Motor size Vs. Fat Sac limits?
 

Hey, my family is looking to upgrade our boat for a newer one. We currently have a x-star with a 400hp motor, and I High pitch prop. We put in 4 500lbs sacs and stock 1000lbs ballast and people. If one was to buy a 350 Hp motor and a High pitch prop would it still come out of the hole with al the weight or struggle? thanks

350hp propped right will get 3,500 out of the hole.

propped correctly, no problem

I realize this is a specific question, but... Gearing or power. Can't speak on how it'll do, but you're always better off with more power and less gearing. Engine will last longer, burn less fuel, and you always have more room to grow. You only have so many RPM you can run sustained or risk damage to the engine. I wouldn't want to be turning 4000+ RPM all day. Either big block or a small boat with a small block in a small boat that doesn't need as much weight. Alternatively, with all the newer small block boats you can always rebuild the small block with a stroker kit to get more displacement and keep RPM reasonable.

If it were me, I'd stick with at least 400hp, and the best prop you can get.

Technically, it''s a low pitch prop that gives higher rpm, but we know what you mean. A high pitch prop would be the one that struggles out of the hole.
For myself, I've never seen anyone complain about having too much power.

In my experience, if you have the bigger motor, you'll just keep adding weight. ****, why not?

I have the 350 propped as low as I can get it. Honestly it does ok, wish I had the 400. The 350 is a gas freaking hog, you'll quickly make up the difference in the engine prices in fuel. I run the fly high over flow kit and another 250#'s in the bow. More then 3 people in the boat I need to empty some out of the back. 2000+ stock you'll be fine all day just will go through a lot of fuel.

Hey Cory, I've thought about messing with my engine when it's out of warranty. I always thought a bore was the way to go. How come you would suggest a stroker kit? I thought strokers where better at lower RPMs and running in boat application where you are constantly running 4000+ RPMs a stroker wouldn't really be the best choice.

Sorry for the thread jack.

stroker is def easier than boring it and low rpm power will improve holeshot

If you are rebuilding, you are going to bore it out a little, as normally there is more cylinder wall wear than a hone can take care of (usually it's a .030 bore). You can bore a little more out of your standard SBC block, but not much to get any significant amount of cubes, and then you start thinning out the cylnder walls and are asking for trouble.

If rebuilding a 350, I'd say go with a 396 stroker (383 is a waste, as parts prices are pretty much the same, the block will already be in the machine shop to be bored over and the extra block clearancing isn't much money). You can still turn a lot of RPM's with a stroker, but I wouldn't do it with cheap stuff.

That said, the stroker will give you more low end (where you need it); upgrading the heads/cam is where the power is really found.

^ This. There's no displacement to be had from boring. You're talking a few cubic inches. Even on a motor with a longer stroke you're not likely to get more than 10 cubes out of it. Blocks have been thin wall castings since the 60s for the big 3. .060 is about max, .080 is really pushijng it, and every block is different. In a marine application you want your cylinder walls thick and strong due to the loads as well as raw water cooling and corrosion from the coolant side.

Stroke is where you get displacement. Heads are what make the power. If you want more power look at heads first, unless you're bottom end is due for a rebuild. Upgrade the heads to aftermarket or do some port work on your iron. Get rid of the restrictive cast center risers and get some proper headers or at least higher flowing cast manifolds. On stock displacement this will make a big difference in power and should improve efficiency as well. I'm not a Chevy guy so I can't recommend what components you use in a SBC stroker. If it were a Ford I'd be able to tell you, but don't want to guide you wrong for a Chevy. If you're handly with mechanical work it would be a fun winter project, though I wouldn't pull apart a perfectly good engine to do it... I'd wait until it needed a rebuild unless it was really struggling.

Stroke, as we discuss it in your typical SBC/SBF or BBC/BBF doesn't mean much to RPM. The differences are that small. For higher RPM you need to be worried about using good rods and keeping rotating weight light (lighter pistons, good valvetrain, etc.). I shift the BBF in my truck at 6500 RPM, and I consider that a lower RPM build and cheap with stock rods. I've had people tell me everything from big blocks won't turn that kind of RPM at all, or it'll self destruct if you try. Some people just don't get it, typically Chevy guys which is likely because the BBC is such an inferior platform and is very limited in what you can do.

Whenever the BBC is my boat dies it'll be getting a 460 based stroker (545). With the 454 I'm turning 2300-2400 RPM at 21 MPH with 1320 lbs in a 23' boat with no struggle at all. Not much difference with or without the weight in how the engine pulls. With more weight I might have to drop some pitch and gain a few hundred RPM but I can't fathom seeing 4000+ RPM to do riding speed. It's just not necessary with a bigger engine. In a 545 package you can easily get 600 HP and 800+ ft/lbs and maintain a nice idle so it has good dock manners. Heck, is a 393 stroker (Ford 351w) you can push over 400 HP easily and not need to turn that RPM. I'd assume you should be able to get similar from a SBC as SBF and SFC are very similar. If you're turning 4000+ with a stock 350 you should be able to shave at least a 500 RPM, if not more, with a 383 stroker build with torque in mind (build it like a truck engine). Focus on your rotating assembly, valvetrain, and oiling system if you'll be turning sustained high RPM. Oiling can be a major issue in stock engines at sustained high RPM.

BOOM. Kids, thats why you stroke an engine. Good stuff Cory