99 Head Build
 

I have a 99 miata with an FMII kit on it, nothing else special.
I'm building a motor now with Wisco 8.5 pistons and Manley rods.
My head needs a valve job and I'm debating on upgrading it some. I doubt I'll ever turn the boost up over 15psi, but maybe one day I'll get froggy. It is my first turbo car.
I'm keeping the stock cams and I'm debating on buying the +1mm supertech valves and springs. I haven't been able to find a before and after review for the +1mm valves. Is there a substantial gain in power?
I'm starting to think all I might need is better valve springs.

I'm not worried about the extra machine work to fit the valves.

Just do it.

The upgraded valves will handle the heat better, do inconel exhaust valves and do bronze valve guides to help pull the heat out of the valve. If your gonna replace valves do +1,

I also went +1 and got the small springs (from 949, thanks Emilio) to compliment the single ST spring set I had with my BP4W motor. Wondering if I should have shot for the heavy spring kit but too late now. I'm lazy.

OP, what usage? Track or street?

Which FMII kit are you running? Which computer? What injectors are you running?

My opinion is that you're probably fine with an ordinary head refresh with upgraded valve springs at most. Your main worries are going to be poor cylinder sealing and valve float, not flow. Before you start going for oversize valves and the supporting headwork ($$$$), you should definitely consider turning up the boost higher than 15 psi. See how you like that before you start pouring money into the head.

It's sillly to talk about power gains from getting a few grand in head work but saying you aren't interested in the power gains from adjusting your boost controller. Flow is flow. There isn't some magic durability or safety gains that come from making a certain amount of flow at a lower amount of boost. The amount of fuel is the same and the strain on the drivetrain is the same. That being said, don't go above 18 psi on a Link based FMII or you're going to have a bad time.

If he's spending the money on a valve job and refreshing the head anyway, the initial investment isn't that much more than some additional cost in components (certainly not thousands).

Why not future proof it if he's already building the bottom end. I'd shit my pants if I turned the boost up to 15psi and realized later down the road I have the novel opportunity to rip apart an already rebuilt head all because I was too lazy to do it this first time around and now I'm addicted to more.

Then again....

It'll be street. I might hit the track once a year, but probably once every other year.

I bought the kit a few months ago. Hydra computer and 1000cc injector dynamics. My original plan was to drive it around for a year on 9~10psi with the stock motor so I could decide if I wanted to build the hell out of my spare motor. I only had the turbo installed for 2 weeks and had the boost as low as possible before it came apart on me. The car didn't give me a lot of time to decide on a build.

So what happens at 18psi?

Thanks for yalls input. I'm going to keep reading the forum, sleep on it, and order parts in the morning.

Ok, so you've got the good computer and you've got big injectors. In theory, you should be good in the 20+ psi range. Your main limitations are going to be tuning ability, drivetrain durability and the flow characteristics of your compressor and turbine. What size turbo are you running?

At higher boost levels, you're going to be fighting against the left side of the compressor map, so it's entirely possible you won't make your target boost until 4k rpm or later. Otherwise it's mainly just a bigger kick in the pants.

After I turned up the boost I ran into limitations in my turbo. The compressor was inefficient and the turbine was a bit small which was killing power up top, so I went with a newer and larger design. Everyone here has different computers and turbos and a different story I'm sure. The point is that you need to get the untapped power from your current setup first then address the limitations as you find them.

On a Link past 18 psi, the MAP sensor that comes with the kit doesn't really work anymore.

Honestly, for a street machine (street RPM's), I'd keep the head OEM.

I'm running the GT2560R turbo.
I opted for the +1mm supertech valves, inconel exhaust. Machine shop said they wouldn't charge more for the +1mm, so that made up my mind.
Fab9 suggested the 63lb valve springs because they create less wear than the stronger springs.

My wallet is a little lighter.