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I just bought a 1990 Arriva 20' with a Mercruiser 350 Magnum and Alpha 1 outdrive. I did an oil change, but otherwise haven't touched the engine. I can hit 58 mph, with the engine around 4500-4600 rpm but it's porpoising pretty bad by that point. What modifications will get me to the 70 mph mark? Is this boat worth messing with? It has a 21" Laser 2 SS prop on it, and through-hull exhaust.
I would really appreciate any advice I could get.
Is that GPS or Mickey Mouse speedo on the dash? I would think 58 is very good for a stock 350.
I got it with a handheld GPS. The stock speedo was about the same. I am very pleased that the boat will even do 58 stock- thing is I would like to go faster... I'm sure everyone here can relate wink
I'd like to be non-stock pretty soon- I just need some recommendations.
Does anyone have an opinion of Speedcoat by EM inc? A retailer said I could get 2-3 mph by doing that. That might be less hard on the outdrive then the extra power I'd need to get there. Then I just need to come up with 5-10 more mph...
Are you aware that 70 mph is a number you will not be able to live with, when you reach it? Stop, before the addiction sucks up your cash. Once you go 70, it won't be enough. I'd leave it alone, after you speedcoat it. When you want more, buy a bigger engine, boat, or a different style of boat.
58 mph is great. The only real performance improvement at this point, short of a supercharger, would be to install a better camshaft. A roller camshaft with 212/218 intake/exhaust duration on 110 degrees of LSA would really wake up your engine.
Dennis Moore
Dennis, I read your book cover to cover twice, and keep it in my work bag for when times are slow. I really appreciate hearing from you regarding my boat. (everyone else, too)
I was actually thinking about a set of Vortec heads and the Edelbrock RPM airgap manifold w/edelbrock carb. Do you think I should just skip that and go for the cam? I was planning on a Crane 109631 cam also, but not quite yet. My thoughts up to now have been to increase RPM to increase speed. Am I wrong in thinking that? should I just keep the stock heads and quadrajet, go for the GM high-rise intake, and put a cam in it?
Is my prop as goood a choice as any at this point? (21" Laser 2)
Thanks again.
4800-5000 is as much as you want to spin that motor.Vortec heads and intake along with the cam will give you substantial improvement over what you have.You'll have a good sleeper and since you just bought it you should be happy for awhile.
You already have the high rise intake on there. You can't go wrong with the Vortec/Edelbrock set up for max power. Make sure you install a camshaft with a 110 degree LSA.
Dennis Moore