I duped this from my post at tt.net I was searching through some posts on here about over-balancing/balance factor for the crank etc and read the following: "The Z doesn't have a harmonic balancer, the crank is internally balanced which means there is no need for one." I am confused about this because most threads I read on aus300zx include 'harmonic balancer' 'vulcanised rubber' etc when talking about the crank pulley. My car is a j-spec and when I posted a question about balance factor/over balancing, no one knew what I was on about. I am in the process of getting the entire bottom end balanced. I was curious about what sort of balance factor most people used with their setups that are making about 400+rwkw @ ~5800-6000rpm? What parts have they used? I couldn't find much on search besides ash'z post. I read that ashz was balanced with a factor of 47%. What is the standard factor? p.s if you read this mike c, thanks again!
Hi Method This is from TTNet. It kinda explains both points, you balance the engine by modifying the balancing weights on the crank, So when you put in lightweight pistons, the counterweights on the crank need to be changed/reduced to exactly match the opposing piston weight. I think they put the shortblock together (pistons, rods, crank, flywheel, pulley, all the rotating parts) then balance. 47% is probably how much Ash had to take off the counterweights to match his lighter pistons, your reduction would be specific to your setup. This is also why I argue that the underdrive pulley does not need a harmonic balancer if the engine is properly balanced. If the balance is out slightly (common in mass production lower quality engines) then a harmonic balancer will absorb this. Proper balancing will give reliability and more power and considering how expensive the parts are I would think it is well worth the bucks. Cheers Mike C
I had mine balanced even though I kept stock pistons.. probably a waste if they're balanced from the factory.
Usually they weigh each part totally independantly and shave etc to ensure that easch piston, rod, cap bolt etc etc etc is within a certain tolerance of the rest this is called ? (static maybe) balancing there is also another form they do which is assembled balancing which is done while rotating the crank assembly (dynamic maybe)sort of like wheel balancing cant remember the specific names though. For a high rpm or hp engine spend every last cent getting it right though Method as most of the parts usewd will run tighter tolerances than factory parts so balancing becomes all that more important. I am taking my assembly to a few different engine builders to have it done when its ready as I dont trust anyone 100% to do the job correctly.
Actually, a lot of aftermarket parts use larger clearances than factory. Factory piston pins for example, say 2-7 tenths of a thou, crower informed me that that would sieze up almost instantly when using their rods and gave me the correct specs to use. Usually aftermarket (forged) parts, need bigger clearances as the parts expand a lot more than cast parts. Also, in regards to rods, the factory ones are forged but I don't think the material is as strong as most aftermarket quality rods which is also why they can get away with using lower clearances, likewise with pistons etc.
Thanks for that mike, I know the counterweights have to be matched up to the new mass of each piston, pin, clip, and rod but why do people over-balance? I was thinking that you can balance the crank to be perfect for a specific RPM range.. say if everything is balanced in conjunction with each other, it might be 99% balanced at 5000rpm, but if you were making peak power at 6000rpm, you would over balance so that at 6000rpm, the engine is at 99% balance? Could you also elaborate on why there is no harmonic balancer needed? Why is the stock pulley using rubber? Aren't all engines balanced at the factory, and all come with harmonic balancers? Thanks again
yeah.. took my flywheel etc in especially for it to be done but I dunno how an already balanced flywheel would make a difference.
I asked around about overbalancing and got the same answer either its balanced or its not. No one had heard of overbalancing. One side is the pistons etc, the other side is the counterweights. No matter how fast you spin surley either it is balanced or not? Most engine balancers weight all the items ie pistons etc and shave try to get as consistent weights as possible so less balancing is required when the do the final assembled balance. The flywheel is part of the process as you need to balance both ways, i.e piston vs counterwieght (top vs bottom) and then front v rear - so to make it as smooth running as possible. But getting a bit out of my depth here. Re underdrive there are two schools of thoughts --- Destroying the world in your Z32 --- underdrive pulley install TTZ's of Dallas --- The Danger of Power Pulleys & Understanding the Harmonic Damper article By Steve Dinan some BMW engine builder Plus I personally have run my first engine for three years with underdrive no prob, new engine for one year no prob. So I will take the cheaply otained horsepower any day .
Thats what I thought Mikec(nz) re balancing thats interesting about the pulleys and balanced rotation and makes sense when you think about it. Does anyone know if the NISMO spec cranks for the VG30dett differ much from stock and worth the money.
They don't balance it fully assembled as there's no way to do that. They measure the weight of each piston, rod, etc, and modify to make them equal. They'll then modify the counterweights to correspond to the mass of the pistosn+rods. Then they spin the crank up to peak rpm and make sure its balanced.
I suffered bearing failure, although I don't think it was from the UDP. It happened way after I installed it, and I would say that I had crap in my oil, going by what I saw on all of the bearings. I inquired about an ATI pulley, but they seem to have to be rebuilt very often, and also a lot of people have ordered them and never received them.. fischer isn't around any more either apparently. I might go stock, or buy a new UDP, not sure yet. About the over-balancing, the team that are balancing my stuff said that 90% of people who deal with balancing wouldn't have even heard of over-balancing, so I guess they were right going by what you said. I am going to try to get some more answers on this, as they definately aren't talking rubbish. When I find out some more info, I will let you know.
Why change the crank? If I was going to go a stroker kit, I would get a custom crower one and forget about the nismo one. I still think it is completely useless to go to that effort on a VG engine, i.e. stroker kits. Money could be much better spent on other things, or better spent on a better engine than the VG. But if that's what floats your boat then by all means do it Just stick with crower if you do, you shouldn't have any problems that way.
I am stuck at a cross road really. I can go the Crower stroker kit and get a close to 3.5 litre overall capacity which will power some nice GT3071R turbos nicely and limit lag as much as possible etc as discussed already. This build is obviously very costly and has the potential to fail a few times before it is right. My second path can entail building a very solid bottom end using Pueter rods, nismo or similar crank and other top shelf high HP rated components, stick with a smaller turbo which would be good alround for street and track then at the drags run a dual stage nos shot to boost power to something crazy. So in other words keep it simple and rely on the nitrous to make the dyno queen numbers and leave the engine at around 500 odd hp which is ideal for the street and track. This is my dilemma.
stock pulley is a harmonic damper, not a harmonic balancer. it dampens torsional vibrations (ie crank twisting). that is the purpose of the rubber. these vibrations are mainly a problem when engine operates at the resonant frequency (and overtones) of the crank. as such, crank pulley must be tuned/designed to dampen most effectively at certain frequencies. i think this is required regardless of whether engine is internally balanced.
That's correct, they can't balance it with the pistons and rods, unless they did it in the block Those weights are adjusted to match the weight of the piston/rod/pin/clips etc.
If you are going to that extent, do it to a vq35 and drop that into the Z, it's much better and is already 3.5L. Either way you're going to have to get everything engineered if you don't want trouble anyhow. There is no point changing the stock crank, it's already strong enough, it will not fail if everything is right from the word go. I saw a turbo 350Z the other day and it did move quite quickly!! There is also a new skyrine getting around, looks awesome. I am getting a new GTR when they come out in 08 unless something else comes out which is just as good at the same time. In all honesty, going to that extent on a Z (stroking/custom internals) is a waste of money (except for custom pistons) unless you are going to make it a straight drag car i.e. 350mm wide tyres, no interior at all etc. Keep it simple, but do it well, and you will not have any regrets.
I think it is more a hamonic balancer isnt it... Wasnt it more for harmonic 2 and 3 frequencey put out from the engine. I for one ran a UDP which caused vibration. The rubber does absorb the vibration but the weight of it also alows for the counter weights to stay balanced... The UDP is substanially smaller and has no vulcanised rubber possibly causing it go out of balance.
