Modify or Upgrade?

[GregGTR]

Hi Guys,

I would like you opinions here as I want to go faster 95-100Mph;

Rig:
Ski/Speed boat 19' Mid weight Hull, with Pad (similar to the Australian Bullets)
225Hp Venom Johnson 1997 with nose cone (70Hrs) (420Lbs)
Solid Hydrolic Steering
10" Jacking plate
26" 4 Blade Shooter

Current Speed Mid 80's @ 6300rpm on 97Ron Fuel

Question:

Do I modify the Venom?
Do I sell the Venom and buy a ProMax300?
Do I sell the Venom and buy a Merc 280HP?

All options will end up costing me around the same dollars

Which motor is better the PM300 or the 280HP?

Note Speed is important to me but so is reliability, I don't want to rebuild the motors every season

[G-Train]

In my opinion,
I'd probably get the 280. The weight is a factor, as well as the potential of the 280 to spin higher rpm's (by changing electronics to the 260 stuff). The 280 stock should be a very reliable motor. You should be able to prop your boat to hit at least the 95 mph figure. You should dump the 4 blade prop for speed. I'd try a NICE Chopper 26-28, or an ET of same pitch (this type of prop will "carry" your boat better than a Cleaver, or Yammi style). A 28p should put you pretty close, if not over your goal, while maintaining the rpm's the 280 spins in stock dress.

The 300 would probably have a lot more low end grunt, but the top end, and weight I think favor the 280 for your rig.

I'm don't know much about the OMC's, they can be made to go, but the Merc's are more plentiful, and lots of hi-perf parts are out there for them.

Remember, a lot is going to depend on your setup also. Post a pic of your boat, and maybe someone has a similar hull, and can advise.

Good Luck

Greg

[FCnLa]

The first thing you need to do is change the prop. If you are going to sitck with a four blade, get a Renegade. Over the hub, a OMC SRX should do the trick.

There are way more people that are more knoledgeable that I., But I have studied up on them some. You can stop up the idle holes (in the cylinders) and change the air box for some V stacks (Instigator may still have some).

If you still want more you can up your compression. Some or all of this would require a rejet.

How much does your boat weigh?

[dash]

you need a bigger prop about 30 or 32 cleaver
low water pick up nose cone
get engine up real high
ive had one of these engines putting out 311 hp and run reliably for a few years on a 18ft bullet called rough red .ive had it doing 99 mph with 2 persons in boat(gps speed)
with the right porting and a big prop to keep revs down to about 7000rpm not a lot of after market parts are needed
if you thinking of a merc just checkout the price of parts first and compear that to the mercs
i can get your engine to about 300 hp for not a lot of money and very reliably call me im in newcastle 0243593886 darren
or call eric barrow at barrow marine in melbourne he knows his stuff on those motors

[David]

Assuming equal time at high speed a 300 should last longer than a 280 just because it isn't turning as extreme revs.

Also, the 300 has the convenience of oil injection.

But the 300 weights more. No problem for bigger boats. The fastest boat I've been on (thanks Bob V) had 300's replacing the prior 2.5's (28 Skater), I think for reliability.

If you boat is heavy go with the 300.