Quote:
Originally Posted by sootieoil
I bought a set of cylinder heads for my 7.3 and realized the intake ports are considerably much smaller than my original 6.9/7.3 heads.
The intake manifold is much larger than the ports and it will need much porting to make match.
The exhaust port and bowl looks the same as original I wonder wht the intake was cast smaller anyone have anything to add?
I will post pics soon
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Enter 1988 and the completion of a totally new truck with the introduction of Navistars new 7.3 liter ID!
diesel engine. Although not revolutionary, there are many improvements that accompanied the introduction of
the new engine.
The 7.3 now used select fit pistons at the manufacturer. The pistons were stamped with A, 6, C, and D and
had to coincide with the letter stamped at the base of the cylinder bore. Replacement pistons were stamped
with an S. New plateau honing procedures accompanied the select fit pistons for better ring seating and
engine break-in. Also the lower rear corner coolant passages at the head mating surface were blocked to
coincide with plugged coolant passages on the heads. This was an effort to reduce coolant seepage during
cold start and warm-up.
Most of the changes were made to the heads, making them not interchangeable between the 6.9 and 7.3. The
precombustion chamber volume was increased to 20.42 cubic cm for emissions certification. Even though the
pre-cup chamber inserts are physically interchangeable, the throat was re-designed and an 88 stamped on
the 7.3s to distinguish them. The glow plugs were now off-center and the injection nozzles retracted .060 for
emissions. The injector lines were also now .060 shorter to coincide with the injector retraction. However,
this is negligible and the injector lines are still interchangeable between the two engines. The new 7.3 valve
stem shields are larger to reduce emissions and both intake and exhaust shields are now color coded, though
they are interchangeable. Also the 7.3 exhaust valve metallurgy has been changed, increasing the nickel,
chrome, and silver content while reducing the manganese content. This makes the 7.3 valves usable in a 6.9,
but not the other way around. The gasket cutouts between cylinders were eliminated to prevent cosmetic
corrosion and improved viton oil drain back seals were added to the gaskets. The 7.3 also used a new
embossed front cover to aid in gasket sealing and eliminate water pump replacement due to seepage.
Specifications for the 7.3 are as follows.
Max HP 185 © 3300 RPM
Max torque 338 ft/lb © 1800 RPM
Cylinder bore 4.11
Stroke 4.18
Displacement 7.3 liters or 444 cubic inches
Comp ratio 21.5:1
Top deck thickness .560
Oil drain back holes 7/16
Cylinder head bolts ½ -13 UNC 6 long
Head bolt washers .134 thick
Head bolt torque lOOft/Ibs new or used
Head gasket fire ring ID 4.22
Glow plugs off center in pre-cup
Pre-combustion chamber volume 20.42 cubic cm
This might help in determining if you have the right heads, hope they didn't send you 6.9 heads.
and found my old post, so I updated.
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