342 vs 373 Real world experience

[nards444]

Had another thread but thought I would break it out.  Either way got a diesel order in, and have a diesel now, and scared to give up the diesel for the gasser for obvious reasons.  With that said I tow a 10k lb boat about 10 times a year 30mins away.  And then haul various smaller loads another handful times a year.  I know the gasser can go do it, not the issue.  Problem is the diesel so much more efficient in mpg regardless of what it is doing.

 

Fuely shows the gasser averages like 12.3mpg over 40k miles, and only like 14 on the hwy, ouch.  Where as I get 15-16 in town and 17-18 on the HWY.  Even if diesel costing a buck more its still a savings in the long run.

 

So anyways.  I see there are 342 options for the gasser vs 373.  373 are obviously better, but for the low amount of haul trips wondering if the 342s save that much more gas.  I keep seeing 11-13mpg and 8mpg towing with the gasser and just hard to think about making the switch the diesel is 30-50% better on fuel. 

[redwngr]

Presumably you are looking at a new 2500.

 

The 20+ 6.6 gassers are all 6 speed with 3.73's

The 20+ 6.6 diesels are all 10 speed with 3.42's. 

 

Yes, you could change them after taking delivery of the truck. 

 

Yes, the 6.0 gas used both 4:10's and 3.73's. (availability depending on year and truck trim/version.

Yes, the dmax had 3.73's when it used the 5 and 6 speed allisons.

 

There are no optional ratios.

 

The powerbands are MUCH different on the gas vs diesel.

 

At highway speed in top gear, the gasser needs to, and will be, to be turning quicker.  

 

 

L5P 

 

LT8

[sheath]

2 hours ago, redwngr said:

LT8

 

Thanks for posting this chart.  

Now I see why GM chose the transmission programming they did.  Pulling heavy feels just like this chart.

Compared to the Ford 7.3L it's easy to see why the Ford tows heavy much better than the Chevy.

That wrote, the 7.3L requires 93 octane to tow, and gets less fuel mileage. 

Next time I'm doing 45mph up a steep climb to keep the engine from rev'ing it's guts out, I'll have to remember that, and smile a little bigger.

 

[swathdiver]

9 hours ago, nards444 said:

Had another thread but thought I would break it out.  Either way got a diesel order in, and have a diesel now, and scared to give up the diesel for the gasser for obvious reasons.  With that said I tow a 10k lb boat about 10 times a year 30mins away.  And then haul various smaller loads another handful times a year.  I know the gasser can go do it, not the issue.  Problem is the diesel so much more efficient in mpg regardless of what it is doing.

 

Fuely shows the gasser averages like 12.3mpg over 40k miles, and only like 14 on the hwy, ouch.  Where as I get 15-16 in town and 17-18 on the HWY.  Even if diesel costing a buck more its still a savings in the long run.

 

So anyways.  I see there are 342 options for the gasser vs 373.  373 are obviously better, but for the low amount of haul trips wondering if the 342s save that much more gas.  I keep seeing 11-13mpg and 8mpg towing with the gasser and just hard to think about making the switch the diesel is 30-50% better on fuel. 

 

With all the gears in the transmissions, the axle ratio is not as critical anymore.

 

For example, a truck with a 6-speed and 3.42 gears puts more force to the ground than a 4-speed with 4.10s.  More options with the 6 and 8 and 10-speeds.

 

I've made calculators for comparison before with Excel.

[nards444]

6 hours ago, swathdiver said:

 

With all the gears in the transmissions, the axle ratio is not as critical anymore.

 

For example, a truck with a 6-speed and 3.42 gears puts more force to the ground than a 4-speed with 4.10s.  More options with the 6 and 8 and 10-speeds.

 

I've made calculators for comparison before with Excel.

 

Yeah I messed up I saw 342 as an option and didnt see it was diesel only.  So 373s.

 

But your point your right.  But then again 6 gears is not a lot for these days.  Biggest complaint I read the last few days was GM not putting the 10 speed with the gasser, which all considered seems like a major blunder considering the 10 speed was there.

[swathdiver]

2 hours ago, nards444 said:

 

Yeah I messed up I saw 342 as an option and didnt see it was diesel only.  So 373s.

 

But your point your right.  But then again 6 gears is not a lot for these days.  Biggest complaint I read the last few days was GM not putting the 10 speed with the gasser, which all considered seems like a major blunder considering the 10 speed was there.

GM has a history of making changes incrementally.  When the 2007 2500 Suburban came out, it had a 4-speed transmission.  The next year they replaced it with the 6-speed.  2 years later they replaced the engine with the FlexFuel version and so on.

[sheath]

I'd like to see an efficiency study on the 10 speed.  I would prefer not to give up efficiency, or create more heat that has to be mitigated. 

That wrote, I can see adding two gears for sure.

One between L1 & L2 to smooth the up and downshifts at low speeds, and one between L2 & L3 for pulling heavy on grades.  For freeway towing the big help would be L2 & L3.

I'd like to see the downshift from L3 to L2 only drop about 600-800rpm.  This would help maintain speeds in the mid 50mph range on 6% grades, when towing in that 14k lbs range, without rev'ing in that 5Krpm range.

I don't want to give up the 4.030 first, because in low range off road it really helps climbing over boulders, ruts etc. to maintain forward momentum and limit trail damage.

 

Looking at the maximum validated GCVW in the chart below (from GM Authority), the 6L90E is not validated for pulling the maximum GCVW some of our trucks are rated for.  I'm over this with my combination, even though I'm over 2K lbs under the max GCVW of the truck, per the data tag.

So there is a good reason to make a transmission enhancement. 

 

Gear Ratios
First:	4.030
Second:	2.360
Third:	1.530
Fourth:	1.150
Fifth:	0.850
Sixth:	0.670
Reverse:	3.060
Maximum shift speed:	6200 rpm
Maximum Validated Weight (GVW):	15000 lb (6803 kg)
Maximum Validated Weight (GCVW):	21000 lb (9525 kg)

[mandrewbot3k]

@sheath, damn, that 7.3 powerband is impressive. That was going to be what I ordered if the local chevy dealer didn't have the L8T coming in so quickly.

 

@nards444I have a 2022 L8T, and I only have a couple gripes about it. But towing isn't one of them. It FEELS sluggish, but it's really not that bad. If you try to gas it while it's towing, it scoffs at you, and basically says, "I'll get there, gimme a minute, geez....". Going from a 1500 to a 2500, it just feels like I'm going slower than I am. When I'm cruising at 65 towing, it felt like I was going 40. Not a bad thing. The exhaust is pretty quiet on the L8T too, so I think thats part of the perception. My 5.3L seemed throatier and was noisier in the cab. 

 

I'd say if you're only towing ~10x / year and worried about tow mileage , I think the fuel cost difference would be fairly negligible, especially relative to the extra $10k for the diesel. Definitely factor in that added cost when doing the fuel cost savings. If you only plan on having the truck for a few years and trading in, it may not be worth it to go duramax. If you plan on keeping for the long run, might pay itself off. 

 

That said, I just towed combined weight of 16520, with 7240 on my trailer axle for 3 hours. I got about 8mpg, but it tows so nicely, especially compared to my 2019 5.3 1500 i just traded in. I don't have hill descent help, but i never really had to tap the brakes coming down grade, which was about 6-10%. It just held at 55mph and didnt struggle or anything. 

 

I was able to get from 55-70 pretty easily to pass semis when needed, but I think those are the instance when I wouldve really felt the difference with the diesel. 

 

Ultimately for me, I decided on the L8T over the duramax because 1) availability, 8 days from deposit to delivery and 2) my normal commute (getting about 11mpg) is pretty stop and go. I felt that would be bad on the diesel being in regen like 98% of the drive time, especially for an extra $10k. IU only tow my travel trailer about 10x year, so didn't seem worth it to me.  

 

If you currently have a diesel, you might miss it. The other factor might be based on your driving routes. My full 36gal tank is only getting me about 400 miles tops probably on the highway, though I haven't done much of that driving. If you're running a long ways through barren land, it might be worth it to have the extra mileage of the diesel. But I really like the L8T.

[nick112288]

On 6/19/2022 at 4:12 PM, mandrewbot3k said:

@sheath, damn, that 7.3 powerband is impressive. That was going to be what I ordered if the local chevy dealer didn't have the L8T coming in so quickly.

 

@nards444I have a 2022 L8T, and I only have a couple gripes about it. But towing isn't one of them. It FEELS sluggish, but it's really not that bad. If you try to gas it while it's towing, it scoffs at you, and basically says, "I'll get there, gimme a minute, geez....". Going from a 1500 to a 2500, it just feels like I'm going slower than I am. When I'm cruising at 65 towing, it felt like I was going 40. Not a bad thing. The exhaust is pretty quiet on the L8T too, so I think thats part of the perception. My 5.3L seemed throatier and was noisier in the cab. 

 

I'd say if you're only towing ~10x / year and worried about tow mileage , I think the fuel cost difference would be fairly negligible, especially relative to the extra $10k for the diesel. Definitely factor in that added cost when doing the fuel cost savings. If you only plan on having the truck for a few years and trading in, it may not be worth it to go duramax. If you plan on keeping for the long run, might pay itself off. 

 

That said, I just towed combined weight of 16520, with 7240 on my trailer axle for 3 hours. I got about 8mpg, but it tows so nicely, especially compared to my 2019 5.3 1500 i just traded in. I don't have hill descent help, but i never really had to tap the brakes coming down grade, which was about 6-10%. It just held at 55mph and didnt struggle or anything. 

 

I was able to get from 55-70 pretty easily to pass semis when needed, but I think those are the instance when I wouldve really felt the difference with the diesel. 

 

Ultimately for me, I decided on the L8T over the duramax because 1) availability, 8 days from deposit to delivery and 2) my normal commute (getting about 11mpg) is pretty stop and go. I felt that would be bad on the diesel being in regen like 98% of the drive time, especially for an extra $10k. IU only tow my travel trailer about 10x year, so didn't seem worth it to me.  

 

If you currently have a diesel, you might miss it. The other factor might be based on your driving routes. My full 36gal tank is only getting me about 400 miles tops probably on the highway, though I haven't done much of that driving. If you're running a long ways through barren land, it might be worth it to have the extra mileage of the diesel. But I really like the L8T.

 

You actually do have hill descent help. It comes in the form of the throttle body butterfly valve. That closes when no throttle is applied and the engine works against itself.

 

Diesels need the added exhaust brake because they have no throttle valve. No exhaust brake, the engine doesn't work against itself.

[nick112288]

On 6/4/2022 at 8:36 PM, sheath said:

 

Thanks for posting this chart.  

Now I see why GM chose the transmission programming they did.  Pulling heavy feels just like this chart.

Compared to the Ford 7.3L it's easy to see why the Ford tows heavy much better than the Chevy.

That wrote, the 7.3L requires 93 octane to tow, and gets less fuel mileage. 

Next time I'm doing 45mph up a steep climb to keep the engine from rev'ing it's guts out, I'll have to remember that, and smile a little bigger.

 

 

93 is NOT required to tow. They just say it's recommended for best performance to prevent knocking/pinging. If you are towing and not having that issue, no reason to run 93.

[sheath]

On 6/28/2022 at 7:25 PM, nick112288 said:

 

93 is NOT required to tow. They just say it's recommended for best performance to prevent knocking/pinging. If you are towing and not having that issue, no reason to run 93.

Sounds like you haven't tried running 87 Octane while pulling heavy with the Ford 7.3L.   It pulls out power and sounds terrible, on long grades.

[nick112288]

5 hours ago, sheath said:

Sounds like you haven't tried running 87 Octane while pulling heavy with the Ford 7.3L.   It pulls out power and sounds terrible, on long grades.

 

You're right, Ihaven't. But I frequent the Ford forums quite a bit and you're the first time I've seen someone say they needed premium to tow their load.

 

You pulling in the rockies, at the max limit, when it's 100+ out?

[unit]

Diesel fuel isn't the only expense with the Duramax.  You have to figure in cost of DEF on any diesel and that does add to the expense calculations.  Newer diesels tend to use a lot of DEF while towing and it's about $4.00 / gal at the pump.

[nards444]

1 hour ago, unit said:

Diesel fuel isn't the only expense with the Duramax.  You have to figure in cost of DEF on any diesel and that does add to the expense calculations.  Newer diesels tend to use a lot of DEF while towing and it's about $4.00 / gal at the pump.

Not really. I have 16k miles and maybe filled it up 3-4 times. It’s a cost your right not denying that but it’s not crazy. 

[sheath]

3 hours ago, nick112288 said:

 

You're right, Ihaven't. But I frequent the Ford forums quite a bit and you're the first time I've seen someone say they needed premium to tow their load.

 

You pulling in the rockies, at the max limit, when it's 100+ out?

I've pulled from the coastal mountains up through the Rockies.  But the Ford experience was pulling a cattle trailer (a bit over 15k lbs) from just under 5k'asl up over 7k' asl, and back to about 5k'asl in Utah.  Temp ranged from high 70s F to mid 80s.

Screwed up and put in 87 octane.  Truck did not like it one bit.  Told my buddy what I did to his truck, and he just laughed. He'd done the same thing on purpose with the same results.

It also got real bad fuel mileage on that pull.  Somewhere around 5mpg. 

I thought I'd damaged his truck, but I refilled with 93 and it was OK. 

Won't make that mistake again.

He's pulled heavier, but now only uses 93 octane, except in the dead cold of winter when he drops to 89 for better cold starting at altitude. 

I run 85 when above 6k' in Utah for the Chevy.  Pulls fine at a bit over 14k lbs.  Doesn't seem to affect fuel mileage when towing.