Cylinder Head Temps?
 

Hi folks,

So....work is about to recommence on my 964 Turbo project after finding many shattered piston rings, horror-story all detailed in my signature link below.

One question I need to find a specific answer to, is that of the max temps I'll see down the spark plug holes.

We're trying something a little experimental on the ignition side, meaning I need to modify some coil-on-plug units by shortening them. As stock, they're a good 1-1.5" too tall.

The units can be broken down into 3 sections; the centre section is some kind of plastic. I'm planning on turning-up some new centre sections which will fit into the rubber boots at each end. But I need to know the max temp that a COP is likely to see in a Turbo application.

I've just spoken to an engineering plastics supplier I've used before, whose recommendation is PEEK for the max temp resistance. This is 4x the price of PTFE, not that we're talking huge $$'s for the small amount I need, but I am wondering if I can use material that I already have (Delrin), or something else, (OCD Mode=on....PEEK is natural white....I want black ideally, to look stock!)

I bought a rod of Delrin some years ago to make some collars for the Denso COP's, that hold the pencils central to the holes in the valve covers...they've survived very well, but valve covers won't be seeing the same temps as those down the spark plug 'ole!

Input welcome as always folks,

Thanks
Spencer

I think Lycoming (aircraft engines) would like to see around 350 degrees in cruise conditions with obviously higher permissible at high power settings (T.O. and climb). I think around 500 is the maximum they would like to see.

For what it's worth the old turbocharged Corvair Spyders and Corsas had a cylinder head temperature gauge that topped out at 600 degrees. I think the most I ever saw on one in a Kansas summer and running hard was a little over 400 when running hard. (The oil temperature warning light would come on first.)

I would expect Porsche's air-cooled parameters to be similar to these; no way to tweak physics and materials.

I thought I'd heard that 500-600 degrees F is much too hot for an aircooled 911 engine when measuring at the sparkplug hole. I recall that you want more like 250. Curious to hear what others' experience is.

Scott

Anything over 425 deg F is bad news in a Porsche head.

Yeah, I've never seen much over 300° from my 3.2 head temp sensor.

I lived in South TX with many days busting right through the 100's.

400 is what I bring them up to for setting new seats:

To me if you're seeing more than 350F something isn't correct. I aim for 325, tops 350 is OK climbing a long grade.
I see many people lugging air cooled engines which is bad, you should always be trying for at least 3000rpm, if you're below 3000rpm you're in the wrong gear.

I know it's not a six, but my highly modified (nickies, stroker, EFI, 911 trans, etc.) 2.6L type 4 engine, in my '67 bug, rarely sees over 300F head temps.

Gents, thank you - very useful info indeed.

Of course, the COP's won't be in direct contact with the heads @ c.300-350°F, but I'll use that air gap as the safety margin when choosing materials.

For info, the PEEK rod available through this vendor is rated at 260°C (500°F) continuous, 300°C (572°F) short exposure and a melting point of 343°C (649°F)....plenty of margin!

Cheers
Spencer