Interesting posting Bob,
I learned this "average power" idea when I put too wild a cam in my rally
car years ago-- power was up, rpms were up, top speed up but my special
stage times were down. If you are changing gears at all, "average power"
through the gears is an important concept.
On changing valve springs, I've often done it (on various engines) without
removing the head(s.) Just feed soft nylon cord into the plug hole, bring
the piston up towards TDC slowly and when it tightens up, put a socket onto
the valve spring cap and give it a firm whack with CBT #1 (Common British
Tool #1, medium sized hammer/mallet.) Prior to all of this of course close
any holes/places where the collets/caps may fly to and drape plastic/towels
etc. around the heads so you don't lose one of those little buggers. If you
lose one you may suspect it's in the engine somewhere and do a complete
teardown/rebuild only to find it later hidden behind a brake line-- not that
this ever happened to me...
Can anyone help with tiger header pictures/suggestions??? Please :-)
cheers, derek
>Larry,
>
>The 80% value comes from the ratios in the transmission and is really
>different for each shift, and depending on what transmission/gears you
have.
>I have an article that covers this on the TigersUnited Website that has
more
>of the details, but taking an example from that article, if you shift at
>6,400 rpm, going from 1st to second you drop to 4,662 rpm, 2nd to 3d you
>drop to 4,885 rpm, and 3d to 4th you drop to 4,961 rpm; and that's with a
>close ratio box. The average rpms through each of the gears is around 5,600
>rpm, so this would be optimized for an engine that gets its peak HP at
about
>this rpm. Actually, since the HP curve falls off faster on the high side of
>the peak, it's probably optimized for somewhat higher peak HP point; maybe
>even 6,000 rpm, depending on how quickly it drops off. You have your own
>motor's dyno curve, so take a look at it and guestimate where you would
need
>to shift to get the most area under the curve between the shift points. I
>know this is not totally precise because you really need to use a
>time-weighted curve for example, but you can probably get as close as you
>need to just eyeballing it. Compare this method with what, for example,
>someone who shall remain nameless, but who probably represents a lot of
>racer types, do. Have Dave Drahle build you a motor that gets 425 HP @
7,200
>rpm, and then shift it at 7,000 rpm because you're afraid it's going to
>break. This is nonsense. A motor that puts out a mere 375@6,500 would
>undoubtedly beat it every time if you shifted at 7,000 rpm because it's
>average HP output would be greater than the 425@7,000 motor.
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