Posted in the Scarab form but nobody got back with me so I thought I'd post here.

21' 1987 Wellcraft Scarab I, 350/260HP Merc Crusier with Alpha Stern.

At WOT I'm running almost 5K RPM's. Top speed trimed out I have reached was 44 MPH via speedo; I don't have a GPS reading. That was with a load of 3 adults and two small kids. I also had a large "whale tail" fin on the back that I'm sure wasn't helping much.

The current prop that is on it is a Quicksilver 48 3 Blade. It also had the numbers 16316 45 19P on it. In relatively good shape. I also believe it is stainless steel. RH motion.

How fast is one of these boats supposed to go?. I've seen cruising speeds of 40MPH to 50MPH with WOT speeds of 52-63MPH. I just want to know how far off off top end I am vs. stock so I can start to make my performance mods. First thing will prob be a new prop; then a 4 barrel carb up top. Then????

Please, any help would be great.

I assume you are talking about the 21ft? I had one a couple years ago. It was a 1984 with the 350/260 Alpha. I believe i was turning a 19p 3 blade and running 54-56 @46-4800rpm on a handheld gps. Its not going to be a real fast boat, just enjoy it. They sure ride good for a 21'.

I think you will find that doing "here and there" performance mods really won't get you much, if any speed. I had a 20ft Formula Spider years ago that had a tricked carb, prop, and breather on it. The boat ran basically the same as when it was stock. Unlike cars, the weight of the boat will command at least 50hp more to see any mph increase no matter how light it is.

If you want to have a little rocket I would look into a procharger, or whipple setup. Those will give you immediate results that you will love and you won't break the bank or the boat doing it.

I would contact "Clay Washington" here on the board for some details. He has a single engine Crown Line with a whipple and seems to love it.

My friend has a '87 210 Elite. With a 350/260 he was going around 50 MPH. He put in a 373 with 320 HP and he is going 54 MPH.

So do you all think 55-60 is easily possible with prop/carb/intake?

55 Maybe, 60 doubtful. My friend was expecting better numbers. The Elite and the scarab probably have the same bottom. I would enjoy it the way it is and start saving or searching for a "Fast" hull.

I'm a little confused by your post...but if you are only seeing 44 mph on your speedo, I would be willing to bet that your speedo pickup tube is bent or partially clogged. get a handheld gps and check it again!!

So I will aim a stock speed of 50; and a modded speed of around 55 for my goals. Does this sound about right?

Will also go and borrow a GPS on the next run to see what numbers I can come up with.

Plan on being on the boat most of the weekend if it is nice.

Agreed I had an '86 and loved it to death. You could regularly catch me flying at LOTO on Holiday weekends whenever the "OBNOXUS" sled was broke or at Lake Perry, KS

I kinda doubt it with just a carb and intake. The prop might give you the most results, but probably not 5mph. 5mph is quite a bit of increase in a boat.