[TR] zenith or su's ?

[Anthony Rhodes]

Wayne,

I totally agree.  With few spring selections, probably there is only one
spring that makes sense.  But how do you know that the springs in those old
SU's are 1) the original type, and b) still have their original "springiness"?
You would have to measure their spring rate.  Not a difficult proposition.

The case I had in mind when I was saying that maybe someone would need to
change springs is in the 3-carb conversion.  I think it is quite likely (and
probably necessary) if you are going to have any real increase in breathing,
that you would need springs with about 2/3'rds the spring rate.  You would
need a greater spring rate than that if you develop more HP in a modified
engine.  I.E.  I'd guess that if you had a 50% increase in HP, then that would
bring you back to the original springs.

As I said before, there are enough variables that it is a little difficult to
predict, and you might need to verify the actual amount of lift at full engine
breathing.  I presume that people can predict the flow based on displacement,
compression ratio, HP and RPM.  Then a flow bench could verify the actual
lift.  A dyno might be easier to find.

-Tony
  ----- Original Message -----
  From: Wayne Lee
  To: Anthony Rhodes ; Triumph List
  Sent: Friday, January 01, 2010 9:54 AM
  Subject: Re: [TR] zenith or su's ?


  Hi Tony,
    The Spring Rate first is a no brainer of course since the HS6's would come
with a Spring in the Ballpark
  for the application We were discussing..
    The reason You don't spend much time on altering the Spring rate is
because they make only about 2-3
  possible Spring rates at the most for any general Application, and about 25
Needle profiles that could work.
    I've never had the stock Red or a Yellow Spring not get me into an area
where a sweet Spot couldn't be
  found by going a step or 2 in either direction with a Needle profile. How
about You?

  Tony Wrote:
  "Of course you will have to select different needles for the different
spring rates"

  Not when there are only a couple possible choices of Springs that make sense
out of the 4 Available, and 100 Needles to choose
  from.
  Wayne
  wayne at sucarb.com



  From: Anthony Rhodes
  Sent: Wednesday, December 02, 2009 9:37 AM
  To: triumphs at autox.team.net ; wayne at motorcarriage.com
  Subject: Re: [TR] zenith or su's ?


  >You don't want to compensate for bad Needles with Springs. The Needle
  >Profile or what Jim called "calibrated" is the
  >most important part. Sort the Car out on the road using the Volvo Needle
  >then see where you are rich. At idle or popping on the Highway.
  >Then take it from there. The Springs should be your last concern.
  >Wayne

  Wayne,

  I'd say that you need to figure out your spring first, since it (as you say)
determines which part of the needle profile is operational at any given power
level (and controls the amount of "constant depression").

  The way to determine this? Not simple.  You can guesstimate it from the
spring used on other cars with similar HP and carb choke size.  You can
directly determine it by looking for just reaching full piston lift at maximum
flow rate.  Unless you get a child to ride alongside the engine as you race
down the road, I suppose the only way to do this is on a dyno.

  Excessively strong springs will work, but will cause greater restriction on
air flow than necessary.  I.E.  you have smaller choke carbs!  Excessively
weak springs will also work OK, until you get to maximum lift.  At that point
you lose the ability to control the misture with the needle, and the mixture
is determined as if the carb were a fixed choke type.  Mixture will be
dependent on airflow to some degree.

  Of course you will have to select different needles for the different spring
rates.

  -Tony


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