Will Chevrolet Low Cab Forward Get Another New Gasoline Engine?
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Isuzu just announced two new gas engines for the N-Series at the NTEA Work Truck Show in Indianapolis, including a 6.6L V8 for the Class 3 NPR and Class 4 NPR-HD, as well as a 6.0L V8 for the Class 5 NQR and Class 5 NRR. The 6.6L unit in question is the GM 6.6L L8T V8 engine, but the 6.0L unit is a new heavy-duty, gasoline-powered engine from Power Solutions International (PSI). While not yet confirmed, there’s a good chance this engine will also be available in the Chevrolet Low Cab Forward 5500, and PSI will take over the 6.0L engine option after GM drops it later this year.
As we covered previously, Chevrolet Commercial also announced a new engine at the NTEA Work Truck Show, namely the new 6.6L L8T V8 gasoline engine for the Chevrolet Low Cab Forward truck. The new L8T engine will be offered for the 2021 model year starting later this Summer. Output is rated at 350 horsepower and 425 pound-feet of torque, and it will mate to the 6L90 six-speed automatic transmission.
As for the new 6.0L gasoline engine from PSI, specs include output ratings of 311 horsepower and 353 pound-feet of torque at 4,150 rpm when equipped in the the Isuzu NQR and NRR. Transmission duties will be handled by the six-speed Allison 1000 RDS transmission. Interestingly, the engine is based on a GM Small Block Gen 4 Vortec architecture.
When it debuts on the Isuzu NRR Gas model, the new 6.0L will help to create the industry’s first gas-powered Class 5 low cab forward truck with a 19,5000-pound GVWR. Isuzu says that availability is anticipated for either the fourth quarter of 2020, or early in the first quarter of 2021.
Would you be interested in seeing the new 6.0L engine from PSI in the Chevrolet Low Cab Forward 5500? Let us know your thoughts in the comments, and make sure to subscribe to GM Authority for ongoing GM news coverage.
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Great news! Now if we could get similar news on the Silverado MD….
The 6.6 liter gasser in the pickup trucks has a very high 10.8 to one compression ratio. It’s too high for a truck rated with such a high GVW that Class 5 to Class 6 trucks have. This is why GM will offer a lower compression ratio version with only 425 pounds feet of torque and 350 HP. Ford has done the same with it’s 7.3 liter gasser in the heavier GVW rated F-450 to F-750, it’s got a reduced power, by probably dropping the compression ratio from 10.5 to one down to whatever. The detuned Ford version also is downrated at only 350 HP from the pickup truck version of 430 HP.
I suspect the reason the 6.6 L8T is not in the Silverado MD yet is because of the transmission. To this point the L8T is only teamed with the MYD 6L90 6 speed automatic, which is limited to a 15,000# GVW/21,000# GCW. That is perfectly adequate for a Silverado/Sierra 3500HD chassis-cab or a 3500/4500HD LCF, but would not be enough for the Silverado MD or an Isuzu NRR. Despite the revised 6.0L having less horsepower and torque than the L8T, it teams with an Allison 1000 series transmission which supports that higher GVW. The 6,0L/Allison 1000 powertrain sounds like the same package Powertrain Solutions sells to Fuso and Freightliner for their trucks.
GM can’t get enough medium duty Silverados made because of the much smaller production line at the international truck plant who make them for Chevy. GM still does not offer the medium duty Silverado in Canada, it’s only sold in Canada by Navistar’s International truck dealers. GM knows that if they offer a gasoline engine that the orders would double overnight, especially for the lower GVR 4500HD version. Maybe GM is still deciding if they want to spend the money to modify the newer design 8.0 liter big block to have cam phasing, to get better performance with the heavier loads of the 5500HD and 6500HD versions. Freightliner and others use the 8.0 liter version in motorhome chassis and full size long school buses, in a choice of either gasoline or propane/CNG.
The 8.0 is not offered in any motor home chassis. Power Solutions did promote it a few years ago but the availability never came to be. The rumor of it being offered by Workhorse when they were investigating going back into the motorhome market, died when Workhorse changed its mind.
The PSI engines are not designed on the GM engines, they are GM engines. The only thing that PSI makes different is the propane fuel injection system. They add the different exhaust valves that are able to withstand the very high temps of using propane. The 9.7 to one compression ratio in the GM gasoline 6.0 liter engine is the same as PSI. PSI does not increase the compression ratio to take advantage of the 104 octane rating of propane. The GM rated torque on the factory 6.0 liter engine is 380 pounds feet on gasoline, so the drop down to 353 on the PSI engines will hurt MPG and power. This type of truck needs over 400 pounds feet of torque to compete with the same diesel offered in these cabover trucks. The 4 cylinder Isuzu diesel has 520 Lbs feet of torque in the same truck. That’s too bad, as a higher CR when using LPG will give not only give more power but better MPG. The other problem with PSI engines is that they are one fuel only, meaning only propane and not dual fuel gasoline and propane. That means the PSI engines are for local delivery type work. GM offers an LPG Ready_To_Convert 6.0 liter Option ( code KL8 ) for an extra $315, so the end buyer or new truck dealer can job out the conversion job to a shop that will set up the trucks for a dual fuel operation. This means no route planning if you run low on propane. Our shop here has been telling buyers for 40 years to only go dual fuel, this way, you never run out of fuel, be it propane or gasoline. Just order the LPG Ready-To-Convert 6.0 liter option ( $315 ) and find a reputable shop to do the dual fuel conversion for your truck. I’m not sure of the prices in each area of the United states for an LPG conversion, but since it’s your money, shop around, not for the best price, but for a shop that has been doing it for at least 10 years. Don’t go for cheap on an LPG dual fuel conversion, you will regret it. Also spend a little extra and go for a much larger LPG fuel tank. Propane only weighs 2/3 of the weight of diesel fuel, so you can carry a lot more propane and still not loose load carrying capacity for you Class 4 or Class 6 truck.
Sorry for long explanation above. Just wait to order the 2021 cabover trucks with the factory gasoline engine because the it’s changing from the 6.0 liter to the 6.6 liter gasser. Here is why…the 6 liter has a compression ratio of 9.7 to one while the much high compression ration in the 6.6 liter gasser, the pickup truck version has a 10.8 to one CR. This means better MPG by at least 15 to 20 percent and of course much higher torque at the same RPM. This means faster acceleration and sooner upshifting of the gears in the automatic trans. Now GM will offer a lower HP and torque for the 6.6 liter gasser when used in these cabover trucks, but it’s 425 pounds feet of torque and 350 HP. Arrange for your 2021 truck to get an aftermarket dual fuel LPG conversion, and you will end up with more power than the factory option from PSI and you can use either gasoline of LPG at will. No running out of fuel if you use the dual fuel aftermarket conversion and you will save at least 15 percent on fuel costs because of the higher compression ratio of the 6.6 liter engine, which has cam phasing.
Freightliner recently dropped the 8.0L from their Thomas school bus line and replaced it with the Powertrain Solutions 8.8L. Not sure what the current status of the 8.0L is, but it is still on GM Powertrain’s website.
The 8.8 liter version is the same engine just with a longer stroke than the GM factory version to give more low end and a higher torque rating. The GM factory version of the 8.0 liter has only a 4.25 inch stroke, which is even less than the old 8.1 liter 496 cube that had a 4.375 inch stroke. They ( both the 8.0 L and 8.8 L ) are the same cast iron high deck block allowing for a 4.75 inch stroke. For an engine originally designed in 2009 to mainly run on propane, you want the longest stroke possible, because the longer stroke allows more exposure to a longer cylinder wall, allowing for better cooling. The 8.0 liter produces 475 pounds feet of torque on gasoline at 3200 RPM ( 375 HP ), but it’s 525 pounds feet with the longer stroke in the school buses. GM doesn’t list the torque or HP on propane just CNG for the 8.0 liter. This extra cooling factor is ultra critical when burning propane because it has a 37 percent hydrogen content and it burns hotter than Hades.