@allan downes I have a tuned 300Tdi - full width IC, and tuned pump. EGT probe is where the EGR valve was..
IF you are anywhere near 740, I'd suggest it'll end in tears, and quite quickly. These temperatures will anneal the alloy head, and you can guess what happens next.
I have been told, and it is backed up by Internet searches that the head is Ok to about 719C -
but, and it's a big
BUT - at 720C it's all over - ECT will be irrelevant at this point IMHO, and in any event, you are
not monitoring this with the standard sender and gauge - it is simply a guesstimate, and probably a poor one, and simply unable to respond in a timely manner to such an extreme situation.....
I'd suggest extreme caution, and that you speak to someone who has more experience than me. Have a nosy here,
www.jeremyjfearn.co.uk
and IMHO, try and speak to him - IIRC he works away a lot now, but you might be lucky....
Also , as above, 1250 F is 676.667 C - so "safe" enough, given the figures I mentioned above....