Upgrading a SBC (Dennis jump in here...)

[CB]

Hello all, been lurking here for a while and decided to come on in.
The Boat:1983 21'6" Lavey "Performance cruiser" 260HP Mercruiser/Alpha (1.48)
Currently running: upgraded aluminum exhaust with SS risers, Thru transom, Performer carb, 750 holley DP.
I can spin 5200-5300 with a custom cupped 22" 3 blade (minimal out trim) No GPS or speedo but I go by a buddy's 58MPH boat like he is sitting still (at least thats what I like to tell him).
I figure 67MPH or so... Don't want to argue that number and all real boat owners will lie about top speed anyway.
My first question, an observation really, is that my 260HP is running real strong. Stronger than it should with a stock cam. The PO did the carb and manifold and I have always wondered about a cam as well. Would a relativly stock 350 turn my numbers ?
Now the good stuff...
I want what all boaters want, better performance. Dennis, I have gone through both your SBC and BBC books several times and have more questions than answers.
First let me define what I want to accomplish. The normal role of this boat is a river runner and tow machine. We ski and board 3-4 times a week during the season. With that in mind I am considering a 23" High five. Have never run one but it seems to be optimized for my needs. Would like to plane a little sooner and hold speed when towing. I would also like 70MPH... (hard core "hot Boaters" stop laughing)
Some options I am considering.
Bolt on stuff.
1. Inject my current set-up
-Custom marine TPI, Holley TBI, or edelbrock PFI.
2. Vortec Heads/Intake
-What will vortecs do on my motor. I don't want to change pistons (A cam change is an option if desirable)
3. Roller rockrs, ignition, etc...
Build-it
3. 377, 383 vortec stroker
-(Bolt the heads on this season and build the motor next winter).
4. 400 marine conversion
-(How does a person externally balance a marine SBC )
5. 400 vortec
-( exploding Alpha ??)
As far as Alpha's are concerned, will they like more prop and less RPM (Torque) or more RPM and less prop (horsepower). The MR was replaced by a current model and set a little "tighter" (or so the builder says) If that makes a difference.
Ignition choice, I run 34 dgrees and the plug called out (RV12YC) in "Small Block Chevy Marine Performance". Whats a reasonable upgrade to my factory system ?
Head choice ?? The big question is how will Vortecs run on a stock 260 lower end. Dennis you did not mention this combo in your book ? Was it because the manifold wasn't around yet or is there quench and compression compatability problems ? The vortecs are the best bang for the buck on the automotive side and I am wondering if that is true in this case as well.
Let the fun begin ...

[Havasu Hangin']

CB:
I can spin 5200-5300 with a custom cupped 22" 3 blade (minimal out trim) No GPS or speedo but I go by a buddy's 58MPH boat like he is sitting still (at least thats what I like to tell him).
I figure 67MPH or so... Don't want to argue that number and all real boat owners will lie about top speed anyway.If your tach and prop size are correct, at 10% slip...your probabaly getting 65MPH...so your probabaly in the ballpark.
Since you asked Dennis the rest of the questions, I won't comment.

[CB]

Directed the questions at Dennis because I have read his books and respect his opinion.
Any real experience with small blocks and Alpha's is very very welcome. I especially would like some input from somebody who has DONE the vortec swap on a boat. (I suspect fuel burn would go down under normal condidtions and would like to verify...). Higher HP Alpha applications are also of interest.
Don't be shy.

[1BIGJIM]

CB, are you sure you are looking at the correct ratio for an ALPHA drive. To my knowledge they never made a 1.48 ratio. 1.5, 1.65, 1.84, 1.98.
I think they started making the ALPHA in 1984?
Could be wrong(not the first time) just my 2cents
:rolleyes:
[ May 15, 2003, 01:16 PM: Message edited by: 1BIGJIM ]

[CB]

1BIGJIM:
CB, are you sure you are looking at the correct ratio for an ALPHA drive. To my knowledge they never made a 1.48 ratio. 1.5, 1.65, 1.84, 1.98.
I think they started making the ALPHA in 1984?
Could be wrong(not the first time) just my 2cents
:rolleyes: Somebody is paying attention...
This was originally an MR 1.5 drive but was replaced with a Gen 1 Alpha...
[ May 15, 2003, 02:35 PM: Message edited by: CB ]

[canuck1]

I would suggest you have a look at the ZZ4 or the Fastburn 385 gm crate engines. The vortec heads work really good but the chamber is 58cc so you need to know what pistons you have so the comp ratio doesn't put you where you have to run premium fuel. I just replaced a marine power 330hp vortec with a 383 rpm alum head,performer rpm,holley 650. I'll let you know the difference after the weekend

[77charger]

those numbers sound good.I have an eliminator 21 ft with a 350 mag 270hp?very close.
Your motor is making some decent hp for what it is.I run a 21 pitch 3 blade that has been reworked by hill propellers and get 58-60 @4800-4900 rpm and my motor is stock.sounds like you got more than carb intake exhaust.I would think you are prob at 65mph.When i need to rebuild my motor i will bump up the cam a lttle as well as a carb change but plan on keeping it mild since it is the family boat.

[DogHouse]

I ran a hot 406 with an Alpha for a couple of years. My Alpha had the HD upper gear set in it (same as Alpha SS). They were fine but the lower gears finally gave up. Anyways, you didn't really say how much you want to spend, so I'll assume that you can spend some bucks. I would take your good 350 block, get a decent forged 383 rotating assembly with 6" rods, flat top pistons with 1.120" pin height, and 76cc chamber AFR 190cc or 210cc heads. That will get you just a bit under 10:1 compression. Then I'd use a hot hydraulic roller cam, something in the neighborhood of 240@.050 duration cam with mid-.500s lift. I'd top it off with a complete EFI/direct fire ignition system from Electromotive. That should get you up over 450hp and hopefully not make too much torque to kill the Alpha right away. The EFI will help keep the idle manageable for shifting.
-brian

[HP350SC]

CB,It all depends how much you want to spend.Your motor and drive will handle the vortec heads just fine.That should run you about $700 with performer intake and head gaskets.You will gain approx. 5mph.Step up on the cam next.In my opinion fuel injection is costly for any negligible gain.Roller rockers won't give much, if any, bang for the buck.My friend and I both have 350's with 144 blowers.Mine is a '92 with dart heads,crower cam,7 lbs. boost and a 1.5 bravo.I run a 25p high five prop 5000 rpm.My buddy started with a '97 350 2 barrel alpha,first step was 4 barrel,vortec heads and crower cam and springs.He went from 48mph to 68 mph.Now he's drilled his vortec heads to accept the old style intake,and bolted on the 144 blower at 5 lbs. boost.Hauls f.....g ass for what it is!Incidentally,he still has the 1.47 alpha drive (turning a 25 Mirage 4900 rpm.) holding up at 20 hrs. You just have to take it easy on the hole shot and use common sense.It'll probably grenade this summer!By the way,I have a brand new in the box holley marine 144 blower COMPLETE I 'll sell for $1500.E-mail me if interested.Have fun!

[HP350SC]

CB,I just noticed you're in Portland too.Just give me a call if you want to b/s. :D