Offshoreonly.com - BBC Spark plug help. Not MR43t

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Quote:

Originally Posted by BillK (Post 4747492)

The other thing is you probably should get with your engine builder and find out what pistons he used. Those heads are closed chamber heads and typically result in a pretty high compression ratio on a 454. You will probably have to run at least premium fuel. Make certain so you dont run into detonation issues.

This might be the most important paragraph in this thread. What was the failure after 10 hours? Has the issue been resolved? Usually if an engine fails from "builder error" it doesn't last 10 hours, it's pretty quick. Did this motor slowly detonate itself to failure?

The photos of the holes in the head LOOK like taper seat. Not gasket seat.

Quote:

Originally Posted by BillK (Post 4747492)

Wow,
Those are old heads. 1967-1972 If you get plugs for a 1970 Chevy truck 402 they should be ok. Although I have built plenty of marine engines I have never really used a "Marine" spark plug. Typically use an NGK plug that fits the engine. Looks like NGK YR5 is the oem replacement ? Or an AC Delco R44T should work fine too. Those are gasketed short reach plugs probably like the one you bought to try. There might be a marine equivalent.

The other thing is you probably should get with your engine builder and find out what pistons he used. Those heads are closed chamber heads and typically result in a pretty high compression ratio on a 454. You will probably have to run at least premium fuel. Make certain so you dont run into detonation issues.

i talked to my engine builder and the pistons they used with those heads they calculated the compression ratio to be 9.56 to 1. Fired it up for the first time yesterday and is running good. Only weird issue is the starboard side exhaust got pretty hot. Not the manifold or riser but the rubber exhaust from riser to transom. Very strange. Stainless Marine exhaustPort side was fine. Plenty of water flow. Engine temp at 130 running on muffs. Gonna take it for a trial run on Saturday and see how the exhaust is in the water if there’s any difference