renardracer

Hello.
I have got some trouble with my built.
i actually run a 1.8 1998 mx5 with a home turbo built.

My settings:
Holset hx30w (internal WG), with in my hand a 5 - 7 - 10 psi spring actuator.
Rx8 yellow injectors
Coil on plugs ignition system with bre7 ngk plugs
2.25' intercooler piping
Full 2.5' stainless exhaust without restrictions
Home reroute kit
Me221 ECU

My problem:
I just cant calm down the turbo ! At low and middle range, all is ok, the pressure is ok with the spring i use, but over 4500rpm, the pressure go up to 20 psi. Of course, the ecu cut the ignition to prevent the engine to blow off.
The wastegate is internal, so, i imagine it has been calibrated to the turbo level...
I checked the membrane, the hoses, the springs, verifed the opening of the WG valve, everything is ok.

Do you have any idea ? Why this turbo is so angry at me ?
Thx a lot

renardracer

Some photos of my built

deezums

iTrader: (3)

That airbox and reservoir are bad ***.

Lots of us will carve at the IWG port to make it as big and free flowing as possible, otherwise you'll get the creep. You might also make sure the wastegate is dead nuts in alignment with the wastegate flap. My brand new 6258 and turbosmart dual port were terribly out of alignment till I shimmed them a little.

https://www.miataturbo.net/diy-turbo...stegate-69813/

renardracer

Thx for the reponse.

I checked the actuator, and it makes the valve open really freely, without problems.
Do you really think grinding some extra will keep my turbo to overboost ?
some of you have done it with good results ?
I am really surprised that this hx30, who is mount on Big 3L blocs bloc cannot handdle this little 1.8L miata...
The miata force could be so high, that it could Maje Big turbo overboost ? 🙄😄

I could make some good photos next time off my custom builds

deezums

iTrader: (3)

If you think about it a 3L motor is going to be able to eat everything that turbo can toss at it while a little 1.8 probably won't, for long at least.

To slow the turbo down you need to allow the pressure pre-turbine to drop more easily. If the hole that allows this is too small the pressure to spin up the turbine might actually be less than exiting the wastegate port, so it does. Adding more restriction in the exhaust should also help, but that's a super lame fix.

It probably also doesn't help that a miata quits flowing up top, at least as well as it does through the midrange. A larger wastegate port will react quicker to the demands of the engine. A binding flapper causes overboost on a quick hit, but will gently roll up into boost just fine.

renardracer

Ok, anderstood.
i will check this tomorow (it's midnight here in France)
Thx guyz, i will give you news.

renardracer

It wooooorked !!! Thank you so much guys !
The pressure is stable, no more creep

i will post the photos later.

deezums

iTrader: (3)

Glad to hear it!

If you have a template for that airbox I'd love a copy!

renardracer

The hole was about 20mm

I stuck it in the machine ("fraiseuse" in french, don't know the trad)




Then i started grinding...




And i get there...





Then, i worked with a Dremel to make it smooth and good flow





Thx again guys, this forum it wonderfull

renardracer

I made it directly on the car, sorry. But its not complicated. A good grinder, a good Tig welder, and let's go.
As the reservoir and the heatshield, i made it with 1.5mm alloy. Easy to work, easy to weld.

Maybe those photos could help

deezums

iTrader: (3)

I think over here we call that a milling machine, that one kind of looks like it may be what we call a knee mill, like a bridgeport, maybe a tormach. Sure beats using a dremel to move all that metal!

No biggie on the template for the airbox, I figured you just kind of started fabbing. One of these days I'll make something similar!