MT.net standard reroute parts list:

Spacer ($93): BEGI Rear Thermostat Spacer 1990-2005

Waterneck ($23.50): Miata Thermostat Housing

OEM Thermostat Gaskets x 2 ($3.62 each): GASKET,THERMOSTAT (B621-15-173) - $3.62 - B62115173

Front Waterneck Block-Off ($20): Trackspeed Engineering

Radiator Hose ($15 -- partsgeek.com link provided but get wherever): 05 2005 Cadillac Escalade Radiator Hose - Cooling System - AC Delco, Dayco, Gates, MacKay, Lower, Upper - PartsGeek (Dayco Radiator Hose -- Upper)

Plus some odds and ends. If your thermostat is old, replace it while you're doing this. Look at the condition of your heater hoses and bottom radiator hoses too. Lots of pictures of the reroute I did in my Silver car build thread. I also removed and plugged all those little, annoying coolant lines that run all over the engine and tossed the 1.6L Air Valve (made an aluminum block-off for that). Bottom line, uber-reliable.

I have an MSM engine with the stock headgasket and did some measurements by fitting an additional water temp sender in the front thermostat housing using the Maruha spacer.

On a local track here with lots of long straights, I never saw more than 2 degrees C delta between the front and the back of the head:

https://www.miataturbo.net/attachmen...ine=1401270187

Obviously ignore this data if you have an older engine.

Cheers

Well, the thread's been bumped anyway, so...

To clarify, the BEGi "Rear Thermostat" reroute does not always look like the right-most image. In their original design (which is the best one, incidentally,) the heater core return goes to the mixing manifold just like it does in the OEM MX5 configuration, the OEM 323 configuration, and the traditional DIY rear-therm reroute.

This business that they recently added of the "Bypass Option" basically adds the worst feature of the "racer" reroute to the street version, causing heater-core water to enter the radiator 100% of the time, even when the thermostat is closed.

So this is what a standard BEGI rear-therm config looks like:

https://www.miataturbo.net/attachmen...1&d=1401289633

This shows that Mazda's engineers did a good balancing job with the NB headgasket.

But the point of a reroute on an NB is to increase radiator efficiency by increasing radiator flow. A rear head reroute will change the balance of water going to the radiator vs. the heater core with the thermostat open. More flow to the radiator increases its heat transfer capability. The downside, in my experience, is that your heater doesn't work as well in the wintertime because you don't get as much flow to the heater core.

Thanks for posting the data. Data = goodness!

Yeah thanks for sharing Tim, that's actually very interesting info indeed

And back in the Pleistocene era I suggested improving the standard reroute by adding an oil t-stat to the outlet of the heater:

https://www.miataturbo.net/attachmen...1&d=1401290804

So when the the coolant is hot the flow through the heater will stop, and all coolant will flow through the radiator for maximum cooling. If you then turn on the heater, the coolant in the heater outlet will cool down, and the t-stat will open, so you will have heat in the cabin, and when overheating the heater can function as an auxiliary radiator.

Shaikh has tested this and found no problems with heat in the cabin. When the engine is hot the temperature of the heater line after the oil t-stat is indeed cool.

Sorry, nobody in SoCal can claim to have positively tested heater effectiveness. LOL.

This is exactly how I have mine for a number of years now. thermostat on the heater core line doesnt let coolent flow out of the heater core until the coolant coming out of it is below I think it was 160F. coolant only flows through the heater core if it is transvering out sufficient heat otherwize the bulk of the coolent flow goes to the more efficient radiatior.

Bob, is this on your mega power track car?

If you have the time I'd be very keen to see some pics of how you have it installed and a link to the thermostat you are using!

Cheers