CHT Temp, What is the upper operating limit? Options

[ericread]

Based on the converstaions here,I drove over to Corona, CA (Aircraft Spruce) this afternoon and purchased the Micro 1000 CHT, a sensor and a 15 foot extension cable. It's all installed and looks great in my original center console.

So where is the danger point? Some posts say that hitting 400 degrees will cause a valve seat to fail. Others say they regularly see 375 to 400 degrees on their longer, higher speed drives. Where is the point that indicated engine heat danger? BTW: 74 2.0L all original FI w, standard exhaust.

My thanks.

Eric Read


NOTE: Please note that this was originally posted in a CHT topic post. After about a day, I received no responses, so I am re-posting it as a unique topic.

Cross-Posting Disclosure: Cross-posted to the "other" BBS (Saturday, 10/11/08) as a result of no response on this BBS.

[ericread]

By the way: The cost for the gauge, sensor and extension wire came to $108. It took me about 2 hours to install, including running the wires in the tunnel and modifying the old center console clock hole for the 2" CHT gauge.

I drove all over LA today, and experienced CHT temps from about 390 degrees (80 MPH uphill on the 57 from Santa Ana to Pomona) to about 275-300 degrees driving stop-and-go around downtown LV (watching batting practice at Dodger stadium and picking up free Clippers tickets at Staples Center).

It seems to work pretty cool, and the analog gauge doen't take anything away from the overall stock look.

Eric Read

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[davep]

About all I can recall at the moment is Len saying he uses a 400 degree oven to allow the valve seats to drop out of the heads. Based on that I'd say 350 is a decent limit.

[7275914911]

There is a good info on CH temps in the Tech Articles by Raby under 914Info.

jkp

[toon1]

your good! (IMG:style_emoticons/default/biggrin.gif)

Those temps fall well within the safe range.Jake say's 315 to 385 is normal operating temps. 400 is a high temp but I have seen 407 on my CHT gauge with no prob. I don't feel comfortable with those temps but they are rare. Mine runs consistantly in the 320 around town and 360 range on the highway at about 13.5 to 14:1 AFR with about 25* ignition advance @ 3k to 3100rpm ( hwy SPEEDS AT 70MPH)

[ericread]

There is a good info on CH temps in the Tech Articles by Raby under 914Info.

jkp

Thanks! I will review that article.

Eric

[r_towle]

If you take a head and put it in the oven with the chamber facing down...then heat the head to 400 degrees and let it sit like that for 20 minutes....you may see the valve seats come loose.

that is the tolerance for these heads so if you are running temps that high, your timing may be off, you may need different oil, you may want better plugs, your cooling tin may not be attached correctly/leaking/missing parts...
Your engine may also be filthy underneath the head tin...

Rich

[toon1]

If you take a head and put it in the oven with the chamber facing down...then heat the head to 400 degrees and let it sit like that for 20 minutes....you may see the valve seats come loose.

that is the tolerance for these heads so if you are running temps that high, your timing may be off, you may need different oil, you may want better plugs, your cooling tin may not be attached correctly/leaking/missing parts...
Your engine may also be filthy underneath the head tin...

Rich

This is true. I don't like seeing temps that high.

But there is one factor that might come into play, the cumbustion chamber temps are very high changing the expansion rate of the valve seat.

When I saw temps that high, the engine had 1500miles on it, timing was about 25* and AFR was 13.5:1.

The biggest factor was , I was pulling a long hill on a warm day(85*) into a good head wind.

I was definetly not comfortable with 407*. I pulled the same hill again in different conditions and the temps where about 385*.

[Jake Raby]

Sensor location is key! You must install the sensor under the spark plug, no where else!

I keep heads under 400F for longevity, but you can run over 400 for short periods of time.

Past 400 if you have not updated the valve seats with a procedure and component enhancement like ours a failure can be experienced at any time. At 420 seats start to fall out.

315-385 is the sweet spot for expansion, wear and MPG. The key is to keep the temps as stable as possible, huge CHT differentials are what necessitate more frequent maintenance, valve adjustments and head re-torques. The heads on my 912E have NEVER went over 375 and due to that the engine hasn't needed a valve adjustment since February 2003, 125K miles ago.

[ericread]

Sensor location is key! You must install the sensor under the spark plug, no where else!

I keep heads under 400F for longevity, but you can run over 400 for short periods of time.

Past 400 if you have not updated the valve seats with a procedure and component enhancement like ours a failure can be experienced at any time. At 420 seats start to fall out.

315-385 is the sweet spot for expansion, wear and MPG. The key is to keep the temps as stable as possible, huge CHT differentials are what necessitate more frequent maintenance, valve adjustments and head re-torques. The heads on my 912E have NEVER went over 375 and due to that the engine hasn't needed a valve adjustment since February 2003, 125K miles ago.

Jake;

Your article in the 914 info section is really appreciated. My main concern was running in the 375-390 degree range during my high-speed freeway runs (~75-80MPH). From what I can see, I am in the "sweet spot" for head temperature.

My thanks for your advice, and for sharing your experience with us.

Eric Read