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RickSE
05-30-2000, 11:46 AM
A while back I had a post on changing my 96 2-barrel 350 to a 4-barrel, http://206.150.187.82/ubb/Forum1/HTML/000160.html. The change over is now done and I’ve had the boat out two times. Here are some results if anyone is interested.

Parts used:
Holley 4-Barrel #0-80599, 650 CFM, 4150 Double Pumper.
Edelbrock Performer Intake #2104 for pre-Vortec heads.
3-blade 19P Quicksilver SS prop.
4-blade 21P Revolution 4 prop.
4-blade 19P Revolution 4 prop.

Best performance with the 2-barrel and a 19P Quicksilver was 4600 RPM, & 53-MPH w/full trim, at 3700-ft elevation. My first ride out with the new carb I left on the original 19P Quicksilver prop. I could really feel the extra power in the mid and upper ranges, motor ran up to about 4900 RPM, close to 45-MPH. I changed to the new 4-blade 21P prop expecting to drop to around 4500 RPM. Nope, instead of seeing the expected 200 RPM/inch pitch change I saw 400 and dropped to 4100 RPM. Mercury says to expect between 200-400 RPM change for each inch of pitch change. 200 seems to work if you stay in the same family of props, but 400 seems to be the number when changing from 3-blades to 4-blades.

So what now? I came home and ordered a 4-blade 19P. My thought was that the 19P 4-blade should drop the engine speed 400 RPM’s irt. to the 19P 3-blade.

We went out this weekend with the 19P & 21P 4-blades. I also advanced the timing to 10 deg. and leaned the secondaries in the carb from 74 to 72 and then 71 on the water. Here are the results.

19P 4-blade: 4600 RPM at WOT & 56 MPH, 75-80% trim.
21P 4-blade: 4200 RPM at WOT & 56 MPH, 75-80% trim.

The only thing I am curious about is what a 21P 3-blade would run. I would expect to see 4600 RPM’s, but could I get more speed??

I think the old 2-barrel cam is really holding back the potential of the 4-barrel, so I’ll probably be putting in a new roller cam soon.

So about $900 and 3 MPH, $300/MPH. I hope future speed increases come cheaper.

Forrest
05-30-2000, 03:33 PM
$300 per MPH is about right at that level . . . it only gets more expensive from there - ask GEOO!!!

Also, you may need to get your RPM up near 5000 to make use of the higher flow capacity of new carb/intake, especially once you get a little more cam. Consider ditching the four-blade props and trying a three-blade 21" Mirage or Stiletto.

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Forrest

[This message has been edited by Forrest (edited 05-30-2000).]

RickR,GroveCity
05-30-2000, 04:41 PM
Rick
See what happens if you remove the spark arrestor and or hatch.
Or course make sure you us your blower.
Air in Air out, what kind of exhaust do you have? (it may not make a difference below 5000RPM)
3mph gain is pretty good you probably added 25HP.
I agree with Forrest a cam is your next step.

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RickR mailto:riggerb@aol.comriggerb@aol.com</A>

Barry Phillips
05-31-2000, 12:09 PM
Rick: Lose the 4 blade, if your looking for
more speed 4 blades just creates drag. If
you can spin a 23 pitch prop at 5000rpm you
should run a lot faster. Try a Stilletto,
Ive read good things about them. My 18 runs
an honest 65mph with a 23 pitch 3 blade
Vengeance at 4600 rpm. Can you increase the
limit of your rev-limiter to 5,200, this
will not hurt a motor thats in good shape.
Good Luck
SO-SLO

GEOO
05-31-2000, 03:07 PM
Rick, Have a Prop Shop add some pitch and cup to your 19" Three Blade. GEOO

RickSE
05-31-2000, 03:30 PM
I'm beginning to agree about the 3-blade. It can't hurt to try, it's only money.

RickR, I'm using a 9" K&N air filter now so I should have low restriction on the intake side. The exhausts are stock Mercruiser w/Silent Choice, but I hope to replace the risers with IMCO tubes soon.

I more than likely will change the cam now, probably to a Crane marine roller, 276/284 dur. & .488/.509 lift.

Barry, I don't think I could ever turn a 23P at these altitudes with my engine. 21 is probably as big as I could go. A 21 3-blade should work pretty good with the cam and riser changes. Thanks for the info guys.

AVickers
05-31-2000, 04:33 PM
One nice thing about higher altitudes is that you can up the compression ratio and still not have to get too radical about octane ratings.

If you have access to car pump premium gas, (as opposed to at-the-dock premium), the best, cheapest way to increase power in your boat engine is to up the compression ratio. Deck your block, find some small chamber heads (or angle cut your existing heads slightly -- to preserve intake manifold geometry), use domed pistons, etc. (Be careful w/ old Small Block heads 'cause lots of the old smaller chamber heads didn't have hardened seats -- a real problem w/ unleaded fuel. You could install seats in them, but I've heard that in marine applications, they can come loose 'cause of the rapid cool cycle of raw water cooling systems...but I don't know for sure.)

The next thing you can do is get it to breathe better -- carb & intake manifold (you've already done this); smooth, gasket-matched ports; headers; blower; etc.

In my opinion, the best/cheapest combination would be to get a good cam, a good intake manifold and carb (you already have these), and bump the compression ratio up to the mid-10s. (You might be able to put a knock sensor on and get slightly more compression, but retarding the ignition will certaily scrub power gains away quickly. And if it knocks, the system will retard the spark.).

Another thing would be to get wet extractor/headers, but I've heard that good ones are expensive in a major way.

Also, the fewer the number of blades, the higher the ultimate speed. Four and five blade props look cool and give a better hole shot (and they are smoooooth), but they cost you in terms of top end speed...

And that's my $0.02.

Barry Phillips
06-01-2000, 07:30 AM
Rick: have you considered blower? This
might be the way to go in your high
altitude situation. I've seen dramatic
results with a ProCharger on a 454 22.
Frank Civitano a member of this site also
just installed a ProCharger on his 22ZX.
A quality set of wet headers like CMIs
will cost you almost as much and I don't think will produce the speed you want. A cam
is a good idea but a blower will compress
the air feeding you cylinders overcoming
your thin air problems, and might be more
cost effective in the long run giving you
the most bang for the buck. Frank can you
give Rick any advice on the ProCharger?
Good Luck
SO-SLO

RickSE
06-01-2000, 09:39 AM
I have considered a blower but I think a cam is the next logical step. I've pretty much decided aginst a roller cam due to cost. A nice flat tappet hyd. cam will only cost $150 w/lifters.
I have to decide how far to take this boat. My biggest concern is the Alpha drive, especially since my lube already has metal shavings in it. I could always install a Bravo but for me it makes more sense to buy a new 22 Classic w/BBC & Bravo. At this point I'm only looking to get 60MPH out of the boat and I'm already pretty close.