M2 (NB) head swap

If you decide to do a M2 swap, think about doing a coolant reroute at the same time. The head is off anyway which gives you easy access to the back of the head.

The M2 head swap is a very straightforward swap. You don't need to fabricate anything, just make sure that you have these parts:

M2 head (without valve cover, just use the old valve cover)
M2 intake manifold
M2 fuel rail
M2 fuel supply hoses (the M1 hoses are too short)
M2 Vics solenoid (mounted on the back of the M2 intake manifold)
M1 throttle body
M1 injectors
M1 fuel pressure regulator
head gasket (absolutely necessary)
intake gasket (possible but not advised to use the old one)
exhaust gasket (no problem using the old one)
throttle body gasket
O-ring for the thermostat housing
gasket between the 2 parts of the M2 intake manifold
optional: EGR gaskets (one for the metal tube and one for the EGR valve on the back of the head)
valve cover gasket
O-rings for the injectors
O-rings for the camshafts
timing belt, timing belt idler wheels, O-rings for camshafts etc

I'm not going to give you a full procedure to remove the old head (you should know what your doing and it's not very difficult).

In short, drain the coolant, remove the upper radiator hose, remove intake parts, remove radiator, remove belts and pulleys, remove valve cover, remove plastic bits around the timing belt. Mark timing belt and remove it. Basically, everything you would do to change the timing belt. If you don't know how, take a look at http://www.miata.net/garage/timingbelt.html.

Undo all electrical connections to the head and intake (injectors, throttle body, coils etc). Remove the fuel rail and the fuel supply hoses. Remove the fpr from the M1 fuel rail. You'll need it later. Remove exhaust manifold. Undo the coolant line that goes to the back of the head. I found that if you heat it for a couple of minutes with a hairdryer, that it comes off very easy. I left the intake in place and lifted the M1 head and intake in 1 piece out of the engine bay. Of course do make sure that you remove the 2 bolts holding the intake to its support.

When you are ready to lift the old head off (you might want to tap it loose with a wooden / rubber hammer), go very easy, there's probably a few connections that you forgot to undo (or couldn't get to like the sensors on the back of the head)

When you get the M2 head, I suggest you do a valve job. You might even want to polish it or do a gasket match, but that's up to you of course. When you remove the valves, make sure not to mix up the parts!
Valve lash:
IN: 0.007 - 0.009 in (0.18 - 0.23 mm). I aim for 0.23 mm
EX: 0.011 - 0.013 in (0.28 - 0.33 mm). I aim for 0.30 mm

Since I had no spring compressor, I made my own tool, which worked flawlessly. Put the tool in a vertical press and you can simply push the spring together. If you put a socket under the valves, the angle is just right. When I put them back together afterwards, I had no access to the press so I did it by hand! I made a handle from an old hammer and compressed the springs by hand. It's was a lot harder this way, but it worked too. It took me about 15 mins to get all the valves back in.

Since the bottom bolts of the intake manifold are a pain to get too once in the car, I bolted the intake up to the head before lifting it in the car. I did leave the upper part of the intake manifold off to allow easy access to the fuel rail and the wiring loom for the injectors.

Torque the head down and reinstall the timing belt etc. If you marked the camshaft pulleys on the old head, put them on the M2 head. They're the same and it'll make belt installation a lot more simple.

You can't use the M1 fuel rail as it sits too high. Use the M2 fuel rail and replace the dampener at the end with the M1 1.8 fpr. You'll notice that on the M2 fuel rail, the fpr sits on the other end. You will need to install the fpr upside down or the vacuum nipple will hit the camcover. You can use a 1.6fpr but you have to cut the hard line as it doesn't clear the head.
Reuse the M1 injectors. They are a straight fit. You might want to replace the O-rings on them though. Make sure to put a drop of oil on the O-rings when installing (and don't get any oil in the injector). If you don't, they WILL break. Don't say I didn't warn you!

Use the fuel fuel supply hoses of the M2 fuel rail (they're longer). The fuel supply hose runs under and through the throttle body to the metal line on the frame. The fuel return line (the one to the fpr) goes from to frame, under the intake and up between runner 2 and 3, then towards the fpr. It fits fine and looks very stock that way.

You will need to reuse the solenoid for the fpr of course. On the M1 intake it's mounted on top on the manifold. The M2 intake has not enough room to install it there. Instead I moved it to the side of the intake, a bit under the vics actuator, next to the throttle body. The wiring harness is just long enough to reach it. The vacuum source for this valve comes from the back of the head. I used the nipple that normally goes to the VICS valve on the back of the head. Since I have a turbo, there's obviously no vacuum in the manifold under boost, hence the VICS won't work. It'll have to get it's vacuum signal from the brake booster.

At this point, I have not yet connected the VICS as the solenoid on the back of the head was missing. I didn't install the solenoid and left the actuator at the front of the intake disconnected. This way, VICS is always open (hi-rpm position). If you run a vacuum line directly to the actuator, it'll be permanently closed (lo-rpm position). If you want to be able to switch it at a certain rpm (stock is 5250 rpm), you obviously need the solenoid and have something activating it at the desired rpm (an MSD RPM switch for example). The Link has one output that can be used for this, but I use it for my boost control valve so this wasn't an option for me. Contrary to what some people believe/say these butterflies do not vary the length of the intake runners by redirecting air. in fact what they do is open an additional resonance chamber, much like the external helmholtz resonance chamber found on the intake crossover tubes of the earlier Miatas which is beneficial at low rpm/low velocity intake charge.

I do urge you to hook up the VICS though. The dyno run on the left is with and without vics on a '99 6psi turbo (the upper curve is with vics). The dyno run on the right is with and without vics on a stock '99.

red curve: vics normal operation
green curve: vics kept closed (vacuum applied)
blue: vics kept open (no vacuum applied)

Interesting observations:
The vics kicks in a bit too soon.
Judging from these dyno runs I'd say that it's best to have it kick in a bit later, say at 5600 rpm. Notice how torque (red curve, normal vics operation) suddenly drops when the vics kicks in at 5250. Interestingly, on an NA, there seems to be an adverse effect in having the valves closed all the time (drop-off above 6k), but not so on a turboed car. This means that if you really want to deactivate the vics, then keep the valves in the low-rpm position, meaning CLOSED (vacuum applied).

FWIW, other folks that have used VICS with boost say that it's best to switch the VICS as soon as boost comes on rather than waiting until 5K+.

Don't use the M2 throttle body as the connections are different. Simply bolt the M1 throttle body to the M2 intake. Use a new gasket. Reuse the M1 throttle body. If fits fine. Put the end of the throttle cable (it'll be a bit too long) in the upper hole and it'll fit fine. You'll have to bend the 1st hole a bit to get the cable through. Just bend it back when you're done.

I didn't reuse the EGR. If you want to reuse it, you'll have to modify the metal tube. Neither the M1 nor the M2 tube are a straight fit. I think the M2 can be bent to fit though. I couldn't be bothered with it and decided to remove the EGR. The hole at the back of the manifold can be left open (the one where the metal tube normally goes). Remove the EGR valve from the manifold and leave the bottom hole open (the channel goes to the first hole I mentioned, nothing else). The top hole must be plugged as it comes out in the manifold. I drilled it out a bit, threaded it and put a plug in it. I used the drill bit and tap that was used for the oil return line from the turbo. Like I said, the 2 other holes can be left open. You could of course make an adapter plate of some kind and block both holes, but to me this seemed the easiest, cleanest and fastest method. Without EGR, there's no need for the 2 solenoids on the chassis, next to the metal fuel lines. They can be removed from the car.

There is an unused vacuum nipple on the top back of the manifold. I'm planning on using it for the map sensor as I want to move it closer to the manifold (to get a more stable signal).

There's no reason to use the 99 cam cover since the 99 camshaft retains the cam angle drive. This means that you simply slap the M1 CAS on the 99 head. It is a direct fit. You only need to remove the blockoff plate at the back of the 99 head. There's no need for the 99 sensor on the intake cam sprocket so you don't need the special cam cover.

home