305 TO 383 ENGINE SWAP

[Mike Catman]

Has anyone on here done an engine swap from 305 to 383 in their 233. The ole 305 in mine is pretty tired and ineed of replacement. I have been looking at several options from newer vortec 350 engine combos to basic 350's and also stroker engines.  I am leaning towards a stroker 383. I am thinking that I will go with an older design with a 2 piece rear main seal to keep everything simple and the same for re assembly.  I would like to have a boost in performance and cruise speed. I am not looking to break any top speed records but would like to be able to cruise at say 35 mph without sucking the fuel tank dry or straining the engine. My thoughts are a performance 4 bolt  383 would be happy to run at 3600 -3800 rpm all day with no problem.  Anyone with personal experience with this would be appreciated.

Thanks!

 

[Glenn Sawyer]

I just built a 383 stroker on my 6th year resto. on my 233. I had it dyno,d 360hp @ 5400 and 413tq @4000 this combo pulls hard 2400 rpm had 380 ftlbs . I built the motor myself and got the cam from Marine Kinetics. I'm running a 750cfm edlebrock,afr eliminater heads,  rpm airgap intake,full roller cam. Fresh water cooled block and headers.This motor has good all around performance etc. Note I had to buy Stainless Marine Exhaust w/long tailpipes to keep from reversion.If your thinking about any kind of cam changes you need to think about investing in the exhaust 1st $$$.(call marine kinetics and talk w/ Bob Madera,he is a great guy w/tons of knowledge. He said if I invest in a Holley Hp carb this combo can push 400hp no problem (I went w/the edelbrock for simplicity and should be way better on fuel) I'm in the process of picking a prop for my volvo 290 now to put her in in the spring. Hope to break 60mph, but will be happy to get to 50 quick. Also you can go w/a one piece remain motor w/factory roller.It will save you tons off $ rather than converting to roller. My block is a 1969 bored >.080 yes .080. Makes it a 394 cubic inch stroker. Don't waste time on an old used and abused block,I went thru 3 to find a good one.Depending on your drive year etc you can go w/the right balance internal/external etc. I dont know what drive you have i'm going to guess alpha w/305 but you'll need to invest in a bravo or volvo 290 if you going to pound on it,Mercruisers are much more plentiful and cheaper. I could go on and on hope this helps, Glenn

[John Farabee]

Mike...I have two 355 Vortec Roller Cam motors along with Bravo I Drives going in my 255 Liberator in the next few days. They are replacing 260 HP 350's and Pre Alpha Drives.

I agree with Glenn in advising that you upgrade to Bravo. With the Bravo being in production for 25 years now the drives and Transom Assemblies are readily available on the used market and can be had reasonably. With the upgrade go ahead and get a 98 or later L31 Vortec Block that came with a roller cam set up originally. Roller is the way to go...you can run more cam and retain better dock manners with a roller set up as opposed to a flat tappet cam.

As for carburetion, I recommend Holley or Quick Fuel 750 GPM Double Pumpers for these motors...that carb really wakes a stout Vortec SBC up. I have seen that carb on a dual plane intake make 20~25 more HP in dyno tests over the Edelbrock with every thing else being the same. Since you only have to buy one carburetor get a Double Pumper...you won't regret it.

Don't fool yourself into thinking the Alpha will live with 400+ Ft Lbs of torque...you are going to beat on it so get a Bravo set up and be done with it. If not...keep 4~5 spare Alphas on hand so you can rotate them in and out of the drive shop replacing the gears..your choice.

A well built 350~383 Vortec will live at 4000 RPM all day with good cool oil and good cooling...an Alpha drive won't do that where a Bravo will.

[Mike Catman]

Thanks for the advice. It sounds like a sure thing to upgrade to Bravo gear.  My project has been put on hold for a little while I am trying to buy a house. I have also been toying with the idea of going to a 454. I have found a few good deals on a few boats with the 454 and bravo 1 on them. I would by the boat as a parts doner for my Formula and overhaul everything before putting it in my boat.  I really want to be able to cruise easy at 30-35 mph with about a 50 mph top speed. Most of all I want reliablility.  Most of the guys that I know all bad mouth I/O setups for anything other than lake sports.  I fish in the Atlantic here in Florida. I want to be able to go offshore with out the constant worry of mech. breakdowns.   Also, another factor to consider is fuel economy. I would hope to be able to get about 2 mpg at cruise of 30 ish.   Sound possible with a big block or built small block?

[John Farabee]

You can get the kind of economy or better with a Bravo III Drive. They aren't great for over 60 top end put on your boat with big torque you could cruise at 3000~3500 all day and be very economical. If you ever decided to go back to Bravo I all you need to do is change the lower unit.

[Eric Uschold]

Glen,

What kind of numbers did you get in your boat this season, thanks for the update.

[Glenn Sawyer]

53 loaded 4 adults 2 kids. cruises 2800-5500 can't be happier. Went out last weekend for 3.5 hours all rpms and cruise about 3000-4000 and hot rodding and only used 25 gallons. The motors not working hard at all. But could not hit 5500 rpm w/23 3blade prop. Changed to 4blade solas 19 pitch. Hole shot machine, can firewall it from stand still and throw everybody out if you want. But it is great @ every rpm. I'll get sum better #'s ,just can't keep my hand out of it. The hull likes chop. 2-3 foot 40-50mph no problem. My guess is if I put the holley gas eater I could get a little more hp/$ and clear 60mph wth trim tabs etc. Don't need it, I 'm in Buzzards Bay Mass. and it can be Mill Pond in Morning to 6-8 by lunch on the way back in the Cape Cod Canal etc.. I and very happy w/the results I have and put 20 hours plus dyno so far. Family and friends very comfortable even when it gets NASTY. I'll get sum pics this weekend!!!!!!Tach and rpm almost dead on 3000 -31mph cool!

[Mike Catman]

Glen, That sounds great! So it performed best with a 19 4 blade? Top at 50 with the 4? 53 with the 3? Maybe a 21 3 blade would be the perfect match to get you the rpm and mph. Thanks again for the update. Im looking forward to some pics and final numbers.

 

[Eric Uschold]

Same here

[Glenn Sawyer]

53 mph w/19 4blade @ 5500rpm., 4adults full gear , full fuel 85 gall., w/23 3 blade, 4 adults and gear 45 gallons fuel.  hit 52-53 but could not hit the 5500 rpm that I needed. Funny it seems to hit 53 like its a speed limit on the hull. Cruises 30-32 mph @ 3000 rpm.  No trim tabs , drive down. Note raised x factor by 1.5 inch Volvo penta 290. May have blade tweaked this winter.