Re: bayliner hotrod project, help w/ top speed!!
that's exactly the same cam that's in my 383.I would say it'll be iffy in a 350. You can see the idle quality I get in the vid below. Note that that was with world products sportsman heads, ported, and running about 10:1 compression ratio. Usually you can assume that going from a 383 to a 350 is work about one step in cam duration (more displacement same overlap acts like a smaller cam). I am running long risers. the next step down in that series of cam would be a safer bet in a 350, but it depends a lot on how you're going to use it. I would probably use the xm270h you're looking at as a starting point. use 1.6 ratio rocker arms. mine will idle down to 500-600 rpms, but again on a 350 you'll get a little rougher idle with the same cam.
You might watch on ebay for a set of the longer risers that bolts on to a factory merc manifold... never know. I bought my imco powerflows for a total of about 800. the manifolds were unused and in a box for 600, the risers off ebay for 200 used and in great shape. that's far less than the almost 3000 for the same set-up new. just be careful, leaking manifolds or risers will destroy your engine in no time.
Agree with John on compression ratio, but note that if you run a cooler thermostat, and if the blocks been zero-decked to give a tight quench, you can get by with a little more than 10:1 with no problems on 93 octane pump gas. My cranking compression with the wp heads was 195 on all 8 and I never had a ping on pump gas. I did run it a little fat to keep things cool though...
note that I run my alpha drive behind 450 horsepower and have run it turning 5000+ rpms for 10s of minutes or more without letting up on more than one occassion. run good lube, change it often.
If you're going to run the boat hard, definately get a good sized external oil cooler - your bottom end will thank you. take the oil pressure off the front of the block and watch it drop during a hard run as the oil temp rises... it'll make a believer out of you...
Your boat will be faster with the 1.65 / 1.62 gear in it and higher pitch props. The sweet spot for prop efficiency at the diameters you'll be running is 26-29" pitch. You'll still be below that with 1.65. prop it and go. I'm seriously contemplating having a 1.65 mor even 1.84 gear set put into my alpha ss....
