Come dyno day, we'll see if indeed I might have too much lift.
Midget, et all,
I know this is hard to visualize without a graph or chart, but please read along and I can answer anyone's specific question in a later post. In a phrase, "It is more complicated than that." And what I mean by that is, that changes in the rocker ratio change more than just the lift curve. Although 'overlifting' valves is related, the other change is to the EFFECTIVE duration of valve timing events. Because higher ratio rocker arms increase the valve displacement at EVERY POINT on the valve displacement curve, they also have the NET effect of increasing the EFFECTIVE duration of ANY cam used. Now we could argue all day about what net valve lift value constitues "EFFECTIVE" camshaft duration, but I'm going to get all passive/aggresive on you guys by saying: "The only valve event I care about on this engine @ this time is: 'EFFECTIVE' inlet valve closing". And I reserve the right to change my opinion, at any time, without notice.
IF, substituting a lower ratio rocker arm assembly produces more torque at a given rpm, (& therefore more hp) the inference is that the valve events are too "long", ie, too much duration,
OR, the inlet valve 'effective' closing point is too late for the engine's combination of build geometry & gasflow,
OR, the engine does not have enough compression ratio to take advantage of 'long' duration valve events,
OR, a combination of the above,
AND/OR, other build geometry/gasflow factors I did not include, etc, etc, etc.
Also a factor here is that the smaller the displacement of an engine's cylinders (and this is different from TOTAL engine displacement) the more 'sensitive' it is to 'effective' valve timing events.
The risk of this test is that peak hp MAY be compromised by the gasflow loss at net total valve lift at, and around, full open intake/exhaust valve events. However, an increase in peak torque, even coupled with a loss of peak hp, (subject to analysis) would typically indicate the engine needs 'less' cam duration and/or more compression ratio. These types of tests are part of the engineering/tuning process. I am expecting to see a rise in peak torque AND, a slight loss in peak hp, and analysis of the data generated will indicate what other changes (if any) should be made. I am particularly interested in seeing what sort of BMEP this engine produces, regardless of rocker ratio. See how simple that was........
Kind of like a chess game, lots of pieces, lots of moves, net result: It's complicated. Lots of guys smarter than I am spend endless amounts of time debating about this stuff. As for me I'm simple, all I care about is: net results.
Fordboy
Topic: Milwaukee Midget (Read 3583610 times)