Lightweight Crank Pulley Check-In

[spoonman]

I have used an aluminum crankshaft pulley on one of my engines for years (4-5), with no ill effects. The car is a DD with around 350 HP. The engine was built with an OEM 6 bolt lightened crankshaft, aluminum rods, and lightened JE pistons (extremely light rotating assembly). It has a very light weight aluminum flywheel also. The crankshaft was properly balanced, believe it or not but I-4 crankshafts do need to be lighted and balanced if you use different rods and pistons. If your machinist try's to tell you that I-4 engines are naturally balanced slap him in the face.

Torsional vibration can not be eliminated but it can be reduced, by lightening the rotating components thus effecting the moment of inertia.




I started using one after stumbling into a thread on NABR with many members using them for YEARS. Although it was still debated as to whether or not using a aluminum pulley would cause catastrophic failure on a properly built engine. If anyone wants to compare the two, put both on an engine dyno and examine the torque figures. If the aluminum pulley has lower torque figures it will be the result of the crankshaft flexing.

. The rotating mass helps launching the car and keeping the revs up when shifting.

Although a heavy rotating assembly does help keep the RPM's from falling off when you shift, a heavy rotating assembly does not help any vehicle accelerate from a stop. This is a very common misconception. Rotating components store rotational energy as well as having to be accelerated in a linear direction. The faster a component rotates, the greater the amount of rotational kinetic energy that ends up being stored in it. The absorption of this energy could be seen as adding more weight to the entire vehicle itself.

 

[viperlp01]

Although a heavy rotating assembly does help keep the RPM's from falling off when you shift, a heavy rotating assembly does not help any vehicle accelerate from a stop. This is a very common misconception. Rotating components store rotational energy as well as having to be accelerated in a linear direction. The faster a component rotates, the greater the amount of rotational kinetic energy that ends up being stored in it.

I have launched a car with a stock flywheel(my car) with an ACT 2600/ ACT disk and one(97 gsx with hx35) with a fidanza flywheel and same clutch components and it was much easier launching the car with the stock flywheel. I don't know if it "makes the launch faster" but it helps me get to car going when I am on anitlag at 5500 rpms in a full weight 2g.

So in a real life situation the stock flywheel always seemed easier to launch on.. Its less prone to bog

 

[ramsack]

Heavy rotating mass does help with launch, and that's it. A heavy rotating mass slows down acceleration, though. It's basic physics. A heavier rotating mass will store more energy for when it needs to be released, but at the same time takes for energy to spin it up in the first place.

The engine is balanced at the factory. If you change components you will have to have it re-balanced. This applies to ANY engine regardless of cylinders. The balance has nothing to do with say a 6-cylinder being perfectly balanced. That is purely harmonics, not the balancing of the components.

 

[spoonman]

Rebuttal!



Replacing a stock flywheel with an aluminum flywheel on our cars is similar to removing 100+ pounds from the vehicle when accelerating from a dead stop. The effect is less dramatic the faster the vehicle is moving.



Heavy flywheels are good for drive ability.

 

[ramsack]

Heavy flywheels are good for drive ability.

And launching.

 

[viperlp01]

So if I put a lightweight flywheel on I will lose a couple tenths in the quarter and 10-20 more horsepower?

 

[ramsack]

I would say it would be more worth it for road racing. I can't say what would happen with drag racing, you may break even from losing launch hardness or not.

 

[spoonman]

Lightening any component that is rotating will not increase the power produced by the engine. But lightening the component will make more of the power produced by the engine available to propel the car forward.

 

[ramsack]

I see what you're trying to say, but it's wrong. If the car accelerates faster, you are indeed making more power. Regardless of flywheel hp, you are still getting more wheel horsepower. It just depends on where you want to measure it. Flywheel horsepower doesn't matter as a way to compare cars because they can all weigh different and have different drivetrain losses or gear ratios. Wheel horsepower matters a little more, but still doesn't factor in weight. At least with wheel horsepower you can easily show power to weight without any other variables needing to be involved.

 

[laserspeeddemon]

Well. OE replacement dampened pulley costs $50. OEM costs $100 which is the same as the OBX lightweight crank pulley cost (2g). The Unortodox costs a tad over $200. And the Fluidampr costs $280. Out of any of these, I've personally never seen more than 8 horspower and that wasn't a fair comparison, because it was a modified car. On the crap end of the stick, I could potentially lose my engine 10 years down the line.

To me the benefit does not outwiegh the risk.

 

[DashLaflash]

Ok when you talk about the vibrations breaking a crank over time doesn't seem to be accurate. I think of a glass shattering from singing the correct note (Same frequency that the glass rings at) when I think of this debate. Unless you sing loud enough the glass will not break. The glass can flex a little and be fine it just can't be pushed to the point of breaking. So it seems that the crank would only break if it rings at the correct frequency severely enough. So i'm kinda thinking if it doesn't break on start up then you would be fine for a good long time. It would take the perfect storm so to speak for the frequency to break the crank (Ex. too much horsepower but Slowboy Joe already said it has handled quite a bit of power).

Also all of you naysayers only have theory on your side. You have not provided one example of an actual crank failure from one of these pullies. The other side however has provided several people saying there is no issue running one of these pullies.

 

[viperlp01]

If our theories don't change your mind then just run it. Whats the worst that can happen. Crank kits are cheap

 

[ramsack]

Unless you sing loud enough the glass will not break.

So more power from an engine doesn't compute to more audio amplitude in your mind?

Also all of you naysayers only have theory on your side. You have not provided one example of an actual crank failure from one of these pullies. The other side however has provided several people saying there is no issue running one of these pullies.

Did someone not post a picture of a broken crank?

Do what you want. It is your car. It seems like you came in here with a set opinion looking for it to maybe be changed, but I think you started this topic to not have your opinion changed. They don't make things like the fluidampr for nothing. Also the types of people that commonly buy these underdrive pulleys are on a cheap budget, so do you really think they will have the time or money to deal with suing the company that made their underdrive pulley?

 

[Calan]

An undampened crank will have more deflection due to torsional harmonics, which directly leads to increased wear on the main bearings. The effect can be more or less pronounced depending on engine geometry and power levels.

Enough cylinder pressure will break any crank if it's the weakest link; an undampened crank is just more susceptible due to the increased harmonic vibration.

I've seen cars run the same timing belt for over 200,000 miles. So is it safe to say that they only need to be changed at 200,000 miles because 1 or 10 made it that far? Or do you use some engineering and a bit of theoretical MTBF (mean time between failure) data, and recommend changing them at 60,000 miles?

Engineers spend lots and lots of hours with their heads in books for a reason. It's up to you if you want to tempt the laws of physics, or trust what the math tells us.

 

[donniekak]

Heavy flywheels, and large torsional dampers, actually help cars running high rpm's. The rotational speed measured in rpm's is an average of the fluctuating rotational speed of the crank. IE, the crank is spinning faster right after tdc on a power stroke, than right before tdc on a compression stroke. This whipping and slowing down of the crank is transfered to the valve train, and can lead to premature valve float. Anyone who has watched a crank, or cam twist, and untwist under a strobe, knows this. Much can be learned from the v8 nascar guys, turning 10,000 rpms for 500 miles.

 

[DashLaflash]

Well its clear I sparked another big debate over the lightweight crank pulleys without really solving anything. I didn't wan't the thread to get all cluttered with opposing opinions but I guess there is no way around that. I just wanted people to post their experiences with using one not the possible problems it can cause as there are many threads already containing that information. In the end I guess its all a matter of what each person wants to believe. I already bought the autozone stock crank pulley and I'm sure it won't last very long. I don't like the underdrive pullies because of the strain they put on the accessories. If I ever decided to get one it would be a stock size aluminum pulley. In the end I will most likely buy a new OEM one unless I decide to get brave. I just don't want a stock pulley coming apart and possibly taking out my timing belt.

People should continue posting their personal results with using one of these pullies.

 

[viperlp01]

Not many big horsepower guys run them because of this exact debate. Almost everyone that I see putting up big numbers are running an ATI or other type of dampener.

 

[DashLaflash]

Ya I really hate this debate . I just hate how a company like unorthodox says its totally ok to run one but fluidampr says its better to have one of theirs. Both companies are trying to sell you a product so who are you supposed to believe. Unorthodox has been selling these for 13 years it says it right on their site. I don't see how somone could make a product that's so dangerous for an engine and get away with selling them for so long if that were really the case. Believe me guys I like taking care of my engine I just have never really seen any hard proof that the lightweight pulleys cause damage. In the end I guess it would be best to get a fluidampr as they are around double the cost of a new oem pulley but will last forever and haven't had any bad reports that I know of.

Here is a thread I found where a guy posted actual pictures of his bearings after 50k miles of having an unorthodox crank pulley installed. The car was driven hard many times and he said the bearings seemed to have fairly normal wear. Let me know what you guys think, if this sways the argument one way or the other.

dsmtuners.com/forums/bolt-tech/145566-main-bearings-after-50k-##-underdrive-crank-pulley.html

The two ## in the link are the the letters U and R. Dsmtuners automatically edits it out because its improper grammer so hopefully you guys can get the link to work.

 

[ramsack]

Just because other cars can get away with having a solid pulleys doesn't mean it's good for the 4g63. That's what most of us are saying. There are indeed engines that come OEM with solid pulleys. Since the 4g63 is damped from the factory, then if it was me, I would stay with a damped pulley.

 

[bmoha2]

I went to a Fluidamper crank pulley and haven't had a problem since. I'd never put a stock back on my car. I might wear an unorthodox pulley on a chain around my neck but I'm sure as hell not putting one on my car

 

[turbo addict]

I love to argue, so....

You could say that our motors came with motor mounts that were designed to flex to allow the motor to move and that installing prothanes or solid mounts is against the factory setup and bad for the motor (undue stress).

Same goes with the brackets on the intake manifold, TB, and downpipe. (these are the parts that everyone throws out). You could even say that 2g's were designed to run 10-12 psi as the wastegates were set to open there and the bov from the factory will leak if you try to run over 12ish- psi. So the 2 things that would or could control boost are set to keep the boost to 12psi. Why would you go against this as this is how the factory designed it.

I run a ebay special pulley that cost me $20shipped. It has worked fine I rev the car to 8800rpm, and 35+psi. It was one of the first things that I had done to the car as mine was on its way out (almost broken) this was in 2002 and over 50,000miles. it is still on the car with no ill effects.

 

[Calan]

You could even say that 2g's were designed to run 10-12 psi as the wastegates were set to open there and the bov from the factory will leak if you try to run over 12ish- psi. So the 2 things that would or could control boost are set to keep the boost to 12psi. Why would you go against this as this is how the factory designed it.

Anyone with common sense wouldn't...without properly modifying the car to support the additional boost. And this has nothing to do with the stresses that a rotating 4G63 crankshaft sees and why it needs to be dampened.

I run a ebay special pulley that cost me $20shipped. It has worked fine I rev the car to 8800rpm, and 35+psi. It was one of the first things that I had done to the car as mine was on its way out (almost broken) this was in 2002 and over 50,000miles. it is still on the car with no ill effects.

Congratulations and I hope it continues working for you. This also has nothing to do with whether or not it's the "right" thing to do, but it is a good example to show that everyone gets lucky sometimes.

 

[turbo addict]

Anyone with common sense wouldn't...without properly modifying the car to support the additional boost. And this has nothing to do with the stresses that a rotating 4G63 crankshaft sees and why it needs to be dampened.



Congratulations and I hope it continues working for you. This also has nothing to do with whether or not it's the "right" thing to do, but it is a good example to show that everyone gets lucky sometimes.

it wasnt suppose to have anything to do with the crank, just a point in modding. reving the car higher is going to change the dynamics on the crank though. the point is that you could say that everything that we do to these cars is not in the best interest of the car. But with proper maintenance you are going to increase the odds of stuff not breaking. But modding the car to make more power will shorten the life of the car.

As a side note I have a built car that I am putting together, with a twin disk and that I will be pushing harder than my DD, that I have a fluidampr.

the machine shop said that I would most likely be fine if I balance the motor with the solid pulley, but with the money and stresses I'm going to just use the fluidampr.

a better arguement would be leaving in the balance shafts as they are there to equalize the crank vibrations.

as I said I Just like to argue;-)

 

[ramsack]

it wasnt suppose to have anything to do with the crank, just a point in modding. reving the car higher is going to change the dynamics on the crank though. the point is that you could say that everything that we do to these cars is not in the best interest of the car. But with proper maintenance you are going to increase the odds of stuff not breaking. But modding the car to make more power will shorten the life of the car.

As a side note I have a built car that I am putting together, with a twin disk and that I will be pushing harder than my DD, that I have a fluidampr.

the machine shop said that I would most likely be fine if I balance the motor with the solid pulley, but with the money and stresses I'm going to just use the fluidampr.

a better arguement would be leaving in the balance shafts as they are there to equalize the crank vibrations.

as I said I Just like to argue;-)

Revving a car higher does not change the "dynamics" in the crank. Only changing components around do. Things like fluidamprs are some of the best things for an engine with aftermarket stuff because the forces change and the frequencies that need to be damped change, and fluidamprs are not just set for one frequency. Balancing has little to do with the torsional flex that a crankshaft takes!

The balance shafts are there for comfort. They are called silent shafts, technically, and not balance shafts.

 

[pboglio]

From my understanding, you can have a highly balanced dynamic rotating assembly, but the inertial forces are only part of the total force loading, the other part is the forces generated by the cylinder pressure. That goes up with an increase in horsepower and I can't see how you can counteract any harmonics with a solid pulley hub design.

I'd venture a guess that the inertial ring mass and MOI and rubber cross sectional area where designed and tested to absorb the most severe harmonics or critical resonance points. Whether that was done to reduce NVH or actually save the rotating assembly is open for debate. For sure no-one here is a NVH powertrain design engineer, my point is there is so much that goes into a design that we don't have access to, yet clearly there is some pretty compelling info out there.

If your rocking 400 w.h.p., is another +8 w.h.p. going to make a difference. For me, no way. I'm thinking of ways to increase reliability, and this one is so questionable.

Interesting article I read in race car engineering about chopping down the crankshaft counterweights. From a top WRC team manager, they pretty much admitted the dynamic imbalances greatly increased bearing wear and was a pros vs. cons type mod. Makes you think.