View Full Version : NEW TO ME 98 4.3 alpha 16" NEED GUIDANCE

10-21-2012, 10:06 AM
Bone stock 2bbl alpha. What will my top end prop be? Has anyone personally swapped out heads/manifold/carb for some high performance heads and a 4bbl manifold and carb?

10-21-2012, 08:13 PM
I'm just doing that swap on my woodie boat right now.

Ditched the 250 IL6 for a 4.3L V6...bought some real vortec heads, Edelbrock 2114 manifold/ 1409 carb (withcalibration kit)...decided on the most up to date stock camshaft (431-803186, from the 230 HP version) but stickin' in 1.6 roller rockers.
Currently mulling over exhaust options. IMCO Thumpers are out (as they cannot be used with a diverter)...GLM are cheap...but, they're cheap. And Hi Tek look to be the front runner if I can sell a kidney to pay for them.

I'm told my once 175 HP anemic V6 should breathe somewhere between 220 and 250 HP as well as be about 100 lbs lighter than it was. Plenty good for my lightweight plywood woodie. Prop spec work will be done once she's wet. I am looking to go to a Merc High Five stainless to pull a bit better.

I'm up in Canada where it's starting to get cold now so, I will not know just how this lump goes until may or so.... stay tuned.73437

10-21-2012, 08:34 PM
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You have vortec heads on the 98 . you might gain 2 maybe 3 mph going to a 4 bbl manifold and carb . i had the same set up and did the same thing and in hindsight i would have left it alone ..

10-22-2012, 06:52 PM
i agree that manifold and carb alone are not worth it. there must be someone here that can give me a report on doing heads and cam as well. heads cam and a 4bbl has got to be a 75hp gain which must translate to 10mph gain.

10-22-2012, 07:11 PM
75 additional horsepower won't get you 10 mph in a 16. Don't forget you are going to be fighting the hook in the hull. I would look up Jim on here as he has a lot of info on the 4.3.
I think you can build a reliable 4.3 with 300 horsepower but you will be money ahead doing a swap to a V8.. I think a 4.3 pushing 300 horse power would get you into the low to mid sixties.

10-22-2012, 10:15 PM
who is jim?? how much hp can you feed an alpha?

10-22-2012, 10:24 PM
Jim... Buizilla he will chime in I am sure. An alpha will hold 300hp after that who knows.

Just Say N20
10-23-2012, 10:58 AM
A 1990 Donzi Classic 16 with an OMC drive, 21” stainless prop, 190 hp version of the 4.3 V6 will run 53 - 55 GPS mph all day long.

My 1967 Ski-Sporter, Volvo Penta A290 with trim, 1.61:1 gears, 24” Ultra SS prop, 270 hp 350 ran 57.3 GPS.

The 4.3 boat runs much more level, flies/lands better, and is almost as fast on top end. It doesn’t accelerate like a V8, but then 190 hp shouldn’t behave like 270 hp.

I would think a 300 hp V6 would be a 60 - 63 mph Classic 16. At sea level. On a cool, dry day.

I went with the V8 because I prefer “the sound."

10-23-2012, 11:30 AM

10-23-2012, 09:27 PM
that was a nice review of street car building v6's. can i run aluminum heads and intake when i use the boat exculsively in salt water?? even if i flush it for a long time and spray it down with oil after each use, i can only believe within a year ill have a pile of pitted junk ...or am i wrong??

10-24-2012, 10:11 AM
Quote: "heads cam and a 4bbl has got to be a 75hp gain"

As mentioned you already have the Vortec heads...minimal gains to be had there.
General consensus from my on-line research says about 20 HP for the 4bbl and manifold. so now you're at 210ish HP.

The next gains are in the proper cam...difficult to predict as there are many choices and you can't go too wild due to reversion. So let's say you get another 10-15 HP out of the cam and 1.6 rockers...call it 225HP.

Last area is the exhaust. Add approximately another 7% overall on a performance exhaust and you are at 240 HP.

Now you can't really just add up the performance claims an state 240 HP definitive. Best to give a +/- and say somewhere between 230HP and 250 HP. That's the ballpark.

In this scenario you are at best, a 60 HP gain from where you have started and as pereviously mentioned...that ain't gunna buy you 10 MPH. (I don't think you'll be breaking 60MPH). Now, if you are going to spend serious money on the 4.3 and also move to a forced induction system you can do better...but how long will it last?

If you're happy flirting with the 60 MPH number massaging the 4.3 may be the way to go for you. It certainly is enough on my antique boat. But IMHO, the best performance for the dollar spent is to move to a SBC.

10-24-2012, 11:56 AM
An alpha can handle 450+ if you don't nail it at every holeshot and watch your landings if you catch air. GLM's are inexpensive but I would not say cheap. Barr & Osco are more inferior with both quality & performance in my experience. But $300vs$2000 is a big leap.

As far as the 4.3 goes, aluminum will last maybe 2+ years in salt before it corrodes. Motor can be saved depending what corrodes and where the pieces go after they break apart. As far as performance goes, follow their advice here and pretty much leave it alone or find a used 4bl intake & manifold and call it a day. Do you have thru-hull? If not just wasting time.

Lastly I love 16's but it is still a 16. Since you are new, drive it, enjoy it and see if you have 2ft itis after the first season before youdump $5k into a V8 swap. Easier and cheaper to buy an 18 than modify yours.

10-27-2012, 07:44 PM
I've decided to keep this thing 100% stock. I'll play with props and thats it. In the meantime ill start putting together a nice 350 that makes a solid 350 hp on pump gas and the first sign of the 4.3 having any issues ill do the swap. Thanks for all the input.

Just Say N20
10-28-2012, 11:52 AM
As a confirmed speed freak myself, I was surprised by how much fun I had driving around a friend’s 1990 16 with the 190 hp V6. It was an absolute blast!


10-28-2012, 12:57 PM
The 4.3 is a nice little motor and may not give up so easily...

But if you start building your SBC now and plan it over some time you can build your "dream engine" without the big "sting". As a bonus you get to research and fret (and change your mind over and back) over every detail.

When it's ready... the 4.3 will be worth good money (the 190 HP versions command some decent dollars in my neck of the woods)

Have fun!!!!