The Stovebolt Site Forums The Shop Area Engine Shop 302 GMC Inline 6

I will soon be a Suburban owner, of a vehicle without an engine. I am leaning towards old school for it, at least to begin with. I've read and heard bits and pieces about the 302, but want to here more thoughts on what it's like to operate.
Any and ALL thoughts and comments related to the 302 would be welcome.
Thanks, Bill

The 302 is the holy grail of engines in their era. It was highly desired for racing engines for years. Even stock one would power your Suburban nicely.

When you find one it will most likely be from a big truck. The bell housing, flywheel and clutch won't fit in a smaller truck. Nor will the oil pan. The parts from a 1-ton or smaller with a 228, 248 or 270 will fit. You don't say what year Suburban so be aware the bell housing mounts changed in 1954.

There are civilian and military blocks. The military one takes some modification. There is info on that at oldGMCtrucks.com. You'll need to sign up read the discussion forums.

Also head over to inliners.org site, lots of 302 nuts over there.

Sorry for posting in the wrong place. I should have looked a bit more at my options of topics.
SuBurban I believe is a '49 or '50, haven't determined that yet, no title, and picking it up this week. I could have asked for the tag info, but at this point, doesn't matter. I'm buying!
I've heard a couple times now that they are pretty thirsty engines. Is that a rule, or can that be remedied some with modern carb.?

A 302 will use more gas than a modern fuel injected engine. A 302 could have come with a 3 bolt Holley or a 4 bolt Stromberg. They are both good carburetors and a carburetor is a carburetor. They use gas to produce horsepower. Going to a 3.55 rear will help some. Keeping your foot out of the carb will help a lot, but that takes the fun out of it.

another nice thing about the 302 is there is some fella still making 12 port heads, (aluminum) I am pretty sure his name is Mike Kirby, @ Sissels automotive. Even if you don't want/can't afford one it is a cool website to go to. If I were to swap out the 216, I would definitely go with the 302.

Billo57
You didn't say if the suburban is a Chevy or a GMC. If it's a Chevy the 302 will not fit in a stock Chevy frame without modification.

I have a spare 302. If you are looking for a 302 let me know. In regards to the military 302, the differences includes a cast boss just above and forward of the starter motor. It is best described as 1 inch by 1.5 inch cast bump out from the block and it has to be ground off to fit the starter. Also, the fuel pump cutout is part of the block cast, meaning that hole will need to be cut open to fit a mechanical fuel pump. If I recall, the drilled and tapped holes are in place to mount the fuel pump...(I can't remember if I drilled and tapped the holes). Your other option is to leave it alone and install an electric fuel pump. You will need to locate a 270 flywheel to bolt onto the military 302 crankshaft.

Another upgrade will be the replacement of the military oil pan and oil pump with a matching oil pan and pump from a 270, 248, or 228. And consider installing an external oil filter system rather than a stock oil filter that, at best, filter about 10% of the oil pumped through it. Same would apply to a 270, 248, or a 228..

Another solid engine for consideration could be a GMC 270. A 270 will power the Suburban just fine. And theret may be some cost savings in fuel consumption.

I like the old school hotrod 6 bangers. California Bill prodcued two books on the subject that will be rather helpful to you. They can be found on Ebay. Dual exhaust, modifed camshaft grind, and dual or triple carb intake manifolds will really increase the power output. Any combination of these improvments will make a difference depending on your budget. A 100.00 camshaft 3/4 grind by Delta Cam in Washington state is well worth the small investment. Assist it wih dual exhaust for starters.

Many swear that balancing the crankshft, flywheel and balancer is a must. The other school of opinon is that they come balanced from the factory...assuming that you ae not mixing and matchng these parts from other motors.

The catch 22 is - you can sink money to add these improvements to 270, or even a 248 to improve power, but a stock 302 will give you that already.

If it is a Chevy frame then locate a later 261 with the full pressure oiling system. That will bolt right in, although you will need to locate an earlier bellhousing to fit the frame crossmember. The 261 is great motor and can be hopped up as well... Find a 235 "848 head" for improving compression values rather then the stock 261 head...but the difference is not significant...but, in combination slight modifications do add up to more power.... Its a matter of how deep you want to reach into your pockets.

There are 4 barrel intake manifolds that may help with fuel economy. Tom Langdon can help, or give Patrick's a call to ask about this. Also James Larrowe has a catalog for these modifications...and sells flywheels, harmonic balancers, 848 heads, blocks you name it. Check Ebay as well (be prepared for price inflation on parts!). or post a wanted ad here. You more than likely will find a better deal here, but it may take some patience for someone to reply to your ad and have what you are needing.

Or buy a 270 for parts!..that is, if you want to work on a 302.

Tom

Hi Tom
It's a GMC Suburban. There's a lot of good info here. You most have been around a 302 a little. I know a lot of people opt for.......a modern v8 let'ssay,and would be a great idea, but there's something about the old engines, especially if they will perform well. I know, there's nothing like the sound of a v8, but, we like the old vehicles because???
The inline 6's, to the best of my knowledge are a "thing of the past", so just seeing one is neat. I like the GMC's, one reason is the neat GMC script here and there. It's got the old school style, it's kind-of folk art-ish, and the script on the valve cover is real cool. Them poor old Chevy's never got that attention. Lol
I appreciate the wealth of info that is given here, please keep it coming, it's priceless.
Bill

If you check out Tim Lederman's home page there is a great article from an old HotRod Magazine that he saved on his site. The magazine performed about 6 different tests on a 261 motor. Starting with a stock set up through dual exhaust test only, to dual exhaust and duqal inteake manifolds, to 3/4 cam grind, to more improvements. The summary says that a 6 cylinder motor has just as much capabilty as a V8 and if not more. And that 6 cylinder motors should not be ignored for their durabililty, power, and ease of improving them. They are built like a brick [censored]-house. There is nothing like a spilt exhaust sound coming from a well tuned 6 cylinder. Everone has a v8, but these 6 cylinders will hold their own against one, on any day. I think you will fit right in here! Check out Inliners Internation website. Oh by the way...I even have a nice Ford 300- 6 cylinder in a 62 Ford 4WD pickup. That 300 sounds just great too...and very powerful. I just like old trucks..whether chevy, gmc, ford, doge, international...they are all just great.

I have Chevy Suburban project and I will be putting in a 261; although I do have a preference for the GMC motors over Chevy...and I always thought a GMC Suburban looks great.


On a 1946 GMC project I am still sitting on the fence and trying to decide whether to put the stock 228 back in after a re build, or pump it up and install a 302. Decisions, decisions, decisions. No wonder I can't sleep at night. This hobby tears a fella down over time and his pocket book too.

302's are sort of hard to find, look just like 228, 236, 248, 256, 270, SN stamped on machined surface on right side of block by starter, start w/ displacement, i. e. 302xxxx. Some smaller, earlier, (non-270/302)engines have small bellhousing that won't take large(11")clutch. Adapter plate available to use modern bellhousing that is much easier to R & R(InlinersInternational.org). Two 'Good' heads(larger valves, ports), two 'average' heads; casting nos. tell diff, both come on 270/302's. All heads not interchangeable w/ all pistons. Patrick's in AZ has 9:1 pistons, lots of other parts, good catalogue w/ casting nos. Good luck.

Hey Tom!
I guess I've been with the understanding that an inline 6 is naturally balanced? Anyway, the more info I am receiving and gathering from different sources, (and thanks so much for yours) I am seriously considering going that route.
Did you say you had one? I do know three guys that have one or more, and know that one will sell one. I haven't approached the other two yet about a sale, but heard one of the others probably would.
Duals on a 302? I have seen split exhaust on a 6, but didn't know it could actually be a performance thing.
I like a floor shift, and the Suburban I'm buying had this. To the best of my knowledge, a floor shift model meant a 4sp., which meant a granny gear. Can I still use the same shift set-up with a later transmission? This may be a topic for a different area here, but there it is just the same.
GMC'S are cool, and there's fewer of them.
P.S. What is the going price on a 302 builder?
Bill

Thanks Ed!
Great info here. One of the 302's that may be available to me locally, is in a military 6x6? Is that a strange version? And, what head might be one that installation?
thanks, Bill

Yes duals. Fenton dual exhaust headers. Make sure you are ordering these for a GMC and not a chevy; there is a difference between the chevy mounting flanges and GMC.

Going rate for a 302 builder?: 600.00 to 1200.00 or more depending on variables. Yes if you have a local source, then go for that as it will save you about 300.00 plus in shipping costs.

You can PM me or e-mail me at [email protected].

Nope, the 302's were commonly used in the 6x6 transports. There is military truck website that has information on the gmc's too. Head is llikely to be the stock head.

Yes, floor shift more than likely the 4 speed. Patrick's has a rear differential conversion kit to modify your gearing from a 4.11 (perhaps) to a 3.55. That will help with mileage and shifting. You can also install the 16" rims and tires rather than 15" (if it comese with 15" rims) More than likely it has the 16" rims.

The military maintained their motors and it's not uncommon to find a military rebbuilt or very low mileage rebuilt 302. I purchased a 302 a couple years ago, and it was squeeky clean inside and out, and the pistons and rings were new. Along with bearings, valves, head etc. etc. That was dumb luck, as I expected it to be a builder. I will send the crank etc out for balancing as these parts came from different GMC 270 motors.

Might be worth your while to locate a cheap 270 just for the parts you are going to need to modify the 302 for civillian application.

You are more likely to find a 270 than a 302 in Military configuration as noted. The M135 and M211s were not produced in anywhere near the numbers of the CCKW. Best number I could find was less than 80,000 trucks, compared to 560,000 CCKWs.

Plus the M44 chassis (the M35 series) but the nail in the coffin of the M211/M135 so they were quickly given away as Military aid to our allies (aka left in Korea/Vietnam)

If you can find a military 302 you'll be able to tell your friends that your motor is capable of underwater operation (with the proper snorkels). That's the reason the block was never cut for a fuel pump... its completely sealed.

The 302 cam has the lobe for the fuel pump and it is possible to cut a hole in the block for it using an old gasket for a template. I prefer to use an electric fuel pump. There is a big hump on the block that needs to be ground off so a starter will fit. No big deal except a lot of grinding. I have a military that will still take standard rings and pistons. The originals sat so long that there was electrolysis between the rings and pistons and stuck the rings to the pistons. NOS standard rings and pistons can be found quite easily because most civilian blocks don't go standard any more. I bought another 302 on eBay a couple of days ago simply because it was only 75 miles from here. Its a civilian, but I haven't picked it up yet. I prefer the civilian version version because you get a usable distributor and most of them take a 3 bolt Holley. I have a bunch of them that came off of old Y-Blocks. They work well after I block off the Load-o-Matic advance that Ford used through 1956.

19563? that is a long way in the future

Year: 19563. Ford built their trucks and motors to last, I guess. No planned obsolecense on their parts. Submiited with respect. Tom

I fixed my goof. I use the period on the number pad and I fat fingered the period and got a 3.

it was fun for a while

Thanks again for the great info.
I'm having fun learning and picking up parts for the one I don't have yet. Don't they call that "putting the cart before the horse"?
Oh well, it's what makes my little world go 'round some days. Always been car crazy, and these truck are a "new" endeavor for me.
I greatly appreciate the willingness of you guys to take your time to share your knowledge. It's really awesome.
Now, if one of you kind gentlemen would just send a nice clamshell rear light my way........................ Lol
Bill

Found a few civilian 302s and a couple civilian 270s. Going to buy at least one of each. Same guy was a GMC enthusiast for many years. Used to haul pulp with the old trucks so has some larger vehicles, also a larger school bus, etc. etc.

302 engines tend to appear in spurts. I recently bought two of them, and a guy I know bought a really good one recently. However, it had been a long time since I had seen one for sale reasonably. If it doesn't wreck your budget, I would buy several. Especially heads because they are prone to crack.

Whatever happened to the rumor about the "new in the crate" military 302's that were available, supposedly produced to power DUKW's? I heard that story 5 or 6 years ago, but it seems they were a figment of somebody's imagination!
Jerry

I heard that rumor too from a drag racer who runs 302's about that long ago or maybe longer. Nothing since so one must consider the rumor mill as accurate as always.

I heard that rumor at one time, but i didn't really think too much of it at the time. The military sleeved a bunch of the 302 engines back to standard so it wouldn't seem that they would produce crate engines. I had one of these engines some time ago, but I traded it for something else. 25 years ago there were a lot of 302 engines to be found in 450 series farm trucks that were still standard and didn't have the hump to be ground of to put on a starter. I even still have a NOS short block that I never have installed. I've had it so long that its kind of like someone told me not long ago, "If you build a motor with it, its no longer NOS" I wish someone would come across a stash of NOS heads. NOS military valves for a 302 come on eBay ever so often. But I never have seen a military surplus head. Maybe they welded them when they sleeved the blocks.

Bach in the early 1950's a lot of milsurp 270'a were used in dirt track race cars. They had so much torque the flathead Fords were halfway down the straightaway before the Jimmy-powered cars got the wheelspin under control coming off the turns.
Jerry

There are a few available, and a couple or so 270s. What parts on these engines are variable if engine no good. I heard that exhaust manifolds crack? Also, heads crack? Any other reason to pick up parts engines?

Heads are the most vulnerable. Exhaust manifolds are around. Lots of guys put on headers and have left over manifolds. Heads can be repaired, but I prefer one that hasn't been repaired. We used to refer to GMC heads as glass heads.

don't let anyone worry you about gas mileage. I have a supercharged 270 and get a solid 16 - 17 mpg on the high way and I like to stab it now and then. Also talked to a guy from northern WA. with a 302 with 3 carter Webers ( stove bolt eng. co. )and lots of other goodies, all in a 39 coupe. He said he was getting around 19 mpg and he was pulling a tear drop also. If I were you I would bump the comp. up a little 8.5 - 9.0. use a small port head if its just a cruiser. Headers and good carbs not the old stock dribblers. then hook it to an overdrive trans of some kind t-5 or 700r4. you'll have one nice driver that won't look like all the others. I really dig the old suburban's

Hi,
Thanks for your input. You mentioned maybe a smaller port head, such as?
. . Bill

Jay D, can we see some pics of your supercharged 270?. What supercharger did you use? What kind of internal mods did you do to your engine? Thanks. Jim

i'm having trouble getting pictures on here. I don't understand we can put people on the moon and do almost anything with computers but put pictures on a forum easy. some forums are easy some not.
anyway its a 270 with a 471 blower, 7-1 forged pistons a blower grind cam. it has a big port 302 head with oversized valves and hei ignition everything else is stock gmc
trans is a stock 700r4

i'm also in the process of building another 270. This one is going in a 31 chevy pickup as a daily driver. Its going to have 3 carter/webers headers and a mild rv type cam. This is an econo job so i'm going to run the stock pistons for now and a small port head. I'm looking for tork and mileage. I would like to bump up the compression but pistons are mucho money and I already have a set of good stock pistons. This engine is getting a close ratio t-5 trans with a 4.10 rear for now
Jay D

BILL, gmc's had about 4or 5 different heads, LARGE PORT HEADS yes these have huge intake ports and huge valves, Great for a performance engine like my blower motor. I had a small port head on it when I first built it, it had gobs of tork down low and gas mileage was good near 20 on the hwy. all was good but the top end just wasn't there like it should have been. So I found a large port 302 head that had been on a drag truck, it had over sized valves springs and a port clean up. With this head I lost low end tork and mileage dropped down to around 16 but my top end really came on. So if your building a cruiser and want good mpg find a small port head. there are 2 or 3 different styles and they all fit, you just need to match the correct piston with the head. if your going to buy aftermarket pistons you will need to cc the chambers so you'll get the right compression. check out PATRICS catalog it gives a some what description of gmc heads GOOGLE will help also
Jay D

There are no direct picture uploads to the forum. Some of our members pay for their internet by the pixel, apparently, and photos run the bill up. Post a link to your pic host and people can choose whether or not to view them. For instance:

Crankshaft drill/tap guide:
http://www.hunt101.com/data/500/Drill_and_tap_guide_2_005.JPG

Jerry

Great information! I have a line on at least three 302's and one or two 270s but must wait till spring to acquire. (MN winters/snow, cold) I'm excited and feeling real fortunate to have this stuff "fall in my lap" so to speak. Funny thing too, it came through 2 older gentlemen, both named Frank. Lol
I got all "booked up", when I decided I was going to own a AD suburban, and know what I want to do with it. I do have a "Patricks" catalog. Just waiting for the "stork" to deliver. Christmas and birthday have passed, so...................
Thanks so much for your input.

It's great to see another GMC suburban owner going with a 302. If you decide to go this route, make sure you do your research first. I was relying on a friend to work with me on mine. He's no longer available to help and I am squirming with all of the issues of putting one of these together without first hand knowledge.

Check with Langdons or Patricts before you go any father. It makes a difference in which parts you use with the way you are going to drive it. Performance or daily driver.

Parts for these are drying up fast and the prices are getting higher. Decide if you want headers, bigger carburetor or multiple carburetors first. Are you going to go with a remote oil bypass? Make sure you read up on that first and locating it can be a hassle. Running hot water to the intake manifold is a must according to Langdon, so getting the right components is essential when you start putting this back together. Vacuum advance is another must according to Langdon.

I went with an alternator, so a 3/8" water pump and harmonic balancer are a must. Finding them is another story. Purchasing a core 270 is a big plus, lot's of usable parts that will save you grief. Oil pan, harmonic balancer, water pump, flywheel, bell housing, starter, head etc.

Good luck………….g

I have been doing some research into electronic fuel injection, it doesn't appear so intimidating as I first thought. Even sequential seems to be extremely possible. However reading up on it and actually doing it is another story. But it sure is intriguing.