At first glance, you'd think there's nothing to a Y Code frame. What's there to know? Once you start restoring one, a bunch of differences appear. Stuff you didn't realize until you order parts and realize they aren't the same. Or until you buy a replacement frame for your rusted or bent original and discover stuff isn't the same. We're going to walk you through the frame differences and show you.
Let's tackle the 1971 GTO frames first. Since a lot more of them were made than 1972s it stands to reason you might consider using one as a donor. For 1971, Pontiac issued three separate frames for that year. PN 3992389 was the standard frame for engines up to 400 cid displacement. It was open channel, swept hip perimeter design.The only areas boxed were the engine cradle frame horns and the side rails along the rear suspension and axle kick ups.
Frame Part Numbers :
The 455 engine frame used PN 483709 and featured differences in construction from the basic frame. This one used rear frame reinforcement straps leading from the rear axle to the rear suspension bulkhead. The 455 also used a 12 bolt Chevrolet axle assembly instead of a 10 bolt. The engine cradle had special 455 frame to motor mounts installed. Otherwise, it was the same as the standard 400 frame save for the part number and build sheet code. The third frame was PN 483710 and was used for convertible applications and as an optional, HD boxed frame application. It has enclosed side rails instead of open channel and in the case of 455 engine usage it would also have rear frame reinforcement straps and the 12 bolt axle assembly. Reproductions of these parts are readily available by the way.
For 1972, Pontiac used 3 frames again but with different part numbers. The standard frame PN6263668 was used for engines up to and including the 400 CID. It was open channel swept hip perimeter construction. The 455 engine order paired the body to PN 487227 which was open channel as well but supplied 455 motor mounts, 12 bolt axle with rear frame reinforcements. This was what you got with a Y Code hardtop or coupe order. Since the GTO option wasn't available on a convertible this year, the LeMans Sport was the model you needed to order to get PN 487228 which was a HD boxed frame. It was also used when you ordered the HD boxed frame option for your car. It is theoretically possible to find this frame in a Y Code hardtop or coupe. It will be the frame used in a LeMans Sport convertible.
Engine to Frame Brackets: The 455 engine used different engine to frame brackets from the 400 engine. While you can install 400 engine to frame brackets in your car and they will work, the reason the factory used a different set was to handle the notable increase in low end torque the 455 produced. While it seems overkill for a 1972 era 250 hp engine, the parts were made in 1970 when it was still a high compression engine kicking out 500 lbs ft with over 10:1 compression ratio. It's cheap insurance!
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| These are the 400 cid engine to frame mounts. Note triangular shape and bulge leading to the inner mounting hole. This is your key ID method and the different location compared to the 455 mounting in engine cradle. |
Anyway, here is a pic of the standard 400 cid engine to frame mount set. Niote they are triangular in shape with a pass through for the rubber motor mounts. Various vendors sell these and they're cheap to get. If you plan to put your car back to original specs, use the 455 specific engine to frame mounts. Here is what they look like.
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| For lack of a better word, the 455 mounts are more squared off and lower than the 400 mounts. These are also more expensive too. This set appears to be black coated while mine are dimpled metal in silver and thick. |
As you can see, the 455 engine to frame mounts are slightly different. Notice how the metal is shorter and lower. There isn't a steep rise going up to the pass through. It's compact. The location is different on the engine cradle as well. Next have a look at where the 400 engine mounts go in the cradle and compare it to a 455 engine to frame mount. Unmistakable difference once you see it.
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| 455 engine frame mounts, note different shape and overhang on front of frame. |
Above is a pic of a 455 chassis with the 455 engine frame mounts in place. Note how it overhangs the front of the cradle slightly? The 400 mounts aren't placed there.
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| Here is another angle of a 455 engine to frame mount. See how far out they reach past the cradle. Ron Bavis pic credit: |
Now that one is cropped a bit so you can't really see much in terms of placement in relation to the engine cradle. I have another photo taken farther away and on an angle so you get a better idea just how high up and far they stick out.
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| 455 rubber engine to frame brackets are unique as well and must be used if installing the engine using 455 engine to frame brackets. |
455 Engine Mounts: In addition to special frame mounts, the 455 engine required different rubber engine to mount brackets. They were shaped differently from the 400 parts and you cannot mix 400 rubber mounts with 455 brackets. You CAN install a 455 using 400 engine frame mounts but you got to use the 400 rubber pieces as well. Above is a pic of the 455 specific rubber engine to frame brackets.
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| More often than not you will find these braces on a 455 powered LeMans or GTO. The ins and out of their presence hinged on whether the car was ordered with rpo Y99 or if it was a WW4 or WW5 ordered car. |
Frame Bulkhead Reinforcements: These goodies are part of the F41 heavy duty suspension option for Olds 442 and Chevelle SS cars. You will find these goodies on 455 powered Pontiac LeMans and GTOs. Pontiac's term for their handling package was rpo 724 or Y99. It wasn't standard on a GTO, you had to order it separately OR order a WW4 or WW5 package. WW4 was the 400 4 barrel engine, 4 speed manual transmission, Saf T Track axle, power disc brakes, custom carpets and handling package. On a WW5 you had to order the GTO option first and then WW5 triggered a massive upgrade including 455 HO roundport engine, Turbohydramatic or M22 four speed, Saf T Track axle, body color sport mirrors, formula steering wheel, roof drip moldings, power disc brakes, custom carpets, rally gauge cluster and handling package. So the bulkhead reinforcements weren't 455 exclusive but indicated the car was ordered with Y99 suspension which is a pretty good thing!
2023 Patrick Smith images phs media archives.
PHS Collector Cars 1972 LeMans/GTO Y Code Registry
