GMC inline 6 where to start for killer motor

yah, i know about the pistons, i just heard alot of guys did that back in the day. and i didnt realize they went out of buisness, i talked too a jimmy builder about a year agoa dn told hime i wanted to run a new wayne head and he said they still make them, so i didnt question him, anyways, ill still get when, just now ill get an old one and have to look for a while. thanks for the heads up though.

 

Your thinking of GMC 305s, they were V6s (not 305 v8). i have seen inline 302s

 

all 302 gmc truck motors came w/2 barrell carbs. easy to spot when you checking under hoods only a few rare 270,s came with 2 barrells. be sure and get the flywheel w/your 302 as they are 302 only.216/235 bellhsg will fit the 302 but not the flywheel. the 12port is about a $5000. deal for the head and belive me any body that has one knows what they are.you can get about 340ci fairly reasonable out of these with bore, rods, and offset grinding the crank.

 

What's the deal with putting a 302 crank in a 270? How come?

 

I've only known people to do the opposite--use a 270 crank in a 302 because the 270 crank weighed less.

 

You can get 12 port heads and speed equipment from Don ...... www.ardun.com

Here's a photo of one of their motors ''resting'' before Bonneville

 

might have an easier time finding a chevy 292....thats what i have....torque beast of an engine!

 

Yeah. That's what I did. 270 crank in a 302 block. I thought you could buy Arias heads (repop Howard) from the Arias piston people.

 

I know this is painful for GM owners, but the biggest bang for the buck is the Ford 300.

 

Maybe so but just try to get them to let you run in XO with the 300 Ford

 

in thinking about i would suggest a 261 chevy truck motor. same family as the 235. will bolt in where the 235 came from. bore it to 270. check with patricks in casa grande for the skinny on chevy 6 hot rod stuff.

 

That Chevy 261 was also installed in some Canadian Pontiacs in the 60's. Might be worth looking for one of those to get a little newer one.

I have a GMC 270 and they are great motors.

 

Check out this link for a 302 punched out to 341.... this 'ol boy knows how to build wild sixes.. You can even hear it run.. turn up your speakers.

http://stoveboltengineco.com/tomsride.htm

 

Ok boys, here is the scoop on the COE GMC 302. IT WAS A STRAIGHT SIX! It was only available in Cab overs, like big milk trucks. It was the first time a 2.02 valve was used by GM.
These engines are scary torquey. They will tear up all kinds of stuff. Love em.
I sold my last one about ten years ago. The only way to tell if it is the RIGHT ENGINE is first, hopefully its still in a COE. If not you have to have the right head casting number and remove the valve covers. I have that # somewhere but it should be available online.
We had a dirt oval here in the 50's and 60's. Everytime this little chopped 32 Chevy coupe showed up (It was always in primer, never painted) you knew that big 302 inline six was going to take home the gold.
In the early 50's (This article appeared in Car and Driver in the early 90's) the euro sports cars were dominating all the road courses here in the US.
At breakfast one morning one of the guys said, "I know I can build a car and beat those boys." Another one of the guys, they were all sick of seeing the Triumphs, Alfas, MG, Jaguars winning, spoke up and said I will sponsor the car, you build it!
So they did. It was a frame up sports car with the GMC 302 motor. During the next road race season, he won all the races he entered. When it came time for the ARRC (Thats todays name for the championship of Road Racing, American Road Race of Champions) They show up for qualifying the night before and checked into a local motel. When they woke up the next morning the engine was gone!
I can tell you that Patrick Dykes put one in his GMC pick up and it scared the hell out of him...lol
He bought all Weiand's molds and rights to produce parts for us guys. He is still in business, a great guy, and you can find him online. Dual stuff, cams, etc.
Im going to tell you, there is no need to modify that head for increased flow because it already flows like a hurricane!
And, truthfully, I kick myself every time I think about having sold my last one which was totally complete. I pulled it myself.

 

848 heads are for the smaller 235/261 Chevy six engine and won't work on a 248/270/302.

 

There's an old 1959 school bus parked behind a barn down the road a ways (still runs good). The farmer showed it to me a day or two ago. The inline 6 engine is huge looking (about two inches longer than a Chevy 235). I asked him what the engine is, and he said its a "292". But, with "GMC" embossed on the valve cover, it's got to be a 248/270/302, right?. As I recall, it had a 1-barrel carb, so I guess that means it can't be a 302, huh?

 

the bmr racing team's '32 five-window ran a blown, injected '59 gmc six (from a dump truck, no less) to well over 200mph on the salt a few years back. they can make big power and have some inherent advantages over v layouts, mainly in reliability and torque production per cube. i'm not an expert on the gmc stuff, but from what i do know, the late fifties/early sixties motors are the ones to get, particularly the industrial application units.

 

bored hudson motors are absolutely bitchin', too, and make good power, and the ford 300 is one of best engines ever built, imo, in terms of power potential and durability, if you're not married to a gm engine family for this build

 

The 302 GMC first was installed in 2 and 1/2 ton Army trucks around 1951. I changed the oil in plenty of them. I personally have run 302 motors out of a school bus, a flatbed truck and a ready mix truck. None of which was a COE. Bored 1/8 inch it becomes a 320 inch engine. Bored to 341 it becomes an anchor.

 

Rich,how do you get that huge GMC flywheel to go into a 235 bellhousing,or is there a flywheel that will adapt? Edit in, So,anyone have a 248 or 270 flywheel they want to come off of?

 

I used an aftermarket steel flywheel as required by the SCTA. I believe an iron wheel from a GMC pickup with a 228 or 248 that is late enough will have the required 6 bolt holes and fit into a Chevy bellhousing. Finding one might be a pain. You could join Inliners International and run an add in the news letter. Or just give up and buy a new billet one.

 

So, did these big Jimmy sixes come mostly with manual transmissions? Are those what are best for racing? The engine in the '59 GMC bus I'm looking at (a few posts above) has a 'Hydro' transmission behind it, according to the farmer. Still trying to find out whether it's a 270 or 302 engine.

 

The first 3 digits of the engine number stamped on the pad by the distributor are the engine size (cu in).

 

This won't make your GMC go any faster, but they look nice. We make them here in Oregon.

 

Well, it is a finned aluminum valve cover. I am having trouble getting picture on.

 

Yes,a 6 bolt PU truck flywheel from a 248 or 270 will work,weighs about 30 pounds like a 235 Chevy flywheel but not interchangable with the Chevy.Comes in two version,139 teeth for 6 volt and 168 ish for 12 volt. Takes a typical Chevy V-8 11 inch clutch set up.48-54 GMC and Chevy pu truck bellhousings are identical except for the casting numbers.
The military 302 block is different than the civilian truck block.Military block has extra lumps and no mechanical fuel pump opening. Lumps can be ground off,many guys have cut a fuel pump opening into the military block.

 

IIRC the GMC V-6's were turds with a capital "T", next biggest turd was 366 V-8.

 

Hi my name is Dave from New Zealand I have a 270 gmc, I would like to know where I could get a fined alloy valve cover with gmc in the middle, could you help me with this information, thanks for your time.

 

Dave, try Larrowe & Sons http://www.34-chevy.com/ Is this for your old digger?

 

Back in the mid to late 60's a friend of mine raced a 38 Chevy Coupe at the Yellow River Drag Strip near Covington, Ga. The car ran a 4-bbl and sometimes a 3-2 setup. The Class was H Gas and Jodi held H Gas Champion for a few years in those days.....
I have been thinking about one of those for my 33 Chevy Truck but the adapter to hook up a 350 Turbo is money I could spend on something else. Guess I will go the cheap but reliable route (350 SBC and 350 Turbo) Sounds Dull compared to a Screaming GMC 302...................... Jeff