2020 Cummins IKE pull

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4x4ord wrote:
^^^ So, based on my observation I would say the wheel brakes were largely what was holding the truck back. The computer recognized the need for a downshift to produce more exhaust braking. After the downshift the back pressure and rpm increased to produce the maximum level of exhaust braking the engine was able to do .... the wheel brakes made up the difference.

Nice theory, but owning a Cummins and having been on that road I would have to disagree.

I've never felt any indication that the exhaust brake on my truck ever engages the wheel brakes. My opinion is only based on five years of owning the truck so maybe the guy who watched a YouTube video knows better.

ShinerBock wrote:

4x4ord wrote:
^^^ So, based on my observation I would say the wheel brakes were largely what was holding the truck back. The computer recognized the need for a downshift to produce more exhaust braking. After the downshift the back pressure and rpm increased to produce the maximum level of exhaust braking the engine was able to do .... the wheel brakes made up the difference.

Nice theory, but owning a Cummins and having been on that road I would have to disagree.

You've been on that road with 30,000 lbs in tow?

IdaD wrote:
I've never felt any indication that the exhaust brake on my truck ever engages the wheel brakes. My opinion is only based on five years of owning the truck so maybe the guy who watched a YouTube video knows better.

My theory does line up with what Mr. Truck had to say at the beginning of the video, which like I said, doesn't mean a whole lot. The other thing is that I have no idea how your truck works .... it's not a 2020 is it?

ShinerBock wrote:

4x4ord wrote:
^^^ Exactly so if the turbo was holding enough back pressure to hold the load back at 2000 rpm (which is impossible), the engine would have been generating 175 reverse HP. Now, if, the transmission downshifts from 3rd to 2nd, the rpm would increase from 2000 to 3000 rpm. So even if the back pressure remained unchanged (The only reason the back pressure would remain unchanged would be if the valves started floating otherwise the back pressure would increase dramatically because the engine would be trying to push 1.5 x as much air past the turbo) the reverse HP generated would go from 175 to 262 reverse HP. So if 175 reverse HP was holding back about right and now all of a sudden the engine is holding back 1.5 times as much the truck would quickly start over braking while the turbo adjusted to relieve back pressure.


(and because the increase in engine rpm would not only cause 1.5 x as much air to be compressed it would also be compressing that air to a higher value ( ie the back pressure would go up ) so the reverse HP would rise even more than 1.5x )

So based on the behavior of the truck, it is my opinion that the exhaust brake was not the only thing holding the truck back.

But it wasn't hold the truck back at 2,000 rpm and was gaining speed which is why it downshifted to a higher that not only allowed it to hold speed, but also slowed it down. After it slowed it down to desired speed then the turbo vanes probably actuated between 95-99% to keep it there.

Also, the IKE is not 7% all the way down. There are sections that are as low as 3%. Especially the section coming right out of the tunnel. It is steep when you first come out and the decreases the grade for a short distance.

I've actually never even rode in a 6.7 Cummins equipped vehicle. How much back pressure are they able to produce at 2000 rpm? Pumping 237 CFM @ 60 psi requires 68 HP if the air pump is operating at 40% efficiency. An engine operating at 40% efficiency as an air pump is just a guess, but I can't imagine it being a whole lot less efficient than that. It would have to be able create 60 psi back pressure at 2000 rpm and be only operating at about 15% efficiency to hold back that load in 3rd gear which, is what they said it was doing at the top of the hill.

Edit: in other words there is absolutely no possible way it could have been holding back enough without the use of wheel brakes.

These threads always turns into defending what we own.....how great art thou.

I've owned many Dodge, Chevy and Ford pickup's over 40 years, still haven't found much difference.

This year it's.....????

4x4ord wrote:

ShinerBock wrote:

4x4ord wrote:
^^^ So, based on my observation I would say the wheel brakes were largely what was holding the truck back. The computer recognized the need for a downshift to produce more exhaust braking. After the downshift the back pressure and rpm increased to produce the maximum level of exhaust braking the engine was able to do .... the wheel brakes made up the difference.

Nice theory, but owning a Cummins and having been on that road I would have to disagree.

You've been on that road with 30,000 lbs in tow?

No, and neither have you. Although I have been on that road to know it is not 7% grade the whole way through and it varies between 3% and 7%. I have also driven/towed the 6.7L Cummins in other medium duty vehicles both when I worked at Cummins and at my current employer. None of them use the vehicles brakes and yet they apply the same kind of exhaust braking that my truck does at max going down grades when towing.

I was wondering when I saw the engine temperture at 217 degrees in a cold day what would it be during the summer months? Fun to watch all 3 but better on the same day testing.

chevman

blt2ski wrote:

noteven wrote:

NRALIFR wrote:
Chains? I don’t think so.

Aren’t you limited to about 30 mph with chains.

:):)

I think CO requires towing vehicles to carry chains in winter?

Most of Western States require chains to be on ANY vehicle, be it commercial or private us over single or combined GVW of 10,000 lbsto carry chains Nov 1 to April 1. Washington St is that way, been awhile since looking at Idaho and Oregon laws, they were real similar. They go by registered wieghts, not door sticker warranty ratings.

Marty

IIRC CO requires ALL vehicles to have chains in the vehicle on passes. If you get in a crash and block lanes of traffic without having chains IN the vehicle its a $15xx fine.
I was just on the IKE last week in a truck and trailer with no chains, luckily not snowing. But I was a bit surprised at the signs regarding the chains. I thought it was trucks with trailers that didn't have snowflake tires that required chains.
Lots of darned traffic on that road....There was no way we could go up the west side (side that TFL uses) without getting off the go pedal because of traffic, semis going slow, cars go fast.

I was in a SRW Duramax that easily handled the IKE, of course it had a pretty light load, 6000ish. Had LOTS of brake applications on way down east side because of traffic.