I recently came in possesion of a 1975 tahiti Torino Jet boat that was equiped with a 454, the otehr guy pulled the motor to drop in a Vette and left ALL of the stuff he didnt need, so basically I have everything except an engine block, The question is, what would it take to convert over to a small block 350, I can easily get my hands on a couple with power outputs in the 300 hp range. Obviously I am going to need different exhaust manifolds, any ideas where to get them, I plan to maintain the enclosed engine compartment and through the hull exhaust.
IMHO get a big block to replace it. The pump absorbs a lot of power so the SBC will work, but you will not be happy unless you put a lot of money into the motor. Remember the old saying there is no replacement for displacement. THe BBC are torque monsters. Sell one of your sbcs and get a big block.
Just my 02.
T.J.
www.tjsperformance.com
I'm with TJS. That is a fairly big and heavy hull. You will likely be disappointed with its performance with only 300hp unless that power is being made at a fairly low rpm.
Now, if you go ahead with the swap, the existing bellhousing will work but you will need a SBC front mount, exhaust system,possibly a driveshaft coupler(aka PTO) and a host of incidental items.
PTO will work, flywheel pattern is the same, Flywheel will NOT work. 454 external balance, 350 internal. R/ motor plates are the same bolt pattern, but not necessasarily the same position, up/down, f/mount is different. SBC exhaust pieces are not cheap, seems that those that have them, keep them. I would encourge you to stay with the BBC, gonna be cheaper in the long run......MP
PS: I have a set of Merc type top exit SBC exhaust manifolds, A1 condition, PM me if you're gonna need them.........
R/ motor plates are the same bolt pattern, but not necessasarily the same position, up/down, ..
BBC and SBC bellhousings are the same, so the BBC bellhousing/mount he has will work. Crank centerline relative to bellhousing bolt pattern is the same.
looks like the general opinion is unless I can get 300 hp at 3000 rpm I better stay with a BBC. Im not used to boat motor's are there any things I need to keep in mind, besides the obviouse using a marine gasket set.
I don't think the marine gasket set is all that mandatory ( I didn't use one and am just fine). Plan your Big Block to make plenty of muscle from 3k to 5,500 and you will get something that impresses you.
BEWARE OF PLUMBING ISSUES OF COOLING WATER. Raw water cooling feed from the pump is simple but people misunderstand it and cause themselves problems (water in oil from blown gaskets) from overpressure at mid to high RPM. You do NOT need a water pump on the engine so forget that. Then sometimes folks run injected headers which add complications as I've seen in a lot of threads. I'm running my stock logs for their last year, they are 27 and about shot, corrosion issues. Thru-transom jacketed headers this winter.
The folks here are glad to field any questions you have and will give you our best info.
After reading everyones response in this thread and another I started I started wondering, when I look up the brochures for the tahiti's they almost all list fairly low hp (225hp) 350's as standard equipment and with the lack of availability of a good chevy BB ($1500 for a junkyard motor and they want 200 for a core which if I had I would build) If I can get 300hp out of a 350 and I dont mind paying for some exhaust, what would be the main problem with building a small block, after all everything I have right now with the exception of the exhaust will fit. Im only looking to hit 50-55 mph (the lakes in my area arent great for big speed)
1st question that probably needs answering is what impeller is in the pump now? If it's an A, youwill probably be better off to go with a B impeller and the small block. The B will allow the motor to rev a couple of hundred more R's.
I was going to do a small block conversion myself. My thoughts are you would be better served to get the sb to about 400 hp peaking at around 4800 to 5000 rpms. You will also want to get as much torque as possible and have it peak somewhere in the 4200 to 4500 range but with a rather flat tq curve. The cam I was going to go with was like this
Rpm HP TQ
2500 205 415
3000 250 433
3500 305 452
4000 353 463
4500 398 464
5000 432 454
5500 443 423
The actual numbers will vary depending on heads, exhaust, intake, carb, and many other factors. I just liked where the curves were for a small block. It's my belief that building the sbc to close to equal tq/hp of the BBC, you should be able to run the boat equally as good especially with the weight savings. The thing you don't want to do is build a engine with a lot of lower end torque, it will do you no good.
Too bad you don't live arround here. I see a lot of used big blocks (usually 454's) for sale in the newspaper clasifieds for well under 1,000. Often running motors for $750. Those are from pvt folks so no cores.
A gearhead buddy of mine said that the big block & small block flywheels (although balanced differently) were the same diameter so the bellhousing starter should work. It COULD need some shimming though to match depths.
I'd follow Cas's advise if you decide to go small. the requirements from the big block aren't much different so neither are the specs. It's just the biggies are better at making the lower torque muscle to drive bigger impellers effectively while still making the power to spin them hard.
You're gonna have to work a bit to make a SB wear a BB's shoes but I've seen it done. I friend of mine has a 383 in a Tyalor SJ that'll run 60 with any of the stock ford or chevy BB's.
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