I've got a 55 GMC suburban I'm slowly doing over. Some where along the way a 350 ended up under the hood. (now removed) my truck was originally born with a six cylinder in it, but I'd like to put in an original style pontiac V8 in it. I can buy a 55 pontiac 287 engine and hydromatic transmission from a car locally for rebuild. my question is how direct other than mounts is it? what are the differences from truck to car to truck? any help is appreciated. Thanks
The only GMC V-8 truck I've ever known was a '56 that had a Poncho 347 in it. Ran like a scalded cat!
'cause it would have a had a Pontiac V8 in it from the factory if it were originally a V8 truck. Classic Garage- I will be watching this thread to see what you find out. My '58 GMC had a SBC in it when I bought it but I have always wondered about the original mounts too and whether they were the same as Pontiac car mounts. The Hydromatic may be another matter. I'm not sure how they were mounted in the trucks as opposed to the cars. The standard truck trans (3 or 4 speed) would have been a bellhousing style mount. My guess is (and only a guess) that the Hydromatic might have had a rear mount considering how big and heavy those suckers were.
Well,Ya learn something new every day, I admit, I did not know that What about the second series 55? GMC or Chevrolet while Im busy stickin my foot in my mouth? 265 maybe?
I had a die hard Ford buddy that bought a GMC Dually P/U to tow his Ford powered flat bottom drag boat back in the 80s. When everyone got on him about the BB Chevy he'd say it's not a Chevy...it's a Pontiac!
I've always looked for these GMCs at wrecking yards, cause I'm curious too and haven't ever seen one. I think the trucks were a good source of manual trans pieces to put into cars and dragsters. I would maybe look for something newer than the '55 287ci. The mounts are the same on all the Pontiac car engines up to '60? I think. Just be nice to have some extra cubes in a Suburban.
I have a '57 GMC Suburban NAPCO 4 x 4 in my shop with the driver's side front fender off. It has the Pontiac 347/turbohydramatic auto with power steering & brakes. I can take pictures if you would like. PM me & I'll see what I can do.
I've seen a few of them but never paid attention to the mounts. The Chevy trucks 55-59 with the hydramatic had a funky center crossmember under the bellhousing, like on the manual trans trucks, but the center of it unbolted, and this crossmember supported the trans (from the bellhousing) GMCs did have slightly different frames....my guess is they used a single mount at the lower front of the engine? but that's a guess
Back in the mid '70s a friend of mine had a '55 Pomtiac ambulance with what appeared to be a 287 and a Hydramatic. He overhauled the engine and the only real parts issue he had was with the main bearing set. The new rear main bearing (I believe it was) was maybe 1/4" to 1/2" narrower than the original bearing. The machine shop came up with the correct width bearing by ordering the part for a GMC 288 cu. in. engine. If I remember correctly the specs for both engines showed the same bore and stroke. I guess it was just GMs way to distinguish between the car and truck versions of the same basic engine. This engine had no GMC markings on it and even had the Pontiac nameplates on the valve covers. It might have had stronger pistons or a beefier timing chain and gears in it, but nothing else that complicated building the engine. But apparently since this was a "professional" car it was considered a commercial chassis and got the GMC truck engine upgrade.
GMC's had a Pontiac till 59. 55-57 matched the displacement of the Pontiac cars. 58-59 had a small bore 336 both years instead of 370 and 389 for those years.
i have had 4 55 pontiacs,i would have to ask why a 287?if your going for the right look get 347,389,421. i had a 421 with slush box in my last one -not many knew it wasn't a 287.until i stomped it
A 55 dual range hydromatic is going to be pretty expensive to rebuild, let alone getting parts and finding someone who can do it. You would be better off using what you can find locally like the 287 and get a trans adapter from Wilcap or find a newer engine 64 and up and use a th400 . Unless you really want to go for more the original look.
I too am building up a '55 GMC shortbox. It originally came with a Hydromatic trans. and a 287 Pontiac engine. those are long gone and a tired 283 chevy and a tired 350 trans are in it now. i wanted to put a 348 in it. It is getting pretty pricey though. An engine builder I know just pulled a 400sbc with 5,000 miles on a rebuild. He drove the '66 Vette it was pulled from. The owner wants an original 327/35 setup. That 400 is mine if I want it. I can make that motor look like just about any vette motor or anything I want. That's my dilema too. Tried and true running motor or build the 348 and blow the budget. Thanks,
I had a '56 with the Poncho many years ago-weren't they a 4 speed hydro for this special truck? was a good combination. but, unless you have an original why bother unless you find an original eng/trans set up. always have liked the GMC trucks because they were not typical belly button GM trucks.
Prior to developing their own engines, GMC used the Chevrolet Straight-6 engine and Pontiac V8 engine. They used the Pontiac 287-cubic-inch (4.7 L) motor for 1955 and 316-cubic-inch (5.2 L) motor in 1956, but advertised the engines as the "GMC 288" and "GMC 316". They used Pontiac's 347-cubic-inch (5.7 L) in 1957. For 1958 and 1959, GMC reduced the bore of Pontiac's 370-cubic-inch (6.1 L) to 3.875 in (98.4 mm), resulting in a displacement of 336-cubic-inch (5.5 L). In Canada, however, GMC used the Chevrolet Small-Block engine rather than the Pontiac.
I was wondering about the Canadian aspect as well. Never really understood the logic/marketing of Canadian Pontiacs and GMCs, but I guess there's another thread for that....
Not Buick, but Oldsmobile. Used in heavy duty while Pontiac engine used in light and medium duty. 370 A special 370-cubic-inch (6.1 L) variant called the 370 was used in GMC trucks alone, not shared. 371 Making its debut in 1957 as standard equipment on all Olds models,<sup id="cite_ref-5" class="reference">[6]</sup> the 371 was produced through 1960. Bore was now 4.0 in (100 mm) (same as the 327 and 350 Chevys) and stroke was increased to 3.6875 in (93.66 mm) for 371 cu in (6.1 L). 1959 and 1960 371s used green painted valve covers. 4-barrel models used 9.25:1 compression in 1957 and 10:1 in 1958 for 277 hp (207 kW) and 400 lb·ft (540 N·m) and 305 hp (227 kW) and 410 lb·ft (560 N·m) respectively. A 1958 2-barrel version was still impressive at 265 hp (198 kW) and 390 lb·ft (530 N·m), but had problems with early camshaft failures due to the high preload valve spring forces. Then, power nosed downward for the 1959 and 1960 88 model: 270 hp (200 kW) and 390 lb·ft (530 N·m) for 1959 and 240 hp (180 kW) and 375 lb·ft (508 N·m) for 1960. It was no longer available in cars in 1961.<sup id="cite_ref-6" class="reference">[7]</sup> The 371 was also used in GMC trucks.
1950.s Gmc 6 cylinders where not chevrolet straight sixes. The Gmc straight 6 was full pressure displaced 228 , 248,270 and 302cu in . they came with zollenger forged pistons. It also was longer than the chev engine, I have a 55 GMC with a 287 and three speed the trans is the same muncie as a chev except for the side cover. It uses a front mount and two on the bellhousing the center of the bellhousing crossmember unbolts. OldWolf
you could get a 322 buick engine in a 56 chev truck tractor. I not shure if it was availble in anything else. I have never seen a buick engine in a GMC. OldWolf
------------------ '55 GMC's used the 287 Pontiac V8 and '55 Chevy trucks used the 265 Chev V8. In '56, the GMC got the 316 Pontiac, in '57, the 347 and in 58 and 59. a unique GMC-only 336 cubic-inch 'small-bore' version of the Pontiac 370. In the Chevies - at least in the pick-ups and 'light-duty' Chev trucks, you couldn't get anything bigger than the 283 from 1957 until 1962 or '63. In the bigger, medium and heavy-duty Chevy trucks though - ie - 2 ton and up - and depending on the year and model, you you could order various Buick and Olds V8s - and from 1958 and up, the 348 Chevy V8. Mart3406 ================
In the heavy duty trucks, GMC used Oldsmobile engines, but Chevrolet used the Buick 322 in their heavy duty trucks http://www.hotrodders.com/forum/1957-gmc-truck-24670.html
I was the lot boy at a Olds, Caddy, GMC dealership when the 56 GMC,s came out. Man wotta blast! They would shit'n get with that dual range hydro, and then the J-2 Olds in 57, it was pretty exciting times.
My truck was a V8 Hydro truck originally and now has a 1970 Pontiac 350 and a turbo 350 in it. A lot of people really think it cool that it still has a Pontiac V8 in it. The next question i would be asking is, how much and how far am I going to drive it ? Because you then want to consider availability of parts if it breaks with the 287 in it ? The expense of doing different can be as crazy as much as it is neat, depending what you are doing of course . I will attach a picture of the Poncho in my 56 GMC.
Anyone that knows Pontiac v8's will spot a '60 or newer Pontiac V-8 simply by looking down at the water pump. 55-59 used the reversed flow cooling system, later ones did not. So I don't know how original you want it to be. The 287 I have from a Pontiac car has front and bell mounts, with a slant pan hydro.
I don,t know why a stock rebuilt and restored GMC from that era would be unreliable. I would carry a few things that might be hard to get in emergency. Extra waterpump, fuel pump, belts, and points, would probably be good to have on any oldtimer. I used to carry that stuff in the 60,s. In California you can be far away from anywhere, at anytime. In fact coming home from Bakersfield my 55 Ford stopped dead in middle of Pearblossom in front of the only gas station on Sunday at sundown, and the whole town was closed up. Finally found a broken wire in the dist. fixed it under light of a cigarette lighter.
The Jalopy Journal
