The list is nearly complete
If any of you on the current list below have participated just for the
enjoyment of the Q&A session thats great! I have enjoyed the answers
and learned some things too! If you really dont want to participate in
the Roller Rocker installplease say somaybe Ill post a few new
questions and open it up a little. I would never claim to know it
allnobody does, but I can come up with some things to think about.
Many people have asked.why do it?
Well think about it!
If I tell you that I have RRs for sale and they are the best thing
since sliced breadwill you believe me of course not. It is already
the general consensus that they dont really make a big difference, (all
on their own), in performance.
If a dozen unbiased TR-6/250 owners tell you they work great youll be
more inclined to believe it.
Current standings:
Stephen Hanselman
#1) There were 2 reasons why electronic ignition was developed? Both
answers pertain to the consumer, or auto owner.
In my mind electronic ignition was developed first to get a hotter
spark. My dad put together one back in '67 or '68 for our Plymouth. He
found one problem in the spark coil though, the fire was so "hot" it
would arc over the top of the spark coil. Now days, driven by the left
coast again, emission requirements are so tight that pulse to pulse
timing is a major factor in controlling what comes out the tail pipe.
This, of course, has no relation to any increase/decrease of power out
of the engine.
Alan Salvatore
#2)A hydraulic cam is supposed to be quieter running and have less
maintenance then solid lifters, (the manuel tappet adjustments required
by stock tr6's)i have read that they are supposed to deliver power over
a wider rev range and maintain idle quality. Too bad they don't make
valve covers out of lexan. lol Al Salvatore 76tr6 daily
Jamie Palmer
#3) What does an air pump, (smog pump), do? Explain the entire
cycle...peripheral equipment!
Pumps in air into the exhaust stream right at the cylinder head,
theoretically allowing unburned hydrocarbons to combust while in the
exhaust stream.
#4) Why will roller rockers of an equal ratio open the valves further?
Vance Navarrette
#5) What performance gains will you achieve by installing a long
duration...(extended period of valve opening)..., high lift, camshaft
in an otherwise stock engine?
As they say, "It depends". All other things being equal, this is true.
But if the cam is *TOO* big, you will end up with less power everywhere
in the RPM range, because the rest of the motor cannot keep up with the
big camshaft's demands at high RPM.
Also, if the lobe centers are closer together, a longer duration
cam might give more power *LOWER* in the RPM range than the stock cam.
Lift and duration are not the only cam parameters that affect amount of
power and it's location in the RPM range. Two other very important
factors are lobe center spacing (in degrees) and valve acceleration (in
inches/degree**2).
The above is why it is simply impossible to compare cam timing
and draw conclusions about which is "best" except in a very broad sense.
The cam manufacturers do not give enough information about their
profiles to make precise comparisons. You cannot even compare the rated
durations because there is no standard method for measuring them. The
only values you can compare are net lobe lift and duration at a known
lobe lift (most often 0.050"), and many cam makers will not even give
you that much information!
Jeff Dewey/John
Jeff Dewey
#6) Why does an early Ferrari have a "true" 5-speed gearbox, but a 2003
> Toyota does not?
The early Ferrari 5-speed gearboxes had a 5th gear with a 1:1 final
ratio.
Late model production gearboxes could best be described as 4-speed +
overdrive, ie, 4th gear is the 1:1 ratio and 5th is an o/d ratio.
John
I'd say the Toyota doesn't really have a 5-speed because the 5th ratio
is an overdrive so it's a 4-speed with overdrive. I'm sure the ferarri
5th gear is 1:1, and the lower ratios are nicely spaced for performance.
#7) Suppose you have two 152ci TR engines side-by-side; same, make,
model. One engine has a compression ratio of 12:1 with a static
compression of 90. The other engine has a compression ratio of 7.5:1
with a static compression of 200. Which engine would you want in your
car? Why?
#8) Is compression ratio related to static compression? Yes or No, and
why?
Shane Ingate
#9) You're speedometer shows 60MPH. You're Tachometer shows 3000 RPM's.
You're in 4th gear at 1:1 with a final drive ratio of 4:10. What is
the outside diameter of your tires?
27.56"? (I can only remember PI to 3 significant figures). If that9s
the case, this is pretty close to a 215/70-15 tire.
Erik Quackenbush
#10) Casting is the art of pouring molten metal (hot!) into a mold to
form a shape. Forging is the art of banging on a solid (usually hot)
piece of metal to bend it into shape. Machining is the art of using a
cutting tool (usually with a lathe or milling machine) to trim a piece
of metal to shape. In general, forged parts are stronger than cast parts
but they cost more to make. Forging is a good way to make connecting
rods. Parts with internal passages are usually. Casting is a good way to
make cylinder heads. Parts that are JUST machined (carved from a billet
of solid metal) are the most expensive to make but not the strongest.
Machining is a good way to make ONE of something. In real life most cast
and forged parts have surfaces that that must be machined to make them
useful (bores, decks, journals, etc.)
Terry Geiger
#11) How are engine firing orders determined by the engineers? Is it
rhyme or reason?
Firing order is set up to that the engine is "load balanced" on the
crankshaft
so that vibration and stress on the cranshaft is minimized.
Easiest to understand example is a 4 cylinder engine:
Cylinders 1 and 4 are 180 degrees from cylinder 2 and 3. When 1 and 4
are at
TDC, 2 and 3 are at the bottom of their stroke. For this arrangement to
work
the firing order would be 1-3-4-2 which would alternate the power
strokes to
where if 1 is in a power stroke 3 is in a combustion stroke, if 2 is in
a power
stroke 4 is in combustion and so on so that anytime 1 or 4 is in a power
stroke
then an opposing cylinder (cylinder 2 or 3) is simultaneously in a
combustion
stroke.
Hugh Fader, Mark Hooper
#12) If the piston to be fired is approaching compression...(15 degrees
BTDC)... and you have the timing set to fire at 10 degrees Before
TDC...why doesn't the piston travel back down...moving in the direction
from which it just came...?
First of all, the piston is not approaching compression. Compression is
nearly completed at this point. The simple answer is that the force on
the top of the piston is less than the force on the bottom.
Forces on the bottom of the piston are: crankcase pressure acting on the
piston bottom, inertia from the spinning crank transmitted through the
connecting rod, and in a multi-cylinder, forces from other pistons on
their expansion strokes transmitted through the crank and rod. Oh, I
almost forgot the inertia of the piston itself.
Forces on the top of the piston are: pressure due to the compressed gas
acting on the piston top and pressure due to combustion.
Now, in an optimally timed combustion event (MBT), peak cylinder
pressure occurs about 12-14 degrees after top dead center. The
combustion pressure has yet to even get started developing at ignition.
So the force due to combustion cannot overcome the other forces at this
point.
Hugh Fader's answer while correct is limited in that he omits to mention
that although ignition of the gases is almost instantaneous at the spark
point, the flame front still has to propogate thoughout the compressed
gases and then raise their temperature to the point where they press
against the piston (and cylinder walls/head of course) with the force
required to drive the overall engine. It is this propogation that
actually chews up the time and requires the preset of the ignition. Once
uniformly ignited, a correctly designed engine can have a much smoother
action by having the gases continue to burn and heat well after TDC and
with correct engine sizing, maintain anconstant cylinder pressure even
though the piston movement is changing the cylinder volume in a
non-linear fashion due to the eccentric crank movement.
Thanks to those of you who have participated!
If I have left anybody out...please let me know.
I realize that many of you answered all of the questions...I simply
chose one to attach to your name.
3 more to go...
4,7,8 remain...they have been inserted above...for those who do not have
the original post.
Don't copy/paste I'll know.
Jim
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