Don't know about the rest of you, but i've tried a couple stock head temp sensors with the megasquirt, and get flaky readings above 340deg. I found this http://www.newark.com/epcos/b57540g0103f00...stor/dp/43J3535
and just ordered 2 of them. Should be a much more accurate thermistor. It will be a lot closer than the VDO head temp gauge for sure. That thing is junk!

Stock head temperature works fine with mega squirt it only used during the warm up cycle. Don't try to use that as a CHT reading it will be way off!

Thats why I want to use the NTC unit, it should be accurate to a couple deg. and super cheap !

I'm not running a head temp sensor for MS on my MS powered car. I've got the GM style coolant sensor in the 3/4 valve cover and it gives a nice stable temp reading that is really pretty reflective of the actual engine temp. Are you hooking the head temp sensor into the coolant sensor location on the harness??

The only way Jake says to do it is a sensor mounted under the spark plug. I'm
planing to use a VDO CHT sensor under the spark plug and use the circuit shown
in Megasquirt manual.

As said before, with MS it is used only for warm up enrichment. I have been using the stock head temp sensor with MS for years with no issues. Just be sure to tweak your sensor values in the MS.

The reason you see strange values at high temps is because MS was not designed to see coolant temps in the 300+ range. It does not make a difference though because the motor is warmed up and enrichment has stopped before you are even hitting that range anyways.

Don't use MS to view your head temps. If you want to know your exact head temps get something like the Dakota digital setup. Even with the VDO you are still guessing.


-James

sorry to hijack but I am gonna attepmt to make some changed to my haltech system in the next few weeks. My car runs very rich below 3000rpm and also doesn't start making power until after 3000 rpm. Cruising speed it below 3000 and the car doesn't seem to like that very well.

I figured I would look at the timing and injectors below 3000 and slowly make some changes til it runs better.


But if you guys have any links to stuff I can read on general tuning it would be much appreciated.

You can use the coolant temp gauge for head temp on megasquirt and it is accurate. You just need to enable the coolant temp setting for high range. The reason the stock sensor does not work is the taper falls off after about 340 or so, not very linear. The VDO setup is about useless, and you would not be able to use the vdo thermal couple type anyway. I would put this setup if calibrated correctly against the dakota digital one any day. And if you use Megatunix as the display, you can even re-name the gauge to head temp.

Actual temp is head temp. Oil temp is just guessing.

The only place to get the real head temperture is under the spark plug, any
other place will take too long for it to show the real temp. If it gets over 400F
under the plug you are taking chance that you will drop a valve set real quick,
while other spots on the head will not show this right away.

I agree with the lag, but the only thing that will fit under the spark plug that i've seen is the thermocouple setup. That won't work on the megasquirt. The VDO one has too many cold joints in it, and does not use the K TC wire to the sensor, just an extension wire. I'm sure the Dakota one is better, but i'm sure it's still a TC, and TC's just are not as accurate as a thermistor. I think the best way would be to pot a thermistor right next to the plug.