I have notice from playing with 400's in trucks that it seams the steam holes came in diffrent sizes (ie depended on what drill bit was chucked up that day) Seams to me the bigger the better and make shure that all three Gasket Head and Block match. Rag's

i built and run twin 400 sbc. ive got 30 hours on them.port engine is a 1970(060.")over,starboard is 1976(030.").fresh water cooled with a 5"X24"exchangers,they say that salt water will plug up the steam holes. longer connecting rods are not worth the clearence problems (cam/oilpan rail)and balancing.short rods make more low end torque and are less prone to detonation.short track guys prefer them and go 6500rpm or more.head gaskets need to fit perfect and you need to make sure the fire ring is large enough i used felpro marine the stock felpro wouldn't even fit the 030."over 400

I know two people with 408" sbc's. One in a 20' bowrider and 3 in a 30' Magnum and all four work great. The bowrider has slightly worked Vortec heads and the triples have aluminum heads , all drilled for steam holes.The bowrider dynoed at 450 hp and the others with aluminum heads were aboud 490hp.

Mopower- 450 and 490hp.....wow......very cool......how many hours on these engines?........do they hold up in the long run?
Dirtyplumber- how high do you spin yours??.....what kind of boat/drives....doug

You can get the same power out of a 383 for less money and less problems. Running higher horsepower 400s in a cool water (160 or so) cooling system will cause cracks from the steam holes to the head bolt hole as illustrated below. And NO you shouldn't run them in salt water. These steam holes are true to their name in the fact they run very hot. This will separate the salt from the water and will build up and eventually close off the steam hole altogether. it is very important to run a closed cooling system with these engines. Mainly because the steam hole will boil off the water inside it and once your off the throttle they will cool too fast causing the cracks I mentioned. 400-SBCs are great for sanctioned cu-in drag racing because of the short runs. I wouldn't count on them to last. Besides there is no point in having them when you can have more horsepower and reliability out of a forged cranked big-block.

Roby

Can you explain that to me a little better? Maybe it's because I'm very tired today but that went right over my head.

Roby

They won't' have anymore reversion than any other SBC with the same cam & exhaust. Wanna get real technical they will have less because larger cams have less effect or larger inch engines respectively

Roby

I never heard of this but if some had larger steam holes they are prime candidates for cracks. NO WAY should you attempt to drill them larger.

Roby

Short rods will give you the desirable torque you seek in a marine application but the increased piston loading will cause accelerated cylinder wear, (very common in these engines) especially if you use forged slugs. I recommend a good hyperutectic piston if you want to keep this mill for a while.

Roby

Hi ! I'm back. I ended up parting the boat out. It seems that it would only be worthwhile if I was going to keep it. I still may do a 400 project. Thanks to all, BBB