What is a 604 Crate Motor? | 604 Crate Engine Explained
What is a 604 Crate Motor?
Crate motors are a popular way to repower a muscle car or classic truck, but they are also a terrific way to bring parity to a spec racing series. The GM CT400 crate motor is a small block Chevy displacing 350 cubic inches assembled with a specific set of legal internal and external components, including GM’s Fast Burn 62cc aluminum cylinder heads with LS-style beehive valve springs, which is sealed using special bolts and serialized tags to prevent modifications to the engine. This provides a level playing field in circle track racing or anywhere these “GM 604” crate engines can be utilized.
The sealed 604 crate motor is used primarily in dirt late models and modifieds. The sealed engine format means racers spend less time on the engine and more time behind the wheel, with engines only requiring oil changes and other light duty service parts, easily lasting an entire season. When it comes time for a rebuild the engines must be sent to a registered rebuild facility with the ability to reseal the engines with new bolts/tags upon completion of the rebuild. Speedway Motors is not only a source for new 604 crate engines but can rebuild and tune your GM 604 crate engine as well.
Why is it Called a 604 Crate Motor?
While the crate engine started life as GM’s CT400 (CT referring to circle track) crate engine, the 604 circle track engine is derived from the last three digits of the GM crate engine part number, which is 19434604. Introduced by Chevrolet Performance Parts to run in various Late Model racing series, the 604 became racer “short hand” for the high revving IMCA 604 crate motor when discussing racing classes and the engine itself. This 604 late model engine name stuck and is now the preferred description for this crate engine vs the CT400 name it was given.
What Classes Use The 604 Race Engine?
Why the 604 race engine then? It all came about due to the ever increasing costs of motorsports in general, but specifically dirt track racing. In the world of circle track racing, it is often those that have the biggest wallet and thus the best parts. To bring racing costs down and parity to the race cars (letting the driver and limited tuning be the real effort to get to the winner’s circle), dirt late model sanctioning bodies created racing classes with specific rules requiring a sealed crate engine to be used and Chevrolet Performance Parts introduced a series of sealed crate engines specifically for circle track racing in 2002.
The most common racing series you’ll find the 604 crate racing engine running in are often the entry and mid-level classes, which include the IMCA Late Model and Modified classes. Regional series, such as the Mid-East 604 Late Models, Fastrak Racing Series, Indiana Late Model Series (IMLS), Crate Racin’ USA (CRUSA), and others use these sealed crate engines as well to keep costs in check and provide a full field of exciting racing for fans from track to track in the series. Many of these series allow the 604 with a minimum race car weight. Note: for many sanctioning bodies, crate engines directly from GM Performance may not yet be race legal. Several sanctioning bodies require additional seals and verification by authorized verification/build/repair facilities to be race legal. As always, consult your series or track rules to ensure compliance.
604 Crate vs Open Motor
What is an open motor and is it different than what is a 604 crate motor we’ve discussed above. The 604 crate motor is a brand-new small block Chevy V8 manufactured using all GM components and then sealed using special anti-tamper fasteners on key components. Whereas the open motor allows customization of components with varying performance outputs and generally higher costs associated with them.
Open motor class racing carries far less restrictions, which in turn, makes a level performance playing field that much more challenging than a crate motor class like those that use the 604 crate motor. Learn about Increasing Your Lead in Crate Motor Classes and be sure to read up on legal 604 crate engine “cheats” in our Toolbox if you opt to go the open motor/claim route. Note the quotes here, as our 604 crate engine cheats are not truly cheating, just legal parts to gain a competitive edge. However, when comparing the 604 crate vs open motor rules and costs, it is easy to see the crate 604 benefits.
602 vs 604 Crate Motor
We are discussing the popular GM 604 crate motor here in this guide, but we’d certainly be remiss to not mention it’s sibling, the GM 602 crate motor that is used in some crate engine class racing as well. Like the GM 604, the 602 is a sealed crate engine built using all GM parts, though the 602 uses cast iron Vortec cylinder heads which produce lower horsepower and torque. Our focus here is the popular 604 sealed crate engine, but if you’d like to know more about the 602 sealed crate engine you can read all about the 602, including full specs and supporting components in our GM 602 Crate Motor Guide elsewhere in the Toolbox.
604 Crate Engine in Street Car
We are often asked “Can I run a 604 on the street?” and the answer isn’t so cut and dried here. While the 604 crate engine block is simply a 404 horsepower aluminum headed small block Chevy, in many street applications you may find yourself having to swap components (such as the race-specific 8-quart oil pan) to allow proper fitment. Furthermore, the sealed aspect of the engine can make any modifications or upgrades to be more challenging, as you must cut away/destroy the bolt seals to tear down the engine or remove major components. Will the GM 604 sealed crate engine work for street use? Sure, but there are better crate engine alternatives out there for your street cruiser. At the end of the day, you have to remember just what is a 604 crate engine, and that IMCA 604 crate motor is a sealed racing engine for circle track use. As such, it is probably not the best use of your performance dollar to run a 604 crate engine in street car applications.
Chevy 604 Crate Engine Specs & Parts List
If you’re contemplating a 604 sealed crate engine racing class, we have provided not only the current 604 crate engine specs, including the GM 604 crate engine horsepower and torque (in case you’re wondering how much horsepower does a 604 crate motor have compared to other crate engines), but a GM 604 crate engine parts list of supporting bits that you’ll need to get your GM 604 crate engine installed and running in your race car. Besides the parts listed below, our 604 accessory drive kit is a great option to consider as well with everything you need for your water pump and power steering drive systems.
- Horsepower: 404 hp @ 5,600 rpm
- Torque: 406 ft-lbs. torque at 4,600 rpm
- Displacement: 350 cubic inches
- Bore x Stroke: 4.00 inch x 3.48 inch
- Compression 9.7:1
- Block: Cast iron, four-bolt mains
- Cylinder Head: Cast aluminum “Fast Burn” with 2.00”/1.55” intake/exhaust valves, 62cc chamber
- Crankshaft: Forged steel, one-piece rear seal
- Connecting Rods: Powdered metal, with 3/8-inch rod bolts
- Pistons: Cast aluminum
- Intake: Dual plane high-rise aluminum
- Camshaft: Hydraulic roller, .474”/.510” lift, 208°/221° duration @ .050-inch, 112° centerline
- Rocker Arm Ratio: 1.5:1 – Aluminum Roller
- Oil Pan: 8-quart, baffled pan with dual kick-outs
- Recommended Oil: 15W50 Synthetic
- Fuel: 92 octane premium unleaded
- Maximum Engine Speed: 5,800 rpm
- Spark Timing: 32° BTDC @ 4,000 rpm
- Firing Order: 1-8-4-3-6-5-7-2
Carburetor:
A 650-cfm carburetor with a 4150-style mounting flange is the recommended carburetor to use on the 602 race engine. The carburetor jetting should start with #73 jets for both primary and secondary circuits.
Air Cleaner:
A standard 14-inch diameter air cleaner with at least a 3-inch tall filter element is recommended for adequate airflow. A 4-inch element is preferred if there is enough clearance for one to be installed.
Flywheel:
The GM 604 crate engine uses a one-piece rear seal, so be sure that whatever external balance flywheel you order is machined for that.
Flexplate:
The same can be said for automatic flexplates. Only use a flexplate designed for one-piece rear main seal small block Chevy applications and with external balance.
Pilot Bearing:
The 604 sealed crate engine’s crankshaft is machined to accommodate the standard “small OD” roller pilot bearing originally used in the C5 Corvette, 4th Gen F-body, and GTO applications.
Starter:
We offer a variety of gear reduction starters for the small block Chevy that will work with both 153 and 168 tooth counts that are perfect for spinning over your Chevy 604 engine.
Fuel Pump:
To feed your 604’s four-barrel carburetor you’ll need a high volume mechanical fuel pump capable of maintaining at least 6 psi of fuel pressure with the engine at WOT. There are many options available at Speedway Motors.
Headers:
The GM 604 sealed crate engine has been tested to work best with a stepped header using 1-5/8-inch primaries stepped to 1-3/4-inch, with 32-36 inch long primary tube length. Ensure the header you choose has a gasket flange designed for the “Fast Burn” cylinder head’s D-port shape.
Spark Plugs:
The 604 crate engine’s Fast Burn aluminum heads use a standard 14mm tapered seat spark plug with .670-reach. We offer several dedicated crate engine spark plug offerings for the 604.
Spark Plug Wires:
For the 604 we recommend a high-performance plug wire set with a minimum spark plug wire diameter of at least 8mm. On our long block IMCA 604 crate motor we offer they are dressed using Moroso Ultra-40 spark plug wires.
Best 604 Crate Engine Carb
Knowing the best carburetor for 604 crate engine racing will depend on several factors, including your racing class rules, track conditions, and more. For four-barrel carburetor classes, a 650-cfm carburetor works best according to GM’s 604 setup documentation. A 4150-style racing carb, such as these crate engine carburetors are a great option.
Best Fuel for GM 604 Crate Engine
Believe it or not, the best fuel grade for 604 crate engines is the easily available premium fuel octane found at your corner gas station. That’s right, GM recommends premium 91-93 octane fuel for the 604 race engine, mainly due to its friendly compression ratio, and is another effort to keep racing costs down without the need for expensive high octane racing fuels. Standard E10 pump gas is fine, however if you do find it easier for transport, IMCA does allow racing fuel (of similar octane) to be used. Note that E85 and methanol fuels are allowed in many of the classes the 604 is legal for. No performance additives are allowed, and like any sanctioning body, IMCA does inspect and test fuels of all race participants.
604 Engine Oiling System
The oiling system in the 604 is a wet sump system, again to keep costs down. The sealed crate engine ships with a steel 8-quart capacity oil pan designed for circle track racing. Per the rules, a one-inch inspection hole with plug is mounted to the pan. For open, or “claim” engines the same rules apply, however, you have your choice of 350 Chevy small block V8 wet sump oil system components when building your claim engine.
604 Crate Motor Timing
As is the case with most racing sanctioning bodies, there is only so much you can do with your ignition timing. GM recommends total timing of 32 degrees at 4,000 rpm with a spark plug gap of .045-inch. The 604 does not include a distributor. You must source your own HEI or performance distributor and your ignition control box must include a rev limiter feature. For an HEI distributor you can utilize a MSD rev-control unit. No other ignition system upgrades, such as a crank trigger system, may be utilized.
Best GM 604 Crate Engine Oil
As Mobil 1 is the official oil of Chevrolet Performance and as such the official GM 604 crate engine oil, the recommended oils to use in the CT400/604 crate engine is Mobil 1 Racing 0W-50 or Mobil 1 15W-50. That said, there are certainly considerations to be discussed with your engine rebuilder or tuner to use other viscosities and brands of motor oil with your 604.
604 Crate Motor Common Problems
The 604 sealed crate engine is built using all new components and spun on machinery to confirm oil pressure and proper sealing of gaskets. However, it is not actually run on a dyno or given any real break-in procedure. This means that breaking in your new 604 crate motor properly, following the Chevrolet Performance instructions, is critical to engine longevity. You will find many authorized 604 rebuilders/sellers offer a break-in package on an engine dyno or even fully dressed engines ready to race and we strongly suggest you take advantage of these packages to reduce any failures due to improper break-in and reduce the chance of having any 604 crate motor problems in your racing program.
604 Crate Engine Builders
Due to the sealed nature of the 604 crate engine program, you can’t haul your race engine off to your local builder for a refresh or any internal repairs if you have a failure. This prevents non-authorized builders or race teams from cracking open their crate motor for a little “something extra” for a race day advantage. The 604 sealed crate motor must be freshened up/serviced through authorized GM 604 crate engine builders, such as Speedway Motors. Our in-house circle track engine building facility can take care of your 604 rebuild, including using all the correct and legal GM internal components to 604 crate motor specs, and secure it with the proper sealing bolts/tags to keep track officials happy. Learn more about our engine building services, dyno testing, and certified repair center offerings at Speedway Motors Racing Engines to help you get back behind the wheel of your race car and into the winner’s circle.
Speedway Motors 604 Crate Engines We offer dyno break-in services, tuning services, and 604 crate engine packages that are fully dressed, dyno tested, and tuned that are ready to drop into your chassis, such as our tuned IMCA 604 crate motor. You’ll find a full line of 604 crate motors from Speedway Motors for IMCA and other racing organizations that have 604 crate classes.
