pipes

Good morning. I recently purchased a 1986 convincor 251. stepping up from a chris craft scorpion 230. Haven't had a chance to have it out on the water yet. I n the process of putting engine in. I purchased it without a engine. I am putting in 450 hp 454 with factory ex manifolds with silent choice and 4.5" thru hulls. It has a alpha one out back. Not sure what prop to start out with. I have a ss 21 and a 23. From what I have researched about this boat it appears to be a pretty fast hull.

sabo

iTrader: (2)

I would say 450hp in that hull should put you mid to hi 60's, and depending on rpm and drive ratio we can then select a prop, with 1.5 ratio, 23P and 66mph you will need to turn around 5200rpm. What worries me is if you truly have an alpha out back is it going to hold up? You will really have to baby it with that kind of power. And yes the 251 is a relatively fast hull

pipes

Thanks for the reply. I know that I will have to baby the alpha but a bravo upgrade isn't in the cards right now. I will start out with the 23 p for now and see where that takes me. The outdrive is a 1.5 ratio. I have read that these boats like to cruise around 30. do you still have your 251 hows it do with a blower motor

sabo

iTrader: (2)

yes I do, best run so far is 88 gps, it is fun to be one of the oldest boats in the group, yet the fastest!

Powerquest_Baby!!

If it were me I would keep my eyes open this winter for a complete bravo setup. The odds are VERY good that you will destroy your alpha next summer with that much hp and torque. When that happens you will already have the parts needed to do the upgrade. Just my $.02

WHIPLASH

My 89 251 has a stock 454mag with GLM exhaust manifolds , Fastglass stainless risers and a Holley 800 carb. With a tuned 23 Mirage 3 blade it does 69mph and with a 22 Bravo 1 4 blade it rides better but only 66mph.
BTW the boat has been major refurbished , upgraded and customized and the best part- wait for it- it is for sale!
I tried! Good luck with the new ride. Go easy on getting on plane and feathering off waves, get a Simrek drive shower and use synthetic oil in that Alpha and it should last you.

pipes

so let me ask you guys this. On my 450 hp build I was going to use ported oval port bbc heads. I now have access to Brodix heads. They are alluminum with 2.25/1.88 valves. 300cc intake runners and 132 exhaust. I know there will be a huge weight savings, but I am concerned about losing to much bottom end with having such large intake runners. But I think I can compensate for that because I am using a predator carb set up for marine. Let me know what you think. The heads are practically being givin to me so I would like to use them.