Hello fellows. we usually work with N/A engine.

First miata turbo in our shop is becaming fast a good nightmare.
The car is a 2003 1.8 VVT engine. The engine was rebuild and strong. The customer ask for the classic recipe 0.6 bar (8-9 psi) for the win.
The customer had already bought manifolds (kraken top) and turbo from ebay (it seems genuine) Mitsubishi TD04-L. Unknown turbine and impeller.

We "fell" for it (it is a good and reasonable customer, the best kind) and developed the whole engine bay on the kraken top mount T25 and its TD04-L
Then we go on dyno and problem arise fast: the car goes vey well until 4000 rpm then it boost creep all the way to 1.4+ bar (20 psi). Then wastegate (internal of the TD04, it's a td04 with that odd 4-bolt pattern) became competely irrelevant.
We then test the car with the wastegate stuck open: no boost until 4000 rpm then rapid boost creep.
We get in contact with a respectable italian turbo builder which easily told us that the turbo is too small, that the problem we encounter they have the same with 1.6 engine (altought different engine brand) and that he will make up a more correct size turbo for us.
Ok, no problem pal, go on.

He came out with a TD04-HL, enlarged 23mm wastegate hole, 18T billet aluminum impeller, T25 hot inlet flange, odd 4-bolt hot outlet flange. It seems all good, but then on the dyno we encounter the very same problem at like... 500 rpm later?
The turbo looks like it build up its PSI with likely zero lag or spooling. At 2000 rpm the car is ready to take off with the target, correct boost.

It seems not a problem on the intake side on the engine. Except for the wastegate becaming irrelevant and turbo creep, all the rest (ie: blow off valve, engine, start, wiring) seems ok.

Turbo aren't my world, but i need some advice. It seems to me that the turbo matching is again very off, and the turbo builder is shading away, leaving me with more question and less money. It's okay sometimes but i least i want to understand the problem.

 

What kind of system do you use for boost control? Can you take a log and attach it here?

 

The boost control is completely mechanical. Direct hose from cold side to wastegate actuator.

The problem Is NOT related to wastegate functionality as on dyno we get the problem arise also with the wastegate stuck open
W/ wastegate mechanically locked open, we got no boost until 4300 rpm (the wastegate waste off exhaust pressure correctly) then we get turbo creep up to 14-20 psi rising with rpm. It seems a sizing of turbo problem.

 

It's a gate problem. Like a flow problem it seems. I'm not sold on the TD04 sizing problem, because tons of people have no problem with controlling boost down to 10psi or so even without modding the housing.

Does it have a very free flowing exhaust? Why I ask: With a more restrictive exhaust, gases will find their way to/through the gate easier and vice versa. Does the flapper have FULL movement?

In other platforms, where everyone is using external gates, people still have boost creep even with big gates and the solution to stop this once and for all is to weld a flange for the external gate right to the turbine housing.
This will cost a good chunk of money and space might be a problem, plus you need to modify your dump.

Why does you customer buy a T25 manifold and a TD04 turbo in the first place? Just go for a regular T25 turbo like 2554, 2560, 2860, G25 with atp housing

 

TD04 was choosen by the customer because here they are dirt cheap, cheap to rebuild and a lot of business rebuild them in a matter of hours. Also, they have a reputation to be some kind of very very reliable. So i think it was for these reasons.
The flapper can outperform the actuator movement so i think it's not a flap cinematic issue. Also, when we deatach it from actuator and seize it full open, i think we gone PAST the maximum allowable movement of the actuator without actually resolve the problem for testing purposes.

Also the exhaust flowing is an interesting issue. We got 2.5" downpipe but the car has the cat coverter. Also, we got two 90° bends in the downpipe, so i dont think is so free.

The matter is: the TD04 is a whole family. Which impeller-turbine-housing are these tons of peope running? just for data collection, then i will speak up to the turbo business to came to rescue.

 

It is common when using small turbos to need to open the port before the flapper using a grinder. The exhaust flow from the engine is too great for the tiny turbine and small wastegate hole. Depending upon the A/R sizes of the housings and the trim of the turbo he may have just chosen an incorrect combination. TD04 is not one turbo it is a family of many sizes and combinations.

 

I'm not familiar with that turbo but, my turbo did the same thing until I ported the wastegate.

 

For future reference:
the turbo itself was an hybrid unit not suited for application
That was the price we got to pay for our newbieness in the turbo world. We trusted a well known turbo builder here in italy but he make us pay the turbo then vanished when it does not perform as requested.

We got to pick up a subaru unit (PN 8M04-400-541) and the creep was gone. We managed to control the boost level up to 7000rpm so for what is worth was good.
We then got other small problems (if you want, see below) but the creep was gone.

https://www.miataturbo.net/diy-turbo...0/#post1651016