if someone experience the same problem please help

just did a new motor from top to bottom its a 572 dart block with merlin heads ,
i did the first 5 hours on this motor not exceeding 3000rpm so yesterday i decided to change oil and plugs .
when i was changing the plugs i found water in cylinder 3 , 5 and 7 !!
oil was clean no water in it .

can someone please help ?

it's either going to be the intake gasket, head gasket or exhaust, leak down test should rule out heads and gasket.
probably can rule out intake gasket if you have no vacuum leak and steady idle, no sign of water.
that leaves exhaust, could be the header leaking (new headers/), reversion due to cam, or even the exhaust manifold gaskets or exhaust manifold ports being smaller than the ports on the heads which can also lead to reversion. Are you running flappers in the exhaust?

Thanks for replay , yes headers are new aswell, it's a full dry system with rubber flappers . Exhaust ports are D shape and headers are round type .

You could pressure teat the cooling system, from the point where water enters the block as far as the water dumps into your exhaust. I have never been around a dry system that experienced reversion so no experience there.

How do you do pressure test on the water system ?

don't know what setup you have, but basically there should be one main line that comes off the oil cooler that is where you could insert water fitting with valve, then there may be two lines that enter the headers from the engine, disconnect and plug these, one with a gauge, set air pressure to about 20ibs close all valves and see if pressure holds.

picture of front and side of motor would help btw. should also be possible to test headers in similar way, pressure at first inlet and gauge at point where water dumps into exhaust

make sure you have the plugs out before testing incase water/air gets into cylinders, be sure and run engine less than a minute to dry things out by removing sea water pump belt or maybe spray some wd40 or similar to protect rings/valves from rust

bump, any other theories?

slight exhaust leak helping suck some water back in from the rubber flappers.thats my guess.

Today I checked the plugs and only plug number 7 had water in it . The others were dry !

I would pressure test the manifold from that side, new does not guarantee perfect, (though it should)