Engine help
 

First off its a 454mag original motor. Redone the top end 2 seasons ago about 1000 hours on lower. Coming in the other day she started misfiring. Worst fear water was in cylinder 3. Did a compression test thinking it would be a head gasket. To my surprise the cylinder with water was still 150 psi. Now every one was 150 except 5 and 6 (across from eachother) both were 120. Seems very odd. Always runs strong etc. I have Eddie marine exhaust that's about 4 years old so I would like to think that maybe the salt water finally rotted out the manifold and that's where the intrusion came from. So 2 questions. How can I pressurize the manifold to see if it's leaking? And at this point because of those 2 cylinders with low compression should I be thinking about doing a long block or just run it? Any input would be appreciated. Thanks.

Those 2 cylinders (5&6) sit at the rear of the center dump riser and usually take a beating from slight reversion/water intrusion. You need to find out where they are bleeding off compression, if its the exhaust valve, then maybe just some head work. Of course, at 1000 hours on the lower, it's probably time to consider a rebuild.

You could also have rusted through a water jacket in the head, cracked a head etc.

My 89 242LS rusted through #5 and it didn't have that many hours on it. If you didn't hurt the bottom end and wanted to keep running, given that a head rusted through, just replace the top end and keep boating.
I was not so fortunate. The water steamed a piston and broke the rings so it had to be all redone.
Good luck

thanks guys, im thinking its just a head will do leak down test beginning of the week. If that's the case its getting a set of merlins and a nice single plane intake manifold

My 242LS came from MA. I think it saw a lot of brackish water and it rusted the coolant jacket through in the head at 455 hours. Maybe a lot of sit time too for those low hours. The machine shop checked into "pinning" the crack but there was not enough material left in the wall to do that. The hole was through the cooling jacket into the exhaust port so engine side testing did not see that. Pressuring up the cooling side would show something like this. With the hole in the exhaust port of the head, the engine was constantly running in a state of reversion. The PO was tuning and fighting symptoms but could not find it until it was too late because they were always testing on the engine side but not the cooling side.

Looking to be heads after a leak down tonight. Been leaning toward world/Merlin. Anyone had any problems with them? Or recommend something else. Would like to do a single plane intake manifold also.

Engine Quest makes a very good replacement head for the 454/502 Mag. They're the old Pro Topline castings from New Zealand. Can't beat them for the money.

Also, I'd scrap the idea of a single plane. You don't have enough cam/rpm to take advantage of one, and it'll hurt the lowend.

forgot to mention I have a comp 228/236 .537/.555 114LS cam.

So ive decided to do a set of dart iron eagle heads. As for an intake manifold I run mostly in salt water and would prefer something with lined water passages. Anyone have any input on what they run and if they bother with lined passages or just replace every few years? Thanks

The factory aluminum manifold is a good piece. I don't see you really gaining much by changing it out. The brass-lined intakes are big dollars!

TZ