350hp 350
 

I don’t know if this is the right place to post or not but here goes.

i have a 2001 Crownline 225br with a 250hp 5.7 vortec engine. 2 barrel carb Alpha 1 1.5 ratio with a 17p merc racing rev4. Boat weighs about 4000 lbs. with straight through hull exhaust. tops out at 45 mph. I want 55-60. I don’t want a 383 stroker setup.

I’m thinking about doing a cam swap to a 270/276 marine comp cam, going to a thinner head gasket to raise compression a little, Edelbrock rpm air gap intake and a 650 4 barrel (1409?) carb.

Will this setup push me up to the 350-375 hp range.

I am not close to an engine guy but just a cam wont get you a 100 hp gain imo for sure !!!

Well that’s why I’m here to find is peoples opinions on what I will gain. Or what it’ll take to get me to the 350 hp range. I’m pretty sure I can go to a 4 barrel and get to 260, and a very basic cam and get 300. But what do I need to make my 250 5.7 a healthy 350hp?

To get a hundred HP gain your gonna need a top end minimum. New heads, intake, roller camshaft, at the minimum. The trick is going to be keeping it making enough torque to get the boat moving and the peak HP within the allowable RPM range of your short block. Call a few companies like E'brock, Trick Flow, etc and see what they have to say.

From my understanding, it is already a roller cam motor, and I thought the 096 heads were supposed to be good?

I doubt a 100hp will gain you 10-15 mph. More like 6-10mph if you are lucky.

Any decent cam will probably require new exhaust with long risers

Your engine has Vortec heads, so yeh, you’ll be right there for hp.

4bbl carb + intake will put you near /at 300hp.

Those doubting a near 100hp increase maybe didn’t notice he has 2bbl 250 hp engine and adding a 4bbl carb and intake too ?

I’m not sure going to the thin head gaskets will be worth it. Personally I’d stay with normal felpro’s w/stainless core.

stock vortec 350 with a good intake and a 4 barrel is around 325 those engines love to rev its very good right out of the box

When you say good intake and carb is the edelbrock rpm air gap good? What about the 1409 carb? Well this get me where I’m wanting to be? Paired with that 270 cam? Do you think that 270 cam will give me any chop at idle?

RPM air gap, roller rockers, and I used the 218 / 224* @ .050 cam and I think you can get very close to your 350 HP. I added Vortec heads because mine did not have them and gained 8 - 9 mph and ran 60 - 61 mph.

I used the Performer intake not the RPM air gap because I wanted to keep my Quadrajunk carb and the RPM Air Gap only accepts square bore carbs. Mine was a 260 Mercruiser (230HP at the prop). Your Vortec heads will not accept the lift of the cam you selected and I would be concerned about reversion as well with that cam. You will have to cut the valve guides down so the retainers don't hit the stem seals and then cut the valve pockets deeper, or use expensive Beehive springs to accept the lift. I used GM Z 28 valve springs and only used the outer springs since the inners did not fit and the harmonics are fine up to 5000 rpm without the inners. They say the RPM air gap and 1.6 roller rockers (you have to drill the pushrod holes out with 1.6 and that is why I used 1.5 roller rockers) combined are close to 36 HP. Your engine year I believe had 280 - 300 HP with a 4 barrel. The heads I replaced had 76 cc chambers and I kept the stock pistons so my compression was around 9.7:1 when I installed the lower cc Vortec heads. I ran 89 octane and 31* total timing to be safe.

One more thing, you could do some chamber work or pocket porting on your Vortecs to help out a bit, or buy the GM performance Vortecs with the larger intake runners and larger valves but I think they are close to $1000 a set today. I also got rid of the exhaust bellows and installed an exhaust tube but I think you have thru transom exhaust so that should help you out, I had stock thru prop exhaust. I could not even tell mine had a cam in it when it idled but the one you want, will have a noticeable chop at idle but again I would be concerned about reversion and go down a bit in cam size. Mine was awesome on fuel consumption, had excellent mid range and good top end since I only turned it 5000 rpm. If that is all you are going to turn it, I would stay with the cam I used or one size up. If you want to turn it higher and trust your bottom end, perhaps the larger cam is OK if you do not get reversion and don't mind doing the machine work and Beehive springs to your heads. I had MSD coil, wires and stock Thunderbolt ignition and distributor. I upgraded to a double roller timing chain and degreed the cam in.

I too had a 350 in a Formula . 300 hp 50-55mph I swapped it out and got a big block 400 hp 60-65 it's the torque that made the diff. my boat is 4200lbs dry. You need something that will get that boat up and going. It was suggested that I go to the 383 stroker. So glad that I didn't.

I struggled with a 1409 600 cfm on a similar setup both 350 and 383 displacements. Tried about 20 different metering rod and jet combos and always fat off idle and leaned out on top end. Went through fuel lines, pumps, etc. never found the answer. Went to a 780 vac secondary Holley, fuel consumption was cut by a third, power was up, (2mph gain first time bolting it on) and AFR was good across the board. In my experience with a boat just slightly lighter than yours 20hp = 1 mph.

It’s been a long minute since I’ve played with a sbc but what’s the downside of a 383?

Not so much that there’a a down side, just more money then I’ll looking to spend on this boat, and the 383 will over power the out drive and I don’t want to be worried about killing drives all the time

I dont see a lot of money difference in a 383 vs 350 if your trying to make 350 HP. The 383 will not be what breaks the drive on that boat. Your throttle hand might.

Chris

I can do a cam and intake and carb for less then 2k. 383 going to be 5k

So, upgrade your top end and see where you get in HP and MPH for your 2K... if it's not where you want to be, you are obviously into upgrading the bottom end.
There is no such thing as cheap speed or HP - you have to pay somewhere - initially, or parts/fuel/reliability at every change from stock.

That is kind of my plan was just hoping someone would know what kind of power a setup like that would make

I had the 202 CL boat with an efi 5.0. It would top out at 55mph. In my humble opinion your gonna piss away 2k$ and not be happy with the results. The bow riders need torque as others have said since in most cases the "skanks" (quoted from another thread) will be up front enjoying the view. In that style of boat Im sure you will also be pulling skiers and tubing. I would think you would be better off looking for a bravo III if you dont already have one. You must have an alfa if your worried about your drive.

My Cobalt is a little over 24ft and much heavier then your 225. I have a 7.4 but its the 315hp model with a duo prop (same as a bIII) it tops out at 50mph but thats fully loaded. Usually 4 adults and 70 gals of fuel. We spend 90% of our time cruising at 30 mph and riding like a cadillac. Our boats just aren't made for speed. You can make it fast but what ever you do to the engine you will have to do to the drive. Its the same with a car. You hop that engine up and your going to have to hop that tranny up as well to handle it.

Good luck with whatever you decide. On a side note that $ will pay for a lot of gas and beer.

Logically I agree with every thing you said, but my need to change things is itching. I’ve made it two seasons with no changes to the boat and it’s killing my. Every thing I own gets hopped up.....I drive a 2500 chassis duramax powered Tahoe ha.

the fact that the boat will only do 45 is my issue. I would be perfectly happy if I could it to 50-55. Not that we cruise that fast usually. But being able to hammer down and get up and go is always fun.

my boat with a 350 mag 300hp alpha one will do 55 from what I’m told. That’s why I was wanting to get up over 300 hp

If you go through a lot of threads from people looking to go faster in any boat over the history of OSO... the result and advise in the end is - sell the boat as it is reliable and buy the boat that will get you where you want to be mph wise. Cheaper and more reliable in the end.

If you had a B-drive boat, you have more options for your runabout.

Problem with selling the boat to buy what I want is, this boat is paid for and only worth about 15k even with the 6k dollar stereo system the p/o installed. To buy what I want and get a good stereo and the other things this boat already has that I want I’d be looking at 20-25k easily so to put even 3-4K into this boat I’d still have less then 15k in it. Just a matter of if I can get the 55 area or not.

Your Alpha One wont take the horsepower. rated to 300 max. It may last for awhile but your'e better off to a Bravo 1. Check with others for gear ratio compatibility with the new planned horsepower as well.

OP - I swear this website used to bleed performance.

Now it’s ‘sell your boat snd buy something with an outboard, preferably a center console.” My have Times changed. Lololol

That Alpha 1 will be just fine behind his small block. Torque is what kills them. And he's not gonna be in BBC torque territory. Guy run them with mildly built BBC and a light throttle hand and they live quite long lives for most.

there is a saying there is no replacement for displacement especially in the marine world, just because you increased hp in the engine which comes with it's own issue's such as over lap, water reversion, idle characteristics, does not mean the boat will go faster, in most marine applications the focus is in torque, mercruiser makes a 357mag 325 hp this still will not be enough to get you the the speeds you are looking for, the optimal pwr plant would be the mercruiser 383 carb bravo 350hp 427 foot lbs of torque

yes the alpha out drive is only rated for 300hp we have put way more hp thru the and the have held up, if you smash the throttle to the dash you will brake them, if you looking to bark them over the waves you will brake them. check out ACTION PERFORMANCE MARINE CORPS WEB SITE. THE 19' MONZA HAS A 650 HP BIG BLOCK IN FRONT OF ALPHA GEN 1 OUTDRIVE 1.32 RATIO WITH A 27 PITCH MARIAGE PROP TURN IT TO 6500 RPM @ 92 MPH AND A 27 MACH 1 WITH A PAIR OF 383 STROKERS WITH ALPHA 1 OUTDRIVES 1.50 RATIO TURNING 5300RPM @ 74MPH

Years ago, I had a 19' Executive open-bow with a 260hp 350 Alpha Mercruiser. I put on a B&M 144 blower, Holley carb (double pumper of some sort), and thru-hull exhaust. After getting it tweaked, it ran high 60's, lower 70's. Alpha drive lasted about 2 years until I started pulling some big boys skiing. Bottom gears went out the first summer, upper gears the next. Someone saw it and loved it more than me, so it found a new home.

As long as you don't go crazy, Alpha can last awhile I think.

Isn't RPM the Key to MPH?
 

It seems like you could calculate how much more RPM you would have to turn the engine to achieve your objective. (Engine RPM X OD Ratio X Prop Pitch subtract for Prop Slip) RPM @ 45 MPH could be 4800 rpm, RPM @ 55 MPH could be 6000 RPM. Still doing 45mph at 4800. I am more than 3/4 of the way through building Twin 427 Stroked small blocks that dyno tested @ 450hp and 500ft.lbs NA with 215 heads 9.5 to 1 and 276 cams. Peak Horsepower was made at 5300 RPM and peak torque was at 3900. These engines with the addition of twin superchargers should easily do 600/600. I am building torque monsters so I can change the outdrive gear ratio and ultimately lower my engine RPM..... Without significant gear ratio change 300hp at 5000rpm is the same MPH as 600hp at 5000RPM.

I used to build a few SBC back in the day, most of the 350+hp 350's would not be suitable for marine use, but that was hot rodding on a budget lol. I would think you could get there with "new" technology in heads and cam combo. Before I would spend the money on your heads, I would consider some out of the box ready to bolt on aluminum heads. Those and a good marine grind cam, and intake/carb combo you should be real close and not breaking the bank. If you are even considering removing the engine for low end work of any kind, I would highly recommend considering a used B1 set up with a complete ready to drop in big block. I see them all over the market place for under 10g. Your alpha set up should bring close to 1/2 that, which makes the B1 set up very affordable.

I have a Mirage 23 footer with Volvo 350 and duoprop drive. I top out at 58 mph on gps with 2 people and no gear on board. I am very happy.

350 hp? big block right?

No It’s a Volvo 350 small block fuel injected and duoprop. It is supposed to be 300 hp but I have read it’s more like 320. The seller told me 55 but when we gps it’s 58. I have talked to guys with the lower horsepower 454’s in the same boat and they get about 62 with single prop.