Alexanderlindahl

I am in the early planning stage for a bbc 454/496 stroker for my Donzi 21 hornet.

it has a 7.4mpi engine in it now, and was first considering buing a efi 496 for it. But i could probably build a Nice carbed 454 stroker for less money and more hp newly refurbished. Im not the biggest fan of carbs, but i will try it i think.

not new to build engines, but first boat engine/bbc chevy build.. im located in sweden so i have mostly built german and swedish engines..

im shooting for ~550hp, from the info i have gathered it should be pretty straight forward?

i would like som tips regarding som parts.. heres where i am at:

454 bottom .060 (does generation really care?)
4.25 Crank With i beam rods and new pistons around 9-9.5cr (any particular brand? Scat? Eagle?) Weighted and balanced.
Roller cam (dont know suitable model?)
heads? Would prefer a set of OEM ones i can port (if needed) and rebuild. With new valves Maybe ill go alum later.
a Nice valvetrain,
rpm air gap intake
carb, 750 cfm enough?
imco powerflow exhaust.
would a TB IV work or should i go aftermarket ignition?


the boat has brand new bravo transom, brand new mayfair 1 ram steering, and getting a xr drive with -2 sportmaster.
So it Will handle the power.
i Will build this engine while i use the boat with the 7.4mpi..

LakeHuronPower

Gen 6 is going to be your best bet. Revised oiling system, factory roller block, and all are 4 bolt main.
I wouldn't use stock heads unless your budget doesn't allow aftermarket, if using stock heads look for a set of older Gen 4 heads, either the big oval ports or rectangle port heads, the Gen 6 279 heads are good for compression but are garbage for flow.
Crane 168731, or 169611, or even 169621 (500 EFI) if it isn't too much for your build.
No point in dual plane intakes on a boat in my opinion, ditch the air gap and use a vic jr or a Dart single plane
Use a Holley sniper if you don't want a carb.

Rookie

iTrader: (4)

Let me preface this with I have been running 550HP-600HP 454's for nearly 14 years. Different head and cam iterations over the years.

Quick inexpensive build I can think of.
9:1-9.5:1 forged pistons
Promaxxx 317 bare castings (you install good components)
Single plane intake
850 holley or Sniper EFI
Comp Cam range ~235°In / ~240°Ex, around 0.635"/0.635" lift
Comp 933 springs
Good exhaust

I'm changing things up right now (going EFI) and have cam, ignitions and intake in swap shop.

Alexanderlindahl

Thanks for the reply, seems like i have to do some more reading.. Especially regarding the holley sniper!

im chasing a 4bolt bottomend as we speak (on this side of the Atlantic ocean, ill see what comes up.)

ThisIsLivin

Definitely dump the TB IV ignition and go with Daytona Sensors. It's totally programmable and has idle control feature along with a lot of other features.

Rookie

iTrader: (4)

Just curious, why dump the TB IV? He's not building that extreme of an engine. I agree the Daytona Sensors will have more capabilities, but for this build would they be beneficial/cost? If he can't get a 550HP 496 to idle there are more problems than his ignition choice. I've used Crane boxes with the 7 canned programs, TB IV's and a Daytona box. Now I'm going full programmable Holley EFI CNP timing.
Just curious because I'm having a hard time justifying going full Holley CNP timing.

hogie roll

The air gap doesn’t give up anything to a single plane in the 550hp range and will make more torque.

ThisIsLivin

I'm just going off my experience, I'm probably running a bigger cam the OP is looking at. I was running an MSD 6M box and a carb and getting my boat to idle well in and out of gear, especially trying to maneuver in narrow ramps in a swift river current was just plain embarrassing. When I switched to the Daytona Sensors ignition and did a little programming along with their idle control, it's like night and day. I also don't run a choke and I boat in water that in spring is only 34 degrees. So when you add it all up it makes it hard to keep it running smoothly getting out of the boat launch. With the Daytona System, I only need 30 seconds of warm up and at a much lower rpm than before. For me the difference was very dramatic. Yes I did try everything from custom advance bushings to locking the distributor with the MSD system. All I can tell you is that my boat now idles in and out of gear like a small cam EFI motor. I can run down the river at 650rpm for an hour even in the cold. Before I found the Daytona system I was seriously looking at using a Microsquirt ECM to manage timing. I run 93 octane premium and where I boat the best I can get at a marina is 90 octane, the Daytona sensors box has an input I use to retard timing 4 degrees for marina gas.

LakeHuronPower

Pretty interesting dyno test video involving a 496 here: Not a boat application really, but it isn't a 7k rpm drag engine. From this data sounds like tunnel ram is best at all rpm if you have the room.

cigrocket

iTrader: (3)

I agree don't dump the TB IV on the easy build. I have to say the TB IV is simple and always works. I have seen them look like they were at the bottom of a swamp, lit on fire and corroded as hell and still fire up and get the job done. Unlike the many different engines I have had with MSD Marine Boxes. Keep it simple stupid. KISS METHOD.