As I have bored you to tears with I have too much heat at the head. The #3 CHT kisses 400 at 60mph and passes it when I hit a hill or want to do 70 for a distance. I have made some changes that made this number come down but it seems persistent.

I have the idea that the problem was caused by my increase in compression ratio and the addition of a non-stock cam. If so how would you know?

My son put it another way: If I am doing 70 in the 2056, I am generating the exact same power as a stock 1.7 (or 2.0) doing 70. Why am I having temp woes when the stock mill isn't? I suspect part of the issue is looking at the gauge at all. A prominent vendor of 914 parts once told me not to put in a CHT gauge because "It will just scare you."

The idea I am getting is that I built something wrong, but exactly what wrong eludes me.

Also I am running those silly 1976 heat exchangers. Would headers pull some of the heat away?

Thanks folks.

REVISION

Along the way changing away from the 1976 heat exchagers was suggested. Denizens of the world helped me backdate my exhaust system to an ssi 2.0 or similar set. New muffler, no 2 into 1 at each side, letting hot exhaust linger beneath the heads, but instead free flowing exhaust back to a collector near the muffler. At least 50 degrees cooler at cylinder 3, and even the oil is cooler. I can drive 70 without damaging the heads!

So, thank you. Thanks to those that chimed in and also to those that would have but chimed in to help someone else. This was a major obstacle keeping me from enjoying my car. Also, it was finished in time to keep up with the 911s at autocross today.

Driving at 70mph, you may create the same amount of power a the wheels as a 1.7 but the efficiency is not necessary the same. The heat in the heads is just power that was not transmitted to the wheels.
Simple things that influence head heat are ignition timing, A/F ratio, valve timing and of course cooling. I guess the ignition and valves are set correctly (and tested...).
- Ignition can only affect one cylinder if its plug or wires are bad.
- Valve timing may be different due to valve lash/geometry/dropped seat. I remember you cut new pushrods so make sure you're all good there.
- A/F can be wrong due to a bad injector or restricted air intake. I would try to cross 2 injectors and see how it goes.
Apart from all this, #3 is normally hotter than the others due to restricted cooling.

, over!

I couldn't resist.

Those pipes could easily affect the mixture in one cylinder differently than another.

Thanks Chris. I like heat here in the northern whatever. But these are seriously weird. So headers are on the list.

Definitely out of tune or misconfigured. No reason for a 2056 to be anywhere near that hot.

intake manifold leak?

the heat exchangers are killing you.
they ru the heat forward and then back again under the same head.....'

at least go for the back dated heat exchangers.

Yep, find a set of SSI 2.0L exchangers and all the right heat ducting parts plus a Bursch exhaust to get rid of the exhaust heat. Then adjust the MPS for AirFuelRatio to set it to 13.5 to 1 at part load and 12 to 1 at WOT...Timing is another issue so make sure that is correct too.

or use the cheaper 1.7/1.8 SSI
ID is the same, performance is same, better price

I have all of the heater parts for the 74 and older heat exchangers if you need them.

Of course this is without the actual heat exchangers.

Nobody has asked the question yet.....
How are you measuring the temp?
Are you pinging ( you SHOULD be with head temps in the 400s).

The stock CHT sensor pegs at 300 deg.
I would find some way to get an independent measurement on that sensor. Even my craftsman DMM has a thermocouple input.

Dakota Digital under the spark plugs. Two separate units gave the same temps. No pings unless I advance the spark. I had a VDO there previously with similar but slightly higher numbers.

Well, this is what I am asking about. The heat exchangers make sense to me. The problem is clearly load-related and doesn't show up until I drive the car the way I want to.
So, some such as comments would help me a lot. Even if I pull the engine I have to look for something wrong.

Making that plug lean? Hmmmm.

Thanks. I am running slightly richer but very close to those numbers. WOT spikes richer than 12. Advancing the timing until it started to ping and then backing off helped some.

I think I am in the need of a new exhaust.