mxeven

I need some advice on head temperature sensors. I am pretty much finished with my engine rebuild/modification and EFI conversion but I have some issues with cold start enrichment. I took the "easy" way by using the oil temperature sensor for cold start compensation but I am not satisfied with the result. The enrichment works fine when starting a cold engine but when I start it after letting it cool down for a while it does not run smooth. I guess the heads cool down faster than the oil and the enrichment compensates for oil temp=engine runs lean.

So, I guess a head temp sensor would work better. Which sensor are you guys using? Is the sensor for the NA engines suitable? Do I need machine the head to fit the sensor?

Thanks
/Mattias

Geoffrey

You need to machine head number 3 for a cylinder head temp sensor. I'd recommend the 3.2 Carrera version, although the 964/993 would also work. All of them are 2500 ohms at 20c, just like a standard Bosch air temp or engine temp sensor, so the calibration should be fine provided your ECU supports a Bosch temp sensor or has provisions for a custom calibration.

mxeven

Thanks Geoffrey! I will get a 3.2 carrera sensor. I can custom calibrate my sensors in my ECU so that should work fine then.

DonE

What is involved in the machining of the cylinder head?

DonE

Geoffrey??

Geoffrey

Sorry, been at the track the past 4 days. Cylinder head number 3 needs to be drilled and tapped for the 3.2 Carrera cylinder head temp sensor. The engine tin needs to be modified so the cylinder head temp wiring goes through it. Simple. Obviously you do need a fixture to machine it the same as the 3.2 Carrera head was done, so it it probably best left to someone like Ollies machine shop.

DonE

Is cyl head temp a better way to measure engine temp than measuring oil temp? I imagine the real benefit would be for warm up (EFI). Oil temp works pretty well for everything else.

My heads are at JB so machining a fixture would be easy to order.

Geoffrey

Although not ideal, I prefer cylinder head temperature to measure engine temperature over oil temperature.

DonE

Head is being machined Monday. After being involved with EFI conversions for the past 2 years, I am surprised at how many tuners have stated they prefer CHT over oil temp when operating the aftermarket EFI. This is the first I have heard this much support for CHT over oil temp.

m42racer

I think all the systems I have had in the past all used the Oil as the Temp. I think the issue is how long the Oil takes to heat up. I think it is only a factor with the engine start, warm up and accel features if a cold accel feature is available. I see no reason why the fuel settings could not be altered to take into account the slow Oil warm up. Surely the higher and quicker Head temperature increase will have to be taken into account also. I think it will all come down to how much control the EFI system you are using has in the cold and warm up functions.

Don, I know the system you are using, and it has many warm up features and works really well withb the Oil used as the Engine Temperature. Have both and test one against the other. Best of both worlds, can't beat that.

Bruce M.

Cold start is a matter of trial and error, and educated guessing, with oil temp. With a CHTS, it is much more precise. Otherwise, oil temp works just as well.

Were I to do my engine again, I would defintiely add a CHTS.

mxeven

I agree oil temp works fine for cold start and warm up but the problem I have noticed is when the engine is left to cool down for just a while it runs lean after start up. My guess is that the oil temp is still pretty high which makes the ECU compensate for a warm engine but the heads have cooled down more hence the volumetric efficiency is higher. I will certainly add a cylinder head temp sensor to see if the problem is cured.

DonE, I would love to see a picture of your cylinder head after machining.

DonE

The cost of machining the head was small, so nothing ventured.... The warm up using the oil temp worked fine too, so I'm interested to see how the work side by side.

DonE

Here ya go. While they were there, JB Racing also welded the exhaust smog ports closed. No more plugs falling out while sitting at a light.