Head advice

[toymex]

I have got a nova sport with a modified engine i dont know the spec as it is new to me , but it has been r/r at 113 bhp 96lbft everything has been fine until sat when i started it the car only ran on 3 cyl for about 15 secs then it cleared itself and ran finefor a 40 mile run only a bit lumpy on idle which i put down to carbs need adjusting. i went to start it sunday and it did the same again run on 3 then cleared and all seemed fine when i got home i noticed ther were a lot of fumes/ smoke coming out of the catch tank and when it cooled down i noticed the water header tank is a bit low. i compression tested it today and no 3 is down to about 75psi (warm). I have removed the head cant see any evidence of gasket failure , are these heads prone to cracking any other thoughts how can i check for ring damage bore s all look ok but i am no expert any help appreciated i need to get it fixed asap as i am booked in for the track day on the 20th:thumb:

[John]

sounds like classic gasket failure to me, (miss on cold start/fumes from header etc) but heads have been known to crack. Get it pressure tested, and checked to see if the head hasn't warped. if there was block damage you'd expect to see it with the coolant completely removed?