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Old 12-16-2017, 05:14 PM
Frank Reiner Frank Reiner is offline
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Join Date: Feb 2011
Location: Modesto CA
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Quote:
Originally Posted by rwd4evr View Post
My understanding is that the squish band is there to get as close as possible to the flat "deck" areas of the combustion chamber to allow heat transfer from the piston to help battle detonation. The kjet heads are missing that flat area compared to the djet 3.5 heads if I remember correctly? The djet US motors had the piston down in the bore to lower compression that leads to detonation I think.
The quench (aka, squish) is not to transfer heat from piston to the head, but rather to 1) concentrate as much mixture as possible in the combustion chamber, and 2) to keep the mixture remaining in the quench area at a temperature that is below ignition temperature, hence the term "quench", i.e., to lower the temperature, to cool.

See post #37 of this thread: the total quench area of the 3.5 head is greater than that of the 5.6 head, however, the upper (away from the spark plug) portion of the 5.6 head is greater than the corresponding area of the 3.5 head by virtue of a greater bore diameter.
The downsides of the 3.5 head are smaller ports, smaller valves, and greatly shrouded valves.

Quote:
I have picked up a set of 3.8 euro cams, I believe they say k70 and 71 on them. Have you ever looked at these? I'm looking for high end power and the 92mm bore 3.8 redlines at 6700rpm so I figure the cam timing has to be different than all the others. My 4.5 really falls on it's face after 6000. Not sure if it's Valve float starting or just the cams being setup for low end power with the terrible auto. I'm not even 100% sure its got stock us kjet cams actually. But it just stops revving. Drifting it in third is tough so I really was giving it to it in second.
The 70/71 profile is decidedly mild (179 degrees); 60/61 (190 deg) would be preferred. However, cams intended for use in M116s have less lift than those for M117s. 00/01 and 02/03 profiles would be better yet.
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