doggiedave

Hello, Iknow that this more of a hi-perf site. but I got a lot of advise when building my Scorpion. I have 34 Searay with 2-340hp 454's. I know these are basically truck engines. thinking of replacing with 383 sb's. one engine is reverse rotation. question, if I use the 2-gear setup I assume the cam profile is the same only the rotation and firing order are different. Is this correct? I know about the different seals and possible piston offset. and thanks for any other imput. my goal is better fuel mileage and easier access to engine room About 1200 lbs lighter and 7" narrower on each engine demension

ezstriper

don't waste your time there...thats a heavy boat(had one) and you will have to run the crap out of the small blocks till you kill them...better off building a high torque big blocks...also what year ? after mid 80's the reversed the rotation in the trans(hurth) and engines were the same...you will not gain fuel milage doing this...I have known guys that tried and burned more trying to keep boats like that on plane...if it has prop pockets thats another killer along with sea rays deep V....takes a lot of power to just get those pigs on plane....be better off using a high torque 502

mcollinstn

Some 34' Sea Rays use Bravo 1 and Bravo 3 drives - all of those have standard rotation engines.
Double check and make sure your boat actually has a reverse rotation ENGINE, and not two standard rotation engines with one reverse rotation prop.

ezstriper

with a 340hp its a inboard....

doggiedave

Thanks for the info, it's an 86 model. my plan was to use some good aluminum heads and intake a little hotter camshaft and upping the compression ratio with some good performance exhaust. figured I could shave about 1200lbs of weight off also it has closed cooling so I would not have to worry so much about corosion. and yes it is inboard (Velvet drives) maybe I'll go the 502 route hopefully won't have to repower until next year. Just kicking options arround

ezstriper

you would be way disappointed with the small blocks...been tried...you need torque....and tons of it !!!

doggiedave

Not to beat this post to death, but does anyone have the actual torque production specs for big block mercruiser and small mercruiser engines, they list Horsepower but not torque.which is funny to me as I have a Harley Davidson and they list torque production specs and no horsepower specs we always figured it was because they were ashamed as they surely could have done better, the metric bikes usually have better Hp lol

f_inscreenname

Dog, you better look at all your options before taking out a wrench. R/R motors are a strange beast. The cam is opposite in every way not just spun backward. Also there is only one flat cam available (if it still is) for BBC and it is a lame cam. So unless you plan on making the motor a roller motor and having a custom cam made by Bob you may want to think twice.

MOP

I run a 383 and it is great motor in a light boat, I have to go along with the BB thoughts. I had one of my clients switch from 454 330 to 502 415's in a 37 Silverton sedan, the comparison end result was as follows. Stock his cruise was 23kts at 3200 burning an average of 25 gph, the 502's matched the stock speed of 23kts turning 2600. The fuel consumption at the 2600 dropped to 20+, at 3200 it was almost identical to the 454 but speed was 27kts.

The weights of some of Chevy's past engines
Chevy Corvair flat 6........... 300
Chevy Sprint 993cc L4....... 147
Chevy 1.8-2.0 L4.............. 302
Chevy Chevette 1.6 SOHC.. 300
Chevy Vega L4 .................285
Chevy II 153 L4 ................350
Chevy L6 194-250 .............440
Chevy L6 216/235..............630
Chevy L6 216/235............. 615
Chevy V6-90 229, 4.3........ 425
Chevy V6-60 2.8, 3.1......... 350
Chevy small block V8.......... 575 <----------
Chevy LT-5 DOHC 5.7......... 600
Chevy L98 5.7 V8............... 600
Chevy V8 348/409.............. 620
Chevy V8 348/408 ............ 655
Chevy big block V8 ............ 685 <----------
Chevy 454........................ 675
Chevy 427 ZL-1................. 550

Think about 502's with aluminum heads/intakes which will narrow the margin by about 100 lbs per side, your 1200 lbs total reduction between SB & BB just does not ring true.

doggiedave

Thanks for all the responces, I'm convinced. now do they make a reverse rotation 502 and if not how dificult to get done and who would you recomend to purchase complete engine other than Mercruiser(they are proud of their prices)