Perspective on 6.6 Gasser

TrailBoss1 · August 23, 2020

In the past, I drove primarily diesels; including a 2016 dually I traded for my current Trail Boss. I tow a CC fishing boat that weighs about 5,500 pounds loaded and certainly don’t need a diesel for that. But, towing with a 1500 after the dually, made me decide I just prefer the HD “feel”. In part, the extra weight increases stability. I owned one HD gasser many years ago (when the 6.0 was 300 hp/360 tq) and it felt adequate.

in looking at the new 6.6 gasser, I pulled up specs on the older 8.1 liter Vortec big block. That motor made 350hp / 450 tq (and could be paired with the Allison). So, the new 6.6 with 401 hp/464 tq makes significantly more horsepower and slightly more torque than the vaunted 8.1 big block.

i realize the new HD is heavier and larger than prior generations. Nonetheless, I think this gives me more confidence in the adequacy of the 6.6 for my needs. Is anyone towing a similar sized boat and, if so, your thoughts?

kenny_r · August 23, 2020

If you can handle the sub par fuel mileage, there are no other downfalls to buying an hd gasser for your needs.

TrailBoss1 · August 23, 2020

Thank you!! I recall the 6.0 wasn’t very good on gas either. But, I have a company vehicle during the week so I only drive this vehicle recreationally; about 12,000 miles per year. I loved the torque of the diesel but the LML concerned me due to issues with the CP3 pump; and the LP5, while using a different pump, still comes with increased cost, maintenance costs and complexity. So I think the fuel mileage on the L8T is a reasonable trade off for my use.

Stand By · August 23, 2020

I have a Chris Craft 251 express hard top. 350 straight inboard, rated almost 5000 lbs dry. 2 axle aluminum trailer, full 75 gallon tank, gear, 3 batteries. Only one trip this summer, over an hour drive each way on a winding, hilly road. Pulled like a dream. 2 5/16" ball on a forged, 3" drop insert. A rough measurement was that I still had about a 3/4" rake on a paved, level road. To be fare, my inboard sits almost center over the trailer axles. I would happily be making more trips if the boat engine didn't develope a hiccup on this last trip. Tow mirrors were great, too.

TrailBoss1 · August 24, 2020

Thanks so much. That’s a very cool boat and weighs much more than my Tidewater 230CC (about 3,300 dry before gas, trailer, freshwater and fishing gear). Good luck getting things sorted out with the boat engine; Ive heard it said they are holes in the water we throw money into!! LOL!

Rebel Rouser · August 28, 2020

Well as the proud owner of one of those “vaunted 8.1”s with the Allison, I’m a little partial! But I test drove a new crew cab High Country. I was impressed with the size, the weight, the cab, the tech, and to an extent, the ride. I was not impressed, however, with the power band on the truck. From a dead stop, my big block will absolutely ROAST my 35” A/Ts and chirp out of 2nd gear. Granted, I have 4.10s, intake, headers, custom true dual exhaust and a canned tune, but I did expect more from the advertised numbers from the 6.6. I floored it coming out of the dealership expecting it to pin my eyes back like the 496 does.... not so much.

Higher in the RPM band, it really picked up and THEN it was impressive. So I looked up the torque curves for each engine and confirmed my suspicions. The torque curve on the 8.1 is incredibly flat comparatively. And the 8.1 starts off from idle with 400 ft lbs. The 6.6 on the other hand, starts around 350 ft lbs from idle but climbs. However, the 8.1 reaches peak torque at 3200 RPM whereas the 6.6 is a little later at 4000 RPM. The big difference other than off the line is the horsepower. Over 4000, the 8.1 falls on its face thanks to a terrible intake design. The new 6.6 is a BEAST over 4000 RPM. I think when tuning companies come out with software for this new 6.6 motor, it will be unstoppable!

Colossus · August 28, 2020

You've also got a TON of torque management on the newer stuff. They don't want you to roast the tires, (or the rear diff in the process) they want you to have good traction on acceleration.

Rebel Rouser · August 28, 2020

All true and good points. Can’t wait for diablo or edge or HP, anybody that will make a tune for these new beasts!

Colossus · August 28, 2020

Yup, I bet once the tuners get going, there will be even more happy folks out there. I am running a 3 stage tuner for my Duramax that are fairly conservative as I don't want to limp the thing (allisons are great trannies but if you push them too hard you'll toast them and limp mode them) The tunes turn off the torque converter to some extent which makes a huge difference for me. Not enough to roast the tires unless I power brake, but that would be stupid as the G80 rear diff isn't made to do that and I don't need to spend $2000+ for a new diff. But getting on it is much more fun now. I was able to pull on a 3.5L ecoboost F150 from a roll and he was not happy about it as he had intended to cut me off to make a left turn. Having the top speed limiter adjusted to 120+ also meant I could accelerate strongly all the way thru 100MPH after he let off and so did I.

TrailBoss1 · August 28, 2020

Very cool you have the 8.1. I didn’t mean to imply “vaunted” as a negative. It was a compliment in every sense; that big block didn’t need a lot of technology to make power. Makes sense the displacement produces better low end torque. Hell, I thought my 85 Z28 with the LB9 was impressive making 215 HP from 5 liters. But, comparatively, the 6.6 makes almost 100% more power from a 33% increase in displacement (roughly). I’m looking forward to mine arriving; though it’s probably 10 weeks out.

Rebel Rouser · August 29, 2020

No offense taken good Sir! I’m just glad GM is even going in that direction. You are correct, the stock numbers on the 8.1 are pathetic in terms of hp to cubic inches. Raylar fixes that problem, but my kids still have to go to college so I don’t have a 529 Roth for the big block yet

But, turning the TM off and running a premium tune after you open them up and let them breathe, and the 8.1 reminds you what unbridled instant torque felt like in the late ‘60s/early ‘70s. Puts a smile on my face every time I drive it. I hope the 6.6 does for you and that’s all that matters.

nick112288 · August 30, 2020

I'm just waiting for someone, somewhere to come up with SOMETHING for these engines.

The new Ford 7.3 already has a couple companies with tuners out, a couple intake manufacturers, at least 1 header company, Whipple and Procharger are getting ready to release systems.

Can't find anything for this 6.6l.......

Colossus · August 30, 2020

GM makes it very hard for the aftermarket companies on purpose.

Rmedic · September 8, 2020

Just picked up a 2500 HD with the 6.6, to replace 1500 Sierra that just couldn’t cut it towing my 7500 lb boat, my question is, what is the recommendation for break in period before I hit the road with boat in tow, if any, thanks in advance.

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Limelight · September 9, 2020

2 hours ago, Rmedic said:

Just picked up a 2500 HD with the 6.6, to replace 1500 Sierra that just couldn’t cut it towing my 7500 lb boat, my question is, what is the recommendation for break in period before I hit the road with boat in tow, if any, thanks in advance.

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I towed with mine on day 2. IMO people overthink these things.