then it would not be a very fun car to be in.
Vibration most noticeable between 3000-4000rpm

 

the hormonics from my motor between 3k-4k make my knock sensor freak out as well

 

3K for a crank.... WTF are they smoken.

 

If you've ever priced a custom crankshaft cut from billet, plus the additional costs for crank preparation, you'd not post an uneducated opinion like this. Go do some comparison shopping, after you read the description and figure out what Magnus is offering.

A billet crank is not needed by the vast majority of DSM or EVO owners. Magnus does not try to sell them to someone making 400 horsepower, I expect. If you need one, you'll not ***** about the price. If you don't need one, keep walking. Nothing here to look at.

 

Eagle does the billet crank from the same grade of steel, just without the fancy 'engineered removal of harmonics' strings attached to it, for $750US.

I understand the principles of balance shafts which is why I can't understand how you can remove them via the crankshaft..............

So anyway, I plan on keeping my balance shafts personally, but will be closely researching the tolerances to run its bearings at different temps and pressures along with changing its belt every 5000ks'

 

That is where you have a fundamental misapprehension of crankshaft manufacturing processes. Eagle does not offer a BILLET crankshaft. Eagle's crank is a forged blank. Their ad copy states "These forged 4340 steel crankshafts from Eagle Specialty Products are great for high-performance applications. They feature non-twist forging, go through a multi-stage heat-treatment process, and are stress-relieved and shot-peened. These cranks are X-rayed, magnafluxed, and sonic tested, so you know you're getting a top-quality piece. Each crankshaft has cross-drilled and chamfered oil holes for improved oiling, a .125 in. radius on rod and main journals for increased strength, and the journals are precision-ground and micro-polished to less than 5 RA. A target bobweight of +/- 2 percent greatly reduces balancing time." After you've bought the Eagle crank, there's still additional cost in getting it ready to use, although probably not $2000 extra in a "normal use" build.

Eagle cranks are FORGED, not BILLET. A billet crank starts with a complete billet of the diameter needed to produce the crank. Say 250 lbs or so of uniformly created steel. Then cut off what isn't part of the final product with a CNC lathe. That's about, say 7 times the material that a forged crank starts as, and you can't use much of the steel that's cut off, since it's in very small shavings This is a VERY different process, and dramatically more expensive to manufacture.

Second, crankshafts has a natural resonance frequency that is a function of their physical characteristics. There are lots of descriptions on the web about this, but you can see one, for example, here: http://www.epi-eng.com/ET-TorsAbsrbrs.htm The shape and mass of the "counterweights" is an important part of tuning the crank to avoid resonance in critical frequencies. You'll notice that the Magnus billet crankshaft is very different in shape of the counterweights than a forged factory or Eagle crank.

I'm just pointing out that you're looking at very different products, with different price points, based on what they cost to create. Each has their natural advantages, but they are not the same product. That's the point -- the Billet crank is not manufactured or offered as an alternative for a 400 or 500 HP stroker build -- it's a high cost, high capacity crank to solve a problem that exists from 750HP up... people who have built those kinds of motors know what their crank modifications cost to keep them together, and don't mind paying for a better option. If you were aware of Magnus' history, you'd know that they have been building 9 second 4g63s and strokers for a number of years before EVOs were available in this country...

 

Ok, yes thats one thing I didn't notice, one being billet and the other forged........and yes I know the CNC run-time per hour is quite high. If we knew how many degrees the crankshaft bends at cxertain power levels compared to the forged Eagle or Factory, that would be beneficial in selling their product.

 

People removed BS from DSMs because they rob a little oil pressure. Also by not having the BS belt you lessen the chance of it coming off, snagging your t-belt and ruining your engine. The increased oil pressure also helps alleviate the chances of CW on 7-bolts. So it is just added insurance for a built engine.

It was my understanding that this has nothing to do with crankshaft harmonics. Your crankshaft has to be balanced no matter what, and having balance shafts or not will not change that fact, or affect the engine harmonics internally. The inherent qualities of a four cylinder engine make using BS belts a good thing for a smooth revving engine, regardless. If your crankshaft is not balanced your engine will be toast soon enough regardless of wether you have BS or not.

Since Evos are no prone to CW it might be best to leave them in on a mildy built street car, but then again those types of applications aren't why Magnus developed this piece.

 

The Balance shafts are not there to balance the crank

I respect your knowledge CO_VR4, but I'm not try to get rid of/change the crankshaft resonant frequency.

This is only about the physical constraints of the inline 4 cylinder design.

The only way the balance shafts are even remotely connnected, is that the imbalance the removal of them introduces, may resonate the crankshafts resonant frequency and thus damage things sooner then later.

The imbalance will always be there, but because it may not resoante the crankshaft, it isn't as bad as it could be.

 

They're not the same product but I would assume that the forged stuff is a lot better. Forging usually aligns the grains of the material along the direction of the stress. So the material has greater strength along one direction (hopefully the direction it's designed to take loads in) than other directions. In most cases the CNC time is the biggest factor in cost unless you had a special blank made and/or it's a special material (ie a 3' by 3' by 3' piece of titanium). And sure the coating and other stuff matters too but from the description alone the Magnus stuff is expensive because of the CNC time not because it is really better. The only way to settle this is if Magnus showed a bode plot or frequency vs RPM plot of all the natural frequencies of the stock, Eagle, and their engine. Also note that there's more than one way to move the resonance frequency away from your operating range. Instead of balancing the crank better, you can also add weight, damping, or increase polar moment of inertia (so in essence worse off in every which way). There's no "balanced" crankshaft. You're just physically moving the resonance away from your operating range (either up or down in frequency) and hopefully decreasing the amplitude.

Sure tuning for resonance frequencies is a more elegant solution than a balance shaft but at what cost? The cost benefit ratio and lack of reliability probably doesn't justify removing the balance shaft. It's like kids on this forum getting carbon fiber mud flaps and other dumb **** and claim it's for weight reduction. I like carbon as much as anybody else but it's worthless in terms of performance gains. Ferraris are flat plane v8 (no balance shafts ) and while they sound awesome and rev fast as hell they are also unreliable and expensive. If you want to beat the crap out of your car and maintain reliability keep the balance shaft.

 

Actually, balance shafts do not "rob" oil pressure. The main reasons that balance shafts are removed are (1) to eliminate the very common breakage of the balance shaft belt, which would cause the timing belt to jump time and destroy the valvetrain, and (2) eliminate about 9 lbs of driven rotating weight. The increased oil pressure was actually a downside to the balance shaft elimination, and a solution involved porting the filter housing relief port to permit excessive oil pressure to be reduced and the pressure relief valve to operate properly. There remains a discussion about whether the balance shaft on the back of the oil pump should be "turned down" or replace with a billet shaft to support the back of the oil pump, or whether just replacing it with a stubby shaft, as is supplied in the balance shaft eliminator kits, is just fine. Most just use the kit with the stubby shaft, which is also a Mitsu factory part, albiet for another vehicle...

It has to do with resonance harmonics, which are a function of both the crankshaft design and manufacture and other rotating parts. The balance shafts rotated in counterweight to the crankshaft (and to each other) to cancel out the inherent harmonics of the crankshaft and rotating pistons/rods. You can balance the crankshaft perfectly, but every crank will still have an inherent harmonic, just like every bell will ring when you strike it. If the crankshaft is not balanced, it will also have vibrations caused by the imbalance, IN ADDITION to the natural resonance vibrations and torsional vibrations. The Mitsu factory crank has natural resonance too; the balance shafts simply cause the driver to feel it less.

Balance shaft removal had nothing to do with crankwalk. Evos are not known for crankwalking (like the 2g DSMs), and if you want a smoother feeling engine, that's what balance shafts were designed to accomplish. The risk is that the balance shaft belt will break and take out your timing belt and thus your valve train. That risk can be mitigated by changing the balance shaft belt more often than the factory intervals, but it cannot be eliminated unless you just remove the balance shafts. The tradeoff is the natural resonance "buzz" will be more pronounced, because it is not being offset by the balance shafts...