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What's the
difference between the LT1 and its predecessor the L98?
What's the difference between the F-body LT1 and that in the
Corvette?
Why don't F-Body LT1s get synthetic oil at the
factory like Corvettes do?
Which cars got an engine oil
cooler?
Why has oil coated the underside of my engine and
transmission?
Why has my oil pressure reading suddenly
started to drop at higher RPMs?
What's that foul, burnt
smell coming in the vents at stop lights?
What air intake
(induction) upgrades are available?
How can I make my own
air intake without spending a lot of money?
What's that
plastic tube which runs perpendicular to the air intake?
*What aftermarket performance items are available for the
V6?
What aftermarket headers are available for the
LT1?
What's the size of the LT1 throttle body and can I
use a larger one?
Why and how should I bypass the throttle
body coolant lines?
Why and how should I bypass the EGR
valve/line?
Why and how should I relocate my idle air
temperature (IAT) sensor?
What temperature is the stock
thermostat and can I go lower?
What performance
"chips/programs" are available?
Can I keep the stock
thermostat after installing a performance chip?
Can the
fans be rigged to come on while the engine is not running?
Why am I losing/smelling antifreeze, but nothing seems to be
leaking?
What fuel pressure setting will give me the best
performance?
How easy is it to change the spark plugs on
the LT1?
What spark plugs are available for the
LT1?
Why has my car developed a bad hesitation problem
(Optispark)?
Why does my car have a slight stumble upon
slow acceleration?
Should I use self-aligning or
non-self-aligning rockers?
What aftermarket camshafts are
available for the LT1?
What aftermarket camshafts are
available for the V6?
What's that knocking noise when the
engine is cold?
What's that ticking noise when the engine
is under load?
What's the difference
between the LT1 and its predecessor the L98?
There
is a recent SAE paper that compares and contrasts
the two engines. It discusses history, cooling,
lubrication, breathing, ignition, etc. The name of
the paper is "New Generation Small Block V8
Engine," SAE paper 920673, by Anil Kulkarni of
GM. It can be obtained from the SAE by calling
412-776-4841.
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What's the difference
between the F-body LT1 and that in the Corvette?
The
engines are exactly the same with the exception of
the air intake and the exhaust. Also the Corvettes
have two knock sensors and 4-bolt mains compared to
1 knock sensor and 2-bolt mains on the F-Bodies, respectively.
The Corvette has a larger/wider air intake box plus
a dual muffler/exhaust which accounts for the
additional 25hp. The F-Bodies are also supposed to
have a redesigned oil pan as the Vette one doesn't
fit with the F-body cross member.
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Why don't F-Body LT1s
get synthetic oil at the factory like Corvettes do?
Some
Corvette LT1s do not have a engine oil cooler as
the f-body cars do. Since this may cause the Vette
LT1 to run somewhat hotter, synthetic oil is used
for it's ability to withstand higher temperatures
without thermal/ viscosity breakdown. Although,
Corvettes with the performance suspension are
supposed to have oil coolers.
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Which cars got an
engine oil cooler?
Oil
coolers were only available on the 1993 - 1995
models. And even then, the oil cooler did not come
standard on F-bodies. You got the oil cooler as
part of one of the preferred equipment options on a
6 speed car, or if you ordered an automatic
equipped car with the performance rear axle. It
also came on any car equipped with the 1LE option
package.
So,
you would not get the oil cooler on an automatic
equipped car which came with 2.73 rear end gearing,
and you would not get the oil cooler if you order a
6 speed car and then did not order either the 1LE
option package or one of the preferred equipment
groups.
You
can visually inspect your car for the oil cooler.
It's simply a metal tube running from above the oil
filter to the radiator (carrying antifreeze for
cooling) and then back to engine block. The sticker
in the glove box should also have a "KC4"
which is the option code for the oil cooler.
Some
owners of 1995 Formulas and Trans Ams (which should
have the cooler based on having an option above),
actually claim they don't. It's not yet known why,
since sales literature says they should.
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Why has oil coated the
underside of my engine and transmission?
It's
most likely that the seal around your intake
manifold is leaking. While it was originally
thought to be the intake manifold gasket itself
leaking, it's now found to be the sealant being
used. The reason is a gasket is only applied to the
left and right sides of the manifold while the
front and back are sealed with RTV sealant. If the
sealant is applied to a surface which isn't clean,
the oil will be able seep through. This is why the
oil leak is usually found at the rear of the engine
(dripping down onto the tranny). It can be easily
mistaken for a rear main seal leak. And since the
RTV sealant is used on the front of the intake
manifold, it's not uncommon to find it leaking
there, too. A classic symptom of this intake leak
is a rough cold idle. There is a Technical Service
Bulletin (#476111) which calls for the replacement
of intake gasket with a new and improved one, but
that's to deal with a problem of the actual gasket
(used on the left and right sides of the intake)
laminate burning and causing a foul odor to enter
the car through the ventilation system. If you have
a 1994 F-Body, you might be able to get your oil
leak fixed using this TSB (even though it's for a
separate, but closely related problem). Otherwise,
you'll have to have the dealer verify the leak
which will likely be running black-light dye through
the engine. The revised gasket kit is part #
12524653.
Other,
less common areas to check for leaks include the
oil pan gasket, the oil dipstick tube seal (where
it enters into the oil pan), and the timing chain
cover seal.
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Why has my oil
pressure reading suddenly started to drop at higher RPMs?
A
low pressure reading at higher RPMs can be caused
by 3 things: worn rod bearings, the oil pump pickup
set too low to oil pan, and debris caught in the
pump pickup screen. Have you recently had an intake
manifold oil leak on your car fixed (as described
in above)? If so, it's probable that excess RTV
sealant has broken off and got sucked into the
engine where it's now lodged in the pickup screen.
This will cause oil starvation at higher RPMs. Go
back to the dealer and have them check the pickup
screen for any clogs.
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What's that foul,
burnt smell coming in the vents at stop lights?
First
be sure you don't have the oil leak problem
mentioned above. If not, You may have a problem
with oil leaking from the O-ring seal around the tail shaft.
It drips onto the Y-pipe and burns off with the
odor being sucked into the ventilation system.
Reports of replacing the seal (part # 8673526) and
bushing (part # 6260048) seem to fix the problem.
Check with your dealer as these parts are supposed
to have been improved/upgraded.
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What air intake
(induction) upgrades are available?
A
number of companies sell replacement air intakes
for between $130 and $350. Using of one of these
intakes along with a K&N air filter can be good
for a 10-20 hp increase. An aftermarket exhaust
should be installed in addition to an aftermarket
induction system for the best performance gains.
Although, nothing says one mod should be done
before the other. Here are some companies providing
systems:
Arizona Speed&Marine 602-437-2510
C&L Performance 205-882-6813
Callaway 800-231-1121
Car Pro Motorsports 800-670-8862
GM Performance Parts (local dealer)
Hennessey 703-849-5081
L.G. Motorsports 214-272-7753
Lingenfelter 219-724-2552
K&N Filtercharger (local shop)
Paxton/Granatelli 805-987-5555
Random Technologies 770-978-0264
Saga Enterprises 909-275-0726
Prices
range from $150 to $300 depending on the extent and
the quality of replacement parts. Kits like
Hennessey are plastic and replace the air box right
up to the MAF, while Arizona S&M are chrome
replacing the air box up to the MAF as well. Saga
is a bolt-on scoop which goes under the front
driver-side fender, giving a ram-air effect into
the stock set-up. One other alternative is the
Tornado Air Management System (800-500-8880) which
costs around $70. It's a centrifugal air
accelerator that fits into the air intake between
the air filter and throttle body. It swirls the
air, thereby accelerating it (like ram-air) and smoothes
the flow reducing turbulence and allowing more air
to be available per cubic inch for combustion.
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How can I make my own
air intake without spending a lot of money?
While
it may not look like the aftermarket chrome and
molded plastic ones available, this is a sure-fire,
bang-for-the-buck way to create your own air intake
for a significantly smaller amount of cash.
Most
of the following items can be bought at your local
parts store or speed shop for around $50. The
K&N filter is going to be 80% of that cost. You
will need to buy a K&N filter (RE-0870) 9 inch
conical air filter (or one of similar size and
shape), a 2 to 3 foot long and 4 to 4.5 inch wide
flexible hose (Mighty Flow brand intake ducting
(part# 96074) works very well), two 4 inch clamps,
a 1 inch clamp, and a small Fram (or other brand)
crankcase filter. If the K&N filter includes
its own clamp, then you only need to buy one 4 inch
clamp. If you can't find any type of intake ducting
hose, you can use flexible hosing like that on your
clothes dryer, but this type of hose isn't too
rigid and can be easily crushed by the hood. Plus
it's difficult to clamp since it's relatively soft.
Installation
on the the 1993 cars is going to be a little
tricky. Since the 93's are speed density, they
don't have a Mass Air Flow (MAF) sensor (like the
94+) which connects your intake hose to the rubber
snorkle/elbow going into the throttle body. You'll
need to find an INFLEXIBLE piece of tube or hose
with the same 4" - 4.5" diameter which
you can clamp the intake hose and rubber snorkle/elbow
to, thereby connecting the two. A piece of PCV pipe
will work. Or you can saw off the end of the stock
intake piece (which you are removing), and use that
as your connection. The 94's and later make use of
the existing MAF sensor, so there's no need to find
an extra connecting piece.
On
those cars with MAF sensors, use the rubber gasket
that's on the stock intake piece (which you are
removing) by putting it around the MAF. Then put
your new flexible hose onto that. It increases the
diameter of the MAF from about 3.5" to about
4" which helps the hose fit nice and snug.
Simply
clamp the K&N filter onto the new flexible intake hose and drop it down
through the hole that the stock intake piece was sitting in. Then connect the
other end of intake hose to the MAF (or your make-shift pipe piece for the
93's). Everything should just lay snuggly in place. The last step is to clamp
the small crankcase filter to the air pump hose (which was originally connected
to the stock intake piece). Then you're set to go.
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What's that plastic
tube which runs perpendicular to the air intake?
This
is a noise reduction tube which comes with cars
with air conditioning. It stores air at heavy
throttle as it cuts down on the sucking or howling
sound some engines produce. It's not evident
whether this interferes with air flow, but it's
unlikely. From 1996 and on, all cars had the tube
since AC became a standard feature that year. Cars
with air conditioning "delete" (option
C41), like the '93-'95 1LEs, do not get this tube.
The piece without the tube can be ordered from a GM
dealer. The '93 - '94 part number is 25147210 and
'95 is 25157187.
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What aftermarket
performance items are available for the V6?
As
with the LT1s, available modifications include
K&N free flow filters, air induction kits from
API (800-426-8967), Lingenfelter (219-724-2552),
and RK Sport (800-214-8030). Dynomax and Borla
exhaust systems are available from RK Sport. You
can also get JBA headers, Nitrous Oxide systems,
shorter rear gears, low temperature thermostats,
computer reprogrammers, under drive pulleys, and
subframe connectors. Motorsports Technologies Inc.
(MTI) (404-509-3494) carry most of these mods.
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What aftermarket
headers are available for the LT1?
The
following shows the current aftermarket header
manufacturers and details on their products:
Manufacture Size Flange Tubing Stainless Coating Dual-cat?
--------------------------------------------------------------------
Ariz S&M 1 3/4 3/8 14ga No HPC (ceramic) Yes
Edelbrock 1 5/8 5/16 16ga Yes Black paint Yes
Edelbrock 1 5/8 5/16 17ga No Pro-Tech Yes
Hooker 1 3/4 No High temp black No
Hooker 1 5/8 No
JBA 1 5/8 3/8 14ga No Yes
MAC 1 5/8 16ga No High temp coat No
SLP 1 3/4 Yes Yes
Note
the MAC's high temperature coating covers the
exterior and 2" of the interior. The
Edelbrocks alternate between 1 1/2 and 1 5/8 on a
cylinder by cylinder basis, alternating in the
firing order. The JBAs are AR (Anti Reversion)
style which start out 1 5/8, then into an AR tube,
and come out at 1 3/4. The 1 3/4 Hookers are
full-length headers with no O2 sensor bungs, no AIR
tubes, with a collector exiting near mid-tail of
tranny, and requires a custom y-pipe at tail of
tranny to connect to stock exhaust system.
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What's the size of
the LT1 throttle body and can I use a larger one?
A
stock throttle body inlet is 48 mm in diameter. The
matching inlet on the intake manifold which it's
attached to is about 52 mm. Therefore, you can
safely buy a 52 mm one (like that from TPIS) and
bolt it on in place of the stock one without any
other modifications. Anything larger (like the 58
mm job from Lingenfelter) would require the intake
manifold to be bored out to handle in the increased
volume of air. The larger throttle bodies are not
physically larger, they've just been bored out
making the openings larger.
The
additional amount of HP from the 52mm throttle body
is questionable. Some reports show little or no
increase, yet others claim up to 10 more HP. And
some air foils (to smooth the flow through the
throttle body) claim to get another 5 HP. But even
that is questionable. A 58mm throttle body (in
conjunction with the bored intake manifold) might
provide a larger increase in HP, but once again,
results usually vary.
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Why and how should I
bypass the throttle body coolant lines?
A
small amount of coolant is pass through the small
hoses connecting to the throttle body. The main
reason is so that during the winter months, the
higher temperature of the coolant will keep the
throttle body warmer thereby preventing icing.
That's where the problem lies during the other
months. By warming up the throttle body, you're
warming up all of the air passing into the engine
and thus losing some power (since cooler, denser
air makes more power). It is also believed that
during the hot, summer months, the coolant
pass-through works to cool off the throttle body.
So you must be careful when bypassing this so as
not to lose it's benefits.
To
do the bypass, first remove the small hose going
into the throttle body on the driver side. You will
probably have to remove the rubber intake elbow and
black alternator brace. Make sure you have some
rags handy to catch any coolant that my drip out.
On the passenger side of the throttle body there
are three hoses. Remove the lower one (which is
very short and has a 90 degree turn to connect to a
metal intake manifold hose). You may have to remove
the other two hoses along with the sensors to get
better access to the clamp. Then pull the
disconnected driver side hose over, and connect it
to the metal intake manifold hose from which you
just disconnected on the passenger side 90
degree-turn hose. Hold onto that 90 degree hose in
case you need it in the future.
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Why and how should I
bypass the EGR valve/line?
The
EGR re-routes some of the exhaust gases back into
the intake/combustion chamber. This is basically
done to reduce emissions. Blocking it off will
temperature of the intake since the gases fed back
through the EGR are very hot. Lower intake
temperature produces more power, but the amount of
gases that are passed through the EGR is VERY
minimal and probably won't result in much (if any)
performance gain. The drawback is increased
emissions.
If
you look at the back of the passenger side of the
intake manifold. You will see a tube that runs up
to the manifold from the exhaust manifold. Take the
tube off, pull it back, and look at it. You will
see a two bolt pattern with a hole in the middle.
Make some kind of plate to block the hole and
guided on the bolt hole. You can make the plate out
of any piece of scrap metal (sheet metal is fine).
Put the tube back on with the plate in place.
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Why and how should I
relocate my idle air temperature (IAT) sensor?
The
stock position of the IAT sensor (in the rubber
intake elbow just before the throttle body) causes
it to pick up a lot of intake manifold heat. This
can be an extra 10 degrees F at highway speeds and
30 degrees F (or more) at idle. This causes the
computer to retard the timing (zapping power) and
causes the engine to run overly rich (since the MAF
thinks there's more air going through it than there
really is due to artificially high temperatures).
By moving the IAT towards the air filter (away from
the hot manifold), the ECM will get a more accurate
reading of the actual intake temperature and will
properly adjust the timing and fuel/air ratio.
There's no need to worry about the air heating up
more as it passes beyond the new location of the
IAT since at wide open throttle, it takes the air
15/1000 of a second to travel from the air filter
into the engine.
First,
remove the IAT sensor from the bend in the rubber
intake elbow. Then plug up the hole on the elbow
with something. The site you relocate the IAT to
will depend on what air intake (stock or
aftermarket) you have. You want it as close to (if
not, right in) the air filter. Snip the sensor
wires first, as you can splice in lengths of wire
after the sensor is in its new location. On a stock
air box, you can drill a hole into the back of the
box. On aftermarket intakes, try drilling a hole in
the bottom of the air filter itself (works best on
K+N conical filters) or on the pipe/tube to which
the filter is connected. Either way, make sure the
hole is placed in location which sees the air AFTER
it passes through the air filter (otherwise debris
may ruin the sensor). Then insert the sensor into
the hole. After that, just splice wires to
reconnect the sensor, solder the connections and
protect with electrical tape or heat shrink-wrap.
Note,
on ram air Pontiac cars (Firehawk and WS6), the IAT
sensor is already located in the intake box. On ram
air Chevy cars (SS), it doesn't appear you can
relocate the sensor since the intake sits right
over the hot intake manifold (which you're trying
to get away from).
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What temperature is
the stock thermostat and can I go lower?
Stock
on the 4th generation cars is a 180 degree
thermostat. This should be good enough for any but
the most seriously modified car. Although, you can
go down to 170 or even 160. Hypertech sells a 160
which is supposed to be combined with their
performance chips/programmers. And contrary to some
opinions, the vehicle will not drop out of closed
loop with 160 degree thermostat since that depends
primarily on O2 sensor temperature, not engine
temperature.
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What performance
"chips/programs" are available?
For
the 1993 cars, Hypertech, Jet Technologies, Z
Industried and Superchips make replacement chips.
HP increases vary from 15 up to 30. However, in
1994 and after, chips are soldered into the
on-board computer and can't be removed. Hypertech
gets around this with their Power Programmer, a
hand- held "computer" which plugs into
the PCM module under the driver-side dash, and
reprograms the stock chip. Performance gains are
almost the same as replacing the chip. The
programmer costs about $300, considerably more than
the $150 - $200 you'd expect to pay for a
replacement chip.
The
Hypertech Program increases redline and shift
points (on auto trannies) by about 500 RPM over
stock, and it improves the fuel and timing curves.
The cooling fans are enduced to coming on at lower
temperatures. Any type of speed limiter will be
overridden. It can also adjusting the speedometer
for changes to aftermarket gears (like a 3.73).
However, it doesn't modify the partial throttle
shift points on cars with automatic trannies. Thus,
even with the programmer, partial throttle shifts
will still occur at higher RPMs than with the stock
gearing. But most companies can create a custom
chip or program to overcome this.
The
Programmer can also be sent back to Hypertech to be
reprogrammed to take advantage of modifications
like headers, camshafts, and superchargers. One
other thing to remember is to run 92+ octane fuel
with the chip/programmer. Otherwise the engine is
probably going to knock due to the timing change.
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Can I keep the stock
thermostat after installing a performance chip?
Yes,
however you should do a little research first.
Namely, find out if the new chip modifies the
temperature at which the cooling fans come on and
off. For instance, the Hypertech chip/program
lowers the temperature at which the fans turn on
and off. It turns the fans off at approximately 175
degrees F. This will a problem with the stock 180
thermostat because once the engine warms up enough
to turn on the fans, the thermostat will cycle to
bring the engine temperature down to 180 degrees F
and keep it there. This could keep the temperature
from getting down to 175 where Hypertech turns off
the fans, and the fans could run continuously. This
isn't bad for the engine, but it is bad for the
fans in that it will probably burn out the fan
motors.
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Can the fans be
rigged to come on while the engine is not running?
The
following instructions are for all mid-1994 to 1995
production models. Slide two wires into the under hood
fuse/relay box in the D2 and J2 slots for the #1
fan relay (D) and #3 fan relay (J). Splice them
together and run them through a 1 amp fuse. Hook
another wire to the ground. Then, with the ignition
on, connect the ground wire to the spliced fan
wires and both fans come on at high speed. When
you're not using the setup, remove the ground wire
and tuck it away so you can't see it. The J2 slot
is also connected to the F5 slot in the #3 fan
relay, so you can use either one, it seems. This
essentially provides the ground signal to the
relays just like the PCM would when FAN CNTL A10
and FAN CNTL A11 codes are set in the PCM. The
relays click when you make the connection, so
everything should be working just like if the
computer set both codes.
This
set-up requires the ignition to be in the
"On" position and requires no
splicing/cutting of any stock wiring. This works
great to cool off your car at the drag strip
especially when the engine is off.
1993
and early-1994 cars don't have dual speed fans and
therefore have no #3 (J) fan relay. For these cars
you can just round a ground to D2 for the primary
fan and F5 for the secondary one.
On
1996 and later models, the wiring has changed and
the above procedure will blow the fan fuse and turn
on the Service Engine Light. So instead, in the under hood
fuse box, remove the relay labeled 'F'. Molded into
the plastic on the box itself where the relay was
is the letter 'F' as well as numbers for each
connector. You want to connect the pin labeled '3'
with the pin labeled '4'. Note that this is a real
feed, and bypasses the relay, so use at least 14
gauge wire. Current is 12A startup, and 8A running.
Use a switch that can handle the load.
Solder
the wires to the bottom of the fuse box, and put
the switch just in front of the box where there
already is a unused hole. Black wires and a black
switch makes it looks neat. With this setup, you
can turn the fan on whenever you want, even with
the engine off. Don't forget to put the relay back
once you locate the correct connections. Without
relay, a code is set and the Service Engine light
is lit. If you happen to get a light, it won't go
away until you reset the computer. The easiest way
to do that is to disconnect the negative battery
cable for about 1 minute.
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Why am I
losing/smelling antifreeze, but nothing seems to be leaking?
Assuming
you've checked the radiator cap and main hoses,
it's possible your water pump is leaking. There's a
small (2 mm) weep hole on the bottom of the pump.
Black stains surrounding the hole indicate coolant
seepage which is an early warning sign of pump
failure. Another indication of a pump leak is if
there's green-black staining on the small rubber
hose that plugs into the engine block (just behind
the main crank belt pulley). Any coolant dripping
out tends to drip directly onto the rubber hose
where it then flows down to the hot engine block
and is boils off (leaving the staining). If you
smell coolant at stop lights for instance, it's
from it burning off on the block. Since the coolant
boils off, the slow leak never has a chance to drip
onto the ground, so you'll never see it.
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What fuel pressure
setting will give me the best performance?
Stock
settings on the 4th gens are around 43 to 45 psi.
The best (adjusted) pressure seems to be variable
depending on your cars specific modifications. But
even cars with similar mods react differently to
pressure adjustments. Some people claim 47 to 49
psi is best, while others find a lower setting like
39 to 42 psi is best. From testing, it seems the
computer will adjust itself to a fuel mix level it
is comfortable with. So even if you turn up the
pressure to 53 psi, after a few wide open throttle
runs, the computer will lean out with each
successive run, bringing itself down close to
levels as though you were running 44 psi. So while
adjusting the fuel pressure may have some effect,
the computer retains a great deal (not 100%) of
control as it will adjust the fuel mix based on
each run. So you need to make multiple wide open
throttle runs between adjustments of pressure to
ensure you get to final equilibrium with the
computer. The best way to find what's best for your
car is trial and error.
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How easy is it to
change the spark plugs on the LT1?
The
easiest way is probably to remove the Y-pipe. Soak
all the bolts with WD-40 (best done the night
before) and remove them. The Y-pipe and cat should
drop right out. Doing this, will give you access to
all of the plugs from under the car, except for
plug #2. For that one, it's easiest to remove the
alternator to get at it from the top.
If
you're into doing things the hard way (that is, not
removing the Y-pipe), make sure you have a lot of
time on your hands and a lot of band-aids for your
hands and arms. Before you do anything, realize
that the plugs are supposed to be good for up to
100,000 miles, but only time will tell.
Here's
the best method (without Y-pipe removal) found so
far:
PLUG ACCESS TOOLS REQUIRED COMMENTS
1 Top Socket w/ Swivel Easy
3 Top Socket w/ Swivel Easy
5 Bot Socket w/ Swivel Slightly tricky
7 Bot Socket w/ Swivel Watch out for O2 sensor
2 Top Socket w/ Open End AC & Exhaust AIR Tubes make it NASTY
4 Top Socket w/ Swivel Completely blind on this one
6 Bot Socket w/ Swivel Difficult to reach, but doable
8 Bot Socket w/ Swivel Skiny arms are a MUST
NOTES:
-
Be
sure to replace the heat shield covers on
plugs 6, 7, and 8.
-
If
you're changing the wires, be sure to route
the #7 wire through the the factory heat
shield that runs between the exhaust manifold
and the block. If it makes contact with the
manifold, it's going to burn right through.
-
Use
anti-seize compound on new plugs. The factory
didn't which made removal that much more
difficult.
-
You
may want to do the easiest plugs first,
(saving #2 for last) to give yourself a sense
of accomplishment and to boost your
self-confidence.
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What spark plugs are
available for the LT1?
Here's
cross reference of the different plugs along with
the part numbers: Stock heat range:
Colder
range:
-
AC
Delco R42LTS
-
Accel
514
-
Autolite
104
-
Bosch
HR8DPX
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Champion
RS9YC
-
Motorcraft
AGRF42
-
Nippondenso
T20EPR-U
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NGK
BPR6EFS
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Why has my car
developed a bad hesitation problem (Optispark)?
First,
check to your spark plugs wires and make sure none
have come off. A few people have already
experienced this problem. Then rule out any type of
problem with the fuel system (injectors or pump)
and air intake (loose clamp or hose). If those are
okay, it's most likely your Optispark system. It's
the pseudo-distributor of the distributorless LT1
where all the spark plug wires connect into. If
water gets in there, it's as good as toast.
Definitely head to your dealer to get it replaced
as it will start eating your plug and wires in no
time if there's something really wrong with it. A
hesitation problem due to the Optispark will
usually be noticed in certain RPM range. Most
commonly, it is in the upper range (3500 - 5000
RPM). But it can certainly develop in the lower or
mid ranges as well. You might even get some
back-firing. The problem is most common on the 1993
and 1994 LT1s, as in 1995 a vacuum line was added
from the intake manifold to the Optispark to draw
moisture out of the unit. However, excessive water
can cause even 1995 and later cars to develop the
problem.
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Why
does my car have a slight stumble upon slow acceleration?
If
it usually occurs from idle when then engine is
warm and you get a short backfiring just before
shifts, then it's probably the coil wire or the
coil itself. If you notice the headlights flicker
or flash at night when the car stumbles, it's
almost assured the coil and/or coil wire need
replacement.
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Should I use
self-aligning or non-self-aligning rockers?
You
can use either since the LT1 has screw in studs,
but non-self-aligning rockers require guide plates.
This means longer rocker studs are needed as well
as hardened pushrods. And that means more money.
But the advantage of the non-self-aligning ones is
the reduced valve train noise.
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What aftermarket
camshafts are available for the LT1?
The
following shows the current cams and their specs:
Manufact. Duration Lift (1.5) Lift (1.6) Lobe Notes
Int Exh Int Exh Int Exh Sep
----------------------------------------------------------------------
CompCams 210 220 500 510 533 544 114
CompCams 230 244 510 540 544 576 114 heads, headers
CompCams 230 242 510 510 544 544 112
CompCams 215 224 500 500 533 533 112 custom grind
CompCams 215 224 499 499 532 532 114 2200-5700
CompCams 220 230 510 510 544 544 114 2500-6000
Crane 198 206 480 480 512 512 112
Crane 214 220 452 465 481 496 112
Crane 204 214 429 452 458 482 116
Crane 208 214 438 452 467 482 112
Crane 214 222 498 509 520 542 112
Crane 218 218 498 498 531 531 116
Crane 215 224 499 499 532 532 112 blower, custom
Crower 219 227 498 515 531 553 108
Doug Rippie 222 230 508 528 542 563
GM 450 450 480 480 LT1 stock ('93)
GM 201 208 450 460 480 491 LT1 stock ('94-'95)
GM 205 207 447 459 477 490 117 LT1 stock ('96)
GM 203 210 446 449 476 479 115 LT4 stock ('96)
GM 474 510 506 544 112 ZZ3*
GM 218 228 492 492 525 525 112 LT4 HOT
GM(Crane) 214 224 488 509 521 543 112
GM(Crane) 222 230 509 528 543 563 112
GM(Crane) 234 242 539 558 575 595 112
LG Motors 211 220 500 500 525 525 112 1500-6200
LG Motors 220 220 500 500 525 525 112 1800-6400
LG Motors 220 230 480 480 512 512 110 3000-6500
LG Motors 230 230 480 480 512 512 112 3000-6500
Lingenfelt 211 219 499 525 530 560 112 1600-5200
Lingenfelt 213 219 462 471 493 502 112 1600-5200
Lingenfelt 219 219 525 525 560 560 112 1600-6200
Lunati 213 218 446 468 475 499 110 1500-5300
Lunati 215 218 489 503 522 537 113 1500-5500
Lunati 232 242 510 525 544 560 108 2000-6500
Lunati 242 252 525 540 560 576 108 2200-6800
MTI 210 220 500 510 533 544 114
MTI 230 244 510 540 544 576 112
TPIS 212 226 483 520 515 555 112 ZZ9 ('93-'94)
TPIS 212 226 483 520 515 555 112 ZZ9 ('95-'97)
Note
the ZZ3 requires a longer camshaft dowel pin for
use in 1995 and later LT1s (GM part number
10214485). However, the replacement pin requires
that the pilot hole on the cam be drilled slightly
larger (in depth and width) to accommodate the
larger pin. Note also the hole is tapered at the
top and the bottom. That is, at the face of the
cam, it's 5/8" across, however, as you go in,
the width narrows to 1/2". The depth is 1
5/32", however, the very bottom 3/32" is
tapered inwards to a point. So if you have a flat
pin, then it will only go in 1 2/32" since the
tapered part won't be wide enough to accept the pin
any deeper.
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What aftermarket
camshafts are available for the V6?
The
following 2.8L engine cams fit the '93-'95 3.4L
engine:
Manufacture Duration Lift
Int Exh Int Exh
-----------------------------------
GM 12363220 204 216 427 454
GM 12353919 204 214 420 442
GM 14031378 196 203 394 410
Crane 254112 198 204 401 403
Crane 254122 204 214 423 423
Crane 253901 204 216 427 454
Crane 253941 216 228 454 480
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What's that knocking
noise when the engine is cold?
While
the fuel injectors have a distinct tapping noise
(usually under higher throttle), at a light load
and low speed there seems to be "piston
slap" on some people's cars. This occurs in
some of the Vette LT1s as well. There doesn't seem
to be anything in the service manuals. Most dealers
seem to acknowledge the problem and say it's normal
which it seems to be. For some reason, the pistons
shrink enough in the cold weather so as to
"slap" around a little. Once the car
warms up, the noise should go away.
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What's
that ticking noise when the engine is under load?
It
might be the EGR tube. It might sound like an
exhaust leak from one of manifolds, but check for a
possible crack in the EGR tube.
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