HZ900

2000 Scarab twin 350 Mag MPI with 23* Mirage Plus Props.

Just looking for a couple MPH on the top end, that is all. Any ideas.

I posted something about a programmer a friend sent me a link to in the boat on a budget section. Looked like BS but figured hey why not at least ask.

Not looking to tear down the engine or anything. Some sort of tuning maybe, or full roller rockers, ect, just basic bolt on stuff. What works on these boats to get just a little gain?

hullofjustis

iTrader: (1)

-2 inch imco shorter drive

CDShack

It's a $1000 per MPH to 75.
$2000 per MPH to 80.
$5000 per MPH after 80.

Seriously, I've noticed something about the MPI Merc small blocks. I have a Chaparral with 5L MPI. It runs the same top end with a 19 or a 23. Holeshot is all that changes, but the computer seems to "adjust" for the props. I think alot could be done with programming on that motor.

pondrunner

Go with after market exhaust manifolds, Imco Thumper or Stainless Marine...saves weight which translates to 1-2 mph. Dart or AFR aluminum heads, a buddy ran a 350 small block with these in an identical boat to mine with a 454 and he would pass me, so 1-2 mph. Also the shorties have been posted about many times here as being very effective on the 29 hull for several mph. I've read of improvement boring to .030 over, getting you about 5 horsepower per motor...maybe see another mile and hour from it, but don't think it is worth the trouble doing. Whipple may have a bolt-on stage 1 kit (not supercharging) for the 350MPI, which reprograms the ECU, giving you 5600rpm and 5-8% Horsepower gain, so 2 mph. CMI exhaust headers, good for a couple horsepower, 1-2mph. Lastly, labbing the prop ( I hear Brett at BBlades has a template for this hull and power) might get you 1-2 mph. The exhaust will be my first and likely only mod, maybe the Whipple stage 1 too.

HZ900

I've read this a few places but figured is was big $ and I could get better gains elsewhere for the $. What is the cost on it? I have also read some of the bravo 1 internals will swap out, thus saving a little money.

HZ900

Must be your hull. The previous owner had put 21 mirages on mine and I swapped back to the 23''s and it really woke the boat up from mid range all the the way to top end.

hullofjustis

iTrader: (1)

2 me it is the best bang for the buck. 2 build 2 350's to 400 hp would be minimum $5000 without exhaust and another 3 k with exhaust. minimum to maybe go up a pitch in prop that's not including rerigging fuel lines ignition etc. and then you always have the reliability aspect.
the imco gear cases you can get for under $2000 a piece swap everything but the vertical shafts and you are good to go. I would recommend adding the back half of hydraulic steering minimum if you do not already have it. which you would want to do either way with increasing horsepower
it. I think I read somewhere it takes 15 hp per 1 mph to up to 70mph?
imco lowers CAN increase up to 5 mph . the props will need to be changed to a for blade as well

CDShack

It's odd, I run the 23 during the colder months when we're not skiing, mid-range is better. Run the 21 or 19 when summer hits and all it does is pull. 55mph is all any of them show on GPS. RPM varies about what the pitch dictates. I figured computer was remapping.

Back to OP. A good prop shop that will work with you can easily get you a couple of miles an hour. Just how and where the prop is cupped for bow or stern lift, etc. can make a big difference for little $$$ It's why racers cover their props.

01scarab29

HZ, I've done a lot of changes to mine. The majority not by choice. I have no regrets of the direction I went. I have learned a lot and have lots of information. My next step is -3 Imco's. ,,,,,
I believe the best bang for the buck will be shorties. Measure your prop shaft height. Mine is 7 3/8 deep and bet yours is the same. yes I'm taking a chance, but No one can give me good reason not to or have personal first hand experience or know of anyone who has tried it. Labbed props will cost about 400-850 a piece, maybe more, depending if you use yours or buy new. Rebuilt 350MPI 300hp to 383's 400hp tuned and dyno by Full Throttle Marine. I have MEFI 3 and did have to be retuned. In short I gained 5mph using same 23p mirage plus props because I could turn an extra 300-400RPM. Went from 68mph to 73mph in real good conditions. can tell you more if you like

hullofjustis

iTrader: (1)

01 scarab29 I Highly recommend -3 imco's on that hull. I had a single engine 29 and it was a completely different boat with the -2 imco on it