Overboost Issue
 

So I have been using a 2560r that came with an FMII. I was getting boost up to 11psi on the FM Garrett actuator. So I thought that was where my problem. Before the issue the car would boost up to 8psi and hold nicely through the power band. I went online looking at various waste gate actuators and bought a kinugawa billet one with a 4psi spring. So I installed the actuator and now I am seeing 10psi. If I take out the pre load I have issues with the wastegate not snapping back fully closed. Even then the car will boost up to 8-9 psi. So do you think my next step would be to clean the wastegate. Maybe there is carbon causing it to stick. I am not using a boost controller at the moment to try and eliminate variables. I can move the wastegate open and close freely no isssues so I assumed it had to do something with too much preload but idk right now Im out of ideas.

If you disconnect the wastegate arm and wire the wastegate open for a test, what happens?

Get logs.

I had the same issue when i first built.


I had had to port a channel to the wastegate. As did a lot of people.

Like he said ^ disconnect the arm. Mine still built like 5psi with the wastegate wide open before i ported it.

Have you checked your line going your wastegate?
Have you bench tested the wastegates?
Does boost rise up and fall back down, or stay constant?
What size is your exhaust?
What downpipe flange are you using?

Easy stuff first:
If you have a leak or obstruction in your lead to your wastegate this can cause overboost. Test your line first to see if it has leaks, make sure there's no pill or obstruction in the line. Then test the wastegate with an air compressor and gauge to see if it's opening when it should.

If your exhaust is smaller and/or there is an obstruction or constriction at the wastegate exit it could cause overboost - I had that a long time ago. Smoothing flow out of the wastegate port may help. Opening it up helped me back in the day day.
well.

Test those things and come back.

overboost on the 2560r is caused by an exhaust that is too free flowing. The exhaust finds it too easy to go through the turbine instead of going through the air traffic jam waiting to get around the 90 degree corner to go through the wastegate. The solution is quite simple: Send your turbine housing to BEGi for a wastegate port. Instead of a sharp 90 degree corner, the exhaust can take a relative shortcut through the wastegate opening. This is a well documented issue with the 2560. Garrett will not fix their casting because they tell the miata community "no one else has problems with that turbo, so you're all obviously doing it wrong". Apparently the efficiencies that the miata community sees simply exceed those that the rest of the world sees with this turbo.

/thread

With the arm disconnected I get around 4-5psi


I tested the actuators and both the garret and the kinugawa actuators are open as the should.

Boost stays pretty constant

I am using an FM 2.5 inch downpipe all the way back no cat or muffler.

Ill look into getting it done. I hope its not too expensive. If I put a cat back on would that be an easier fix?

This is a 2554 that had over boost when a larger exhaust was installed. This helped but did not completely eliminate it.
https://www.miataturbo.net/attachmen...ine=1386914128
http://i1219.photobucket.com/albums/...CFA966F695.jpg

Carbide burr and a die grinder.

Yeah. You really gotta hog that thing out.

https://www.miataturbo.net/attachmen...ine=1386926220

Could I just do this myself with a dremel and a ceramic bit?

Yes. Enlarge the wg hole carefully, smooth out its inlet from the turbine, then make a smooth channel in the housing leading up to it from the turbine inlet like BEGi does. Its time consuming but not hard.

good luck with that. I believe you can find instructions on BEGi's website for DIYing this. The trick is to cut a shit ton (approximately 2,000 lbs 10 ounces.) of metal out of the part without screwing it up.

After watching this I think I'll contact BEGi haha. I dont doubt I could do it, but I dont exactly have the tools and would rather leave it up to the experts in case I screw up.

Let us know what BEGI charges to do that, I'm somewhat interested as well.

When I sent mine in, they were doing the porting for free as long as I covered 2-way shipping; if they're charging a fee now, it's probably less than $100. BEGi isn't doing this to make windfall profits; they're trying to provide a service to the community.

Yep, used to be under 100

if it still is, probably worth it to send to them. you'll spend 30 on a proper bit alone

Or find someone local you can bring it to. Anyone with half a brain can figure this out just by looking at a picture. Ideally you want someone who does this for a business. There are a few people on my local forums who specialize on port work. Something like this couldn't be more than $50 and you have it back same day with no shipping charge.

Just a thought.

Here's the results of my porting, no problems with overboosting:

https://www.miataturbo.net/attachmen...00-resized-jpg
https://www.miataturbo.net/attachmen...t2-resized-jpg
https://www.miataturbo.net/attachmen...t4-resized-jpg

I got an email reply from Stephanie and is 75 bucks not including shipping. Im going to get it done next time I order parts cause Im only 50 min away so I might as well drop it off. idk really depends on shipping. I have never shipped a turbo let alone such a short distance.

The turbine housing might fit in a USPS flat rate box.

So I noticed something pretty cool on my gt2871r when I looked inside the turbine housing this weekend to see if it needs porting:

it looks like my turbine casting already has this "port" and an enlarged wg opening. not ported or cut, but cast into the turbine from the factory. Its a new 2871r so maybe garrett finally listened to all the complaints?

I'll snap a pic when I get a chance