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Old 10-25-2012, 03:03 PM   #28
aboothman
Scooby Specialist
 
Member#: 127745
Join Date: Oct 2006
Chapter/Region: NWIC
Location: Humboldt County
Vehicle:
06 WRX 30r 6 speed
99L EJ255 6 Speed

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The guy who consistently attacks board members who contribute, without actually contributing any information himself, should not talk to me about "mudding" up a thread

I will help you out. The formula for the area of an ellipse = Pi*(2*Square Root((1/2 Long Axis)Sq)+((1/2 Short Axis)squared)

Lets use 3.937 as an undistorted bore size.

For the ellipse's long radii we can use 3.938 and 3.937 as the short, as the testing we are referring uses .001 as the distortion between a torque plate bore and without. I realize that this assumes the distortion is only on one axis, but this will give us an extreme. We are, after all, talking about extremes and what if situations, are we not?

But more on this in a minute.

I will spare you the math:

The ellipse circumference = 12.37001072
Circle circumference = 12.36843983

Difference between the ellipse and perfect circle bores = 0.001570895

So I just got off the phone with JE tech support. First, I asked whether they recommend using a torque plate to set ring gaps if one was used to hone. They said yes, that would be ideal. I went on to explain this math question of whether the calc for a circle is correct when a distorted bore becomes an ellipse, or oval. This is where things got interesting.

The tech said the ellipse formula is NOT applicable, as the head bolts/studs will not affect the entire cylinder directly. They actually create smaller "bumps" in the cylinder near the head bolts/studs. Think of small radii circles being introduced into the cylinder.

So a cylinder that is circular (NOT plate honed) before a torque plate is installed WILL have gaps in the ring/ cylinder contact. It then becomes a question of whether the "bumps" push into or out of the cylinder. If they push out, then end gap should not be affected much if at all. This was the opinion of JE tech.

A cylinder that has been honed WITH a torque plate should account for these "bumps" and become circular when a plate or head is installed. Therefore a plate should be used to set end gaps...otherwise the bore will distort out of round without the plate.

In either scenario, I cannot grasp why anyone would recommend against using a torque plate to set ring gaps. Whether one was used to hone or not, and I sincerely hope one was, you will be better off using one to simulate cylinder distortion with the head one. This has been discussed to death, so I will say the same thing I told a buddy recently. You can do this one of 2 ways; the right way that takes more time and is more expensive, or the half assed way that is quick and cheap.

This also brings up an interesting question regarding the Team Scream test, so I will have to ask him. I do not recall whether the test used many different bore radii, or just a few. The reason I ask is because one of these "bumps" could have given false results that would not have shown in a different orientation. It occurs to me that many radii need to be measured and charted, NOT averaged.
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