GM Crate Motor

Last Updated 09/21/06

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Crate Motor Selection and Installation

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I selected the GM ZZ383 Crate Engine 425HP 12498772 motor in July 2006.  I placed the order with Jeg's, primarily because of a $350 price increase on July 1st at Summit, my preferred performance parts vendor.  Summit says they will match the price but I was afraid Jeg's would also increase the price.  It's probably a pass on increase from GM.  All sources I checked were equally high except Jeg's.

I like the torque and horsepower.  Another reason was the requirement to support the smog equipment (EGR) on the intake.  Some of the motors come with intake manifolds but not with EGR support so it has to be replaced.  It should be noted here that it is likely that the EGR will be for appearance only.

I also own a new Holley spreadbore carburetor that I need to use.  All the engines that came with the intake installed only supported the standard bore carburetor.  There's no room to add an adapter under the hood of a 77 Corvette.

The engine will be mated to a new Keisler / Tremac 5 Speed.  Installation of the Keisler kit is discussed in the How To section.

The engine is basically a long block assembly.  Additional parts are required for assembly.  Ordered the following:

  • Intake - GM 12496820 - Lo Rise with EGR - Vortec design - Std or Spreadbore carburetor.  This is what you want if you want to keep your EGR valve and use a spreadbore carburetor.  Exhaust gases for the EGR do NOT come from the cylinder heads.  There is no crossover support on these heads.  If you need to connect to the exhaust for the EGR, you do it through a connection at the front of the manifold near the thermostat.  I am not sure how I'd do this with stock exhaust manifolds on a 77.  The treads for this input are a strange size I have not identified.  They are close but slightly larger than 1/2" NPT.  This port and the EGR mount must be closed or you will have a vacuum leak. 

  • Distributor - GM HEI
  • Thermostat housing - Mr. Gasket
  • Fuel pump - Stock Carter
  • Fuel pump rod
  • Water pump - Edelbrock
  • 2x Dorman original style exhaust manifolds to be ported to match D ports on heads
  • Intake and exhaust gaskets
  • Bolts
  • Heat riser eliminator spacer
  • Chrome / aluminum valve covers


Supporting Links



Total Cost

  • TBP

My Selection Criteria

GM Crate Motors are available from a number of sources.  My primary supplier is Summit but I bought just the motor through Jeg's due the recent price increase.

My primary reason for replacing the engine was reliability and the uncertainty of the current engine.  I didn't know the history of the current car.  The motor looks like is was rebuilt not too long ago.  It seems to have no problems other than very minor (1 drip/day) oil leak and a slight lifter tick.  With the vehicle headed to Europe soon, I decided it was cheaper and easier to replace it while it was still in the USofA.

Choosing an engine to replace my existing L-82 was no easy task and it is full of compromises.  Gas mileage is a factor given it's eventual home.  That's partially offset with the installation of the Keisler 5-speed kit.

Reliability is a concern.  That's my reason for picking a new engine instead of rebuilding the original L-82.  Vehicle inspections in Spain can be tough on little things you don't run into in the USofA.  They don't like oil leaks. 

Ease of installation is important.  I don't have the time to make any modifications in the fit and operation.  Accessory drive brackets must fit.  SMOG equipment must be maintained, at least while it's here in the Peoples Republic of California.

My final candidates

Chevy 350, 330 hp

Cast Iron Vortec Heads

ZZ4 350 C.I.D. 355 HP Engine HT 383 C.I.D. 340 HP Engine ZZ383 C.I.D. 425 HP Engine
$2399 $3788 $4095 $4789


  • 9.1 Compression

  • Chrome valve covers

  • Cost

  • Chrome valve covers
  • Intake included - But No EGR support
  • Harmonic Balancer included
  • Distributor included
  • Roller Cam
  • 9.1 Compression
  • High 435 Ft/Lb Torque
  • Intake included
  • Roller Cam
  • Harmonic Balancer Included
  • Plugs included
  • 449 ft./lbs. Torque
  • Lots of HP
  • Roller Cam
  • Aluminum Roller Rockers
  • Dual bolt pattern fast burn aluminum heads support both Vortec and Standard intake manifolds.
  • GM Intake available for EGR support and it fits under Corvette hood
  • Harmonic Balancer Included


  • Bare engine - needs $1000 in additional parts for intake, distributor, water pump, balancer, and fuel pump.

  • Unable to find an intake manifold that works with the Vortec heads that supports EGR valves.

  • 10.1 Compression - Premium Fuel
  • Long water pump - not usable on Corvette
  • Harmonic Balancer not usable - 8" - Need 6 3/4"
  • Cost over the 350/330 for small HP gain.
  • Power is in the low end - Trucks and towing
  • Painted Valve Covers
  • Cost!
  • Aluminum head reliability?  Personal concern.
  • Painted Valve Covers
  • Exhaust Manifold needs to be ported to attempt to match large D exhaust ports.  Vortec and "882" heads are rectangular.
  • Bare engine - needs $1000 in additional parts for intake, distributor, water pump, and fuel pump.


Optional Parts

The newer motors might not be compatible with existing parts or you might be converting from Auto / Manual shift.  In my case, the existing flywheel is not compatible with the newer SB design.  I ordered new components from Keisler Engineering along with the 5 speed conversion. 

Old parts look really bad installed on new parts.  I took the opportunity to replace the Bellhousing and Exhaust Manifolds with brand new parts.

  • Flywheel (required)
  • Clutch Assy (easy to do)
  • Bellhousing (cosmetic)
  • Exhaust Manifolds / Headers (cosmetic / performance)
  • Water pump (required if motor is supplied with long nose design)

Miscellanous Parts

You run into "things" needed to finish the job.  Here are some of the little things I needed.

  • Spark plug wire holders compatible with the centerbolt valve covers and stock exhaust manifolds.  I picked the Russell parts but had to make some major modifications.  The modifications have been described on this site.
  • 7/8" Plug for the intake.  See below Gotcha's.
  • EGR block plate and gasket.
  • Compatible carburetor mounting studs.  This was a PITA because of the Holley Spreadbore I used.  Had to grid some down to fit.
  • Fuel line




  • Remove old engine
  • Replace with new engine
  • Adjust
  • Test drive!

Ok.  Greater detail will be provided at the end of the project.


  • RAM's Horn Exhaust Manifolds

They bolt up but the square ports don't match the new heads.  You need to do a bit of grinding to come close to matching the "D" ports on these engines.  You will not have 100% match but you can get close.  Pictures and procedure is published on this site.

  • No Exhaust Crossover

There is no exhaust crossover provided with these heads.  The Heat Riser on the right exhaust pipe just below the manifold must be removed or blocked open.  If not, there is no place for the exhaust to go when the engine is cold and the valve closes.  I ordered a crossover eliminator from Ecklers Chevy (not Ecklers Corvette - Same company, different catalog).  There is no exhaust for the EGR valve either.

The intake I ordered supports using the EGR valve.  The exhaust gases must be plumbed into the intake near a 7/8" pipe behind the thermostat housing.  If you are not using the EGR, you must plug this opening and use an EGR block plate.  7/8" plugs are not that common.  I ordered a GM Performance Parts piece from Summit.  Costs almost $20!

  • Water pump must be replaced

Engine comes with long nose style.  Corvettes use short nose.

  • Composite timing cover interference with short nose water pump

There is a clearance problem with one bolt on the timing cover behind the inlet on the passenger side.  Make sure you buy an Edelbrock water pump or one that is guaranteed to work with the composite cover.  Edelbrock has been modifying their pumps to be compatible with the composite cover since January 2006.  It's July 2006 when I'm writing this and many people are not aware of this change to their pumps.

It has been recommended by some to replace this hex head bold with a button head allen design.  I didn't try but a quick visual check during the install tells me it might work.

The other option is to replace the composite cover with the older metal design.  I didn't like the idea of cracking open a new sealed engine and risk oil leaks. 

Now you don't have to do anything except order the right pump.

  • No fuel pump rod for mechanical pump

You need to order a fuel pump rod or use an existing one.  You also need the mounting plate that goes between the engine and the fuel pump.  They ZZ383 comes with a block-off plate.  I have no idea where you find a new plate.  I used the existing plate from my stock motor.

  • Lower Smog pump bracket

There's a problem mounting it to the Vortec style manifolds.  No bolt.  If you are running without a pump, no problem.  If you want to run with the pump, it's going to take some grinding to make this work.

  • AC support bracket that is next to the valve covers

There is no place to mount this on a Vortec style manifold.  I will run without it.  If you use the older style 12 bolt intake. the bolt is there.  I considered drilling and taping the Vortec manifold but I don't think this support is really required.  It is now mounted securely.  No flex.  No vibration.

  • Flywheel

    If you have flywheel from the older 2 piece rear seal type of engine, it won't work.  You need the newer externally balanced flywheel.

    Bellhousing and inspection plate

    The inspection plate from the two piece rear seal blocks won't fit the newer one piece rear seal blocks.  You have to cut out several areas on the inspection plate for extra clearance.  First, enlarge the semi-circle that goes around the rear seal.  I cut away about 1/4" with tin snips then cleaned it up on the bench grinder.  Next, test fit it and you'll see other areas where it will interfere with the oil pan.  Trim those too.


  • Temperature sender

The sensor from the existing L82 and early 350's won't fit into the treaded hole in the head.  It has the wrong thread size.  The stock sensor through 1980 requires 1/2" NPT threads.  The Fast Burn aluminum heads are tapped for 3/8" NPT.  So you have 2 choices.  You can relocate it to the intake or find one with 3/8" NPT that works with the existing gauges. 

Old Sensor Left / New Sensor Right

I unsuccessfully tried to use the sensor from a 1981-82 Corvette.  This sensor uses 3/8" NPT threads.  I bought an AC Delco 25036135 coolant temperature sensor.  The cost was about $35.  It comes with the .24" blade connection too.  This sensor seem to be calibrated differently.  It was reading 20-25 degrees too cool.  There is a possibility that this could be corrected using a different resistor on the back of the temperature gauge.  Maybe someday.  I've already installed the center gauges for the 5th time!  If I have it out again I'll give it a try.  For now, I'm using the sensor as a $35 plug to keep the coolant in the head!

Solution?  I relocated it to the thermostat housing.  There is normally a vacuum valve here used by the smog equipment.  This car will not be required to pass a smog test where it is going.




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This site was last updated 08/14/06