Cylinder Head Temperatures, Calling on the Brain Trust and they Win! Options

[Mblizzard]

OK so I have reviewed the information by Jake regarding cylinder head temperatures http://www.914world.com/specs/JakeRabyHeadTemps.php.

A bit of background.
Engine 2056 based on 74 2.0 engine # GA 014782, stock cam, stock FI, fuel pressure at 31 psi, recently added big valve heads, external oil cooler, valves adjusted correctly with engine install, 150+ compression on all cylinders, stock Trans, Evo Muffler, all stock cooling items in place (flaps and tins), running 123 electronic distributor set to the curve for the 0 231 174 011 dizzy which is correct for the 74.

Timing seems to be correct using the marks as indicated in the photo below. Likely at about 25 BTDC.



At cruise I see temps in the 350-375F range with it being pushed to the higher end and above. On hill climbs it will go quickly to the 400F range and run at that for the duration of the climb. Most I have seen is about 405F. Letting off the throttle quickly brings the temp back down so I have to think the cooling system is working.

I would expect a 2056 to run some warmer but not to be consistently in the upper end of the range I am not sure what is causing this. I have seen lower temps on cruise by richening up the mixture. But overall based on the guidance it seems to be running too hot.

I have suspicion my AF meter is reading too rich so that might be part of it showing an acceptable AF range but could be going lean under load. Changing out the sensor and will recheck.


So given all of that what do I check or where do I start changing things to bring the temps down? Taking a few degrees out of the timing helped but not significantly.

Anyone? (IMG:style_emoticons/default/headbang.gif)

[BeatNavy]

How about:

Engine tin in place correctly and holes generally plugged?
Engine bay seals in place?
Do you have the heating components/air guides in place?

I notice that my head temps, or the readings, seem to go up significantly when I have the heater on. No good idea why. I ended up capping the J-Tubes in the engine bay to try to keep heat from the exchangers from bleeding into the engine bay.

Only other suggestion is to really inspect your cooling flaps to make sure they are in fact moving all the way. I think sometimes that spring will be "sticky..."

[ChrisFoley]

Try again with the timing advanced 2-3 degrees further.

[Mblizzard]

Try again with the timing advanced 2-3 degrees further.

Chris because this has me stumped I have to ask to make sure that I am not thinking about it incorrectly. I was operating under the assumption that advancing the timing beyond the 27 would add heat?

[era vulgaris]

What is your AFR?
What is your cruising rpm?

With my 2270 I cruise in the mid 12's AFR. My head temps are in the 315-325 range for cruising in 4th gear between 3k and 4k rpm. Lower gears will see even less temp as there's less load on the engine from wind resistance.

Beatnavy, my head temp gauge also reads a few degrees higher with the heat or the headlights on. The temps aren't actually higher though- it's an electrical anomaly with the digital head temp gauge not liking the voltage drop that such a large electrical load causes on our 40+ year old electrical systems. I reduced the amount of error significantly by cleaning every electrical contact I could find.

[Mblizzard]

What is your AFR?
What is your cruising rpm?

With my 2270 I cruise in the mid 12's AFR. My head temps are in the 315-325 range for cruising in 4th gear between 3k and 4k rpm. Lower gears will see even less temp as there's less load on the engine from wind resistance.

Beatnavy, my head temp gauge also reads a few degrees higher with the heat or the headlights on. The temps aren't actually higher though- it's an electrical anomaly with the digital head temp gauge not liking the voltage drop that such a large electrical load causes on our 40+ year old electrical systems. I reduced the amount of error significantly by cleaning every electrical contact I could find.

The AF readings are suspect but in the high 12's sometimes going to 13.

Typically running at highway speeds 70+ MPH at about 3K to 3.5K.

Slower speeds drops into 350F range.

[era vulgaris]

On the interstate it is going to be higher due to the increased wind resistance, and even higher still if you've got the top off (even more wind resistance). I'm around 335-345 on the interstate in 5th gear on a flat grade. Taking the top off will increase that by 5-10 degrees on the interstate, about 5 degrees in 4th gear speeds, and negligible if any difference at all in lower gears.

What AFR gauge are you running?
If it's working at all, then you probably don't need to replace the sensor. It probably just needs to be re-calibrated. With mine (Innovate MTX-L) you unscrew the sensor from the bung in the exhaust and leave it in open air, turn the ignition to 'on' for like 30 seconds IIRC and it recalibrates itself. If you have the manual for it it'll tell you what to do.

[Rand]

Try again with the timing advanced 2-3 degrees further.

Chris because this has me stumped I have to ask to make sure that I am not thinking about it incorrectly. I was operating under the assumption that advancing the timing beyond the 27 would add heat?

In my experience, advanced timing raises head temp. Retarded timing raises oil temp. Stock gauge measures oil temp.

[Mblizzard]

On the interstate it is going to be higher due to the increased wind resistance, and even higher still if you've got the top off (even more wind resistance). I'm around 335-345 on the interstate in 5th gear on a flat grade. Taking the top off will increase that by 5-10 degrees on the interstate, about 5 degrees in 4th gear speeds, and negligible if any difference at all in lower gears.

What AFR gauge are you running?
If it's working at all, then you probably don't need to replace the sensor. It probably just needs to be re-calibrated. With mine (Innovate MTX-L) you unscrew the sensor from the bung in the exhaust and leave it in open air, turn the ignition to 'on' for like 30 seconds IIRC and it recalibrates itself. If you have the manual for it it'll tell you what to do.

AEM gauge. No calibration. The instructions state high temp and rich conditions could degrade performance and response. I had both of those so it is something to check.

I am usually topless! TMI I know.

[ChrisFoley]

Try again with the timing advanced 2-3 degrees further.

Chris because this has me stumped I have to ask to make sure that I am not thinking about it incorrectly. I was operating under the assumption that advancing the timing beyond the 27 would add heat?

Don't assume. Verify. Your engine combo isn't the same as stock for one thing. You really don't know where the sweet spot is for combustion efficiency.

Also, is your MPS full load stop screw adjustable? If it is, try backing it out half a turn and see if that makes any difference.

[914_teener]

Compression ratio info? What is it?

Did I miss something here?

[Mblizzard]

Compression ratio info? What is it?

Did I miss something here?

Nothing high. Standard flat top Pistons from AA.

[Mblizzard]

Try again with the timing advanced 2-3 degrees further.

Chris because this has me stumped I have to ask to make sure that I am not thinking about it incorrectly. I was operating under the assumption that advancing the timing beyond the 27 would add heat?

Don't assume. Verify. Your engine combo isn't the same as stock for one thing. You really don't know where the sweet spot is for combustion efficiency.

Also, is your MPS full load stop screw adjustable? If it is, try backing it out half a turn and see if that makes any difference.

You are so right! I will verify.

MPS is adjustable thanks to your kit. Will back out the full stop a bit after answering the timing question.

[Mblizzard]

Update: Well a couple of discoveries. First CHECK FOR VACUUM LEAKS! Looks, like I had a leak on the runner seal going into the plenum. Guess which cylinder? Yep number 3. Have to think it was causing that cylinder to run lean.

O2 sensor was reading way rich. Replaced with nice Bosch unit. Seems to be much more in line with the way you would expect it to read. Got a little more fuel going in now.

And took Chris's advice and bumped the timing back up.

Drove the same circuit and temps were some 20 F cooler. Still pushed 389 on hill climbs but cruised at about 360 to 380.

May still have a few adjustments to make but much closer to expectations.

[HAM Inc]

The thing about temps that has to be kept in mind is that T4 heads (and most aircooled engines) are for more susceptible to damage from high EGT's than CHT's.

And tuning parameters that cool the chamber in the spark plug area (the proper place to read CHT's) often have an inverse impact to EGT's.

A slightly fat mixture with slightly retarded timing will generally yield lower CHT's but may very well yield higher EGT's. Here's why:

When retarding timing from the optimum setting (whatever that may be for the combo on hand) there is less time (chrono time, and crank degree time) for the mixture to burn in the chamber, so some of it will react in the exhaust port, or near the exhaust valve.

Fattening the mixture will, as a general rule, require more time to burn (more fuel, more chrono time. More chrono time requires more crank degree time for a given rpm).

Up to a certain point, what doesn't react in the chambers will react in the exhaust port/system. Too rich and/or too retarded and you may actually blow raw fuel out the end of the exhaust system.

Tuning parameters that are far removed in either direction of optimum can give increases in both CHT's and EGT's.

Highly elevated EGT's can heat the entire head enough to raise CHT's too.

Due to the design of T4 heads ex port area, which cuts directly beneath the combustion chamber, high EGT's can quickly lead to warpage and head leaks.[i]

[Mblizzard]

The thing about temps that has to be kept in mind is that T4 heads (and most aircooled engines) are for more susceptible to damage from high EGT's than CHT's.

And tuning parameters that cool the chamber in the spark plug area (the proper place to read CHT's) often have an inverse reaction to EGT's.

A slightly fat mixture with slightly retarded timing will generally yield lower CHT's but may very well yield higher EGT's. Here's why:

When retarding timing from the optimum setting (whatever that may be for the combo on hand) there is less time (chrono time, not crank degree time) for the mixture to burn in the chamber, so some of it will react in the exhaust port, or near the exhaust valve.

Fattening the mixture will, as a general rule, require more time to burn (more fuel, more chrono time. More chrono time requires more crank degree time for a given rpm).

Up to a certain point, what doesn't react in the chambers will react in the exhaust port/system. Too rich and/or too retarded and you may actually blow raw fuel out the end of the exhaust system.

Tuning parameters that are far removed in either direction of optimum can give increases in both CHT's and EGT's.

Highly elevated EGT's can heat the entire head enough to raise CHT's too.

Due to the design of T4 heads ex port area, which cuts directly beneath the combustion chamber, high EGT's can quickly lead to warpage and head leaks.[i]

It is amazing how I find that the more I read the information posted on the world it becomes more appeant how much I have to learn .

Wish I had the time to get some of your heads for this swap.

[Mblizzard]

OK so I am still struggling with this. I have been playing with timing and fuel and can seem to really bring the temp down to the ideal range. Normal city driving the temps typically remain in the 375 range. But once I get on the highway at about 70 the temps steadily climb and hover at the 380 range and go to 400 on any hill climb.

Changed the plugs and checked the gap at 0.28. I have tried multiple advance settings from the 009 to the stock settings.

I am at a loss at what to do next. I guess I will go back and check the dizzy to be sure it is working off TDC and that all the timing is correct. Checked timing with multiple timing guns. I guess that the only thing I can try next is to really richer it up to see what happens. But as HAM pointed out that has a down side as well.

Looking for any and all suggestions on what to look for next.

[Porschef]

Mike, do you have a wide band AFM set up?


Crap, ok, i see you do... (IMG:style_emoticons/default/dry.gif)

[Mblizzard]

Mike, do you have a wide band AFM set up?


Crap, ok, i see you do... (IMG:style_emoticons/default/dry.gif)

Yep,sure do.

[era vulgaris]

When I first bought my car I was in the exact same boat as you as far as head temps. Typically running in the high 300's and approaching and hitting 400 on the highway.

A couple things that helped me...
Now I have carbs and you obviously have FI, but this might give you some ideas at things to look at.

The PO of my car had a phenolic gasket on the 1/2 side and a pair of paper gaskets sandwiched together on the 3/4 side. I think the 3/4 side had a bit of a vacuum leak. To compensate for this, he had put in massive idle jets rather than fix the vacuum leak. Why anyone would do any of these things, I don't know! But it was one part of my problem.

The other part of my problem was that the carbs were horribly synched. Having the 4 channel gauge, I could see in real time the effects that carb synch had on all 4 of my head temps while tuning. Even drifting slightly out of synch would raise my head temps drastically on the side of the engine where the throttle plates were more open. So basically, the more open the throttle plates (or the more air that was getting in), the higher the head temps. I don't even need to use a unisyn to sync them anymore, I use the head temp gauge!

Once I replaced the intake gaskets with phenolic on both sides, and properly tuned and synched the carbs, my head temps came down to where they are now.

It's possible that you have a very slight vacuum leak somewhere, or that some aspect of your FI system is not allowing a perfect balance in tune between the left and right cylinder banks.