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Exhaust Manifolds
Over the years, from 1955 to the present, smallblocks came with a variety of cast-iron manifolds, and
in some late-models, with tubular stainless steel exhaust manifolds. These manifolds also had differing
shapes, exit angles, places where the exhaust dumped out of the manifold, and bolt bosses to help
mount accessory brackets. Some of the manifold runners ran above the spark plugs and some had
runners that ran below the spark plugs. A few extremely rare optional Z-28 302 Camaro tube headers
were available. These were shipped uninstalled in the trunk of the Camaro Z-28s from the factory,
then the dealer or owner installed them.
1965 300 hp 327 exhaust manifolds Cast iron exhaust manifold on a 1965 Chevelle 327
These factory cast-iron exhaust manifolds for a
’65 327/300hp Chevelle have runners below
the spark plugs.
The cast-iron exhaust manifold found on a ’65
327/300hp motor for a Chevelle. Note the
spark plug heat shields in place.
Exhaust manifold with alternator bracket 1996 LT1 exhaust manifold
This factory cast-iron exhaust manifold for the
driver’s side has a lower generator/alternator
bracket cast into it. Some engines mounted the
generator/alternator to the passenger side, and
the exhaust manifold has a lower bracket cast
into that side.
Shown is the production exhaust manifold found on
a ’96 full-size police vehicle equipped with the Gen.
II LT1 350. Most, but not all, exhaust manifolds will
bolt up to any Gen. I or II production head,
however, the exhaust manifold may not fit in the
engine compartment of a particular vehicle. The
necessary clearance must be there for motor
mounts, front crossmembers, steering columns and
steering boxes, firewalls, etc. If you are going to use
production exhaust manifolds, use a set that was
intended for the particular vehicle you have.
Chevy designed these differently shaped manifolds with the primary goal of moving the exhaust gases
to the rest of the exhaust system while still fitting in the particular vehicle and mounting whatever
accessory brackets were necessary at the time. Almost all smallblock exhaust manifolds bolt onto a
smallblock head, but the manifolds may not physically fit inside a specific engine compartment. Frame
crossmembers, steering boxes, firewalls, upper control A-arms and steering links might get in the way
if you use an exhaust manifold that was designed to be used in a different vehicle. Other manifolds
may interchange and fit in the engine compartment. On some later-model passenger-side exhaust
manifolds, the rear exhaust manifold bolt hole has been moved slightly to the rear to fit seven-hole
cylinder heads.

The least restrictive Gen. I cast-iron factory manifolds were the large-diameter-outlet (21⁄2") Corvette
ram’s horn manifolds that had a straight down exhaust exit. These manifolds are still available from
Chevy under (PN-3797901 LH and 3814970 RH). Both of these manifolds come with mounting bosses
located on the side of the manifold so you can mount a generator or an alternator on either side with
a short water pump and the appropriate upper and lower mounting brackets. (PN-3846563 LH) is
another 21⁄2"-diameter-exit ram’s horn, driver’s-side manifold, but it has a mounting boss on the front
end of the manifold to accommodate a generator or alternator. Most production ram’s horn exhausts
had smaller diameter exhaust outlets of 2". Some production ram’s horn manifolds had a center dump
exit, and others had an exit that was slightly angled towards the rear.
Choke hook up for exhaust manifold
Chevy ram horn exhaust manifold
This exhaust manifold shows the holes and
fitting on the passenger side, which hooks up
to the choke heat tube between the exhaust
and the carb. If you need this feature, make
sure that the manifold you use has a provision
for the heat tube location.
Chevy is still making ram’s horn cast-iron exhaust
manifolds. This one has a provision to mount the
generator/alternator on the passenger side.
Early cast iron rams horn exhaust manifold
Early ram’s horn exhaust manifolds
came with different bolt bosses to
mount accessories. The center dump
may be straight or angled towards the
rear and had a number of exit
diameters, up to 21⁄2" found on some
hi-po Vettes. They are still available
from Chevrolet Parts.
The 1986 to ’90 Corvettes used tubular stainless steel exhaust manifolds that had a center exhaust
dump. These are listed as (PN-10055734 RH and 14087511 LH). Make sure that these exhaust
manifolds will fit in your vehicle’s engine compartment before you do an interchange. These manifolds
do have A.I.R. fittings and tubes.

GM/Performance Parts also has a number of stainless steel Tri-Y tubular exhaust headers available
for 1985 to ’92 Camaro and Firebird applications. The mandrel-bent primary tubes are 15⁄8" in
diameter and have a 3"-diameter outlet. A.I.R. tubes and fittings are in place. These tube headers are
designed to work with low-restriction exhaust systems, including the low-restriction catalytic converters
that are available from GM/Performance Parts, but they can be adapted to other applications.
Depending on the vehicle and model year application, these smallblock V-8 Tri-Y headers are
available under (PN-12341404 through 12341408).

The stock exhaust log manifolds are rather restrictive, so anything you can do to reduce restrictions in
the system will be helpful. GM/Performance Parts has introduced a line of cat-back exhaust systems
that are emissions legal for later model trucks, vans and passenger cars. These cat-back exhaust
systems feature large, mandrel-bent, 2" or 3" diameter tubes and low-restriction mufflers. They fit
stock mounting brackets, and they increase flow approximately 35 percent over the stock systems.
If you are building a performance motor and you have significantly improved the induction side of the
motor, you must also improve the exhaust side of the system. It will do little good to put in a larger
cam, better intake manifold, carburetor and performance heads and leave on the restrictive cast-iron
exhaust manifolds and stock exhaust pipe system. The increased air/fuel volumes flowing into the
motor must also be able to flow out of the motor. The factory production cast-iron manifolds,
especially the log type found on many smallblock-equipped vehicles are quiet and long-lasting, but
they are restrictive. Adding a good, well-designed, low-restriction exhaust system will free up
horsepower in a street-driven smallblock.

GM used cast-iron and a few stainless steel exhaust manifolds on all smallblock motors, and you can
interchange these between Gen. I, Gen. II and Vortec production engines. Depending on the make
and model year, however, changes have been made in the runner shape, outlet angles and the
number of exhaust bolt holes of these manifolds in order to fit various vehicle chassis and engine
compartments. All Gen. I and II smallblock cast-iron exhaust manifolds physically bolt up to any
production Gen. I or II smallblock head, but the manifolds from one vehicle style may not fit in a
different vehicle. In addition, air injection tubes were added to the exhaust manifolds of later models to
help lower emissions.
Cast iron exhuast manifold Cast iron exhaust manifold
cast iron exhaust manifold
Cast-iron exhaust manifolds have
come in many shapes over the years.
Some have provisions for A.I.R. fittings
and some do not. Some have heat
shields and some do not. Note the
various positions used for the exit
dump.
Exhaust manifold with angle plug heads Spark plug heat shields
The exhaust manifolds in the ’96 Camaro Z-28
SS work with angle plug heads.
Spark plug heat shields should be retained;
they help protect spark plug wires from the hot
exhaust manifolds.
Performance muffler Hooker low restriction muffler
More and more race associations are requiring
mufflers on race cars in order to keep their
racetrack neighbors happy. This will drive the
performance muffler makers to provide better
systems with lower noise levels while still
providing exceptional flow without restriction.
Hooker makes a line of low-restriction,
high-flow mufflers. The power levels in many of
the modern muffler designs are equalling, and
in some cases surpassing, the power found
with open exhausts.
To avoid the spark plug access problems sometimes created when using angle plug heads, use the
production exhaust manifolds or tube headers that were designed to provide enough clearance with
these heads. You can also try a spark plug with a shorter, small diameter porcelain section, which is
designed to clear the exhaust manifolds when using angle plug heads.

Gen. III LS1 350 engines use a stainless steel, double-wall exhaust manifold with a good runner
design. This exhaust manifold fits the unique exhaust bolt pattern found on the Gen. III LS1 aluminum
heads. The tube runners are manufactured with an outer and an inner tube, which insulates the hot
exhaust gases from the engine compartment and helps quickly heat up the catalytic converter.
Because of the differing exhaust manifold bolt pattern found on Gen. III heads, these Gen. III exhaust
manifolds will not bolt up to Gen. I or II heads.

Factory cast-iron exhaust manifolds bear cast-in part numbers and casting dates, which may be
important if you’re doing a numbers matching restoration. The casting numbers are visible when the
manifolds are in place. The casting dates, however, are generally on the side of the manifold that
faces against the engine, and they can’t be seen once mounted to the engine.
Be careful when buying used cast-iron exhaust manifolds if they are off a motor. Many of the exhaust
manifolds crack with age and then leak when you install them. The cracks may be under the heat
shields and can’t be seen. If the exhaust manifold is still installed on a running motor, listen for any
cracks and leaks before you buy.

Low-restriction catalytic converters that are street-legal and pass 50-state emissions requirements
are also available from aftermarket sources, as are low-restriction mufflers and exhaust pipe
assemblies, with large pipe diameters. Now, I said low-restriction, not loud. Just because a muffler is
loud does not mean it is a low-restriction muffler. In fact, many airflow tests have shown that some of
the loudest mufflers, are also some of the most restrictive. Shop around. Many aftermarket companies
have spent the time developing low-restriction street exhaust systems. Some of these muffler systems
approach or equal the power levels of open exhaust headers, yet they are much quieter. If you are
racing in a restricted class or at a track that requires mufflers, some power can be gained by selecting
a good, low-restriction muffler system.

With the stock factory exhaust manifolds, try to use a dual exhaust pipe system of at least 2" pipe on a
stock motor and 21⁄2" to 3" on a performance street motor with tube headers.
Previous


This has been a sample page from

Chevrolet Small Block Parts Interchange Manual Chevrolet Small Block
Parts Interchange Manual
by Ed Staffel
Beginning with the earliest small block and carrying through the
very latest "Gen III" models, CHEVROLET SMALL BLOCK PARTS
INTERCHANGE MANUAL provides complete factory parts
interchange information, allowing the hot rodder to custom-build
his own high performance version of the famous Chevy "Mouse"
motor from off-the-shelf parts. Includes factory numbers, casting
marks, production histories, suppliers, component performance
capabilities, etc.

Temporarily Out of Stock - More On their way!


This is a great book and one that any
enthusiast will love!
View Sample Pages
1)
Engine Blocks
2) Crankshafts
3) Oil & Lubrication System
4) Timing Chains & Covers
5) Cylinder Heads
6) Intake Manifolds
7) Ignition Systems
8) Gaskets
9) Exhaust Manifolds
Condition: NEW
Softbound
8.5 x 11-inches
144 Pages
300 B/W Photos
Item: SA55P
Price: $22.95
Click here to buy now!


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