Merlin heads and EGT bore!
 

I have on my 550's Merlin Cast Iron BB Chevy 310cc heads. Now, I would like to drill a small hole in the heads for an
exhaust temp sensor EGT. Is it possible to drill the hole nearby the exhaust port head bolt boss on cylinder No 1 into the exhaust port? I'm not sure, if there is
a water channel under the cast. Can anybody help me?

Daniel

Daniel,

A couple of years ago I did just that. Drilled holes in the top of the exhaust ports. About 3/8" back from the flange. I would have to check the heads to make sure, but there was no water jacket in that area on my heads. They were older Merlin Rectangle port heads. You need to you the exposed thermocouple inorder to have any response time at all. I have found hand held meters for as low as $88 that will read two thermocouples at a time. Being that the thermocouple is so close to the valve, readings are relative. If you could move it down the pipe a bit, you would get a more accurate reading, in respect to other real world numbers. I would see temps as high as 1500 and not get too worried about it. But that was after I did jeting with WOT runs and reading the plugs to get a feel for the temp guage.
Hope this helps. If you want me to measure how far back I drilled, send me an email. The heads are junk now and sitting on the shelf.. Well one head is junk the other is missing it's mate!!

Good luck!!

Dick

I drilled #6 port centering the hole to leave about 1/8 inch of metal between the thermocouple and the flange. I use just the thermocouple not the threaded bos. I drilled the hole just the same size as the thermocouple so that I had to tap ( hammer) it in.

Thank you guys for all your help. I will drill the hole and hope,
there is no water.

Thanks Daniel

There is no water, I drill them all the time

Is this method better than mounting in the exhuast?
I have CMIs and was planning on drilling and welding in place between the water jacket and header.
Thanks in advance,
Dave
:)

I have heard that about 3 inches down stream of the flange is the best location. Mounted in the head will give you high readings because it may be in the flame.

NordicHeat,
I agree with Tinkerboater, you will be more accurate if you are down wind a bit..
Go for it.. but make sure there are no leaks..!!

Dick

:eek: I forgot the last word!!! "between the water jacket and header FLANGE"
Thanks, sounds like I'm headed in the right direction;)

Can you do the same procedure on Canfield Aluminum heads. I can't put temp sensers in exhaust as I have Imco Power Flow plus.