Ok guys, I have read enough about what turbo plugs are compatible with what engines.
So i made a mold to check the threads and taper of different plugs. One mold is made out of novarossi cto6 and the other from an os rp6 plug.
I will update later with some pics.
I have tested novarossi cto6 and ct6, os p5 and rp6, sh t3 and t4, alpha p3 turbo plugs.

The Novarossi glow plugs are the same in threads and taper as the Sh glow plugs.

The Os glow plugs are the same with the Alpha glow plugs and threads and taper.
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Between OS and Novarossi there is a slight difference in taper and thread shape.

​​​​​​Here is a picture of one of the molds I made, this is the novarossi mold with the sh plug.
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Any more updates on this? Got a ProTek Samurai S03 and several Novarossi plugs that I'd like to use but don't want to cause damage.

Unfortunately I don't have any protek plugs to test..
If i get some I will test them and inform you..

The Samurai is OS based and uses the OS P3 plug. I've been told, if you put a Nova plug in an OS head button it will deform the threads slightly and you won't be able to go back to the OS plug. With the unknown status of Novarossi, I would continue to use OS plugs that are still available. We run Nova engines and will be forced to use OS plugs soon due to no availability of Nova plugs.

The Novarossi plug is the only one where the thread runs up onto the taper. All other pluggs have a shorter thread and between the thread and the taper a smaller diameter body. If that smaller diameter body is also manufactured in the head button or a shorter thread then the Novarossi will not fit perfectly.

Dont use nova plugs in os based engines, just don’t do it. U cause the threads to get sloppy as cause air leaks, the deck hieghts are different it’s like using a metric screw when the car uses standard, no different.

If u need a plug that is perfect in a novarossi go get some O’Donnell plugs, they follow a more nova design.

In os engines u can use the p3 pretty much anytime anywhere and get the best results, if u can’t get them then use a #4 or #5 or even #6 if they still make them by the rebrand Kings LM (you know them as werks or the Orion engines) or formerly known as sirio #5 plugs. They rock and the 4 I would assume is even better. I actually really like these plugs and have as much confidence in a new sirio plug as a os p3 but I think the p3 longevity wins out.

U can pretty much categorize engines in two categorize, you have your os type engines and your nova type engines. A lot follow each, some say the alpha engines and arrow engines are there own catagory but if I am right didn’t arrow basically copy a vspec down to the point u could use a arrow rebuild kit in an os vspec? To me that puts them in the os catagory. Picco I used last 10 years ago used an nova style plug (I blewa lot of rods so I may have been wrong but not sure)

Has anyone tried the SH T33 or T4 in a Nova or know which compares best to the NOVA CTO6?

I have tried the T4 and it works fine.. You will need to re-tun a little bit.