October 1, 2020

Information on the GT500 KR with the 4 speed engine

The 1968 Cobra Jet was introduced in April 1968. GT500 KR models all used the Cobra Jet engines. The "428 CJ" is a high performance version of the 428.

The engine code used on the GT500 KR with a 4 speed transmission was "408 J".

You can find this code on the vehicle build sheet. Engines were pre-assembled and installed as units by the production line workers. The build sheet code would have directed the Metuchen assembly line workers to install the 4 speed version of the Ford 428 Cobra Jet. This engine would have the flywheel installed for attachment to the manual (4 speed) transmission.

All 428 CJ engines received thermactor emissions (smog). This includes all cars sent to Canada. All Shelby 428 CJ, 4 speed engines were built to the same specifications. The code number would also be present on the metal engine tag. Factory options, like power steering and air conditioning, do not change the basic engine configuration.

The GT500 KR was the only Shelby to use a true ram air system. The air cleaner assembly is comprised of the base and the heat duct (snorkel). This rare photo of an original GT500 KR engine was taken in 1968.

The base of the air cleaner is the same as a 428 Cobra Jet Mustang. The inside is painted black. The rubber seal is unique to the KR.

This decal is correct for the GT500 KR . This is the only decal on the air cleaner assembly.

In this photo you can see the unique snorkel, it was not used on any other vehicle. The rubber breather hose has a 90 degree bend and was shared with all 1968 Shelbys. At the end of the snorkel is the starter delay. This part was also unique to Cobra Jet built cars. It was designed to prevent damage to the ring gear and starter assembly.

The original carburetor is marked C80F-9510-AA. It is not unique to the KR, but is Cobra Jet specific. There are reproductions of this carburetor.

All cars used the C80E-9425-C, cast iron, intake manifold. On the back are two fittings. The one screwed into the manifold is painted blue. The other one is not painted.

The valve covers are the same used on the GT500 and say "Cobra Lemans". A chrome oil filler cap with a metal fitting is used.

These are the Cobra Jet exhaust manifolds. There is actually a visual difference between the ones made in 1968 and later years.

The GT500 KR uses two small lift hooks in 1968.

One of the primary ways to identify a GT500 KR block is by this casting date. I have decided to share my research of "original" GT500 KR block dates.

1968 Shelby block casting dates

Scheduled build Shelby Number Cast Date
02E 22xx 8D10
15E 33xx 8E11
22E 24xx 8D25
24E 32xx 8E7
03F 33xx 8D13
04F 30xx 8E2
04F 32xx 8D26
04F 30xx 8E15
03F 33xx 8E15
05F 32xx 8E29
04F 32xx 8D31
17F 36xx 8D28
18F 37xx 8E15
18F 37xx 8E14
21F 37xx 8E15
15U 39xx 8E28
16U 39xx 8F7
19U 42xx 8E22
19U 44xx 8F3
23U 44xx 8G5
23U 40xx 8E22
24U 42xx 8F3
25U 42xx 8G6

These engine mounting brackets are bare steel and screw to the sides of the block. Ford stamped one "R" for the right side. They can be installed incorrectly. Ask me how I know :-)

The engine insulator is shown on the right. Original 1968 insulators are painted black and have a red ID marking.

The GT500 KR distributor is usually marked C80F-12127-D. The 4 speed version will have a dual pull vacuum advance. There are three colored vacuum lines.

The water pump bypass hose is actually thicker than regular heater hose. It was painted blue with the engine assembly and tower clamps.

This bracket was used on all big block cars. The alternator is always mounted low and the smog pump is mounted above it. The Master Parts Catalog shows a "non smog bracket" but, it was never used on 1968 Shelbys.

ALL GT500 KRs, regardless of transmission came from the factory with emissions pumps. Here is a picture of one on an air conditioned car.

In 1968, all thermactor cars, regardless of engine size used this check valve. It is for a hose that is 5/8".

The anti-backfire canister is dated and has a part number. Most original valves have a date on the bottom side.

The water pump pulley for an AC car only has two sheeves and is marked C6AE-8509-A.

The fan clutch for a KR without Air Conditioning is the C8OE-C.

408 J GT500 KR / 4 speed

Pulley Pulley ID Number Sheaves
Crankshaft C8AE-6312-D 3
Water Pump C8OE-8509-A* 3
Alternator Steel 2
Power Steering 6AA 1
Thermactor C8AE-9C480-A 1

* No visible stamping on pulley

The fan clutch for a KR with Air Conditioning is the C8ZX-A, however some cars did get the C8OE-B clutch.

There were only "57" GT500 KR, 4 speed, convertibles with air conditioning. That makes this one of the most desirable combinations produced.

408 J GT500 KR / 4 speed

Pulley Pulley ID Number Sheaves
Crankshaft C8AE-6312-A 3
Water Pump C6AE-8509-A 2
Alternator Stamped Steel 1
Power Steering AF 1
Thermactor C8AE-9C480-B 1
AC Idler Fixed C8AZ-8678-B* 1
AC Idler Adjustable C8AZ-8678-A* 1

* No visible stamping on pulley