Some Technical Details on the 1972 Y Code GTO and LeMans

                                                                          By: Patrick Smith

   The bulk of articles relating to 1972 GTO 455 engines deals with the 455 HO round port version; rightly so as it was a real scorcher of an engine. There is little to no data on the 455 D port engine so I thought I'd establish a page that covers what the pieces are for this engine. It will be handy for those trying to document and restore one of these rare flyers. By the way, these codes and numbers apply to the Luxury LeMans Y codes as well. So if anyone owns a 1972 D port 455Luxury MeLans, give us a visit!
 Engine Block: casting number is one of the last good ones, using the 485428 number. It is a two bolt main block although some units may be drilled for four bolt use, they will have 2 bolt main bearing caps. This block casting was used from 1972-1974. Starting in 1975 Pontiac switched to a new casting number, 500813 and that is what appeared in 1975-76 Trans Am 455 HO engines.
Service Replacement (SR) blocks. Occasionally you may encounter an engine without a VIN number and with SR stamped in it. These were service replacement blocks assembled for warranty purposes and some came with metal tags stating it is a warranty replaced block. The suffix code for the D port 455 engine with auto trans is YK.

One of 235 made. How many have survived? Is yours one of them?

Cylinder Heads: The D port 455 heads used on Y code engines are 7M5 castings. They used 1.96/1.77 intake and exhaust valves and had a spacious,114 cc chamber.The part number is 485075.

Carburetors:  The carb is a Rochester Quadrajet 4 barrel unit. Strangely enough, there are 4 variants for the Y code 455 engine! The most common would be the 49 State emissions carb, 7042272. A California State emission carb is 7042262. There were also two separate High Altitude carbs for the Y code 455 engine. Due to the low numbers of cars made, there may not have been Y codes produced for high altitude States. The part numbers are; 7042278 and 7042276. All are automatic transmission units with center fuel inlet. They can be made by Rochester or Carter division under license by Rochester.

There are 4 different carb numbers for the Automatic D port 455. Two of which are JHigh Alt versions and 1 California emission version. Due to low production totals, it's possible the High Alt carbs were service replacements only.

   

Transmission:  Only one transmission was used on Y code cars, the Turbohydramatic 400 three speed unit. UPC code is M40, transmission suffix code on metal tag is PY. It is a heavy duty version of the TH400.

Carrier Codes: The Y code GTO and LeMans used the Chevrolet 12 bolt carrier. It is a series 2 version with a 3.31 axle on non air conditioned cars or 3.07 on air conditioned cars. Safe T Track limited differential was optional for this carrier. The unit will also have upper control arms leading from the axle to the rear carrier support part of the frame which was a 455 drive train specific assembly.
The carrier suffix codes for the Y code cars are as follows:
Safe T Track non a/c 3.31 = XU open differential non a/c 3.31= WU
Safe T Track        a/c  3.07= WT open differential      a/c  3.07 = XT

Frame Codes: The 455 engine LeMans and GTOs had their own frame due to rear axle and engine requirements. There were two variations; the open channel regular frame or boxed HD or convertible frame. The open channel 455 frame was coded XU 40 for the automatic transmission.  The boxed frame was coded XV. We have found that most often on build sheets that the frame code for automatic 455 LeMans and GTOs have XU 40 on them. There is a Heavy Duty boxed frame or convertible frame version, coded XV. You will only encounter this frame on GTOs ordered with the heavy duty frame option. No convertible GTOs were made in 1972. However, it's possible for a LeMans Y code convertible to exist and have this frame. It should indeed have it.  The frame part number is 483709 for the 455 powered GTO/LeMans series. It has the unique motor mounts up front and special upper control arm to 12 bolt braces in the rear.

This is the correct location for 455 Pontiac engine mounts.

boxed frame, also convertible LeMans Sport 455:XV
open frame  GTO/LeMans 455                            :XU (sometimes XU 40 on build sheets)

Early Build vs Later Build Cars: Some legislative changes altered the product mix on 1972 LeMans and GTOs. The new safety standards for cars made manufacturers delete the chrome rear view mirror assembly in favor of a black camera case finish mirror housing, Early build car from December and back usually used chrome housing assemblies. The speedometer was also changed from 140 mph to 120 mph starting in January 1972, The newer speedo also has a lamp for seat belt warning. There is the whole issue of batch build and build out cars which has been addressed in certain articles I penned. This is an ongoing research issue. My car built in Pontiac in the last week of May, received 1971 GTO tail lamps. I switched them to smooth units. Some cars came with LeMans grilles complete with Pontiac arrowhead when GTO grilles were supposed to be used.
   * Article (c) 2015 by Patrick Smith. Images by PHS MEDIA ARCHIVES