The Inevitable Comparison: GM 6.6 vs. Ford 7.3

[dieselfan1]

The 6.6 gas is slower due to engine oil temps.  This motor has alot of heat rejection at gcw and high rpms.  ECM commands the TCM to stay in higher gear to lower rpms and cool oil temps.  You won't be allowed to manually shift around it.  

That's sad

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[C/K Man]

4 hours ago, MTU Alum said:

The 6.6 gas is slower due to engine oil temps.  This motor has alot of heat rejection at gcw and high rpms.  ECM commands the TCM to stay in higher gear to lower rpms and cool oil temps.  You won't be allowed to manually shift around it.  

Sort of explains the 6 speed transmission and 3.73:1 rear gears.    

[kenny_r]

Well the chief engineer did say it will haul at max capacity day in and day out, guess that’s how the truck can do it.lol

[Carolina]

6 hours ago, MTU Alum said:

The 6.6 gas is slower due to engine oil temps.  This motor has alot of heat rejection at gcw and high rpms.  ECM commands the TCM to stay in higher gear to lower rpms and cool oil temps.  You won't be allowed to manually shift around it.  

Nope . It shifts wherever you put it. He could have double pumped the gas pedal and got a downshift. It’s been like that since 2015. The problem is the ratios on those 2 gears . If it was manually selected to downshift you would have to back off a bit to keep it out of red but the next gear ratio is too high for the engine to accelerate at that load and grade as it lands the Rpm’s too low . 4:10 would help some 4:30 would help more and a 10 speed would completely cure it . With all the overdrives in the 10 speed it could probably run 4:10 and not sacrifice fuel mileage. Also the tires on the Chevy was the near 35’s further degrading the Effective gear ratio down to 3.51 from the base tires .  The Ford is running 32 inch tires with a 10 speed , 4:30 gears and 87 octane verses 85 octane on the Chevy. It was a disadvantage all around . Fords 7.3 and 3.55 gear is only rated for 14,700 pounds so it couldn’t even compete . They have a 3:73 option and 35’s rated for 17,500 . That’s what should be used to compare. Funny thing though if you look back at there videos from a couple years ago with the loads that size it’s very comparable to diesels from just a few years ago 

Edited February 6, 2020 by Carolina

[MTU Alum]

So running the truck at higher rpms at longer periods of time is going to keep the the oil cooler how?  If you have high oil temps, more axle ratio and gears will make your issue worse.

 

#iworkforGM 

[ShotgunZ71]

I've had no issues locking out 5th and 6th gears and letting the RPM stay in the 3000+ range. Not sure at what temp the ECM shifts it up, but all temps I can see stay in the normal range. Even locked out 4th and the RPM was 4000 at 70. Didn't mind it at all and it ran great. Now, if someone runs it in the red for extended periods, I can see where some protections may be in place.

 

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[KARNUT]

1 hour ago, ShotgunZ71 said:

I've had no issues locking out 5th and 6th gears and letting the RPM stay in the 3000+ range. Not sure at what temp the ECM shifts it up, but all temps I can see stay in the normal range. Even locked out 4th and the RPM was 4000 at 70. Didn't mind it at all and it ran great. Now, if someone runs it in the red for extended periods, I can see where some protections may be in place.

 

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I pulled from the seventies to the early 2000s, fifth wheels and goosenecks. Even in the early 2000s I didn’t have horsepower an TQ available now. I always stayed  out of overdrive stick or automatic. I’m just curious why you would need to run at 4K RPMs? I usually hovered around 3K. With much less power that’s available today.

[ShotgunZ71]

2 minutes ago, KARNUT said:

I pulled from the seventies to the early 2000s, fifth wheels and goosenecks. Even in the early 2000s I didn’t have horsepower an TQ available now. I always stayed  out of overdrive stick or automatic. I’m just curious why you would need to run at 4K RPMs? I usually hovered around 3K. With much less power that’s available today.

In another post, you see where I stated that the RPM @ 70mph is 3000 in 4th and 4000 in 3rd. Rarely need to lock out down to 3rd, just an example. Locking out 5th and 6th when needed keeps the RPM in the ranges where torque is more readily available.

[C/K Man]

Regarding the TFL testing, I have some questions.  First off, back in December TFL took delivery of a red 7.3L F-250 XLT crew cab with the 5th. wheel hitch package.  Similarly equipped to the 2020 6.6L gas Silverado HD they tested on the Ike.  TFL in fact said they were intending to test and compare that particular truck to the Silverado HD they tested.  TFL didn't state what gears the Red F-250 was equipped with.  Yet, when TFL finally did test a Super Duty with the 7.3L on the Ike, all of a sudden they had a blue 7.3L F-250 with the 4.30:1 rear axle.  Hmmmm.  For the record, a 2020 Silverado 6.6L gas 4X4 crew cab short box with the standard 3.73:1 rear axle can tow 16,600#'s on a 5th. wheel.  A 2020 F-250 7.3L gas 4X4 crew cab short box with the standard 3.55:1 (3.73:1 only available with the 6.2L in the F-250) rear axle can only tow 14,700#'s on a 5th. wheel.  An F-250 7.3L with the optional 4:30 rear axle is rated for 16,900#'s.  My guess is TFL used the blue F-250 probably because the red one had a 3.55:1 rear axle!  That having been said, a more accurate comparison between the 6.6L and 7.3L would have been to use a 6.6L with a 3.73 rear axle against a 7.3L with a 3.55:1 rear axle, both trucks towing 14,000#'s to keep the towing weight under the F-250's maximum.  

[kenny_r]

Yea that red one had 3.55’s. Either way I think that ford still would have burned the 6.6.

[ShotgunZ71]

They might as well do a test with the 6.6 gas vs a 6.7 PS, too. After all, the 7.3 and 6.7 PS are both optional engines, whereas the 6.6 gas is standard. While they are at it, compare both 6.6 engines head to head, also. They never mentioned the fact that it was an optional engine. They basically used an optional engine, optional rear gear and optional transmission to compare against GM's standard offering. It should have absolutely performed better than the GM, but you have to pay more for that performance.

 

The 6.2 I had in my Platinum was a great engine. I had the 3.73 in that and the Torqshift-G transmission. Great combo for what I needed. They should compare the 6.2 to the 7.3 using same rear ends in each to show how much improvement the 7.3 really is over the standard engine. 

[2016HD]

23 hours ago, MTU Alum said:

The 6.6 gas is slower due to engine oil temps.  This motor has alot of heat rejection at gcw and high rpms.  ECM commands the TCM to stay in higher gear to lower rpms and cool oil temps.  You won't be allowed to manually shift around it.  

Id like to know where this came from? And How you think keeping an engine with peak torque at 4000 and peak Hp at  5000rpm will stay cooler running at 3000Rpm?  Sorry this is wrong.   Run it at 4-5000 rpm all day long. Let the Fan do its job and the engine stay in the peak rpm range for Most power etc.  If you run at 3000rpm while towing heavy and long hills you will run hot do to lugging the engine. Risking Higher Knock frequency and ecm will then retard timing etc.  Your trans temp will do nothing but continue to climb etc.  Drop it into 2ond or third and leave it at 4-4500rpm and let it eat. Its designed to do this and so has every other small block prior to it.   You can still lock out the higher gears as stated.  TFL just needs to learn to actually drive the truck!!  Not sure why anyone towing almost max capacity would just let the ecm do what it wants?  The more the trans shifts up and down the more heat it creates and this will in turn cause engine temps to climb.   

[Carolina]

15 minutes ago, 2016HD said:

Id like to know where this came from? And How you think keeping an engine with peak torque at 4000 and peak Hp at  5000rpm will stay cooler running at 3000Rpm?  Sorry this is wrong.   Run it at 4-5000 rpm all day long. Let the Fan do its job and the engine stay in the peak rpm range for Most power etc.  If you run at 3000rpm while towing heavy and long hills you will run hot do to lugging the engine. Risking Higher Knock frequency and ecm will then retard timing etc.  Your trans temp will do nothing but continue to climb etc.  Drop it into 2ond or third and leave it at 4-4500rpm and let it eat. Its designed to do this and so has every other small block prior to it.   You can still lock out the higher gears as stated.  TFL just needs to learn to actually drive the truck!!  Not sure why anyone towing almost max capacity would just let the ecm do what it wants?  The more the trans shifts up and down the more heat it creates and this will in turn cause engine temps to climb.   

Yes I’ve pulled mountains for years with the 6.0 preferably between 4500- 5200 rpms . Never had a oil leak , overheated motor or transmission. That truck now has 300,000 miles on it and I have replaced a battery 

[KARNUT]

This is unreal. If you can maintain speed at 3K RPM there’s no reason to downshift. If you need to run 4-5 K for a prolonged period of time you need to regear or go diesel. No gas engine is going to run hour after hour at 4-5K and live very long. Before diesel in P/Us I hauled with gas one tons. Engines usually barely made 100K just running 3K with out rebuilding. Diesel became popular in 3/4-1tons simply because they made max TQ at lower RPMs, maximizing life. Six - ten speed transmissions allow gas engines to stay in TQ range at lower engine speeds. Steep grades occasionally running higher engine speeds is to be expected. Otherwise no need.

[MTU Alum]

If your heat rejection is not linear to engine rpm at higher rpms your fan can't keep up and heat goes in your fluids. At a certain fluid temp, you will need to lower your rpms to the linear range where the fan can outpace the heat rejection.