[DMCForum] Now that I'm beautiful (Martin G)
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[DMCForum] Now that I'm beautiful (Martin G)



Thought about this while in chair (and if you respond real time Martin
your social life is even more pitiful than mine):

Is major sweeping generalization to merely say "advancing ignition
time increases HP". *PART* of lower HP on Volvo F series is earlier
spark (yes, I know compression is lower too -- turn off the burners). 

Horsepower maximized when power stroke is driven by maximum explosive
force (if flame propogation was instantaneous, this would be ignition
at TDC). Laws of physics require flame to start travel sometime
before. But if flame travel starts too soon, mixture is not only
combusting unnecessarily against compression stroke, but is combusting
mixture before maximum compression. Have seen in print (book -- Robert
Sikorsky's I believe. Will look it up at home) that there's something
like 5 degrees between optimum ignition and point at which valves
start to clatter. Advancing spark towards bottom of that window
actually LOWERS HP.

If Jim Strickland is reading same post: maximum PRV compression was
10.5:1 on Volvo's B280 redesign. Yields 170 HP. Us 9.5:1 boys are
either 145 or 155 HP depending on B27 or B28 (E series). Since
Martin's still running original F series heads, I'd argue he's only
marginally above 135 (whatever benefit is obtained from richer
"jetting" -- old carburetor term).

Wouldn't it be something if Martin's performance gain on what remains
just a B28F -- sans Lamda screwing around with otherwise richer
mixture -- was actually achieved by moving ignition *BACK* to optimum
point in compression stroke...

Bill Robertson
#5939





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