Does anyone know of some good websites/books or whatever that have information on the old GMC motors that were heavily used in old hotrods. years? c.i.'s? parts? what did they originally come in? what should i be lookin for? pics? didn't they originally come in the big GMC trucks? Thanks in advance for the help. sb
the 270 was used in normal pickups in the 50s, the 302 was used in bigger trucks. here's what you're looking for, probably there are other sources too. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=6589140711
GMC or Chevy? I know Chevy 216, 235 and 261 inline 6s were used a lot in rods. There are 2 reprint books (circa 1953) available on hopping them up. One is by Roger Huntington and one by California Bill. There is also a book by Leo Santucci that covers them in much greater detail, but is more focused on the later 250 and 292 6s, but he states that much of the info is transferable to the earlier 216/235 So far as websites go... inliners.org stoveboltengineco.com cliffordsperformance.com stovebolt.com Patricks Antique Truck parts (can't recall the url)
http://www.stovebolt.com/ there's a few sites on the web -- search for "old trucks" or "GMC trucks" I drove a '56 GMC with a big ole six. ****er would climb a tree, but don't get in a hurry. Brother knocked the muffler off one day -- had to stick my head out the window to drive it home without getting all my fillings shook loose!
The 270 was used in big trucks also. I pulled a 270 out of a '53 (?) dump truck that was being crushed. I'd hoped it was a 302, but twern't. Mutt
Keep in mind that GMC made it easy on someone pawing through a pile of engines, fifty years after the fact. There are no codes to remember, because they simply stamped the engine size (228,248,270,302) on the machined pad near the distributor hole. I yanked my 302 out of a '57 school bus, but a lot of guys find theirs in an old army 6X6.
Get ready for ''LONG MOTOR ENVY'' Even with the 228 in my 39 I never found a 235 I couldn't blow the doors offa! I'm pretty sure that next will be a 300+ year for GMCs at B'ville
Pactrics do a lot of stuff for the old GMC motor. Also try www.oldgmc.com I bought a good book a few years ago on chevy and gmc sixes I think I got it from hotrod and custom supply, not sure of their web site.
NFG here... These are the Ronnie Self of hot rod motors. For a too brief period around 1952-5, they held a bunch of records in any auto sport that matters. This is unfortunate timing, as it coincides with racers figuring out how to make the Chryslers, Oldsmobiles, and Cadillacs run right, then the Chevy V8 just about ended it all. Car Craft had a cover article in 1955 on a sports car built by a rodder using a 320" Wayne 12 port pulling 520 HP on a dyno...Hilborns on pop, Herbert roller,Vertex,Chrysler full flow filter. They bolt into anything Chevrolet ever built if you know what pieces go where. Most of the bolt ons from the Chevy fit. Bellhousings from Chevy 6 through 1962 fit. Flywheels (GMC only) are getting hard to find, at least up here. Look for them in wraparound windshield big trucks so you'll get a newer 270 or 302. First 3 digits in serial # on pad beside dist. is displacement - if it doesn't say 270 or 302, you probably don't want it. Look for 5 freeze plugs on manifold side, and a lot of bolts in the side plate - a lot of these trucks got Chevy 6s stuck in them when the farmer couldn't afford to fix the GMC. In the older engines (pre '55), the crank has a 4 bolt flywheel flange that'll give you problems if you wind it up a lot. Most 302 builders use a 270 crank - much lighter. A few years ago, one builder was using 248 cranks in 302 blocks and getting some terrific results. If possible, pull the side plate to check for freeze cracks before you buy a block - these things crack at 34 degrees. '56 up rods have bigger wrist pins. Stock oiling works well with full flow filter conversion posted on Inliners International site (join them,well worth it). 1/8" overbore is standard practice on either block, gives 292" or 320''. '50-'51 270 "H" and 302 cylinder heads have big intake ports, Chevy Fenton headers work if you port match them. Delco HEI distributor fits with a gear change and some machine work. Balancing is the best money you'll ever spend. 9 to 1 compression will work on the street. Any good cam grinder can regrind a street cam, bearing in mind this is a torque engine, not extreme high RPM. The intakes are getting scarce. Bear in mind, none of your Ford flathead friends are going to want much to do with you after you build an engine worth 150 more horses for less money than they spent on their heads and manifold.
The only thing I can add to what 302gmc said is that the 56 up civilian motors are better. The military blocks are the same as the 52 - 55. One of the parts books that I ws looking at seemmed to suggest that the late fifties pontiac fly wheel would fit the six bolt GMC. This seems to make sense, since the poncho bent eights were available in the Task Force GMCS. Jay
Some long motors Nicson equiped 228 in my 39 AC102 The moc-up motor is in my chopped 40 Ford Some guys race motor
the BIG reason for the GMC being the preferred engine for 6 cylinder projects is that the oiling system is far superior to the babbitt rod type engines chevy used in their vehicles prior to the powerglide 53's, when the 235 came into usage A chevy is just as good as a GMC.
Two things to add: 1) It's not oldgmc.com, but oldgmctrucks.com that you want to check. Lots of info about GMC motors and people who know about them in the forums. 2) GMC used a better alloy in casting the motors, which along with better oiling is another reason they were better than the Chevy motors. And Stovebolt.com is a good place for both Chevy and GMC six information.
Hey, a good website for information on the old gmc sixes is oldgmctrucks.com. Ive got a 270 inliner in my 56 gmc its pretty strong runner for a 6 and gets about 20 miles per gal. The old dirt track guys used the 270 and the 302 in thier cars. Good luck.
Ditto. I have a running 57 GMC and would like to start adding some performance gear. Would like to start with intake & exhaust manifolds. I'm having trouble finding 270 CI stuff. Lots of wimpy 235 stuff out there but it won't fit a real engine.
much of the info is transferable to the earlier 216/235 Nothing from the later engine fits except the distributor, the engines aren't related.
A chevy is just as good as a GMC GMC advantages: 1. much stronger rods 2. maximum displacement much larger 3. stock "H" heads have much bigger intake ports 4. compression can be raised without welding etc.
I've heard that a set of Hudson rods can do wonders for the Jimmy too. All of us inline afficiandos need to get our **** in order and build HA/GR cars. I know very little about these engines, but I'm subscribing to this thread just to spy on ya. Hud
FYI I have a low mile Millitary GMC complete engine valve cover to oil pan with no manifolds spotlessly clean $1500 obo if anyone is interested. Cheers
a set of Hudson rods 1. permits slight stroke increase by offset grinding the rod journals: GMC is 2.311", Hudson 2.125" so maximum increase is .186" (typically subtract .005" to clean up the old journal), or about 4.65% increase on a 270 or 302 - not much. 2. the Hudson rod is waayyy longer, which allows a much shorter and lighter piston (no other way to do this since the block is very tall). 3. the 302 deck height IIRC is 11.281"(?), so the new piston's compression distance with this stroke and Hudson rod is 1.073", rod ratio 1.939:1.
If you want the older engine the GMC is fine but for power the later 292 Chevy truck engine has a lot more stuff available for it and will really run. Ive had really good luck with 300 Ford 6s years back in drag cars too.
ive seen split manifolds and the howard 5 carb intake for jimmys still in production, does anyone know if there is any one still making things like valve covers, side covers, or any other speed parts for them. ive got a 270 with a t-5 behind it in my 59,
Look at installing a 1974 Camaro clutch in this ride. I re drilled the holes hole for the new pressure plate.
Lot of speed equipment being manufactured for GMC sixes. Check Inliners International and their 12 Port News.
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