Cylinder Head Temps, My Experience + lessons learned Options

[rwilner]

I drove down to Chris Foley's shop to get his shift linkage installed this weekend. At the charlton plaza on I-90, I stopped to fill up. I usually put premium in the 914 but this time put regular in because it's what I put in my other cars and I was on autopilot. Oh well, I thought...let's see how she runs on 87, maybe I'm wasting my $$ on the good stuff.

Before the fillup, I was running between 300 and 325 F in 5th gear around 70-75 mph.

After the fillup, I was running between 380 and 400! (IMG:style_emoticons/default/ohmy.gif)

I spent the rest of the trip in 4th gear at no less than 3500 rpm to try and keep the head temps down. When I got to Chris' shop, we put the car in the air and drained out 5 gallons. I replaced them with 93 octane before getting on the highway for the ride home. My cyl head temps were back down to 310-350 for the return trip.

Here's what I learned:

• A cylinder head temp sensor and gauge are critical to know what's happening in your engine and should be on everyone's short list. Without it I would never have known of the dangerous operating conditions for the engine. The aircraft spruce gauge/probe are short $$ and a quick install.
• The state of tune has a major impact on running temps (duh). I am still tuning my car with the microsquirt and it's clear I have work to do.
• Higher octane gas makes your car run cooler.

As always YMMV but thought I'd share my experience.
Rich

[ChrisFoley]

I'll add a data point to your observations.
Yesterday on the way home from a trade show in Warwick, RI I filled my tank with 87 octane. I was planning to fill with 89 but at the station where I stopped just before entering CT all 3 buttons on the pump were 87 (IMG:style_emoticons/default/screwy.gif)

My head temps weren't significantly hotter but the engine did start rattling at 3500 rpm if I pushed it a bit going up hills.
My air/fuel mixture is a bit on the rich side right now for moderate throttle cruise so I was pretty sure the head temps would remain stable.

[VaccaRabite]

Oh well, I thought...let's see how she runs on 87, maybe I'm wasting my $$ on the good stuff.

Before the fillup, I was running between 300 and 325 F in 5th gear around 70-75 mph.

After the fillup, I was running between 380 and 400! (IMG:style_emoticons/default/ohmy.gif)

What kind of compression are you running, and what engine size?

On 93octane with 9.2:1 compression in my 2056 I'm always in the 370-400 range in 5th, and so am always driving in 4th on the freeway to keep temps down. Works, but not where I want to be. My area has long hills and that is part of the issue, but I still think I can tune it cooler.

Part of the reason I am going to megasquirt is to try and better tune my engine out of the red zone in 5th.

A good head temp gauge is CRITICAL if you are modifying these engines in any way away from stock. Without the gauge, there is no way I can tell from the drivers seat that my engine is getting hot.

Zach

[rwilner]

What kind of compression are you running, and what engine size?

I have a stock GA 2.0L except for european Ps and Cs, so that puts my CR at around 8.5:1 I think.

I think a CHT is essential even for stock engines because as the FI parts age the mixture will change which will have a major impact on running temps. My car was giving me no indication of poor running except for the high CHT.

[r_towle]

Observation
It was warmer on the way down than on the way back.
From charton to foleys is all long ass highway hills.
Your car is not tuned
You never answered me about last weekend.

Rich

[rwilner]

Observation
It was warmer on the way down than on the way back.
From charton to foleys is all long ass highway hills.
Your car is not tuned
You never answered me about last weekend.

Rich

Rich

80-100 degree differentials are due to more than a few degrees difference in ambient temps...plus, I noticed the spike right after the 87 fill up.

I missed your request for last weekend?

Anyway my O2 sensor isn't working and I've given up on the innovate setup. I bought a completely different AEM setup that doesn't require goofy free air calibrations and doesn't require mounting a separate brain under my car. I'm going to put in this weekend if I can find a few hrs to get into the garage again. After that we can tune it up...until I have a working AFR gauge, we're just guessing.

[mrbubblehead]

Observation
It was warmer on the way down than on the way back.
From charton to foleys is all long ass highway hills.
Your car is not tuned
You never answered me about last weekend.

Rich

Rich

80-100 degree differentials are due to more than a few degrees difference in ambient temps...plus, I noticed the spike right after the 87 fill up.

I missed your request for last weekend?

Anyway my O2 sensor isn't working and I've given up on the innovate setup. I bought a completely different AEM setup that doesn't require goofy free air calibrations and doesn't require mounting a separate brain under my car. I'm going to put in this weekend if I can find a few hrs to get into the garage again. After that we can tune it up...until I have a working AFR gauge, we're just guessing.

rich do you have an innovate a/f gauge you are having trouble with? error codes?

[rwilner]

rich do you have an innovate a/f gauge you are having trouble with? error codes?

yep.

No error codes...the LED stays on solid. I just get either full rich or full lean, all the time...like a narrow band. The gauge was showing me I am idling at 9:1 which of course is impossible, especially when I'm fairly certain I'm running lean.

I've tried 3 O2 sensors now, calibrated probably 10 times, updated the firmware, and swung a dead cat over my head at precisely midnight...no joy.

The innovate forums are littered with people having similar problems and the AEM seems more well regarded so I'm going to try it.

[mrbubblehead]

rich do you have an innovate a/f gauge you are having trouble with? error codes?

yep.

No error codes...the LED stays on solid. I just get either full rich or full lean, all the time...like a narrow band. The gauge was showing me I am idling at 9:1 which of course is impossible, especially when I'm fairly certain I'm running lean.

I've tried 3 O2 sensors now, calibrated probably 10 times, updated the firmware, and swung a dead cat over my head at precisely midnight...no joy.

The innovate forums are littered with people having similar problems and the AEM seems more well regarded so I'm going to try it.

i had the same problem, and did the exact same steps as you. but i finally fixed it. it was pretty simple actually if you are interested. or did you already get the aem.....

mine has been flawless since i added a time delay circuit.....mine didnt work for months. until i built the circuit.

[r_towle]

yah but......

I read innovate can send everything to your iphone...which would be cool.

rich

[rwilner]

i had the same problem, and did the exact same steps as you. but i finally fixed it. it was pretty simple actually if you are interested. or did you already get the aem.....

mine has been flawless since i added a time delay circuit.....mine didnt work for months. until i built the circuit.

Yeah...thanks for the offer. I already bought the AEM setup. I prefer it for several reasons:

• It requires no calibration
• There is no separate brain to mount -- all electronics are integral to the gauge
• The indicator lights are integral to the gauge...not a loose LED I have to mount someplace
• it's a small thing, but you can change the illumination color, bezel, and face of the AEM gauge so it matches the VDO gauges
• All reviews and forum posts seem to indicate it's more robust

Plus, the innovate setup is supposed to be an engineered, plug and play setup. I have a hard time building a circuit to compensate for a poor design...unless of course, that poor design is my own (IMG:style_emoticons/default/wink.gif)

Thanks though and glad you got your setup to work.

[mrbubblehead]

i had the same problem, and did the exact same steps as you. but i finally fixed it. it was pretty simple actually if you are interested. or did you already get the aem.....

mine has been flawless since i added a time delay circuit.....mine didnt work for months. until i built the circuit.

Yeah...thanks for the offer. I already bought the AEM setup. I prefer it for several reasons:

• It requires no calibration
• There is no separate brain to mount -- all electronics are integral to the gauge
• The indicator lights are integral to the gauge...not a loose LED I have to mount someplace
• it's a small thing, but you can change the illumination color, bezel, and face of the AEM gauge so it matches the VDO gauges
• All reviews and forum posts seem to indicate it's more robust

Plus, the innovate setup is supposed to be an engineered, plug and play setup. I have a hard time building a circuit to compensate for a poor design...unless of course, that poor design is my own (IMG:style_emoticons/default/wink.gif)

Thanks though and glad you got your setup to work.

no prob, i had to get mine to work, i was damned if i was gonna buy another set up. good luck and post up your experiances with it.

[rwilner]

no prob, i had to get mine to work, i was damned if i was gonna buy another set up. good luck and post up your experiances with it.

maybe post up your time delay circuit so others that have problems with innovate can try your fix?

Also...I may just put a switch in line between the system ground connection and the ground post, which i'll throw after the car has been running for a bit...a manual "time delay"....maybe this will enable me to tune while I get the AEM sorted out.

[michael7810]

Rich- I've been wanting to add a CHT gauge for the same reason. Your story convinces me it's time to move. Which CHT gauge from Spruce are you using? I've looked at several on the website but didn't know which one to buy. Thanks,
Michael

I drove down to Chris Foley's shop to get his shift linkage installed this weekend. At the charlton plaza on I-90, I stopped to fill up. I usually put premium in the 914 but this time put regular in because it's what I put in my other cars and I was on autopilot. Oh well, I thought...let's see how she runs on 87, maybe I'm wasting my $$ on the good stuff.

Before the fillup, I was running between 300 and 325 F in 5th gear around 70-75 mph.

After the fillup, I was running between 380 and 400! (IMG:style_emoticons/default/ohmy.gif)

I spent the rest of the trip in 4th gear at no less than 3500 rpm to try and keep the head temps down. When I got to Chris' shop, we put the car in the air and drained out 5 gallons. I replaced them with 93 octane before getting on the highway for the ride home. My cyl head temps were back down to 310-350 for the return trip.

Here's what I learned:

• A cylinder head temp sensor and gauge are critical to know what's happening in your engine and should be on everyone's short list. Without it I would never have known of the dangerous operating conditions for the engine. The aircraft spruce gauge/probe are short $$ and a quick install.
• The state of tune has a major impact on running temps (duh). I am still tuning my car with the microsquirt and it's clear I have work to do.
• Higher octane gas makes your car run cooler.

As always YMMV but thought I'd share my experience.
Rich

[rwilner]

Rich- I've been wanting to add a CHT gauge for the same reason. Your story convinces me it's time to move. Which CHT gauge from Spruce are you using? I've looked at several on the website but didn't know which one to buy. Thanks,
Michael

Michael
Here's the gauge I bought -- the 2" one. You'll also want the 14mm probe and the 15 foot extension lead.

You may be able to make the 7 foot one work, I cut probably half of the 15 foot lead off...but better to have too much than too little after you go through the effort of routing the wire.

Prices have gone up a bit, looks like the complete setup is around $120...still a bargain in my book though.

[rwilner]

Also, if you have a few more bucks and want to go first class, Chris sells a scanning digital CHT instrument which monitors all 4 cylinders with 4 probes.

[rwilner]

yah but......

I read innovate can send everything to your iphone...which would be cool.

rich

You need a special module to make that happen, which is $$ and my guess is doesn't work very well.

[ww914]

Hey Rich

Your post is very timely with me putting the engine back in my car. A couple of questions: The A/C Spruce website shows a spark plug probe and a 14mm probe. Does the 14mm probe go where the existng probe is in the head or do you buy the spark plug one. The third one looks like an egt probe.

(Edit) I think, after doing a little more research, I answered my own question. The 14mm dimension is the size of the spark plug, right. Also, do you think it would be worth it to buy the dual guage to read both head temperatures? Not sure we need egt info like you would on a Lycoming engine, right? That might be going a little too far. I do notice that Chris sells these things. Probably wouldn't hurt on a race car though.

Thanks, Warren

[r_towle]

yah but......

I read innovate can send everything to your iphone...which would be cool.

rich

You need a special module to make that happen, which is $$ and my guess is doesn't work very well.

Still be cool.

I looked around...I think I can run a car off an Ipad...with no gauges now.

Rich

[rwilner]

Hey Rich

Your post is very timely with me putting the engine back in my car. A couple of questions: The A/C Spruce website shows a spark plug probe and a 14mm probe. Does the 14mm probe go where the existng probe is in the head or do you buy the spark plug one. The third one looks like an egt probe.

(Edit) I think, after doing a little more research, I answered my own question. The 14mm dimension is the size of the spark plug, right. Also, do you think it would be worth it to buy the dual guage to read both head temperatures? Not sure we need egt info like you would on a Lycoming engine, right? That might be going a little too far. I do notice that Chris sells these things. Probably wouldn't hurt on a race car though.

Thanks, Warren

Warren,
Read Jake Raby's discussion of cyl head temps on this site. My summary and opinions below:

"Cyl Head Temp" is a bit of a misnomer because the temperature of the head varies greatly with location. The best place to measure head temperature is under the spark plug, which, as you point out, is why the 14mm ring terminal (0r 12mm if you've had them welded and tapped) is the probe of choice. So, to properly measure the cylinder heads, you'd need 4 channels of measurement (assuming you're running a 4 cyl)...although #2 is hotter than #4, so if you went for 2 channels, those would be the 2 I'd chose.

The hottest location across both cylinder heads is under the #3 spark plug, so if you're only going to run one channel (like me), this is the place to put the probe. The location of the #3 cylinder combined with the stock cooling arrangement dictates this (Foley's and Raby's horizontal cooling systems are designed to correct this deficiency and deliver much more even cooling across all cylinders).

Measuring individual "spark plug" CHTs and measuring EGT at all is probably only necessary if you're racing your car -- running it up by the redline for extended periods. A race engine may have the ability to more easily adjust the tune of each individual cylinder.

Again, the above is just my opinion based on my limited experience on the street and what I've read. Chris, Jake and others may chime in with professional opinions.