Turbo Upgrade: GT2860RS Disco Potato

J

jjm86m

:
2018 Mazda CX5 Machine Gray
My stock GT25 turbo went bad on me and I'm thinking about upgrading to the GT28RS. I'm trying to gather ALL the information I need before I start buying and tearing into the engine. There are some really good resources here but I still have some questions both tech and otherwise.

My Performance Goals:
- First and foremost I'd love to have my car running again.
- I'd like to run 200-215hp... safely at no more than stock boost


Tech Stuff:

Here is what I've found so far. Please correct me if any of this is wrong

- The T28 is a bolt on part (T25 flange) that may or may not need to be clocked depending on where you get it.
- The stock wastegate, bracket is necessary for mounting properly
- The T28 actuator and actuator bracket can be used with modification (check out link below). T25 actuator and bracket can be used but there the bolt holes don't match up and you will either need to tap a bolt hole in the turbo or modify the bracket.
- FMIC is recommended/ Customsp SMIC is also an improvement over stock/stock SMIC has been run before (not recommended)
- Slim fans are necessary as well as new oil lines (Can someone please verify? I've seen several different posts on this)
Q: According to this thread the oil lines are the same. Also see drawing links below. Oil lines seem to be the same.http://www.mazdas247.com/forum/showthread.php?123798581-gt28rs&highlight=Clock+a+turbo
- T28 runs a higher boost out of the box. ~16psi on the T28 actuator
- Use a boost controller to lower keep boost at a acceptable level or use a forge WGA


Financial Stuff:
- I've got a quote on a T2860RS for $1196.xx. Can I get the T28 to work on my car with a $1500 budget? Only thing I have right now is a CAI.

BOM stuff:
- Looking to be pointed in the right direction fro a EBAY DIY FMIC with minimal mods (i.e. no cutting into the crash bar). Looking to pay no more than $250 to either upgrade SMIC or FMIC the car. Is there a ebay supplier that supplies MSP parts?
- Anyone got gaskets and seal part numbers?

Other Random Stuff
What the is MAM? I see a MAM FMIC and MAM manifold. Is a company? forum user? do they no longer exist?
(Edit) A: Metal Addication Motorsports



Links: For DIY FMIC and Turbo stuff
How To:
Replace T25 with T28
Tips on Turbo Install

T28 Links
Sticky on Turbos
GT28
More GT28
Suppliers for an Turbo Upgrade

T2554 Flange Dimensions
T2560R Flange Dimensions
T2860RS Flange Dimensions
T2571 Flange Dimensions

FMIC links
FMIC vs SMIC
Install Guide
FMIC Discussion
Ebay FMIC How To

I'd love to turn this from a question session to a reference guide if I can pull this off successfully. If there are any other links I should reference let me know. Thank goodness for the "search" feature. Also, huge thanks to HKPRO5 and Zuku26 for answering all my crazy questions in PM.
 
Last edited:
Cx racing on ebay is where everyone on here goes for the DIY FMIC kits. The 9 piece piping kits with the U bends and I say a 27x6x3.5 core. You will be cutting your crash bar and needing extra couplers.
 
I had a GT28RS for a couple years on mine. Yes, its a direct replacement flange wise. You will need to clock the turbo tho. The wastegate bracket can be modified to be used but i just reused the stock GT2554R bracket and wastegate. Was an easy swap.

It can be used with the stock coolant and oil lines. It can be used with the stock fans.
 
@jbrewer: The FMIC install guide linked in the OP doesn't mention anything about cutting the crash bar unless I skipped a section. Does it vary from install to install? They make a 27x6x2.5 as well that would sit farther back and give more clearance width wise but not height wise. The FMIC on ebay are pretty cheap, thanks for the info


The length of the control arm on the actuator controls the boost. So in theory if you used the old actuator then you'd run the same psi. Is that correct?
 
Negative, you have to adjust the arm to fit the length of the 28rs. Since it is longer, you have to loose the adjuster on the arm and lengthen it out. If you make it too tight you will boost more psi. If you make it too loose you have boost less psi. just make it as tight as the stocker and you will not have any problems.
 
So basicaly if i want to swap my stock turbo i just buy the disco potatoe and its bolt on to where my stock turbo was without buying anything else?

sputnik2212
 
The GT28RS isnt a complete bolt on application esp on a bone stock MSP. I think I"m the first member to actually have a GT28RS installed on a bone stock (Im talking Plastic pipes and stock exhaust stock) we actually got it to work with some trimming. Its not recommended because that turbo makes a bit more heat under the hood then the T25. So at minimum get a FMIC and upgraded midpipe. It almost seems like the Stock ECU was tuned for the GT28RS. Since the Stock tune is so rich the Larger turbo leans it out well.
With the CXracing intercooler listed you do not need to do any fabwork to the crash bar!!!!!!!!
 
I just posted the 2871 flange dimensions. I haven't studied them completely but they look pretty similar. I would imagine that the setup would be similar for a 71 as it would be for a 60


If I upgrade to FMIC I'll have trouble running my AEM CAI. Can that be converted into a short ram?
 
The GT2860RS does not make more heat than the stock turbo. It is a bigger turbo so at the same level of horsepower it will make less heat, because the turbo does not have to spin nearly as fast. It is bigger though and so you will be closer to other things like your fans and your thermostat housing.

The horsepower gains from going to the disco at the same PSI is because the air coming out of it is cooler and denser.

The PSI it will run at are determined by two things, the spring on the wastegate, and diaphram of the actuator. PSI is lbs per sqaure inch, and spring rates are measured in force per distance.
Some actuators have an adjustable length rod. What you are adjusting is the range that the wastegate is opened and closed. Make it longer and the wastegate opens earlier, make it shorter and the wastegate opens later. But both of these have negative side effects. Earlier will lose boost response since the wastegate cracks early, later will often result in boost creep because the gate doesn't open fully.

The thing to understand is that a boost controller can not run less boost than your turbo is set up to run with. Read up on MBCs vs EBCs as they both have pros and cons.

Ideally, you'd want an electronically controlled wastegate, which most modern turbocharged cars come with, but that's not really possible for us.

So to get the best response out of your turbo, you want to run the weakest spring you can find and a boost controller set to your desired boost level. That way the wastegate stays shut all the way up to the point that your controller passes on the boost source to the actuator and the wastegate quickly opens so you don't get boost spikes like we do in our stock setup.

That's my personal philosophy and welcome others' opinions.
 
jdwk said:
The GT2860RS does not make more heat than the stock turbo. It is a bigger turbo so at the same level of horsepower it will make less heat, because the turbo does not have to spin nearly as fast. It is bigger though and so you will be closer to other things like your fans and your thermostat housing.

The horsepower gains from going to the disco at the same PSI is because the air coming out of it is cooler and denser.

The PSI it will run at are determined by two things, the spring on the wastegate, and diaphram of the actuator. PSI is lbs per sqaure inch, and spring rates are measured in force per distance.
Some actuators have an adjustable length rod. What you are adjusting is the range that the wastegate is opened and closed. Make it longer and the wastegate opens earlier, make it shorter and the wastegate opens later. But both of these have negative side effects. Earlier will lose boost response since the wastegate cracks early, later will often result in boost creep because the gate doesn't open fully.

The thing to understand is that a boost controller can not run less boost than your turbo is set up to run with. Read up on MBCs vs EBCs as they both have pros and cons.

Ideally, you'd want an electronically controlled wastegate, which most modern turbocharged cars come with, but that's not really possible for us.

So to get the best response out of your turbo, you want to run the weakest spring you can find and a boost controller set to your desired boost level. That way the wastegate stays shut all the way up to the point that your controller passes on the boost source to the actuator and the wastegate quickly opens so you don't get boost spikes like we do in our stock setup.

That's my personal philosophy and welcome others' opinions.
Click to expand...

Mine came set to 7psi. It's definitely not a straight bolt on replacement. There are minor things that you have to change for it to fit. I haven't had spiking or dropping issues in the slightest.
 
If you data log your boost, you should see that 7psi hit anywhere from 8-10 for a split second depending on gear. You'll also see that 7psi is not exactly 7psi. It bounces around quite a bit because pressure in the intake manifold is nowhere near constant.

Even if you set the EBC or MBC to the exact pressure of the turbo, so 7psi for you, you should notice an increase in response.
 
jdwk said:
If you data log your boost, you should see that 7psi hit anywhere from 8-10 for a split second depending on gear. You'll also see that 7psi is not exactly 7psi. It bounces around quite a bit because pressure in the intake manifold is nowhere near constant.

Even if you set the EBC or MBC to the exact pressure of the turbo, so 7psi for you, you should notice an increase in response.
Click to expand...

I don't have an MBC anymore :) Fuel cut wasn't worth it haha. I think taking the butterflies out and machining it has helped tremendously but, you are right.
 
I'm in the process of swapping in a GT28RS right now. I just wonder about whether the fact that my ECU was dealer flashed with the update back in 2004 will cause any problems. I'll have to pick up a wideband O2 sensor soon.
 
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