DIY EGT hookup

tbitz · 09:12 PM

My future project is to turbocharge my 911SC. With that in mind I've been meaning to hookup a thermocouple to monitor my EGT temperature. My 911SC had smog gear at some point in its life which was disconnected and the hoses were blocked off.

First I removed the smog pipe from the head. It came off very easily. You can see the hole going into the exhaust port below:

Here is the smog pipe that fits into the exhaust port.

I had a 1/8" diameter K-type thermocouple in stainless steel sheath. I drilled a 1/8" inch hole on the tip of the smog pipe so that the thermocouple sticks out a bit. Here it is with the thermocouple sticking out about 1/8".

The thermocouple was brazed to the end of the fitting so that it would not slide up and down. I carefully measured the maximum allowable distance the thermocouple could protrode without hitting the exhaust valve. 1/8" seems to be safe.

The assembly was reinstalled back into the smog fitting on the head.

I hooked it up to my digital display and started her up. After a few minutes EGT reached 600C (1112F). I'll take her for a ride tomorrow and see how high the EGT hits. I need to route the wire properly into the cabin and find a nice spot for the display.

Anyone have any insight as too what a dangerously high EGT temp is for the 911 engine?

Cheers,

Natchamp · 05-29-2003, 09:18 PM

Tony, I believe you want to stay below 1600 for EGT's. Short bursts are ok, but you shouldn't have sustained temps above this.

beepbeep · 12:54 AM

Very clever. Exactly what i suggested to Oliver here on forum. It would be very neat if you could do this on all cylinders, and have either rotary switch or "graphic equilizer" displaying results. Other posibility is using surplus instrumentation from old piston-aircraft.

This is good sort of info, much better than CHT and probe is in best place possible. I would drill more holes in smog-plugg though, just to allow exhaust-gases to heat termocouple some more.

About temps, it depends: SAAB-engines for example often see over 900 deg C in short bursts ... 950 deg C is absolute maximum. On aircooled engines, i think 750 deg is safe max. Talk to your local aircraft-buff, they can give you lot's of good info!

Cheers!

RoninLB · 05-30-2003, 02:38 AM

Quote:

Originally posted by tbitz

MyAnyone have any insight as too what a dangerously high EGT temp is for the 911 engine?

I've never read about getting temps from the air injector inlet.. just about all pros say 1inch from the head is correct placement.. so the hard info that I have would probably not be of help.. BTW, I'm doing an install now on SSI.. the placement is about 1 1/2 inch from the head ...............Ron

tbitz · 05-30-2003, 05:55 AM

Ideally I would have one in each cylinder, with a computer automatically switching to the highest temperature cylinder, but that is just too much work. One cylinder is good enough, I think. I already have the laptop hooked up to my Megasquirt EFI which gathers all kinds of data (manifold pressure, wideband exhaust O2, intake temperature, rpm, etc..)

On my way into work today (outside temp 12C or 53F) the EGT was around 750C (1382F) during crusing on the highway. The highest it reached was 815C (1500F). Idle seems to be around 600C (1112F).

911pcars · 05-30-2003, 07:30 AM

Tony,
Because of the location of the thermocouple, I think your EGT temps will be relative to published examples. Most sources recommend installing a few inches from the exhaust port, not because this is the best location but because most engines don't have a convenient access port like yours.

For example, your cruise temp. of 1382 deg. F (sensor in cyl. head) is usually a temp. reserved for WOT operation and 1500 deg. F is melt-down time if the sensor were in the exh. pipe.

With a future turbo blowing through, you may want to consider a CHT gauge to keep another eye on things. Gee, I wonder what your gauge would read with 10 psi boost?

Sherwood Lee
http://members.rennlist.org/911pcars

RoninLB · 05-30-2003, 07:49 AM

Hey Tony...
all I have to offer is the 1in from head temps..
the max of non-turbo should be around 1350 F.. more than that requires ceramic coatings.. a turbo will see 1400-1650 F.. a pro estimated that my 2.7 w/ E cams, PMOs, SSI, etc. will probably see between 1100-1250 F at WOT, between 4700-5000 rpm.. but this is for a probe 1 inch from the head.. another pro said a possible 100 f less for every inch further down the tube..

anyway Sherwood Lee may have some info for you.. he's been waiting for my install so I could feed him my experiences.. that's all I got Tony..................Ron