Michael,
On p.321 Vizard says:
".... but basically we can assume that if you have a standard or near
standard cam in in any engine, higher lift will produce higher power,
especially in the bigger engines." I couldn't find any specific reference
to reduced returns above .350" but on p 323 he states, "....rocker ratios
between about 1.5 and 1.7 are generally optimum for an effective valve
train."
You don't really give us enough information to answer your question. What
are the actual ratios of the rockers? How much has your head been
modified? Even though the lesser rockers "slide -on" to the stock rocker
assembly you may need to replace a worn shaft, thus negating some of the
savings. Do the more expensive rockers have needle bearings on the shaft or
are they bushed? The use of needle bearings may push them into the area of
"diminishing returns."
I don't know who "The Doctor" is or what his rocker sets cost but there are
savings to be had by going to the source. MiniSpares has a set of 1.5:1
ratio roller tip rockers for just over 110 Quid (excluding VAT) by the time
you get them to the US that translates to somewhere around $200. That
includes rockers, shaft, pillars, and adjuster screws, i.e., everything you
need to get them on the head. They are bushed at the shaft so you aren't
paying for that last .001% that needle bearing rockers get you. By all
means purchase as much as you can from your local supplier or somebody on
the list, but the price difference for some items makes it almost foolish
not to go to the source.
Hal
On Wed, Feb 3, 2010 at 10:29 AM, Michael Rowe <mdrowe@optonline.net> wrote:
> Two sizes of roller rockers are sold by "The Doctor." With my cam, one
> provides 0.347" lift and the other provides 0.392" The former cost half of
> the latter because they are slide-ons for the stock rocker assembly. Vizard
> shows relatively little improvement in performance for valve lifts above
> 0.350" and my machinist points out there is little sense in higher lift if
> the head can't breath enough.
>
> What are your thoughts on choice of rockers for a "warm" 1310 street
> engine?
>
> Michael Rowe
> Aspiring engine builder
>
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