Car runs better when cold? Or am I just crazy?
03-11-2007, 01:02 AM
#21
5th Gear Member
Join Date: Jul 2004
Location: Westminster, MD
Posts: 4,343
RE: Car runs better when cold? Or am I just crazy?
When the engine warms up, cylinder bore gets larger asdo the rings like you said. But when the rings are worn and cylinder bore is worn the cylinder bore expands enough that even when the rings expand they do not completely seal. Allowing more blow by.
03-11-2007, 01:58 AM
#22
2nd Gear Member
Join Date: Nov 2006
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Posts: 205
RE: Car runs better when cold? Or am I just crazy?
Bore expansion over the course of even 300 degrees would be pretty minute. Fractional expansion of iron is only .0000067 per degree F. Aluminum is .000013. Compression ring gap limits for a 4" bore engine is .01 to .02 inches. To widen that gap to .03 or higher would require the bore to expand by .0095 inches.
http://hyperphysics.phys-astr.gsu.ed.../thexp.html#c1
http://hyperphysics.phys-astr.gsu.ed.../thexp.html#c1
03-11-2007, 03:10 AM
#24
4th Gear Member
Join Date: Feb 2006
Location: Seattle, WA
Posts: 1,375
RE: Car runs better when cold? Or am I just crazy?
WhenI have installed rings on my engine builds, I have had to compress the rings a fair amount to get them to fit in the bore. I would think the bore would have to be about 4.25" for the ring to no longer touch the walls.
03-11-2007, 06:12 AM
#26
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Join Date: Feb 2006
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RE: Car runs better when cold? Or am I just crazy?
In my experience, it takes a lot of blowby/loss of ring seal toproduce even a small power loss. Either way, if he's hard on the throttle, those piston rings are flared hard against the cylinder walls. Also, I though that as an engine heats up, the pistons are what do most of the expanding.
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