SAMDAHL76

I i just bought my first boat a few months ago, velocity 260 and its got a efi 454 with a bravo 1 drive, its got a bravo 1 24P prop, the engine wont rev past 4500 rpm at full throttle, is that do to the load being put on it by that prop, of maybe some kind of governer or something, so i gues what im asking is does the prop have an effect on how many rpms an engine will turn? will i get more speed and rpms out of a different prop?

Griff

Chnaging pitch will change the rpms. 1" of pitch decrease is good for about a 200rpm gain. Is your engine a 454mag???

Are you trimming it out enough?????

SAMDAHL76

Yes it is a 454 mag, and it felt like it was trimmed right, boat runs awsome, just looking for some more cheap speed, so a 26P would run more RPMs , and faster?

Powerquest_Baby!!

No--you will LOSE 400 rpm if you go to a 26 pitch! The rpm range for your engine is 4400-4800 so you are within the range specified for that engine.

SAMDAHL76

Thanks, well my boat was running good and strong, 68 on gps, what are some cheap upgrades that will give me some more horsepower, i am thinking to do heads and cam in the future, but engine is completely stock right now. So if i ever wanted to go with more pitch on my prop, i need to make more power,

huge

A good exhaust system is a good place to start. Eventually, when you do some engine internal upgrades, you will have to modify the exhaust to see any advantages.
Replacing the OEM exhaust manifolds with cast aluminum manifolds & risers is probably the cheapest way to get some RPM's and HP. Typical prices range from $1400 to $2400 for Imco, Stainless Marine, Rex, etc. This should get you maybe 1-3 mph, whereas water-jacketed tubular s/s headers may get you some more speed, but will be in the $2500+up price range.

fireboatpilot

Exhaust IS a good place to start. You never mentioned what boat you have. 68 mph isn't too bad by any means especially for stock. All boats eventually are limited on speed by how much water the hull can displace. The further out of the water the hull is the faster you can go. Right up to the point of chine walk and loss of control. Depending on what boat you have, how fast can it safely go? It's all a balanciing act. As for the prop pitch you are probly over pitched by 2 inches. A 22P probly would be perfect. The previous owner most likely was pulling ski's or tubes and needed more pull power instead of top end power. When you make power improvements to your engine you will need more Prop/pitch. Prop the boat for it's use and power. Don't build the engine to fit the prop. All a balancing act. Just my 2cts worth.

jeffswav

I agree do the exhaust first. If you plan on a performance cam upgrade later get long risers. There are no cheap upgrades in the Marine world.

Griff

Merc recommended WOT range for a 454mag is 4600-5000rpms. You want to spin it 4900-5100rpms for best performance. Basically prop it to spin about 5100rpm when you are very light on fuel and passengers. That way you'll run 4900-5000 most of the time. You will start hitting the rev limiter just past about 5100rpms.

You really need to have your prop labbed or drop to a 22". A 22" will increase the rpm by about 400.

SAMDAHL76

So if i run the 22 prop will the boat run faster? i got a velocity 260, i was out on sunday and that boat chine walks like crazzy when running wide open. scarry stuff. so i gues i got plenty of speed for that boat. my first issue to adress would be gaining more controll. will trim tabs help with that? Will that 22 prop help with fuel efficiency?