Thank you so much for your help Flusher That was exactly the information and data I was looking for. Have a great weekend! Ill post any  questions as they come up. Ill start a build thread on the boat restoration too.

Joshua

Here’s a compression calculator for ya...


https://www.summitracing.com/newsandevents/calcsandtools/compression-calculator


Sent from my iPhone using SoCal Jet Boats

Thanks. I have my static and dynamic cr listed above. I'm just not sure they're what I need for my goals and uses listed above.

I am shooting for at least 600hp(think this build might do 700ish), and would like to run 87-93 fuel. I think it should be capable of cruising 5400rpm? Rev limit set to 6000rpm? Its a 6 passenger day cruiser, I want to have good marina/no wake characteristics, I want to tow tubes with the family, and be able to punch it and go! I want more acceleration than top end speed. To me 60-70mph probably fast enough top end speed.........My math says im
9.87:1 static compression ratio
7.09:1 dynamic compression ratio

Welcome and congratulations.

I would really recommend against taking a good standard bore block .060 over, that takes all the life out of it.  The cylinder walls will tend to flex more and ring seal will suffer.  You don't  have enough material for another overbore shoud you need.  All that for 6.8 cubic inches, which is about 8 horsepower at your power level?

If your boat doesn't already have a AA impeller, I would strongly recommend one and an inducer.

Thanks Flusher! I'll look into the impeller and inducer. So just .030 over? Or hone and .000 dome pistons? Sorry, I'm new to engine building.

Howdy Yall,
My name is Joshua, go by JW or Farmer on the forums. Been lurking and love the info on this forum. Anywhos, just bought my first boat! Call it a mid life covid crisis. My boating experience is with an aluminum outboard semi v fishing boat. This is my first jet boat, first fiberglass hull, and first BBC. We farm but I do mechanics/fabrication. Ive built a high performance auto transmission before, but never an engine. Been doing lots of research and lots of math. I bought it without a motor, did a float test, all is well, only leak is a small drip at the rope packing, but its been dry for a long time, and didnt give it time to waterlog.

Ill attach boat pics. Its a 1979 DeMarco Daycruiser 21.5ft. All original including the interior. Ill need to repair some cracks in the gel coat, and some interior plywood, but overall I feel it is in great condition. Previous owner said had blueprinted and balanced berkely jet drive. Tags on the drive stamped Model 12JG-ASS, BM NO 7338.

I pulled the 454 from a 1989 R3500 rollback truck. Wanted to use the truck, but rust was worse than I feel comfortable with. Gonna build an aluminum rollback gooseneck . Its a virgin block. Tested 140-150psi comp across all cylinders. Mark IV block, 4 bolt main, stamped 445 high perf.

I need second opinions on my build sheet. I am shooting for at least 600hp(think this build might do 700ish), and would like to run 87-93 fuel. I think it should be capable of cruising 5400rpm? Rev limit set to 6000rpm? Its a 6 passenger day cruiser, I want to have good marina/no wake characteristics, I want to tow tubes with the family, and be able to punch it and go! I want more acceleration than top end speed. To me 60-70mph probably fast enough top end speed.

Rotating assembly:

scat 4340 forged crank 4.25" for 496
scat 4340 h beam rods 6.385" with arp 2000 bolts
wiseco 2618 alloy forged pistons 0.060" over, 20cc dome

Camshaft

comp xm296hr .566/.566 lift, 242/248 @ 0.050" duration, 112 lobe sep

Heads

skip white bravo 274 aluminum heads, 123cc comb chamber, 335cc runners, 2.250" intake valve, intake 320cfm @ .500, exhaust 228cfm @ .500"

Valvetrain
morel pro sportsman retro solid roller lifters .300 tall

comp ultra pro magnum roller rockers 1.7 lift ratio, 7/16" stud

dart adjustable guide plates

arp 7/16 rocker studs

cam retainer plate

billet double timing chain with torrington bearing


Intake
edelbrock performer rpm air gap intake


Carb
quick fuel brawler 950cfm 4 barrel mech secondaries


Ignition
Not sure, but thinking multispark, adjustable rev limiter, perhaps the pertronix flamethrower III distributor

My math says im
9.87:1 static compression ratio
7.09:1 dynamic compression ratio

Questions
For the rpm range, should I instead run these heads
Skip white large oval 300cc intake runners, 119cc comb chambers.

or this cam
Comp xm284hr with .547/.547 lift, 230/236 duration, 112 lobe sep

I can move around compression ratio a little based on piston dome 20cc, 25cc, or 30cc, and my machine shop can shave the heads to shrink the combustion chamber.

Any thoughts, advice, suggestions welcome!
I have a reasonable budget, but its a huge investment for me. Im looking at $6000ish with parts and machine work.
Joshua
aka TFF

PS filter made me remove all the shortcuts?