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Open Roads Forum  >  Tow Vehicles

 > 2020 Freightliner vs 3500 GMC Dually at the Ike

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ShinerBock

SATX

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Posted: 09/07/19 04:28pm Link  |  Quote  |  Print  |  Notify Moderator

The reason why they rise is because you do not have enough air for the amount of fuel you are burning so the best thing is to get as much dense air into and out of your engine as possible with the least amount of restriction of reduce fuel. If your EGT's are high when towing, downshift to increase rpms and back off the throttle. Increasing rpms moves more air in and out of the cylinders. Backing off the throttle reduces the amount of fuel being injected. Most if not all modern diesels will automatically do this if EGT's get too hot.

Mods like an intake, better intercooler, larger/more efficient turbo, and less restrictive exhaust are all things that lower EGT's.

4x4ord

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Posted: 09/07/19 04:39pm Link  |  Quote  |  Print  |  Notify Moderator

Me Again wrote:

4x4ord wrote:

They praise the performance of the engine brake on the Freightliner over the performance of the exhaust brake on the GMC, however, if more weight had been loaded into the trailer the Duramax would have held 50 mph yet the Freightliner would have required additional brake applications. Comparing two trucks on one hill with only one weight in tow doesn't really offer an honest comparison. I'm having trouble understanding why the GM slowed down as much as it did going up the hill ..... something doesn't add up. Even back in 2015 (with 396 HP and 765 lb ft) the Duramax towed 19000 lbs up the Ike in just under 10 minutes. link


I don't think your statement on the Freightliner is correct. The cruise control was holding it at 50 MPH, most likely had a lot more anchor chain in the chain locker. RAM has this feature also when the EB is in auto. I do not use it because it does not brake until about 3-4 MPH above the CC speed.


I think the new GMs likely adjust the exhaust brake in auto as does the Ram and Ford. I believe in the test they had the GM exhaust brake turned to "on" which makes me think auto wasn't available in 2017. With the Freightliner Mr Truck said he didn"t have the cruise set. He said the engine brake could be set at 3 or 6 and he had it set at 6. So the Cummins was braking all it could without downshifting.


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FishOnOne

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Posted: 09/08/19 06:31am Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:

Me Again wrote:

4x4ord wrote:

They praise the performance of the engine brake on the Freightliner over the performance of the exhaust brake on the GMC, however, if more weight had been loaded into the trailer the Duramax would have held 50 mph yet the Freightliner would have required additional brake applications. Comparing two trucks on one hill with only one weight in tow doesn't really offer an honest comparison. I'm having trouble understanding why the GM slowed down as much as it did going up the hill ..... something doesn't add up. Even back in 2015 (with 396 HP and 765 lb ft) the Duramax towed 19000 lbs up the Ike in just under 10 minutes. link


I don't think your statement on the Freightliner is correct. The cruise control was holding it at 50 MPH, most likely had a lot more anchor chain in the chain locker. RAM has this feature also when the EB is in auto. I do not use it because it does not brake until about 3-4 MPH above the CC speed.


I think the new GMs likely adjust the exhaust brake in auto as does the Ram and Ford. I believe in the test they had the GM exhaust brake turned to "on" which makes me think auto wasn't available in 2017. With the Freightliner Mr Truck said he didn"t have the cruise set. He said the engine brake could be set at 3 or 6 and he had it set at 6. So the Cummins was braking all it could without downshifting.


I thought I read a few years ago that in order for the GM to maintain speed while using the exhaust and transmission grade braking system is to have the cruise control on.


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FishOnOne

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Posted: 09/08/19 06:35am Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

The 2019 GMC 3500 C&C Dmax is rated at 445 hp/910 lb-ft just like the pick up version. Not sure how they were able to do this with the different emissions certifications, but they are the same output.


Its simple... Advertised hp and torque is understated in the pick up version.

Also I don't think the GM was defueling either since during initial take off the truck seamed a bit lethargic from what I could tell, but one could say the same about the Freightliner.

* This post was edited 09/08/19 07:07am by FishOnOne *

FishOnOne

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Posted: 09/08/19 07:05am Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

The reason why they rise is because you do not have enough air for the amount of fuel you are burning so the best thing is to get as much dense air into and out of your engine as possible with the least amount of restriction of reduce fuel. If your EGT's are high when towing, downshift to increase rpms and back off the throttle. Increasing rpms moves more air in and out of the cylinders. Backing off the throttle reduces the amount of fuel being injected. Most if not all modern diesels will automatically do this if EGT's get too hot.

Mods like an intake, better intercooler, larger/more efficient turbo, and less restrictive exhaust are all things that lower EGT's.


The hood mounted air scoop was supposed to help with sustained power.

ShinerBock

SATX

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Posted: 09/08/19 08:59am Link  |  Quote  |  Print  |  Notify Moderator

FishOnOne wrote:



The hood mounted air scoop was supposed to help with sustained power.


It probably does for most short inclines, but not under longer sustained loads. If you look in each diesels programming with tools such as EFILive and SCT, you will notice all three have defueling and/or pull timing programmed into their mapping. Various things can trigger this defueling or retarding of timing such as high temps or emissions related problems. It is similar to the ECM putting the truck in limp mode my regulating fuel delivery to keep you at a certain speed/rpm even if your foot is to the floor.

4x4ord

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Posted: 09/08/19 09:03am Link  |  Quote  |  Print  |  Notify Moderator

FishOnOne wrote:

ShinerBock wrote:

The 2019 GMC 3500 C&C Dmax is rated at 445 hp/910 lb-ft just like the pick up version. Not sure how they were able to do this with the different emissions certifications, but they are the same output.


Its simple... Advertised hp and torque is understated in the pick up version.

Also I don't think the GM was defueling either since during initial take off the truck seamed a bit lethargic from what I could tell, but one could say the same about the Freightliner.



The GM was not putting out anywhere near its advertised HP. A truck equipped with an engine making 445 hp / 910 lb ft would have been able to make that run in very close to 7 minutes 20 seconds. I think the high altitude must drastically affect the power these engines are able to make. If the Cummins was producing the power it is advertised to make it should have made the run in just over 9 minutes.

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midwest

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Posted: 09/08/19 09:11am Link  |  Quote  |  Print  |  Notify Moderator

The Ike test, is fun to watch, but it's not a total all out race. They "limit" the run to eight minutes, because they don't exceed the 60 mph limit going up. So they consider an eight minute run to be a benchmark score.

97chevor

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Posted: 09/08/19 10:34am Link  |  Quote  |  Print  |  Notify Moderator

I watched a number of their videos and IMO the fact they are not running both trucks at the same time, the flow of traffic is a variable that can away the results either way.

noteven

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Posted: 09/08/19 10:49am Link  |  Quote  |  Print  |  Notify Moderator

The GMC has a big grille.

* This post was edited 09/09/19 06:55am by noteven *

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