If I remember right the 305's ancestry is a GMC diesel from the 50s, that's why it fit in a '50 truck, I recall a pic maybe in a Motors manual of one in a truck with an Advance Design style cab, maybe 54-55. And that's why it's a low rev gas hog with tons of torque. They just made up some new heads for it and cut the compression to gas engine levels.
I worked for the State DOT repair many decades ago when they ran 478 GMC gas V6s. I will say they did do the job, and even the big same cube Fords and Internationals all ran 2MPG (I was told), pushing snow in the hills.. as they all aged though, the biggest storms usually saw one GMC engine blow on the "biggest hill routes". I don't recall the other brands (all V8s) blowing any engines.
IF I wanted to say ANYTHING more NEGATIVE about this totally worthless piece of GMC "misforurtune" (AKA CRAP!!!!!), I don't know what it would be. They are NOT even worth their weight in scrap. I have NEVER posted such a negative post as this one. That's all I'm going to say. DO NOT LET THIS MACHINIST TELL YOU ANYTHING OTHERWISE !!!!!!!!! You need to seek out a good attorney, and put this "machinist" in their place;. I am so tired of reading about just this sort of situation here on the HAMB , and the "taken advantage of " we read about here!!!!!. Where's my tire iron? I am Butch/56secdandeliivery. \ Seriously, we ALL need to stand up against this sort of "thievery"; this guy today, tomorrow you or I.
Nope the V6 was a brand new design for 1960. Had nothing to do with the Detroit Diesel 2 cycle engine. As far as I know GMC never manufactured any diesel engines on their own in the 1950's. As A matter of fact their truck tractors where lacking power so some came with Olds V8 engines and the Chevy in 1956 had a 322 buick mill. All V8 GMC's in the 1950's came with Pontiac or Olds mills. Now the 478 Cu V6 had two versions a gas and a diesel. I owned a Truck that had the 478 Toro Flow diesel. It was a converted V6. a conversion along the same vien as the Oldsmobile Diesels where. The 478 came out in the 1960's and was never factory installed in a AD truck. Back in the fifties many road tractors where repowered with WWII military surplus diesel engines. Sometines a Newer cab was installed on a military chassis. I knew a guy who hauled new cars nationwide in 1955. They had two trucks one was a Chev with a 261 and 4speed two speed. The other was a GMC with a 271 and 5 speed two speed. He told me he hauled 4 cars. And once on route 66 a 38 chevy truck passed him hauling 6 cars. He caught up with that truck at a truck stop. and looked at the engine. It was a Detroit diesel. The guy claimed it came from a Locomotive and made 300 HP. He told me the guy had stacked washers under the governor rod. and it set at idle horsing the governor. Pulling a grade it smoked so much black smoke the vehicles behind couldn't see the road.
The larger GMC mills had sodium filled exhaust valve stems. and often if lugged too hard the valves got too hot would pop the head of the valve off and thats all she wrote.
THIS ^^^^^^^^^^^ Not defending GMC V6........I agree it is not suitable for a hot rod application, but accuracy about statements should be maintained in any case, Ray
We bought a 4000 series GMC ,1961 model 2 ton in 1963 and still have it,with the 305,C series I believe they are a work horse not a hot rod, 165 horses @ 4800 RPM, we run this one at 3 to 3500 no problems, It won't out run big Ford truck motors of the same time frame but if you have a need to pull stumps this will do it, I had it on a 50 mile daily trip a few years,25 miles loaded 25 home empty, it got 10 MPG, with the orginal Stromburg 2 barrel carb. Old Wolf is correct the 305's came out in 60, the 478 gas was converted to a diesel and was not that good of an engine,kind of a turd they sounded good but no long gevity. GMC did build a diesel engine the Detroits started out as General Motors Corp, but a little glitch along the way, I think I understood it to be in the early 50's, and GM divested itself of the jimmy diesel and it became Detroit Diesel, some horse shit about a monopoly, maybe OW has better knowledge of this.
That's what I've heard about these motors too. You can take them up around 5 grand but you don't want to do it very often. What I will ultimately do is use this one until I get a few other projects knocked out, namely my 30 A, boat, and picked up another mud truck, then this one will probably be ready for a teardown again. Eventually the Y block will probably end up in this, and an early hemi will find its way into my A, but for right this seco d, I'm running outof room and I got to put it somewhere and being out my 292 6cyl this seems like the most logical place to put it. Sent from my SAMSUNG-SM-J320AZ using Tapatalk
My dad bought a '63 GMC 1/2 ton pickup back in the mid 60's that had the 305 V6 and 3 speed trans. He used it as his daily and drove it back and forth from Covina to Long Beach, Ca. everyday. He got about 10 mpg out of it, He had a cab over camper on it that he left on most of the time and pulled a travel trailer with it 10 to 12 times a year. This thing was a beast with gobs of torque, when he reached 300K he pulled the heads, did a valve job and also replaced the rod and main bearings and drove another 200K miles before trading it off on something newer. Back then gas mileage wasn't a big deal to most people but with the cost of gas today, well... As previously mentioned, poor gas mileage and very heavy not to mention limited power makes it a poor candidate for a hot rod engine, imo. The fact of it being free? Of course it is, how else would he get rid of it!
The Detroit diesel was available back in the 1940,s. I ve seen old magazine advertizments touting repowering the M farmalls with the 2 cycle diesel. And there was a diesel version international engine. Spark plugs and carb on one side of the engine and injectors and fuel injc pump on the other. Started on gas and converted to diesel after it warmed up and you pull a compression release lever.
5 to 6 mpg is a damn lie. My 65 305 GMC 3/4 T with ladder rack NEVER got over 4. Uphill with ladders loaded and into the wind pulling a trailer---4mpg. Downhill, empty, and with the wind---4mpg.
Is there a known cause of the 305 V6 high fuel consumption? Low compression, inefficient combustion chamber design, ignition system with unsuitable advance at cruise rpm...?
Ungodly low compression around 7:1, crap carbeuration and exhaust. I have heard reports swapping that carb to a 500 holley 2bbl actually causes a decent mileage increase, as high as 15 with the right gears and tire. I'm shooting for significantly better than that with an OD 5 speed. Sent from my SAMSUNG-SM-J320AZ using Tapatalk
7:1? What in gods name did they intend to use for fuel, kerosene? Oh well, sounds like it should be okay with a descent carburettor, suitable transmission and (if possible w/o causing too many new headaches) milling the heads. Even if gas is quite a bit cheaper in the US than here the fuel savings should pay for the upgrades relatively quickly.
Milling the heads is on my list, but not unless I end up needing to go through it. Sent from my SAMSUNG-SM-J320AZ using Tapatalk
Also you can retrofit an HEI out if a buick odd fire V6 to this motor with a decent machinist and a little welding. Sent from my SAMSUNG-SM-J320AZ using Tapatalk
I don't think you want an 'odd fire' ignition (not even sure they had HEI during the odd fire years) because the GMC is an EVEN FIRE engine being that it is based on a 60* configuration. The odd fire Buick V6 was a 90* Vee and the engine fired 90*-150*90*-150* etc.. The even fire Buick V6 HEI probably would/should work, because even though the block is still 90*, the crank throws are offset and it fires every 120* as would the GMC V6. But that is also true of any Inline 6 that used an HEI...still fires 120*. Ray
Based on your comments throughout this thread, it is clear that you're committed to this path (lots of very knowledgeble people have given you good reasons not to), but your plan above is simply fantasy. Enjoy the shiny red lips on your pig.
I glanced that this thread, then had to look again..., I know everyone responds differently but most people would be much more upset than you seem to be with this machine shop. That said the 305V6 is a pig. Big. Heavy. Thirsty. No aftermarket support. Not good for much more than a working truck's motor. But to each their own. Good luck. -Dave
I had a 1964 GMC with the 305 v6 plenty of power for hauling hay. As I recall 10 mpg with the three on the tree. Back when you could buy a good clean truck for $600.
There were 4-71 and 6-71 Detroit diesels, that's where the blowers that guys use on V8s came from originally. I saw one at an auction a few weeks ago, engine on a stand from a generator or something. Budd RDCs - a self-propelled rail passenger car - had two 6-71s at an angle under the floor. I just remember the picture in the Motors book when I was first reading up on these beasts and you could see the similarity in design between the older diesel and the 305. Prior to the 305 there was a GMC-ized Pontiac, based on the 1958 370, but at 331 CI or so. Had a guy who was going to give me one, with the trans out of a big truck, then never heard back from him. That would have been nice to have, depending on what would have fit the bellhousing.
Reminds me of the story about the guy that exited Las Vegas with a small fortune (he entered with a large fortune ) A decent mileage increase replacing the Stromberg WW with a Holley 500 would also involve the installation of a very large sail!!!!! The WW was and still is one of the better 2 barrel carbs ever built. It has two issues: (1) The aluminum throttle body (any competent rebuilder will install bushings...end of issue) (2) For hot rodding purposes, the WW doesn't come in large sizes. (so use 2, or 3). Jon.
I know where a grain truck is setting. It has the305. And It has a single bbl carb. looks to be the same carb as a 223 ford. and its bolted to a stock cast iron manifold. hasn't run since 2000.
My records show G.M.C. in 1959~1961 had a 305 EXPORT that used a single barrel carb. The early 1959 used a Holley type 1904. The later 1959 through 1961 export used a Zenith type 28. My records might be incomplete; or possibly an export engine is in the truck you mention. The Holley type 1904 was also used on the Ford 223. The domestic versions show as all using the Stromberg type WW two barrel. Jon
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