GMC Crackerbox, a "fun" read.

[QRTRHRS]

I had never heard of that GMC twin six V12 gasser before until I saw one sell at a Mecum Gone Farming Auction. I would love to have heard one of those running.

It's been 50 years but i do not recall that the V12 sounded much different than a V6. The truck was a single axle with a 5spd, 2spd rear used to pull a lowbed to move equipment. Though my hearing was not all that good even then.

 

[number two]

Damn,those 71
Series Detroits with straight pipes like in the video were simply Too Loud!
Only ever owned 92 Series Detroits in my trucks.
2 6v92TT,and 4 8v92TT.
Treated me pretty good,and you could start them in the winter!

Fun read indeed!

 

[5030]

If you drove a double breasted Yamaha for any length of time, your hearing would degrade anyway.

I not so fondly remember parking at a truck stop over night and having to park on the dirt or gravel because the 'puke tubes' puked oil constantly. You never changed the oil in s Detroit, you just kept adding. In fact Roadway used their Detroit's to burn used motor oil up. Had a metering pump that added drain oil to the fuel tanks as you drove along. Recycling before recycling was mainstream.

You want to talk about some sick trucks, Roadway had them in spades. You had to slam your fingers in the door before driving one.

The thing about Detroits was, they were really designed as a vocational engine, not an on road engine. They do best when run at rated rpm for hours or days on end, not the up and down rpm of a highway truck. Why the make excellent standby genset engines or engines in derricks or earth moving equipment where they are running a constant rpm. Outfit I retired from had a V12 Detroit powering their Generac standby genset. Had 4 turbo's and 2 blowers and it was a screamer. Had positive electric lube and when the oil was at pressure it started at rated rpm, what a hoot to watch the black smoke come out the twin straight 8" exhaust pipes. Once it was at rated rpm (I believe 1800), no more smoke, just heat waves.

Detroit's always sound like they are running at some ungodly rpm, but they aren't. It's the Roots type blower that causes them to sound like they are.

 

[5030]

I drove a Silver 92 once in a while. The 430's had issues with injection however. Kind of like the Red Headed Cummins had. None of them had any low rpm torque however. Cat was the king of the highway with low end torque, always was. You could short shift a big Cat and stand on it and so long as you kept an eye on the pyrometer (never run any diesel past 1300 on the hot side of the turbo) you were golden. Past 1300, bad things happen to aluminum pistons. I loved running my 3406's in the company trucks I drove. Torque monsters. Even loaded (163K gross), I could skip gears. I still hear the sound of them spooled up and screaming that song in my head. Ther ones I drove always made at least 30 pounds of boost, sometimes a lot more depending on how deep your right foot was in the fuel pedal. Didn't matter (fuel mileage) back then and we were always told by the service manager at the dealership to keep a close eye on the Isspro. Just so happens the service manager then and now is a good friend and hunting buddy too. We talk about old times, all the time.

Faste3st truck I ever drove and most power was the first Western Star long nose I got when I hired in. It was a glider kit (started out as a Pete but one of the drivers wrecked it in Pa, so they towed it back, pulled the engine and rears and trans out and installed everything in a glider and I got it. Had a Cummins Big Cam 400 with a Eaton 13 speed Roadranger and 44 rears on air and big 11:00 x 24 rubber on polished Alcoa wheels.

The shop spared no expense on any of it either, Tranny was totally rebuilt, rears were too, new driveline and power divider and the engine was line bored, counter bored, new liners installed, head reworked and flow benched, over sized turbo, twin side mount air cleaners with low restriction K&N air filters, but the engine itself was hand built by the best wrench in the shop, the pump was shimmed to the max, fuel pressure cranked outta sight and I was told not to roast the tires... I could bury the speedo in 13 direct (120 mph) any day and when I grabbed a gear, if you were behind me, you'd have to turn on your headlights to see through the smoke and that is no chit either. They dynoed it 560 ponies to the rear wheels in 13 direct with 373 rears. We had a rolling dyno at the shop btw.

Wish I had that truck today. It was a classic in more ways than one.

 

[Norm W]

Still running this one. 6V92 under the seat. I just wish it had power steering. Tight maneuvering is a bit of an exercise.

 

[LouNY]

If you drove a double breasted Yamaha for any length of time, your hearing would degrade anyway.

I not so fondly remember parking at a truck stop over night and having to park on the dirt or gravel because the 'puke tubes' puked oil constantly. You never changed the oil in s Detroit, you just kept adding. In fact Roadway used their Detroit's to burn used motor oil up. Had a metering pump that added drain oil to the fuel tanks as you drove along. Recycling before recycling was mainstream.

You want to talk about some sick trucks, Roadway had them in spades. You had to slam your fingers in the door before driving one.

The thing about Detroits was, they were really designed as a vocational engine, not an on road engine. They do best when run at rated rpm for hours or days on end, not the up and down rpm of a highway truck. Why the make excellent standby genset engines or engines in derricks or earth moving equipment where they are running a constant rpm. Outfit I retired from had a V12 Detroit powering their Generac standby genset. Had 4 turbo's and 2 blowers and it was a screamer. Had positive electric lube and when the oil was at pressure it started at rated rpm, what a hoot to watch the black smoke come out the twin straight 8" exhaust pipes. Once it was at rated rpm (I believe 1800), no more smoke, just heat waves.

Detroit's always sound like they are running at some ungodly rpm, but they aren't. It's the Roots type blower that causes them to sound like they are.

Actually the reason they sound like they are turning high rpms are because they were 2 strokes, you had a power stoke on every revolution instead of every 2 revolutions like a 4 stroke does.
At 1800 rpm you had the same exhaust pulses as a 4 stroker would have had at 3600 rpm, or to dowm
to used rpm's the Detroit had the same number of power and exhaust stokes at 1400 rpm the Mack or Cat had at 2800 rpm.
They also had less torque then a 4 stroker.

 

[BravoXray]

From the factory, almost all 71 series Detroits were governed at 2150 RPM, but we always turned them up to 2450 or 2500 RPM. They made more power up at the higher revs. We also would swap out the N65 injectors for N70s or N75s for even a little more. The N70s usually gave just a hint of gray smoke once over 1800 RPM, but the N75s made quite a bit more and really didn't help the power much over the N70s. You really needed a turbo to get the benefit of the bigger injectors.
Some of the older 6-71s used a larger blower (larger diameter rotors) that was driven at 1.69 times crank speed, but the later ones with smaller rotors turned twice crank speed. There was a trick you could do to the reduction gears in the 1.69 blower, where you machined the teeth off gear driven by the blower drive shaft and bolted it directly to the blower shaft gear, which would then drive it at twice crank speed, That mod with the N75 injectors really woke up a 6-71.