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Discussion Starter · #1 ·
It's something I have wanted to do for some time now, and will be included in my tunes as an option (whenever I finally get that rolling).


The Theory (words, and more words)


First off. How? Well the cruze uses what's called a VGT or variable geometry turbo. This has what are called vanes which are usually a dozen or so flaps surrounding the turbo's turbine. By rotating said flaps to be closed, exhaust gasses become blocked from entering the turbine, creating back pressure. This back pressure will lead to the gasses which do pass having increased speed, making the turbine spin faster (and thus creating more boost!). Likewise, opening the vanes will cause the exhaust gasses to pass through the turbine without creating much back pressure. There is a balance between open and close to make boost more quickly, but that's complicated.

Point is, we can use this to slow down the vehicle. If the vanes are closed, the engine needs to spend more energy to push exhaust gasses through. When zero fuel is injected, this energy will come from the momentum of the flywheel, and the vehicle's momentum itself assuming the transmission is actually connected. Exploiting this fact allows the vehicle to slow down much quicker than it otherwise would have, freeing up the brakes (and sounding cool!).

A big issue of course is the transmission. For the turbo brake to work the lock up clutch needs to be active. Thankfully, Aisin is very generous with using the lock up clutch, and you can pretty much guarantee that above 1800 rpm in any gear above 2 the clutch will be engaged. At gears 2 and 1, ehhh it's a different story. Gear 2 is mostly guaranteed to be locked, while gear 1 you're really at the mercy of the torque converter. This is where the good ends. To use this you of course need to manually downshift two gears to get into the 'exhaust brake range'. Which maybe some of you do already.

The Tune

Basically the idea is to have the vehicle follow this pattern set by some VGT Tables

The stock table (x is rpm, y is fuel). Table is the turbo vane position in % (100 = closed).





The exhaust brake edition.


It is of course like many things, more complicated than that. But in the end the first two rows where the changes are made is what we want the vanes to be at. Note that the brake is only effective down to about 2250 rpm. Why not lower? Well when coasting this same exact table is going to be used, and we don't want to be braking while coasting down a hill, as that would cost fuel economy. 2250 rpm is enough to go up to about 70 mph, above which coasting is not likely to occur at all anyway. Plus exhaust braking below 2000rpm is not as effective as 3000 rpm (which is not as effective as 4000 rpm).

Why not 100%? .... Yeah I have no idea what will happen. Maybe some day I will try it, but for the most part I am assuming 100% is a 'DONT DO IT'. This isn't the first case either. 100% EGR will destroy the EGR actuator. 100% Throttle will destroy the throttle body. <3 German Engineering. If the turbo vanes go out, that is a new turbo. No other option. So for now 98% is the limit.

The Results

It works. From the first sleeper (brrrrt) of a stop sign going 65 mph, it is possible to get down to 10 mph before you have to brake. Which is great, but I can't think of any decent reason to do it other than to be cool. I suppose going down long hills would be useful. Unfortunately I live in the great plains, so not hills for thee. It's also useful for towing, but seriously go buy a truck then. Unfortunately any video I made really doesn't bring justice to the sound, so I will have to wait until I have time to setup some mics inside the engine bay.

Regardless, cool stuff!
 

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Uhh huh.. Im sure some engineer will chime in but if it was pheasable in a production vehicle it would be used by now. Why not just intall a conventonal jake brake?
 

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Discussion Starter · #3 · (Edited)
Uhh huh.. Im sure some engineer will chime in but if it was pheasable in a production vehicle it would be used by now. Why not just intall a conventonal jake brake?
It's in the Colorado diesel if I recall. The 6.6L LML Duramax and 6.7L cummins use a turbo brake as well.

Now they have better software for it, and a toggle switch. But other than that the principal is the same.
 

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theres enough compression braking in the car.

i have a 10% hill for 7 miles, holds 65mph in 3rd all the way down, i dont touch the brakes.
 

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Cummins diesel engine in the 2007 and up use the VGT as an exhaust brake. That said, word of caution. It you have stock emissions, beware. On my Cummins it suspends Regen with the exhaust brake, I'd assume that the ECU is programmed to suspend Regen. Not sure what would happen on the CTD with a regen and exhaust brake action..

Sent from my Moto G (4) using Tapatalk
 

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Discussion Starter · #7 ·
Cummins diesel engine in the 2007 and up use the VGT as an exhaust brake. That said, word of caution. It you have stock emissions, beware. On my Cummins it suspends Regen with the exhaust brake, I'd assume that the ECU is programmed to suspend Regen. Not sure what would happen on the CTD with a regen and exhaust brake action..

Sent from my Moto G (4) using Tapatalk
Ah yes. Good question. The answer is don't worry about it. Basically the 'dosing' of fuel into the cyllinder will be suspended along the same conditions as the turbo brake.

The bulk of a regen happens like this...



As you can see any injection at all will be low if it exists at all. It may not even matter ( of course there are multiple injections, but this is the big one).
 

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It's in the Colorado diesel if I recall. The 6.6L LML Duramax and 6.7L cummins use a turbo brake as well.

Now they have better software for it, and a toggle switch. But other than that the principal is the same.
wow times are progressing fast.

This isn't a jake brake. Way different.
i know that..if you read the original text you'll see i said "Why not just intall a conventonal jake brake?"
 

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Discussion Starter · #9 ·
1. A jake brake doesn't exist for the cruze.
2. No one is going to waste time developing one.
3. No one is going to waste time installing one.

Pretty much sums that up..
 

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1. A jake brake doesn't exist for the cruze.
2. No one is going to waste time developing one.
i know there isent one.. id pay for one as a consumer.
 

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I have this on my 15 F350 6.7. It's not a Jake Brake and doesn't feel like one at all. It's very smooth and does nothing if you drive normal and are unloaded, if I get on the brakes hard it will drop the tranny a gear or 2 and you feel the extra stopping power but you never get the sound of a Jake Brake. When it on with the cruze control it will hold the set speed going down hills. With the cruze off if I push the brake about 1/4 of the way it will hold that speed until I give the accel aerator pedal a solid push. It can do this unloaded or towing an 18000 lb trailer which is the legal limit for my setup even though the truck feels like it has plenty left.

It has become one of my favorite things about the truck, I use it when I'm unloaded any time I'm in traffic. To get the CTD to do this you would have to add the tranny, speedometer, brake pedal and cruze control into the mix, its a lot more than just using to VVT to make a Jake Brake.
 

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Discussion Starter · #12 ·
I have this on my 15 F350 6.7. It's not a Jake Brake and doesn't feel like one at all. It's very smooth and does nothing if you drive normal and are unloaded, if I get on the brakes hard it will drop the tranny a gear or 2 and you feel the extra stopping power but you never get the sound of a Jake Brake. When it on with the cruze control it will hold the set speed going down hills. With the cruze off if I push the brake about 1/4 of the way it will hold that speed until I give the accel aerator pedal a solid push. It can do this unloaded or towing an 18000 lb trailer which is the legal limit for my setup even though the truck feels like it has plenty left.

It has become one of my favorite things about the truck, I use it when I'm unloaded any time I'm in traffic. To get the CTD to do this you would have to add the tranny, speedometer, brake pedal and cruze control into the mix, its a lot more than just using to VVT to make a Jake Brake.
Hmm. The only vgt turbo brake I have used is on a 2011 cummins manual. The behavior is similiar to the way I have it programmed for the Cruze except on the Cummins it operates better with cruise control and can brake at 1300 rpm.

On the Cruze going that low with the brake will mess with the Cruze control, hence why it stops at 2250 rpm.

Actually the code for the LML brake exists. But it would mean adding a switch and running some wires to get it to work. And that would work with cruise control, etc. But that's alot of development time.
 

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Huzzah, I deliever.

Wow that sounds really cool! I'm pretty happy with the stock levels of engine braking when I downshift, but it doesn't sound quite as cool as yours. :)
 

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I hope it only sounds like that when braking? Is it defeatable with switch of built into the firmware? Great video, thanks for sharing.
 

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Discussion Starter · #18 ·
I hope it only sounds like that when braking? Is it defeatable with switch of built into the firmware? Great video, thanks for sharing.
This is with a short intake. So it will sound different with stock.
 
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