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Hi All,

Yesterday morning, before heading home from the Ultimate Callout Challenge diesel event in Indy, I stopped by OZTuner and Corbin Murphy flashed my 2015 Cruze Diesel with their 30 hp tune. On the drive home we picked up about 3 MPG and the hesitation from a stop off idle is almost completely eliminated. Drivability feels normal with a little extra pep! All in all I like it am VERY happy I finally had a chance to get by the shop and get it done!!!

I also picked up the race tune and "lightweight" downpipe in case I ever want to do some racing with the Cruze!!! I have heard some say that the quality of the downpipe and finish was lacking and the one I have and others I saw look great. The weld quality is top notch with excellent TIG work and the Ceramic heat barrier coating is smooth and even. I don't know what others could be complaining about but the downpipe I have and others I saw from inventory look great and are high quality pieces...

BTW they said that their experienced techs take about 2 hours to install the race downpipe, race tune and EGR block-off plates, and that the downpipe only could be done in about 45-minutes by an experienced tech or owner. So you could literally drive to the track, swap out the DPF for the race downpipe, load the race tune then race and swap it back for the drive home with only around an hour and a half of extra time needed... Just a thought...
 

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I read they switched to a ceramic coating after complaints. Mine just had a light coat of high temp paint sprayed on.

It wiped right off effortlessly with some thinner and I put a bunch of coats of the ceramic manifold paint myself
 

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Yup used to be just black paint
 

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BTW they said that their experienced techs take about 2 hours to install the race downpipe, race tune and EGR block-off plates, and that the downpipe only could be done in about 45-minutes by an experienced tech or owner. So you could literally drive to the track, swap out the DPF for the race downpipe, load the race tune then race and swap it back for the drive home with only around an hour and a half of extra time needed... Just a thought...
You cant do that sadly. When you put the Race tune on your car and delete, only GM can retune for DPF/Urea injection, even Fleece cant, ask them.

When you delete, you delete for good. :signs013:
 

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I do wish the downpipe was bigger. Definitely should be able to fit a bigger one in there - which will make for less backpressure...turbo happier, more power, etc...
 
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I do wish the downpipe was bigger. Definitely should be able to fit a bigger one in there - which will make for less backpressure...turbo happier, more power, etc...
Yes, im working on a plan to find a good fabricator to make me a custom 3" downpipe and full exhaust using these parts : Vibrant Performance ::.

And it will be Ceramic coated too. :th_dblthumb2:
 
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Yeah, a full 3" back setup I think would be the most optimal.
 
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Discussion Starter #9
I do wish the downpipe was bigger. Definitely should be able to fit a bigger one in there - which will make for less backpressure...turbo happier, more power, etc...
Yes, im working on a plan to find a good fabricator to make me a custom 3" downpipe and full exhaust using these parts : Vibrant Performance ::.

And it will be Ceramic coated too. :th_dblthumb2:
Yeah, a full 3" back setup I think would be the most optimal.
3-inch seems like overkill to me! My 6.6L Duramax engine came with a 3.5-inch exhaust system and funky downpipe. I believe the aftermarket downpipe is either 3.5 or 4-inch and the rest of the exhaust is 4-inch and my truck runs a MUCH larger turbo AND is putting down 540 HP and 1000 lbs-ft TQ.

OZTuner sized the downpipe appropriately for the turbine outlet, I highly doubt you would see ANY measurable improvement from a larger downpipe... I suppose it goes well with a ricer/gasser mentality, but a larger diameter downpipe is not at all needed for the 2.0L turbo diesel engine. Even with a larger turbo or compounds I think it would be fine with this downpipe...
 

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3-inch seems like overkill to me! My 6.6L Duramax engine came with a 3.5-inch exhaust system and funky downpipe. I believe the aftermarket downpipe is either 3.5 or 4-inch and the rest of the exhaust is 4-inch and my truck runs a MUCH larger turbo AND is putting down 540 HP and 1000 lbs-ft TQ.

OZTuner sized the downpipe appropriately for the turbine outlet, I highly doubt you would see ANY measurable improvement from a larger downpipe... I suppose it goes well with a ricer/gasser mentality, but a larger diameter downpipe is not at all needed for the 2.0L turbo diesel engine. Even with a larger turbo or compounds I think it would be fine with this downpipe...
Since a Turbo car, nothing after the turbo is best. Since i cant put nothing, i will go biggest possible!

Look at video from one of the best for more infos : http://www.cruzetalk.com/forum/9-general-discussion/197690-turbo-straight-pipe-best.html
 

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Since a Turbo car, nothing after the turbo is best. Since i cant put nothing, i will go biggest possible!

Look at video from one of the best for more infos : http://www.cruzetalk.com/forum/9-general-discussion/197690-turbo-straight-pipe-best.html
Exactly.

Plenty of Cobalt SS/TCs see gains from going up from the stock 2.5" exhaust and downpipe up to a 3", especially when they're tuned. I'm running a 2.5" on mine, and it doesn't even have a turbo. If I move up to a TVS 1320, a 3" downpipe and catback will be required, not just because it's cool.

It's a turbo car - as mentioned above - the less backpressure the better. Even though the downpipe is sized to the turbo outlet, you've got a couple 90 degree bends in there...a larger diameter will make those less of a impediment to flow.
 
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Discussion Starter #13
Since a Turbo car, nothing after the turbo is best. Since i cant put nothing, i will go biggest possible!

Look at video from one of the best for more infos : http://www.cruzetalk.com/forum/9-general-discussion/197690-turbo-straight-pipe-best.html
Exactly.

Plenty of Cobalt SS/TCs see gains from going up from the stock 2.5" exhaust and downpipe up to a 3", especially when they're tuned. I'm running a 2.5" on mine, and it doesn't even have a turbo. If I move up to a TVS 1320, a 3" downpipe and catback will be required, not just because it's cool.

It's a turbo car - as mentioned above - the less backpressure the better. Even though the downpipe is sized to the turbo outlet, you've got a couple 90 degree bends in there...a larger diameter will make those less of a impediment to flow.
I understand what you are saying, but again in this specific application I do not think it is necessary or worth the effort or investment. If 6.6L of Duramax diesel with a MUCH larger turbo works VERY well with 3.5 and 4-inch exhaust making 500-1000 HP, I think we'll be fine making less than 200 HP with a baby turbo and only 2.0L of engine!!!

Most of the race and sled pull diesel engines that I am around on a regular basis use downpipes and/or turbo exhaust outlets (typically hood stacks) that are sized to the turbine outlet. Last weekend at the UCC event they were making more than 2000 HP through hood stacks with triple turbo compound setups and exhaust through one or two outlets sized to the turbine outlet complete with 90* bends, some of them with multiple bends.

I think it is better to invest the money from custom OVERSIZED exhaust on your Diesel Cruze in other areas that will actually improve performance rather than one that likely will not make a difference other than lightening your wallet and draining your bank account. But hey, what do I know???
 

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It is funny that the reference video is of Gale Banks. Gale and I are friends and I have sat down with him on numerous occasions. The exhaust on my Duramax truck is Banks Monster Exhaust with a downpipe from ProFab Performance. I know the exhaust is 4-inch and I think the downpipe is as well.

Look at the many exhaust systems shown in the video, Banks Power does not install oversized exhaust downpipes on their engines. Why do you want to??? Freeflowing is freeflowing...
 

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Moving from a 2.5" to 3" exhaust sure worked pretty well on a 1.4T Dodge Dart. Making less power than a tuned 2.0TD Cruze, and about half the torque. And that's still on the stock downpipe.

2.5 vs 3 inch exhaust - Page 3

Keep in mind - with a hood stack, there's no back pressure because it's not that long - it comes out of the turbo and ends. That's fine. But you start adding turns in...you're killing flow. On the opposite end of the spectrum - LT1 Fbodies...switching from a stock-routed CAI, which has two 90 degree turns to the LS1-style lid, which is a straight shot - huge improvement. By your logic, if the CAI was the same size as the TB, it doesn't matter about the bends. But boy does it. Big time.
 
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Moving from a 2.5" to 3" exhaust sure worked pretty well on a 1.4T Dodge Dart. Making less power than a tuned 2.0TD Cruze, and about half the torque. And that's still on the stock downpipe.

2.5 vs 3 inch exhaust - Page 3

Keep in mind - with a hood stack, there's no back pressure because it's not that long - it comes out of the turbo and ends. That's fine. But you start adding turns in...you're killing flow. On the opposite end of the spectrum - LT1 Fbodies...switching from a stock-routed CAI, which has two 90 degree turns to the LS1-style lid, which is a straight shot - huge improvement. By your logic, if the CAI was the same size as the TB, it doesn't matter about the bends. But boy does it. Big time.
You are talking fruits and vegetables not even close enough to apples and oranges in comparison!!!! Gas engines are completely different critters than diesel engine. Intake is completely different that turbine outlet. And finally normally aspirated is completely different than turbo charged... Adding air volume on an intake tract is a great way to help throttle response as well as HP, but again it is totally different that the turbine outlet of a turbo to speak about the intake of a NA gasser.

Hood stacks are short but typically have at least 1 90* bend and in many cases have several 90* or even 180* bends and twists... But again they do not size them much larger than the turbine outlet... Physically the visual stack in the hood is larger, but the internal stack off the turbo is typically turbine outlet sized.

Chase Fleece did 1,855 HP and 2,576 TQ on the chassis dyno this past weekend with his Dodge/Cummins in the UCC competition!!!! Let that sink in a little bit, one of the brothers behind Fleece Performance Engineering made darn near 2,000 HP on a chassis dyno!!! The team at Fleece and OZTuner know their stuff when it comes to tuning and modifying/building diesel engines. I trust those engineers much more than any forum posters when it comes to performance diesel applications. I fully believe that they sized the downpipe for the Cruze Diesel appropriately for the application and I feel that you are wasting money if you have a custom built large diameter downpipe.

If you want to have a custom downpipe fabricated feel free to do so, but do not expect it to provide a dramatic HP or TQ advantage over the OZTuner downpipe. You would be much better off investing the money for the custom fabricated pipe and TIG welding in other areas of your car like high flow injectors, turbo upgrade, performance wheels and tires or brake upgrades or anything else that will actually improve the car not something that will cost a lot of money for little to no gain in performance.
 

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For those of you interested... I have a guy at work that is really considering building larger downpipes for the CTD, completely stainless steel, and larger diameter. They'll cost more than $265, but it will be substantially higher quality. He already has an established business as a down pipe / exhaust fabricator for the whole Volvo and WRX world. If any of you are interested... Look up 8Eight Fab on facebook.
 

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For those of you interested... I have a guy at work that is really considering building larger downpipes for the CTD, completely stainless steel, and larger diameter. They'll cost more than $265, but it will be substantially higher quality. He already has an established business as a down pipe / exhaust fabricator for the whole Volvo and WRX world. If any of you are interested... Look up 8Eight Fab on facebook.
Any chance he'd also be interested in doing a dyno comparison with the two?
 

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I trust those engineers much more than any forum posters when it comes to performance diesel applications.
So I guess the fact I'm an automotive mechanical engineer with a thesis that dealt entirely in fluid dynamics (with an advisor who was the fluid dynamics professor) means I'm just "a forum poster". I wasn't aware I didn't actually know what I was talking about, wow!

/sarcasm
 

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Any chance he'd also be interested in doing a dyno comparison with the two?
My car will be the test car... so it's possible, I will have to find a local Dyno(I know where one is, just not sure if they are open to the public or just for their own tuning purposes, it's a LS performance shop)... But I would be more than willing.
 
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