Cummins new gas engine

[Welder Dave]

Wondering if anybody else has seen that Cummin's has a new 6.7L gas engine for medium duty Kenworth/Peterbuilt trucks? No emissions crap and apparently better mileage than a diesel. I think it said 15,000 mile oil change intervals. They also have a new 7.2L diesel but the gas engine was way more interesting.

 

[pumkinhead]

here's a quote i seen a couple months ago on the gas 6.7

I have dozens of Cummins units now from ISB all the way up to QSK23 and I think this is a horrible idea.

• Turbocharged 6.7L will get **** mileage on gasoline. Rich AFR under forced induction means you need to shrink the displacement to improve mileage, and even then it's dodgy whether you're gaining anything over big NA gas. (see hurricane vs 5.7L).
• Half the benefit of gas 6.4L is simplicity, low cost of repair. Cummins is the worst engine manufacturer out there in terms of cost of replacement parts. Check the price of an OEM Cummins oil pan.
• Heavy as **** and probably 3x more expensive than the 6.4L and 2x more expensive than a Hurricane to manufacture.

So you get an big, expensive, complex engine which makes less torque than diesel and will get half the mileage towing, and the only benefit is improved reliability over diesel 6.7 due to lack of after treatment hardware, and more torque than the 6.4 gas. No thanks, if the Hurricane is reliable just put that in the truck instead.

 

[ozarkag]

Yeah saw that. I have seen small support equipment, (in this case large commercial wood chipper) go to large gas engine, (gm 6.2?) Instead of diesel for total cost of ownership reasons. I like diesel but I also like simplicity so. . .

 

[Truck Shop]

It's why a friend in the towing business is staying with older gas 4x4's. Lighter and gas is less,
and cost to rebuild is about a 1/3.

 

[heymccall]

I've always wondered why couldn't hotrodders never used diesel engine blocks to build STOUT gasoline race engines.

Link to Cummins B6.7 Octane

https://www.cummins.com/engines/octane

 

[Welder Dave]

The Ford 300-6 was basically a diesel block/design and a big reason it's a legendary engine. The 2.7 Ecoboost uses a carbon graphite block that is normally reserved for diesels. The 3.5 Ecoboost performs like a diesel. People loved the early Dodge/Cummins engines for their fuel economy and ever since they've boosted power and added all the emissions crap the mileage went out the window and it was no longer economical to buy one unless you were pulling heavy trailers often. The price of diesel went sky high too which is crazy. It's kind of funny that gas engines could be making a comeback in medium duty trucks. I think a HD gas engine could be a good alternative to emissions loaded diesels.

 

[Coaldust]

The Ford 300-6 was basically a diesel block/design and a big reason it's a legendary engine. The 2.7 Ecoboost uses a carbon graphite block that is normally reserved for diesels. The 3.5 Ecoboost performs like a diesel. People loved the early Dodge/Cummins engines for their fuel economy and ever since they've boosted power and added all the emissions crap the mileage went out the window and it was no longer economical to buy one unless you were pulling heavy trailers often. The price of diesel went sky high too which is crazy. It's kind of funny that gas engines could be making a comeback in medium duty trucks. I think a HD gas engine could be a good alternative to emissions loaded diesels.

You make a good point. The line between gas and diesel has become blurry with direct injection gasoline and low compression/high boost diesel. The Otto cycle and diesel cycle sort of blended together.

 

[Welder Dave]

All the emissions stuff just adds to the cost and complexity of a diesel vehicle that could be run on gas. Diesel trucks are a status symbol for some but the majority never recoup the extra costs.

 

[terex herder]

I've always wondered why couldn't hotrodders never used diesel engine blocks to build STOUT gasoline race engines.

Link to Cummins B6.7 Octane

https://www.cummins.com/engines/octane

They did. Remember the old Oldsmobile 350 diesel, circa 1978? Not the worst engine GM ever produced, but its on the top 5 list. Quite a few of them were turned into gas race engines. Biggest thing that had to be done was shim the main bearing bores, about 1/4" smaller on the radius. Add steel main caps and Batten aluminum heads and away you go. ISTR the cranks were custom made from solid.

 

[Truck Shop]

They did. Remember the old Oldsmobile 350 diesel, circa 1978? Not the worst engine GM ever produced, but its on the top 5 list. Quite a few of them were turned into gas race engines. Biggest thing that had to be done was shim the main bearing bores, about 1/4" smaller on the radius. Add steel main caps and Batten aluminum heads and away you go. ISTR the cranks were custom made from solid.

Which was a real waste of time because the Olds 350 diesel was just a converted gas, and it's
biggest issue was it was weak. I removed about 13 of those and installed 350-403 gas. And at
that time the price of a used good running 350 olds went through the roof {$1,200 to 1,500}.
*
The trouble with diesel converted to gas--weight. I just posted this on 454 thread.
Duramax--------835 lbs.
454--------------680 lbs
350--------------520 lbs
Ford 7.3 P/S----920 lbs
Ford FE----------658 lbs
Ford 302--------475 lbs
Cummins 5.9---1,100 lbs.
*
Consider it another bastuard item from Cummins, they've made several.
But not much reason to spend all the R&D on a diesel block, head, crank, the rotating assembly
is too heavy. Brodix aluminum block, heads are all milled to perfection already, building a hotrod
engine out of a diesel---well that proves nothing except how much money was wasted, the
Brodix stuff is costly enough.

 

[Truck Shop]

Not to argue the 300 ford six design but, it was a basic gas inline six design not based on diesel.
Main reason---the open cam/lifter area, that's not a rigid design for diesel. What made all six
cylinder engines sturdy was the 7 main bearing design, coupled with good oiling and cooling
system, and those three items is where the Ford 300 six shined.
*
But it's hard to beat a slant six, not a power house but keeps on ticking.
*

 

[terex herder]

Ah, the leaning tower of power. #2 son learned to drive in one in a Dodge 1/2 ton pickup. It taught him to feather a clutch so smoothly you didn't know you started to roll, and how to operate a manual choke. After he graduated hs the engine was turned into a stationary power unit.

 

[highwayghost]

I had a ‘86 Bronco with the 300 and 4 on the floor. Great engine, lots of low end toque. The only problem I had with it as it would occasionally break the roll pin on the distributor and die. Got so I could swap in a new pin where ever it happened in about 20 minutes.
When I was a boy the neighbor had a early 60’s POS Dodge Dart, (might have been a Valiant) with the slant 6. Ran so quiet you couldn’t hear that engine running even standing right next to the car. No vibration either!

 

[DDoug]

I see a CNG truck fueling station along the interstate, never seen anyone in there.

How is it penciling out ?

How is it being done ? Diesel engine with CNG addition ?
or spark ignited CNG ?

 

[Truck Shop]

Ran so quiet you couldn’t hear that engine running even standing right next to the car.

Inline six's have the smoothest firing order.
As in my $454 thread--2025 Dodge Charger, inline six with twin turbochargers @ 420 hp base model
and 550 hp option.
*

 

[Truck Shop]

CNG is all over California, those last and perform well for what those designed for, common.

 

[Truck Shop]

Ran so quiet you couldn’t hear that engine running even standing right next to the car.

Inline six's have the smoothest firing order.

 

[92U 3406]

I drove a V10 gasser the other day for the first time. Here I was thinking V8's were awesome.

 

[terex herder]

The geometry of an inline engine lends itself to longer rods and longer strokes, giving more low end torque. The slant 6 had the longest stroke of any contemporary Detroit gas engine. The long stroke gave the engine a low end driveability as good as engines with 50 more cubes, even though the largest of the slant 6 engines was only 225 cid.

 

[Truck Shop]

The geometry of an inline engine lends itself to longer rods and longer strokes, giving more low end torque. The slant 6 had the longest stroke of any contemporary Detroit gas engine. The long stroke gave the engine a low end driveability as good as engines with 50 more cubes, even though the largest of the slant 6 engines was only 225 cid.

At that time, allot of theory has been changed. Mainly because of highway speeds, shorter stroke
larger bore gave way to higher rpm, then the overdrive series of automatics came along. But even
with that in mind a V6 large bore short stroke twin turbo will produce 600 hp out of the factory.
Where the engines of years ago suffer is very poor flowing cylinder heads. CNC machining produces
perfect quinch combustion chambers and perfectly tuned intake/exhaust runners. Next is the ring
seal. Imagine if a engine like a slant six had those qualities way back when.