khubard

OK motor heads.. I need some input. I have a 89 Scarab 22 with a Magnum 350. I engine has had some but I do not no exactly what. I can tell you that it does have a cam in just by listening. The motor is tight and runs good. The top speed that I get at this point is 62mph. To achieve this I am really having to trim high and get the boat out of the water. My RPM's at 62 mph is 4600 rpm. I am running a laser 21 prop. I am thinking of pulling the Quadrajet and the stock intake and replace with a single plane intake and a Holley 650 cfm with a MSD distributor. My thinking on this is to increase horsepower on the top in speed. People have said to go with a mechanical secondary on the carb. I personally think I need a vaccum secaondary in fear that a mechanical will be to responsive and choke the motor down when going to WOT. Any thoughts would be great. Thanks for reading

endeavour32

iTrader: (4)

I seriously doubt you will gain anything by replacing the carb and intake. A single plane is certainly not needed. If you were running it at 6000 + RPMs that would be one thing, but your not. The quadrajet carb is also fine for your application. As to your speed, get a top speed reading with a GPS device the water pick-up speedo's can be up to 7 MPH off and are typically off by 3-5 mph. The only thing I would suggest is to try is a Mirage Plus 21 and see what that does, but if you're really at 62 mph via GPS I think thats as good as your really going to get unless your going to spend $3000 plus to really increase your power level.

mike tkach

iTrader: (3)

i totally agree,new carb,manifold,and msd ignition will yield no gain in mph,bot it will lighten your wallet over a grand,save that money for gas,and enjoy your boating.just my 02.

FIXX

iTrader: (2)

+1 all the above,,save your money..Tf your really looking for speed the cheapest way to go would be either a blower or a procharger..either one will give you 5-10 mph increase tn speed..

dereknkathy

4600 i don't think you can go up in prop pitch. unless you can borrow a small diameter 23 to try out. alum exhaust and intake will take about 100 lbs out of the back of the boat. that might help some. unless you need new exhausts it isn't a justifiable expense. 62 doesn't suck. it isn't like you are being passed by sailboats.

Advantage 575

iTrader: (3)

X1million. Go boating. That's respectable speed

87MagnumII

guys think about this for a minute.

hes got a 21p prop
4600 rpm
assuming its a 1.47 drive ratio
62mph

all of this would equal 0% prop slip and we know this isnt the case.

10% slip is going to put him at 56 mph which is more realistic, not that 56 is slow, but realistic.

i am going to agree with everybody else on this, unless the engine is worn slap out, leave it alone and go boating. i just built an engine for my 20 ft concord. it was old and tired and needed replaced other wise i would have never done it. and once you start adding horses to gain speed you will never be satisfied and will keep spending money, and a lot of it.

leave it alone until its toasted.

Mariah212Z

If you are running an Alpha One, stay away from any Mirage prop which are Bravo designed props and will take away rpms from the motor (diameters are to big). The Laser II 21 is a great prop for light bow narrow beam boats running Alpha drives. Get a GPS hand held for true speed reading. The carb you have may be a Weber 600 Cfm if believe for the 350 mag which is enough for your SB or a good replacement would be an Edelbrock 1409 Marine 600CFm. You may want to check into some GM Bowtie Vortecs along with a dual plane intake like an Air Gap and the 1409 carb which would give you about at least a good 60 to 80 hp. Also you can shed some weight by getting rid of the cast iron intake and some low cost aluminum exhaust manifolds which will save up to 60 to 80 lbs of weight total. Your Scarab has a fast hull which will probably respond well to any addtional HP added.

Good Luck

keith2500hd

you could try open carb spacer, would tell if more carb would give more rpm. with alpha, i would get rid of excess weight, more power will get you closer to alpha's threshold.

endeavour32

iTrader: (4)

Leave it alone, if it runs right! New heads, gaskets, intake, carb, exhaust might get you 3 MPH. Thats going to cost you a solid $2000 if you do the work yourself. Listen to the first few posts. Also 87Magnum is correct with your speed. That is why I asked if its GPS certified. 55-56 MPH is still respectable for a hull of that era with that power. Run it have fun, when you want to go faster just get a new boat. Trust me, its the cheaper way to go!