Miata Turbo Forum - Boost cars, acquire cats. - DIY Turbo Discussion

Tuning Issues

HY7 — Fri, 22 May 2026 22:09:37 GMT

Hi all,
I have a turbo NB Miata. It's a ton of fun but I think I'm in over my head trying to iron out some of the remaining wrinkles.

My target is ~8 PSI boost. I am happy to spend more time/money to prioritize reliability.
I have hardly any experience with TunerStudio but I am comfortable with math.
I swapped out the ECU, confirmed ignition timing, got a shop to install the turbo + exhaust, and then got the car tuned by a tuner. It generally runs well but for some reason is now rich overall.

I would appreciate any advice you might have.

Here's the build:
Vehicle: 2004 NB (~85k kms), 1.8L
ECU: MS3 Pro PnP
Injectors: Flow Force 640cc Injectors
Turbo: Flyin' Miata custom spec turbo system for NB chassis (GT2560R turbocharger) - also with coolant reroute
Blow-off/Bypass Valve: Recirculated bypass valve
Downpipe: FM 3" downpipe, NB chassis
Catalytic Converter: FM 3" catalytic converter for 3" downpipe, NB chassis
Muffler: MagnaFlow 4 X 9in. Oval Straight-Through Performance Exhaust Muffler 11229
Clutch: Supermiata Sport Clutch 94-05 Miata 1.8
Gas: 94 octane (located in Canada)

Electronic Boost Controller: none
Fuel Pressure Regulator: stock
Fuel Pump: stock

Here are some specific problems:
1. Rich Idle
It idles somewhat rich. If I lean out the idle squares on the VE table, I find that the idle tends to oscillate.
I went over the data for my injectors and I'm not sure if I should be changing the injector size (in Engine and Sequential settings) from 640cc to 752cc based on this:
https://goflowforce.com/pages/instru...3LoniVCA9qQxhM
I tried changing it and the car wouldn't start. I'm guessing I'd need a full re-tune.

2. Occasional Stalls
These typically occur on inclines or if there's any load on the electrical system (e.g. A/C). Do I just need to adjust the PWM Idle Voltage compensation? Is there an objective way to do this?

3. Foul Smelling Exhaust
Despite using the FM catalytic converter, the exhaust is quite foul smelling. I am guessing that this is related to the rich idle resulting in unburden hydrocarbon products, but not sure. Would this still be expected even if the tune was improved?

4. Runs Learner over Time
The longer the drive is, the more the car runs lean. Is this due to heat soak? Is there anything beyond what's in the the Flyin' Miata kit that I should be doing in the engine bay?

5. Do I need to install/upgrade other equipment to help address the above problems?
The tuner recommended an aftermarket fuel pressure regulator, but based on what I've read on this forum it seems like that is not necessary when pairing these fuel injectors with the Megasquirt 3. Is that necessary?
I also looked at upgrading the fuel pump. It's stock but also >20 years old. If replacing it makes sense, with my goals it seems like a Deatschwerks DW200 would be reasonable.
I also already have an electronic boost controller that I plan to install.

I attached a log with a drive. I wasn't able to go into boost much, but I think the main issues are outside boost anyways.
I've included some pictures of the engine bay and undercarriage in case I missed anything that could be important.

Thanks for any suggestions!

Attached Files

2026-05-22_06.57.16.mlg (3.47 MB)

1.8L vvti turbo Build

turtlekingmaster — Thu, 21 May 2026 05:14:33 GMT

I am looking to build a 1.8L vvt that i tore out of an NB for my 1992 miata. I was hoping to build it to about 200-250 whp with a turbo. The goal for it is to be more reliable that the old neglected 1.6L that's already in it, but also have some fun and more power.
I will be building as the age of the 1.6 grows older and use that time to reenforce the structure of the car, IE roll cage and safety mods.
I'm new to the modifications of this car and have only done a lot of maintenance on the car such as a manual swap and redoing the timing (about 5 times fml). I have never worked on a turbo before and was also hoping to get into with this.
I've heard that the bottom end can hold my power goal but I'm not sure if that's true.
I am going to redo the rod bearings and seals to refresh the old 1.8 but should I replace the pistons and rods? If no how can i gauge the health of the cylinder walls. Are piston rings worth redoing while I'm in there?
I'm going to be compiling a parts list hopefully too. Please let me know if I'm being dumb.
I appreciate the feedback!

kraken down pipe on sr20 t25 - doesnt fit - common?

shirtz — Thu, 23 Apr 2026 01:33:52 GMT

hi guys im finally starting to put the puzzle peices together for my turbo install. got a Kraken kit a while ago and plan on running an old silvia journal bearing t25 - 5 bolt. when putting the studs in there is no configuation where the hole in the picture lines up with the stud. is this a common thing?

would you try to find a thinner stud or drill out the hole? seems there is a little meat there but im warey of taking too much meat out of the DP. be keen to know if this is a standard thing i need to deal with.

'91 Miata won't start after MS3pro install without afm connected

Acarpous — Fri, 17 Apr 2026 09:20:51 GMT

On a 1991, the engine is bone stock. To recap what I did, I followed the instructions very deliberately, I removed the ST Sign fuse before even installing the ECU. I wired up the AFR gauge and IAT sensor. I have the vtps sensor but am holding on the install until I get a bracket for it. When I try to start the car it won't start. I reinstall the AFM and it starts. The fuel pump won't run unless the AFM door is open or there's a jumper in the DIAG box. I can't engage the fuel pump on Tunerstudio, it says it's on but I don't hear or feel anything. I know I can just put a jumper in and call it a day but I would prefer to wire the pump to the ECU correctly, I just don't know why the ECU can't run the pump.