A Better Design (Continued)
The resultant design is a valve spring that is conical shaped
(or Beehive shape as Comp's trademark reflects.) This design
makes sense from a variety of standpoints. First, valvesprings
unlike other types of spring uses, compress from the top down.
The bottom coils, in fact, often don't compress at all. Therefore
if the increase in pressure is created by the top most coils,
while the bottom remain at a relatively lower rate, you end
up with a spring that serves its valve control purpose, but
also "dampens" the shock from the closing valve. This variable
rate design also helps eliminate valvetrain harmonics - resonance
frequencies that damage metals and lead to loss of control.
The benefits of conical springs doesn't end there. It turns
out the design lends itself to a reduction in spring weight
through three factors. First, the smaller coils up top means
less material AND a smaller diameter retainer - weight saved.
Second, the smaller coils and variation in coil spacing, yields
spring rates that otherwise must be achieved through increased
wire size - weight saved again. Finally, the harmonic dampening
properties of a progressive rate spring and tapered wire allow
eliminating the need for an inner second spring and damper
- even more weight saved.
Give me the bottom line.
These seemingly small weight savings mean a lot in terms of
power. Every gram of reduction in the moving valvetrain components
frees up some 35 rpm. (Obviously the gram needs to be removed
across all eight pairs of valves.) When you consider that
a twenty-gram savings is on the low end of what can be achieved
by just changing the spring set, you quickly see that an engine
can spin another 700 rpm beyond its current redline. Some
are quick to dismiss this as a mere extension at the end of
an engines power curve. This is erroneous thinking. The majority
of dyno sheets that show power flattening out or diving after
peak power is made are not showing that the "cam is done",
or "the heads are choking", but rather that the engine is
likely experiencing the limitation of its valve springs. See
the side bar on page 1 of AFR's real-world proof with their
small block heads.
What's more is that these sorts of advantages are not just
for deep-pocketed racers. Costs are quite reasonable for lighter
valvesprings, retainers and locks. We took a look at a representative
spring set for a small-block Ford with an agressive roller
cam and the benefits and costs of putting the valvetrain on
a diet.
Case Study: Comp Cams "986" Valve Spring
The
Comp Cams 986 dual valve spring is a very popular standard-coil
spring amongst the small block Ford crowd. Comp recommends
it for pretty much all of their 5.0L and 351W hydraulic roller
cams. However Comp also offers a Beehive version, PN: 26986.
We take a look at the benefits of this spring.
Five
Tips for Finding Horsepower in your Valvetrain |
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Use the lightest spring and retainer you
can, and don't exceed recommended open pressure. Griffin
says all hydraulic flat-tappet cams, and most hydraulic
rollers, can use Beehive springs. For solid cams a conventional
spring is usually best. Comp's
online catalog has cross references where Beehive
springs can be used in place of standard ones. |
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Install springs 0.040-0.050" from coil
bind. Amateur engine builders have a tendency to install
valve springs based on their general catalog specifications.
This often results in a spring that is too tall, which
reduces valve control. Griffin recommends measuring actual
valve lift and setting the installed height at this value
plus 0.040-0.050" to avoid coil bind. Set up each
spring individually, or at least setup the intake and
exhaust spring sets separately. |
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Buy the stiffest, largest diameter, pushrods
you can run. All pushrods bend, but the question is how
much. Bending reduces dynamic lift and duration. Therefore
always run a high-quality hardened pushrod. Griffin also
prefers steel rocker arms over aluminum for this reason. |
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Buy your heads bare. Guys like Griffin,
who really understand this stuff, would never settle for
a pre-assembled set of heads. They buy their heads bare
and then work up the valve train themselves. Buying bare
heads also ensures you'll get steps 1-3 done your way,
and not settle for a one-size fits all assembly |
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Check your spring pressures every racing
season (or every year for street cars) to make sure the
pressures are within 5% of the catalog specifications.
Springs that have been stressed will show marked pressure
drops. Replace the entire set if neccesary. |
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Posted by morgan, 11/01/07 07:16am: Great article. If I had to build my 482 CI FE motor over again I would have gone with Titanium Valves to decrease the valve train weight. Posted by ghudnub, 11/01/07 09:05pm: I have the beehive setup on my Edelbrocks. They really do deliver as described. Money well spent IMO. Posted by dpcobra, 11/11/07 11:47am: Just finished building a BBC for a friends car and used beehives for the first time. Along with larger valves and extensive porting, the motor is a rev monster. The results were so impressive I am consider a set for my SBF Dart Pro-1s!!! For a follow-up article, consider posting Dyno run sheets (before/after) - conduct by a third party. Posted by blkfrd, 11/12/07 09:20am: When I rebuilt my Ford 331, I switched to 26986 beehives for my 282S cam. My engine pulls hard 'till it hits the rev limiter at 6800 (as high as I dare take it at this time). Analysis indicates my 1.94 intake valve would not float until 7200 with these springs. Posted by Helmantel, 11/15/07 04:08am: The beehive spring + retainer weights 39% less than the conventional setup, but since one end of the valve doesn't move, wouldn't it be more accurate to calculate an "effective spring weight" (=half the weight of the spring)? That way, the beehive stuff is even a little lighter (42%) Posted by Winder, 11/29/07 03:12am: What are the advantages for lower RPM applications. I know most of the articles are for the go fast crowd, but I was wondering how much these spings would help for truck adn 4x4 applications? Posted by Samickguy15, 05/28/08 09:54am: The less weight your motor has to move around the better. While you may not gain much with a 4x4 app, it does still help.
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Sources:
Comp Cams
3400 Democrat Road
Memphis, TN 38118
1-800-CAM-HELP
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