"big block" GMC I6 engines

[JHZR2]

Some time back there was a page that had huge (big block?) I6 engines that I think were manufactured in a limited fashion for GMC pickup trucks. Big ones, larger than the standard list of GM I6 engines.

Anyone know what Im talking about? Anyone have the link?

Thanks!

 

[Chris142]

Inline 6 or do you mean the huge v6 that they made in the 60's? 305 and 351 cu in.

 

[paulo57509]

http://www.6066gmcguy.org/gmcv6a.htm

http://www.6066gmcguy.org/TwinSix.htm

 

[Chris142]

http://en.wikipedia.org/wiki/GMC_V6_engine

 

[JTK]

OMG how cool is that!

Could you imagine the fuel consumption on that beast in a commercial truck? 1-4mpg maybe?

Joel

 

[Chris142]

Originally Posted By: JTK
OMG how cool is that!

Could you imagine the fuel consumption on that beast in a commercial truck? 1-4mpg maybe?

Joel
Definatly not overcarbureated.

 

[UNC017]

Originally Posted By: JTK
OMG how cool is that!

Could you imagine the fuel consumption on that beast in a commercial truck? 1-4mpg maybe?

Joel


I don't know that they're particularly inefficent. People I've known who had the 305 v6 in GMC pickup trucks generally got very good mileage for a gasoline engine- better than a 350 v8 got in later years for sure. As for the bigger ones in heavy duty trucks, again they were about the same or better than the average gasoline engine. At that point, you're pretty much limited by the amount of energy required to move the beast, not by an inefficiency of the engine. Just as a point of reference, the gold old International Harvester 345 gasoline truck v8 would get about 5-7 mpg in a loaded 72-passenger school bus. I'm told that the Chrysler 413-3 in a tandem-axle dump truck would typically do about 4-5 MPG. The 413-2 in a full-size motorhome was good for around 8-10 MPG..

 

[FL_Rob]

In hot rodding circles ,the blowers on those are known as 6-71's,they came off the six cyl.at 71 ci/per cylinder hence 6-71 it's the style of supercharger stickin' through the hood of EVERY 'cartoons' book.

 

[FL_Rob]

I take that back, thats on the Detroit Diesel 6 cyl.

 

[ekpolk]

I recall browsing a few years ago and finding a whole bunch of information about these intriguing engines. Especially given the technology of the day, they seem very advanced for their time. Sixty-degree design, short stroke, aluminum pistons, sophisticated crankcase ventilation, carburetion optimized for trucks (not compromised for performance pretenses as so many engines are today, through their fuel injection, of course), and so on. Why, all they would have needed to complete the picture would have been Mobil 1 T-SUV oil! Seriously though, these were impressive engines, no doubt about it.

Now, I was wondering, how would that 478 cid (that's a 7.9L in today's parlance...) V-6 would do as a swap for the DOHC 3.5L in my wife's Avalon?

 

[ekpolk]

Originally Posted By: JTK
OMG how cool is that!

Could you imagine the fuel consumption on that beast in a commercial truck? 1-4mpg maybe?

Joel


Nah, no biggie -- hook it up to a modern Toyota or Ford hybrid system, and she'd be good for at least what -- 50 mpg or so??

Suffice it to say, it's already been a long day, and my very, very warped sense of humor is already raging out of control...

 

[ekpolk]

Originally Posted By: JTK
OMG how cool is that!

Could you imagine the fuel consumption on that beast in a commercial truck? 1-4mpg maybe?

Joel


Actually, the one and only thing I'm having a problem wrapping my mind around is why there appear to be four separate oil fill caps, on the only left side of the engine. Are there four more on the other side? Does this monster engine take so much oil that you need four, or maybe eight, filler openings to get oil into it in a reasonable time? Very strange...

 

[Rob_Roy]

Originally Posted By: ekpolk

Actually, the one and only thing I'm having a problem wrapping my mind around is why there appear to be four separate oil fill caps, on the only left side of the engine. Are there four more on the other side? Does this monster engine take so much oil that you need four, or maybe eight, filler openings to get oil into it in a reasonable time? Very strange...


The engine had four heads, and four valve covers. The valve covers are all the same design, (left front would fit right rear, and so on), and one of the caps on each valve cover was for a vent. I believe you could add engine oil from any of the 4 fill caps.

 

[Jim 5]

Originally Posted By: Rob_Roy
Originally Posted By: ekpolk

Actually, the one and only thing I'm having a problem wrapping my mind around is why there appear to be four separate oil fill caps, on the only left side of the engine. Are there four more on the other side? Does this monster engine take so much oil that you need four, or maybe eight, filler openings to get oil into it in a reasonable time? Very strange...


The engine had four heads, and four valve covers. The valve covers are all the same design, (left front would fit right rear, and so on), and one of the caps on each valve cover was for a vent. I believe you could add engine oil from any of the 4 fill caps.


Probably just for the purposes of design and accessibility/clearance options, given that this engine could be used for various truck configurations and industrial purposes.

 

[JHZR2]

Thanks! OK, V6 engines.

Can someone give me the rundown on why these were superior (or maybe they werent) to V8 and other engines? I can get the geometry bit wrt to inline engines and their fit, at least to a point.

Seems that they talk about short strokes, which mean big bore, which to me means poor combustion efficiency.

Also, wouldnt a short-stroke engine be more well-suited for high-RPM use?

Thanks!

 

[UNC017]

Originally Posted By: JHZR2
Thanks! OK, V6 engines.

Can someone give me the rundown on why these were superior (or maybe they werent) to V8 and other engines? I can get the geometry bit wrt to inline engines and their fit, at least to a point.

Seems that they talk about short strokes, which mean big bore, which to me means poor combustion efficiency.

Also, wouldnt a short-stroke engine be more well-suited for high-RPM use?

Thanks!


Change your frame of reference. Think TRUCK and not hi-po automobile engines. Fewer bigger cylinders turning at lower RPM means more usable torque. Lower RPM means there's plenty of burn-time for the large cylinder volumes. "Short" stroke is relative- remember these were designed in the late 50s at a time when much LONGER strokes had been the norm- these aren't particularly short stroke engines by modern measure. Everything about this GMC engine family was optimized for truck use- no compromises to let it also go into a muscle car as you might find with, say, the 454 v8 from a decade later. One of these big v6 engines will haul circles around a 454 in a heavy truck, and outlast it 2 to 1 also.

 

[ms21043]

Here's the twin 6 in the Blastolene B702

 

[JHZR2]

440 - thanks for the frame of reference. Some odd thing brought those engines into my mind this morning, and it is neat to learn... But the aspects of design arent necessarily my forte. Your insight is greatly appreciated.

Thanks!

 

[UNC017]

Originally Posted By: JHZR2
440 - thanks for the frame of reference. Some odd thing brought those engines into my mind this morning, and it is neat to learn... But the aspects of design arent necessarily my forte. Your insight is greatly appreciated.

Thanks!


Look at where the spark plugs are located on the GMC v6 engines- I've always thought that was one of the neatest externally visible things about that engine family. Keeps the wires away from the exhaust heat and makes changing plugs in some applications really easy compared to other V-types (think boat or some industrial applications where the engine sits down in a pit).

 

[Rob_Roy]

Originally Posted By: 440Magnum
Look at where the spark plugs are located on the GMC v6 engines- I've always thought that was one of the neatest externally visible things about that engine family. Keeps the wires away from the exhaust heat and makes changing plugs in some applications really easy compared to other V-types (think boat or some industrial applications where the engine sits down in a pit).


That is an important design feature when talking about HD gasoline truck engines. We used to have a pair of IH Loadstar's with 446 CID V8 gas engines, the exhaust manifolds would glow red when you worked them hard and the spark plug wires were constantly needing replacement. Even a "race set" of plug wires wouldn't last more than a year. Our GMC with the 401 V6 used to get the "snot run out of it" (it was a fertilizer spray truck) and I don't ever remember having a plug wire fail.