Kenneth Brown wrote:
>
> I'm in the process having the head rebuilt for my 1968 TR250 and am wonder if
>I
> should upgrade the cam. I don't plan on racing but do enjoy spirited driving
> around the country roads. If I do upgrade am I just opening up a can of worms
> with idling, timing, emissions (Calif. car) problems etc. Also is it worth the
> money installing roller rockers. I would like to do it once and do it right.
>
> Thanks,
Ken,
A camshaft with more lift and similar duration as stock shouldn't,
I beleive, affect emissions as much as a change in duration will. Double
check with a performance rebuilder on that one though. ANY increase in
duration OR lift over stock WILL increase emissions over stock. This is
the main reason the later TR's are so lame on power. Since you live in
California the legislatorial (if that is a word) mad society it is, be
advised that increase in emissions output could get you in deep ****,
from what I've read on this list. The real question is how much lee-way
are you allowed from the "original" (read "when new") emissions output.
If for example a brand new TR 250 puts out 200 ppm hydrocarbon, and
you're allowed up to 500ppm at a test, then you have some room to play.
That is if EVERYTHING else on the engine is perfect.
There are many mild cam "grinds" available that slightly increase per-
formance and really don't require many other engine modifications. To
fully reap the benifits of a higher perfomance cam, however, such mod-
ifications as a freer flowing exhaust, improved carburation, and per-
haps a change in ignition timming may be necessary. Be aware that these
changes aren't necessary, as you will notice some, albeit not all of, a
performance increase with just a change in the cam.
A mild cam grind should be near "invisible" in that the car will still
idle, use the same fuel, and start, with only slightly less "smoothness".
Unfortunately I can't give you specifics on a cam grind to go with, just
some advice~ be warned that a major increase in "duration" is what con-
tributes to those "can't idle" and "peaky powerband" qualities you seem
to want to avoid.
"Roller rockers" are really a "fringe" modification as I see it. By
this I mean they cost a lot for a small return, and as such, are really
only needed by those people (the "fringe") who need every ounce of power
from their engines. How else can one justify spending $1000 for ten or
fifteen horse power? Drag racers and NASCAR racers need that power (and
the duribility to run at sustained very high RPM's), not your every day
or even ocasional racer does, though.
The thread a while ago on roller rockers pertained to increased ratio
roller rockers, which by virtue of their longer length (on the valve side)
increase the "lift" of the valve. The added benifit, besides the HP gains
of reduced frictional losses, is that one can increase the vale lift with-
out having to go through all the trouble and expense of changing the cam
and lifters.
In your case, where you are changing the cam already, are not in pursuit
of the utmost power, and are not considering sustained high RPM running,
I really wouldn't recomend roller rockers, and living in Califonia as you
do, I would be leery of modifying the camshaft as well. Sorry to disappoint
you, but I think the TR 250 has "enough" power already, anyhow...
JOE IV
TR 250
WALLINGFORD, CT. USA
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