nova 1975 repower 400 SMALLBLOCKs
 

I'm going to repower and try to sell a 1975 25' Nova with Twins. Boat has 302 FORDS. Boat did almost 60mph. 1 motor seized 1 spun a bearing. Have all parts incl. new manifolds. Also know where 4 complete motors are for a few hundred. Alpha's are already rebuilt. I really want to experiment by making up 400SBC motors. Has anyone done this? I have Dennis Moore's books and have all the parts incl. (2) 4bolt 400's. Is this too much power the boat? Will it make the boat chinewalk or unstable. I'm thinking of about 400HP EA and maybe 1.32 upper gears. Do the 400 steam holes pose a problem with salt water and blockage due to rust? Basically a joint venture is what this project is. Last summer we resurrected a 1982 38' Scarab incl. building and installing the port engine. I could put 350's in the Nova also. I'm aware of the holes in the heads on a 400. Maybe I have a hole in my head ! Or My head in my hole!!!
Anyway I'm not too crazy about Ford motors and the outdated accessories. Thanks For any help BBB :crazy:

BBB,
I helped a friend put a 400 sbc in a 23' formula sport cruiser 2 summers ago and despite the rather mild cam, it really brought that 6000lb (gross) boat to life. Added about 10 mph to his top end. There are several things to check though, 1st make sure the heads are drilled for the steam vent holes, 2nd make sure the drives are in very good condition, 3rd use a good center riser exhaust system, 4th if you are going to use Qjet carbs, make sure to epoxy the machine plugs (2?) on the under side of each carb to prevent fuel leakage directly into the intake. I saw the question of salt bothering the steam vent holes answered once before here by someone who said that it hadn't bothered his motors, of course a good fresh water flush after each use would be good insurance against touble. As for the drives, my friends was in less than A1 condition & that 400 ate it up & spit it out. Which leaves the carbs, his was leaking fuel through those machine plugs and in conjuction with a restrictive exhaust cooked all 8 stainless exhaust valves, discolored the iron around the valves almost ruining the heads, and even cooked the rockers. Small items, very expensive consequences.
Despite the initial problems, I like the motor and would do it again with the proper precautions. Strong motor, lauches his formula as hard as my stock 7.4 does my 21 scarab.

BBB,
One other thing, if you looking for 400hp from these motors, I would go with a better rod (5.7") than the stock ones. Something like the new chevy stroker rods or the aftermarket H beam rods so you won't have any clearence problems with the cam. And then use a good roller cam. Should make for a very strong motor.
I believe one of the other members used Vortec heads on his 400 with excelent results. You should put the question out there if your interested.

Thanks CDSCARAB ! I have a 21' Citation Laser(Baja hull) with a 454 that kicks @$$. I'm going to sell it, Alpha 1.32 drive stays together. The real issue was the propshaft rpm and pinion stress with the 1.50 gears (found out later!). I had blown up several 1.50 drives and ended up putting a bravo setup on it brand new out of the box. The Formula 242ls I now have had the 1.32 alpha on it when I bought it with a siezed motor. Knowing that I'm already at a loss with the "Baja", I decided to put the Bravo on the Formula and made the other boat Alpha again . I always wanted to play with a 400 since Merc. never made them as a boat motor. I figure it a great power to weight ratio and reliable h.p. with pretty much stock parts. Thanks BBB

no 400's in salt!!

Is that because of the siamese bores?

steam ports plug up and blow head gaskets!

Thanks Alot guys. One question remains. If I was to flush real good after each use could I get by with the 400's ? I really want to try this out. :drool:

400
 

You must use a Farria head gasket. Its the only one I could get to seal. If not you will blow a head gasket every season. You must drill the steam holes in that gasket. Car people block those holes and do not care. I changed head gaskets every season after finding them just to keep from having a bad day boating.

I had 400's for three years and found the following to work best after lots of $ and trail and error.

Steel heads work best, Merlin SR' s. A single plane Victor Jr and a Holley 750 Double pumper was much better that Qjet. A Linati 235 streetmaster cam was the best for power. Make sure you use a 140 thermostat. Dont waste time on exhaust, but I brazed a 3" piece of pipe on the riser to stop the reversion a 400 will make. Any welding supply can supply the 1 brazing rod you will need.

Very interesting stuff. I really am interested in why the 400 has more reversion. The boat exhaust tips that are on it are above the swim platform and are higher than the elbow outlets, unless the boat is underway. No wonder why this boat suffered water up the exhaust! I was told by many people to raise the X dimension, It might" kill 2 birds with one stone" . I want to play with this boat without spending tons of money(if that's possible) I like the Idea of brazing extensions on the elbows. I have a carbon arc torch that makes it so wonderfull to sucessfully repair cast iron. It really makes the heat you need. It's a shame that this is becoming a lost art and is little known to even some good weldors. I also use the nickel bronze rods. Thanks a million, Keep posting so we all can continue to learn more.BBB

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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.

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

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

Re: nova 1975 repower 400 SMALLBLOCKs
 

Whats that I hear, sounds like 400's boy they sound good, OOOOOOOHHHHHHH crap that sounded like the snapping of a alpha, Damn there went another good alpha. :D

Re: nova 1975 repower 400 SMALLBLOCKs
 

What do you use for a flywheel? I wanted to do this many years ago, but could not find a 400 flywheel that would fit the alfa (then 1 drive) belhousing. The 400 being external balanced and is not the same as a 454? This was always my short fall, whats the trick?

Re: nova 1975 repower 400 SMALLBLOCKs
 

Ok ! You need to take a 454 flywheel and remove 70 grams from the big counterweight.
A good machine shop can do this. The flywheel you would want to start off with would end with 457. You could have motor internally balanced too using a neutral balancer and flywheel. I feel that if it's going to rev high, you better get a good balance job from a really reputable shop. It's amazing how motors are ballpark balanced from the factory anyway. Start mixing parts and all bets are off. Expect to pay at least $300 for the balance job. It really pays off. BBB

Re: nova 1975 repower 400 SMALLBLOCKs
 

They make a counter weight that goes on the crank before you put on the flywheel. Available at any automotive machane shop, it's the same one we use for a 383 stroker, thats a 350 block and flywheel with 400 crank and 5.7rods.

Re: nova 1975 repower 400 SMALLBLOCKs
 

4500rpm is all i go for my inboard sportfish/partybarge. i used speed pro hyperutectic dish side load this!!!i needed big torque and better fuel milage than a big block .i have top mouted starters so i had to cut a step on the fly wheel via lathe to swap the ring gear to the face side . i am confident that my engines will last a good long time.It's not like 350's are much better (350's still have side load and can still blow head gaskets)