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I frankly don't understand how a balanced 4 cw crank could be worse on bearing life than a balanced 8 cw crank... assuming they are all balanced to the same variance specs...
I don't build motors though, so I could definitely be wrong.
I put a 8cw crank in the VE-T. It came out of a DE. It didn't require any balancing with the pistons and rods. At least that is what I was told. The pistons and rods were zero balanced when they got to me, and the crank was still perfect so I just threw them all in.
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99 SE-L. Graphite Gray GT3076R turbo, Protech Mani, 3" all the way! Nismo FPR 740cc, 255 pump, JWT computer,400whp pump is the goal.
I frankly don't understand how a balanced 4 cw crank could be worse on bearing life than a balanced 8 cw crank... assuming they are all balanced to the same variance specs...
I don't build motors though, so I could definitely be wrong.
It's not about balance. You could have a crank with zero counterweights that is perfectly balanced. That doesn't mean it would be OK to use though...
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It's not about balance. You could have a crank with zero counterweights that is perfectly balanced. That doesn't mean it would be OK to use though...
Care to elaborate?
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"I've decided that because Einstein identified that objects travel through time at a slower rate with an increasing velocity, we should go as fast as possible to increase our lifespan."
You have to look at the flex of the crank. When spinning at thousands of rpms a half-counterweighted crank will have more flex because of the impalance. It makes sense right? The weights are there to counter the weight of the pistons and rods, obviously having half the weight to counter would cause balance issues. If it didn't, then no crank would have any weights at all.
Folks,
From what I have seen the Bearing Beam (Girdle) holds the crank in the plane parallel to the main bearing centerline. Because the Block is a deep skirt design there is no need for a Girdle (by definition: main caps part of the assembly).
It is proven that the combination of deep skirt, registered main caps, a bearing beam and a torsional "external mass" damper gives the best overall control of crank vibration.
This is the method Nissan used on the SR20 for noise and vibration control, by extension it gave rise to a rock solid bottom end.
The discussion on 4 vs 8 CTW is a nice one. From what I have seen with my motors and others;
The 4 CTW tends to "vibrate" the NO.4 Main Cap and bearing.
The effect of this is seen on the NO.3 Rod Bearing.
I have not seen evidence of the same on the 8CTW.
I have felt the 4CTW come through a distinct harmonic for a very brief period in the rev range (solid mounted motor and solid all welded chassis).
There is also another thing that happens on an inline 4 motor and that is the fact that on this engine combination two cylinder fire right next to each other (3 and 4). What happens here is that by extension from the leverage forces of the rod journal, the Main journal between the two is twisted at a very high frequency from the unloading of one (exhaust stroke) to the re-loading of the same (power stroke on the other). It typically manifests itself on main bearing NO.4. This is something that every V configuration motor has to take into account in their crank designs (like Porsche got wrong on the first generations of the 928 V8 Motors). There is a lot more to this discussion because the only time it is evident is when the motor is "fired" and live under load, and not static for an imperical calculation on balance of individual components.
My recommendation would be for an 8 CTW for a car that will be pulling through a fairly wide rev range.
Now SUMITUMO under financing of various japanese OEMS studied the dynamics of 4 vs 8 CTW cranks and actually came up with the 4 CTW being better for any specific 4 cylinder motor. HOWEVER, the counter weigts are not egual mass in their design. SUMITOMO was chosen because they make the bulk of the Japanese crankshafts.
Again from my own experience: The Bearing Beam takes power away due to windage in the crank case and obstruction of the attomised oil around the crank. I have not seen this on my Dry Sumped negative pressure sump motor.
Later tonight I will post the two SAE Paper numbers for the crank design and for the vibration analysis on four cylinder engines for any one interested.
rod bearing ?
emm interesting since all the time i never seen this rod bearing included inside the balancing list
basically i receive a lot feed back from friend after balancing the engine internal
the engine rev smoother and feel light..
a big different and worth to do it
this is balancing only.. not lightening.. not intend to lightening
i think i will go with GTiR crank option
The 3 & 4 cylinders fire together? That sounds really bad even in the tightest of tolerances. What benefit would an engine have with that config? Maybe I`m just visualizing this the wrong way.
The reason for the crank flexing at high RPM with the 4CW crank is that Although the counter weights do offset the weight of the piston and rods, they are not in the same plane. The counter weights sit off to the side of the con rod to allow it to clear. With the 4CW crank, each piston only has a counter weight on one side only, which causes a slight bending moment as the asembly rotates. The 8CW crank has a counter weight on each side of the con rod which helps to balance any bending moment.
