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05 VVT Miata

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Hi all,

I'm running a 2005 Miata with an MS3Pro PnP. I've run Speeduino and RusEFI as well on different cars. Other than that, I'm fairly new to in-depth tuning. I can get things to the 60%-70% mark, but after that I don't have the knowledge. I even paid to have my current car tuned.

Car isn't any thing crazy. Stock block and head. Racing Beat header, 2000 Intake manifold with VICS active (at 4250 RPM). Suspension stuff. Wheel well intake.

Unfortunately, it didn't turn out great. Somehow the timing belt stretched, and my exhaust cam went way off. My final pull is attached. I've since replaced the belt, and redid the timing. Now, with how things are going with the world, I haven't been able to hit the same dyno. So I did a few virtual dyno pulls to see if there was any improvement. One of them is also attached. I know that VD vs a real dyno is a big change in testing tool. So, numbers don't compare. I'm more looking for that large torque dip that occurs in the dyno, dyno pull.

I'm looking forward to being able to self-tune my car to the 90-100% mark of its potential.

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Welcome Emil,

Looks like a fun build! You should start up a build thread so we can follow the progress as you go along.

You will find some great courses and webinars which will help you be able to go from doing 60-70% of the tuning to 100%.

Look forward to seeing more.

Just an update on how things are going.

I discovered that Mini Cooper superchargers are a good size for the Miata's engine and engine bay. Fortunately for me, a local Pick and Pull junkyard had a flatrate on supercharges. I picked one up for a very good price, in decent condition and set to install it in my Miata. About 7 tries with bracketry and 10 tries with the tensioner later, I got it running pretty well.

I started off with dual TBs, as I had read that if the intake into the supercharger isn't restricted, then the supercharger is "working" 100% of the time, and wears accordingly. Dual TBs was quite a challenge, and even with messing with different pulley diameters, I couldn't get the pedal feel to be the same.

I junked the second TB, and just ran a single TB on the intake manifold. I added in a blow off valve in addition to the bypass valve, so assist in dumping the excess air out the IC piping when the engine didn't need it.

The tubing is a mix and match of 2.5" and 2" piping in an effort to make piping routing easier/safer.

The single TB has very decent throttle response, but I'm seeing some oddities. I think this might be do to the BOV/Bypass setup. The bypass should open at 0 vacuum, but I'm convinced that its not responding correctly. When I floor it, I can sometimes see my boost go from vacuum to atmospheric instantly, flat line for a second, and then switch to boost. I've tested for boost leaks many times, and never found anything. My theoretical boost level based off pulley sizes, should be 6.2-6.8 PSI, but I only see 3.2 at most. I'm thinking my bypass isn't pulling shut, or my BOV is leaking somehow. Fighting with these pneumatic characters is very strange.

I'm tempted to switch to a modern electronic diverter system. I just need one that can flow enough air (basically a 38mm throttle body, or bigger), and respond as it should.

The car makes decent power under a Virtual Dyno situation. It makes about 40HP more peak, and a relatively flat torque curve. I am seeing a strange behavior with boost, where it increases linearly with RPM. I was always told that if anything, I would lose boost with a positive displacement supercharger across RPM because the engine is flowing more. As I'm seeing a .8PSI difference between 1200 and 7000 RPM, I think the engine isn't tuned well, or my piping is a restriction (or, my BOV is shutting harder?).

Next up is a strange "bump" in my car's output. My torque is flat till 4100 RPM, then it shoots up 20lb ft (from 116 to 136) over 800 RPM.

My engine runs VVT and a on/off variable intake volume system (VICS). I don't see any behavior that would lead me to believe that the VICS is causing this bump. It kicks on at 4300 RPM. Is that close enough to cause this bump?

My VVT table has not been touched, since it was dyno tuned N/A. I see peak intake advance (45 deg) from 3000-4000 RPM. Then it tapers down to 29 at 5k, 20 at 6k and 10 at 7k RPM.

Fueling is rich at 12.2 in boost. I can go a tad leaner without knock, but I track this car, and would like to have a margin of safety.

Getting to a dyno is not possible at the time because of COVID restrictions. Is my next best option steady state road tuning for VVT to check for trends? i.e more advance longer throughout the RPM band, or changing the advance "hump"'s position.

Where are you located? Plenty of dyno's are in operation - it's easy to social distance and wear masks around an dyno.