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Interesting finding on major valve clearance adjustments 200

posted by  Jorrell on  Mon Apr 2 13:20 CST 2007
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last visit: Thu Dec 27 03:00 CST 2012
[RELATED]

Okay, finally got around to doing the valve lash adjustments 8500 miles after a full rebuild. When I set up the engine originally, I made sure the valve lash was very loose so absorbers and valve seating wouldn't potentially cause a too narrow of a gap, sorry hate flamed valves. The average clearance I used was 0.024" cold during the build. Another note, I did replace the factory cam with a VX cam during the build.

I did a G-Tech Pro 0-60 test before adjusting the valves this time around, (baseline if you like). The results over three runs were in the high 80s to the low 90s for HP at the rear wheels.

I then adjusted the valve lash to 0.012" cold, this is the minimal recommended setting. Since everything had seated, I was no longer worried about valve flaming.

The following day, I repeated the 0-60 test in roughly the same conditions +/- 3 degrees F. The three runs varied between the high 90s and the low 100s, on average, a 10HP increase. Granted, a 0.010" mis adjustment is huge in terms of the norm, but this got me thinking as to why there was a significant power increase.

I finally realized that sloppy valve lash retards the opening degree of all valves and advances the closing degree of all valves (DUH). It also reduces the maximum opening "peak opening" of the valves. This means that the intake valves are not open long enough or far enough to get a full fuel air charge. It also means that the exhaust valves are late to open and early to close, the result is leftover exhaust gas in the cylinder for the next combustion cycle.

I know that a huge valve lash setting is rare, but once again, correcting it made for a significant power increase.

Please note that I only consider the G-Tech to be a relative measurement tool not an absolute answer. The cylinders are also bored 0.024" over and the head is ported and polished plus a few other tricks, so the numbers might be higher than expected (compared to stock) as a result.

Just found this to be interesting. Anyone care to add their valve lash adjustment experiences or provide supporting or dismissive results?

Thanks,

jorrell

ps. Kinda Geeked!
--
92 245 245K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently in pieces






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