kiladonut

iTrader: (1)

I am having a hard time figuring out how to troubleshoot an overbooting issue and seek the advice of the community. This subject has been beaten to death but it seems most people get a port and call it a day or go to an external gate. My turbo is already ported and I’d like to avoid going external if possible.

First my car:
01 vvt
Begi S4 kit
Begi separated gases downpipe that flows back into the exhaust
3” exhaust from Abe with a cat and resonator.
Garrett gt2860rs .64ar
Wastegate has already been ported by Begi according to Begi themselves.

I wired the wastegate open and did a 3rd gear pull. The car made 2psi up until ~5k where it creeps to 12+psi verified on boost gauge, megasquirt log, and butt dyno in 3rd gear. With a 7psi actuator with the proper 3 turns of preload the car makes ~15psi. I assume this means either the port isnt capable of pushing out enough exhaust gas or the wastegate’s pipe isnt free flowing enough. Is that accurate? What could other culprits be if any? Attached are 2x pics of how much the flapper opens.

I have seen a few threads on here where people grinded out the exhaust housing entering the wastegate to allow for smoother flow for the exhaust to exit the wastegate. Is that something that is worth looking into? I already have the turbo yanked out of the car at the moment and I plan to take it somewhere to see if they can port the turbo more than it already is if that is a viable option. But short of going to an external setup I am not sure what is worth trying.

stefanst

iTrader: (1)

How about wiring the WG open and check how much boost this nets you? That should be pretty definitive.

Savington

iTrader: (31)

OP, the best you can do is port the hell out of the wastegate, but you may never be able to run 7psi on that setup. You have the worst possible combination of parts for low boost. Tubular manifold + small A/R Garrett turbine + decent downpipe + big exhaust = boost creep city.

I would seriously consider a swap to an EFR setup before investing the money in an EWG mainfold/downpipe for that turbo. The EFRs have none of these issues, owing to far better wastegate design.

18psi

iTrader: (76)

this is very important and likely your only non-expensive option.

the path to the wg port is just as important as the port diameter itself.

you can easily do it yourself with a grinder and carbide burr btw.

aidandj

iTrader: (5)

Install an exhaust restrictor.

18psi

iTrader: (76)

dont' make me ban you

aidandj

iTrader: (5)

Girz0r

iTrader: (1)

Some threads to reference from

https://www.miataturbo.net/diy-turbo...exhaust-80152/

https://www.miataturbo.net/general-m...aterial-80058/

kiladonut

iTrader: (1)

Thanks everyone. You guys pretty much confirmed what I thought. I will likely try to grind the housing and if that helps at all. Maybe check to see if any more of the wastegate port itself can be opened up. If that doesn't get me where I want to be I will look into other options. I will post an update on how it goes.

kiladonut

iTrader: (1)

Just took off the manifold to see what I'm dealing with while I hunt down a carbide burr. Figured I'd give an update before the update. This is my starting point. Going to widen the channel and smooth some of the sharp edges.

nitrodann

Im going to go ahead and ask this question again but.. Do you really need it to not creep up top?

do you have insufficient injectors?

Dann

sixshooter

iTrader: (12)

Either grind the entrance slope to the WG, let it run 12+psi, or switch to a .86 turbine housing.

Braineack

iTrader: (62)

did we do this yet?

kiladonut

iTrader: (1)

If I didnt have stock rods this wouldnt be an issue. The car creeps to 15-16 psi in 3rd gear and it will get worse in 4th, 5th, and 6th. The end goal assuming I stay with this turbo setup is to run 10-12psi wategate with an MBC set to 12-14psi and not nuke the car at an autocross.

With the wastegate wired opened the car peaked at 12.7psi. With the 7psi actuator hooked up it made 15.x both in 3rd gear (same day/air temp/road). Does it stand to reason that with the actuator opened I should only be seeing 12.7psi? I was previously thinking with the actuator attached there is more exhaust gas trying to escape at once when the flapper opens compared to having it wired opened and it venting the entire time. But really, I could just be way off base.

Would the larger .86 A/R housing fix my problem? Large wategate? I need to read some more about how badly that would hurt spool. I am not a track rat so it might not be a big deal.

It sounds like my options in no particular order are:

1. Pray to turbo kitten for unlikely great porting success
2. EFR
3. External WG
4. Larger housing
5. Build motor

Shortpersonbk

Another option is an ewg manifold with a tial 38mm

kiladonut

iTrader: (1)

I have decided against modifying my current turbine housing any further. Its ported to a point where I don't think any smoothing I do will have a significant impact. That coupled with a few cracks forming I think its best to replace it. I am going to hunt down a .86 a/r housing.

One thing I just discovered was the wastegate baffle. I assumed it was a standard piece but it is actually welded in place and not from Garrett. If I get a new housing is that something I am going to want to make sure is on the new housing? Could that be reducing the flow to the wastegate being another culprit to my boost creep?

This is the piece I am referring to:
BEGi

Braineack

iTrader: (62)

you should be able to get it to stay at 13psi with the actuator attached. remove some preload.

Girz0r

iTrader: (1)

Sooooo...

When are you doing this?

kiladonut

iTrader: (1)

First off I am an moron because that baffle is on the other side of the housing. That can't be an issue.

I played with preload (even taking it down to no preload) prior to pulling the turbo with basically the same results.

Braineack

iTrader: (62)

the arm must not be able to open it as far.