OK, I'll bite. ;{)
6. This is an educated guess... The 2003 Toyota has three speed with a built
in an overdrive that can be engaged in either second or third, to give 5
ratios overall?
7. Assuming all the cylinder pressures were roughly equal I would want the
engine with 12:1 compression and a static compression of 90 PSI. It's
obviously got a long duration camshaft to match it's high compression ratio.
8. Compression ratio is the ratio of maximum cylinder volume to minimum
cylinder volume. Assuming flat top pistons: the minimum is the volume of the
combustion chamber+ a small amount determined by head gasket thickness+
another small amount determined by the difference between the top of the
piston at TDC and the top of the block. The maximum volume is the minimum +
the volume swept by the piston. Compression ratio is an IDEAL number. In the
real world the intake valves don't open at TDC and close at BDC, the exhaust
valves don't open at BDC and close at TDC, there is usually some overlap,
and rings don't seal perfectly. I would say that compression ratio and
static compression are only "loosely coupled". Given two stock engines in
the same condition changing one will change the other...
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.)
11. Crankshaft layouts make sure some pistons will be at TDC when others are
at BDC. Camshafts ensure that, if two pistons are at the same height, one
will be on the power stroke while the other is on the intake stroke. Within
those limitations an engine designer tries to arrange things so that stress
and vibration are minimized.
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net]On
Behalf Of Jim Swarthout
Sent: Tuesday, December 03, 2002 3:11 PM
To: 6pack@autox.team.net
Subject: RE: TR-6 performance (update)
To the list:
Especially those who may be getting in on this late!
I would like to see 12 TR-6/250 owners with basically stock engines...
(No wild cams or other major mods to the valve-train)...install a set of
these rockers and write back with comments...good or bad. Nitrous...or
some form of forced induction is fine. Triple carbs and a header...fine.
The reason that I would prefer to give these away to owners of stock
cars is that I don't know that they will be of any benefit on a modified
engine. I can only speak for the performance increase in a stock engine.
If any one of the conditions below describes you! Then please don't ask!
It costs me money to make them. I want to be sure that they will be
properly installed. I want to know that they are being installed by an
owner who enjoys the performance of these cars and will be able to write
back with comments more elaborate than...Gee I almost didn't want to put
the valve cover back on..."These rockers look cool".
You don't own a "6" or a "250"
You don't like to work on your car...garage queen...open wallet at the
local shop...AND...NO...DON'T TAKE OFFENSE...It's just simply that this
won't work for this test.
You drive your car refusing to see the tach go beyond 4000 RPM's.
Your car is currently scattered all over your garage...and it will be
next year before you will get around to installing the rockers. I would
like to get feedback promptly.
Current standings:
Kai, graciously declined, forfeiting his answer to someone else.
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.
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.
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.
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.
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!
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.
7 more to go...
Answers to questions 1,3,5,9 & 12 are spoken for.
2,4,6,7,8,10 & 11 remain
Don't copy/paste I'll know.
Jim
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