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View Full Version : How much RPM?



clayman
01-28-2002, 08:59 AM
Hey Guys,
I was busting ass on my boat this weekend and it is running the best it has since I got it. turned out there was water in my tank. I poured out the fuel filter into a pepsi bottle, and I had about 4 inches of water, and 1/2 inch of fuel. I cleaned out the tank and I am emptying the fuel filter after every run for a while. I also put on some 8mm axcel plug wires and new plugs. my question is, in a little chop, I am turning 4500 rpm, at about 55 mph. the needles bounced to about 4800 / 60 mph . Should I be looking for more RPM? I am planning on continuing to add hings to increase the HP, and hopefully grow into this prop I bought From TED.( mirage plus 21). Any suggestions? IT has a 600 holley auto carb on it now, I am thinkingof changing to a 750 marine? I also have a eldebrock performer manifold to put on, any good?
Thnks for any advise,
James

turbo2256
01-28-2002, 12:37 PM
Just what do you have now and what are your upgrade plans?

clayman
01-28-2002, 02:03 PM
Sorry, I guess your guys need this info,
1986 18' Donzi Classic
350ci mercrusier ( 260 hp?stock)
Alhpa one 1.5 to 1
stainless marine headers
holley 600 (automotive)
everything else stock I guess.
21p mirage plus
I was told that the alhpa can take up to 350 hp , so I would like to get close to that number.
thanks for you help,
james

Rootsy
01-28-2002, 08:03 PM
yeah i'd say 350 hp is running right on the ragged edge of self destruction for the alpha... and try to keep her under 5200 rpm... i believe your motor was rated at 4400-4800 rpm WOT from the factory. If you replace the camshaft then you may need to adjust your WOT point due to a shift in the powerband for where your max hp will fall, the exhaust probably changed your peak horsepower point a tad already. Stick with the 600 cfm carburator for it is better suited to your motor than a 750. a larger carburator will weaken the vacuum signal due to the slower velocity of air through the venturis. this will hurt atomization of the fuel and low speed performance and economy. your 350 running @ 5000 rpm won't reach 600 cfm of air draw. the edelbrock performer should give you a bit of a gain over the stock cast iron piece as well as 20 or so lbs of weight savings. right now i have a 350 in my 97 16 classic with an edelbrock performer, 600 holley, k&n and a set of 1.6 ratio rockers on the production long block and exhaust... i turn 4500 solid with a 21 mirage @ 60 mph flat and she purrrrrrs like a kitten

Donzified
01-28-2002, 09:23 PM
James:
Good info,Thanks

clayman
01-28-2002, 10:22 PM
Sounds like I am on the right path . Thanks for the advise.
James

Ralph Savarese
01-30-2002, 07:23 PM
James what kind of cam are you brunning with those 1.6 rockers ?
i am just courious i was thinking about doing that.
Ralph

Rootsy
01-30-2002, 08:25 PM
Ralph,

My motor has the stock roller that came in it from mercruiser, pretty lame and tame. instead of trying to shoehorn that motor out and go through a lot of work and headaches it was a quick and dirty way to get myself some more lift to go along with my intake and carb upgrade... i am considering a camshaft for the spring though... waiting for comp cams to get back with me on what they suggest... for my desired results...