Fuel Injected CHT under #3, Question about FI and CHT Options

[nditiz1]

So I know that FI cars use the CHT from the factory to make the magic happen (IMG:style_emoticons/default/biggrin.gif) (you D/L-jet guys and your mysterious voodoo) , but do you guys also put an additional one under #3 for cockpit info purposes? Does the factory one shutdown the motor if temps get too high? (Now that would be cool)

[BeatNavy]

So I know that FI cars use the CHT from the factory to make the magic happen (IMG:style_emoticons/default/biggrin.gif) (you D/L-jet guys and your mysterious voodoo) , but do you guys also put an additional one under #3 for cockpit info purposes? Does the factory one shutdown the motor if temps get too high? (Now that would be cool)

Yes, if you want head temp info it is typical to use a sender (e.g., thermocouple) under #3 sparkplug. The CHT is actually located next to cylinder 3, and all it does is send info to the ECU for balancing mixture based on engine temps. It won't shut the engine down (as a safety), but it will shut down the engine if it fails in open mode (e.g., disconnected). The ECU will make the mixture way too rich at that point and essentially flood it.

[tmc914]

So I know that FI cars use the CHT from the factory to make the magic happen (IMG:style_emoticons/default/biggrin.gif) (you D/L-jet guys and your mysterious voodoo) , but do you guys also put an additional one under #3 for cockpit info purposes? Does the factory one shutdown the motor if temps get too high? (Now that would be cool)

Yes, if you want head temp info it is typical to use a sender (e.g., thermocouple) under #3 sparkplug. The CHT is actually located next to cylinder 3, and all it does is send info to the ECU for balancing mixture based on engine temps. It won't shut the engine down (as a safety), but it will shut down the engine if it fails in open mode (e.g., disconnected). The ECU will make the mixture way too rich at that point and essentially flood it.

So, where could I get one of these under the spark plug CHT sensors? Need a gauge to go with it also. Kinda like digital gauge that would have analog graphic too. Ones I looked at from another thread were for all 4 cylinders and seemed like overkill. Anyone recommend a simple CHT sensor and gauge? Maybe a combo so oil pressure could also be checked.

[BeatNavy]

More than a few of us are using this: http://www.dakotadigital.com/index.cfm/pag...prod/prd347.htm

Doesn't meet all your requirements (no analog graphic), but there are others on the market that may do that. I'm sure others can chime in about that or combo gauges. This one definitely works for head temps, though.

[jcd914]

Aircraft supply places like Aircraft Spruce (http://www.aircraftspruce.com) carry CHT gauges and sensors.

Stock 914 spark plugs are 14mm thread size.

Jim

[Tbrown4x4]

Knowing all 4 head temps can be a valuable tuning aid. EGT probably better, but harder to get.

[michael7810]

This is what I use from Aircraft Spruce with pickups under 1&3 spark plugs.

[malcolm2]

I like the extra feedback the gauges give. VW just gave you a few lights, speedo and fuel. So I added a VDO brand CHT plus others.

I understand VDO does not make theirs anymore. Folks told me that they just weren't very accurate. I can at least get a sense of the direction of my head temp with the VDO gauge.

BTW, the sensor on most set ups is a ring that goes under the spark plug. It was recommended to me to cut off the factory spark plug washer when using the ring thermo-couple.

[Mblizzard]

So I know that FI cars use the CHT from the factory to make the magic happen (IMG:style_emoticons/default/biggrin.gif) (you D/L-jet guys and your mysterious voodoo) , but do you guys also put an additional one under #3 for cockpit info purposes? Does the factory one shutdown the motor if temps get too high? (Now that would be cool)

Yes, if you want head temp info it is typical to use a sender (e.g., thermocouple) under #3 sparkplug. The CHT is actually located next to cylinder 3, and all it does is send info to the ECU for balancing mixture based on engine temps. It won't shut the engine down (as a safety), but it will shut down the engine if it fails in open mode (e.g., disconnected). The ECU will make the mixture way too rich at that point and essentially flood it.

As Rob said the factory ECU can not shut down the engine due to temperature. However, if you go to an aftermarket ECU you could program that in. But I would not think that would be safe unless it was for only track use. With Micro Squirt you can limit fuel based on temp. I have not looked into it but I would think that it would be possible to program the use of a different fuel/spark table that is used based Adding more fuel and reducing advance can quickly reduce temp and would be essentially a limp home mode that would not leave you stranded.

[nditiz1]

I actually have the Aircraft Spruce single (m1000) I think. Anyway I was looking about converting to the Dakota Digital since I'm never sure where exactly the analog is sitting at 375, 385, 395?? BTW these numbers are only hitting that up tall hills. I'm cruising <350 on the flats all day long (IMG:style_emoticons/default/driving.gif)
My question originated from thinking about running FI and not knowing if you are ruining your heads.

[Mblizzard]

Very good info to follow http://www.914world.com/specs/JakeRabyHeadTemps.php

by Jake Raby

The following temps are based on the readings I have seen both on my dyno, in my test car as well as every car I own as I do 92 miles round trip daily, all aircooled. I have been able to see the effects of different temps on engines, MPG and come up with basic rules. These readings and parameters are ONLY accurate when your sender is the same place as mine, under the spark plug.

Less than 300F
Your engine is well configured, properly tuned and you probably are not driving it hard enough

300-340F
This is what I consider average for the Performance TIV engine that is well tuned and properly configured. With these temps, you'll be getting the best MPG and efficiency from the engine, it will live a long powerful life and you can do valve adjustments at the normal 6K mile interval, since heat isn't sinking your seats and stretching your valves.

350-375F
These temps are standard for a STOCK engine with a stock cam at cruise speed, if it is properly tuned. Generally, if you are cruising at these speeds, as soon as you hit a hill you'll see a spike to a higher level, approaching 400F. If you experience temps of 375 in 5th gear, you may be doing the engine an injustice by keeping the tranny in 5th, hitting a hill with a shift to 4th will keep load off the engine and that reduces engine heat and increases cooling fan speed- 4th gear is a friend to stock engines.

If you see temps in the 375 neighborhood constantly you'll be having to reduce the intervals between valve adjustments to maybe 3K miles due to the extreme heat cycling the engine and valve train parts are seeing. Engines that cruise at 375 are generally out of tune or may be misconfigured creating more heat.

375-400F
No engine should "cruise" at these temps, not for any reason. Cruising at these temps is a guarantee that under load up hills that you'll be over 400F and thats not acceptable.

400-420F
At these temps the rules change, 400 is the magic number that stretches valve train parts and really where cracking issues begin. 400F is OK for a few seconds if climbing to the top of a hill, but don't allow the engine to stay there long. In a perfect world as the needle starts to climb toward 400 the smart driver will grab a lower gear and remove load to cool the engine some, the extra blast from the fan also helps.

420F+
Well your engine has been damaged. Go home, do a valve adjustment and see how many valves have "tightened up" from your baking experience. Those valves are the ones that have seen the most damage, so make a note of it and upon teardown (that probably isn't far away) see how those chambers and exhaust ports look as cracks will more than likely be notable with the naked eye.

The other big issue is with guys that get their engine really hot and then immediately pull over and leave the engine running! THIS CRACKS HEADS!!!!!!!!
If you get the heads over 400F sustained, the best bet is to slow down and use the tranny to moderate the cool down period. If you do stop on the side of the road, shut the engine off and allow it to go through it's heat cycle naturally. This will keep the heads from cracking in most cases. The dumb guys pull over leave the engine running and watch the needle drop down to 250F and drive again, those guys cool the engine to quickly and crack heads.

[DRPHIL914]

wow that is great information - I am in process of installing this Dakota one this week -

[Mblizzard]

wow that is great information - I am in process of installing this Dakota one this week -

Love my Dakota! it has helped a lot on keeping me from toasting more heads!

[VaccaRabite]

I have a Dakota and a 4 way from Aircraft Spruce (it measures all heads CHT). I keep meaning to put in the 4 way, but have not yet. Maybe some day.

Zach