So I have a 24 ft 1989 Baja islander with a 454 mag and bravo 1. Top speed is 64 mph and i am runninga 3 blade 21p prop with rpms 4800-5000.

I was doing 64 by gps with 4 men and 2 women on the boat.

My first thought is that I can probably go up to a 23 p or 22p 4 blade and get a few mph.

Next question is can I do some engine/ exhaust mods to get a little more?

Next question is should i? Is it safe? what about my hull? How much can it take?

Where should I start?

You won't necessarily get more MPH with a bigger prop. It sounds like you're propped right by the RPM. If yo go larger, same prop you'll likely just drop out of the peak HP RPM range reducing RPM and making it doggier out of the hole. You need more power to spin a bigger prop.

That said, there "might" be some work on the prop that might help a little. Or a different prop. I'm sure someone that has some experience with a boat like yours, or close, can help.

As for the engine, you can always do engine work to get more power. How much more power you want is directly impacted by how much more money you don't need laying around. Bang for the buck, nothing will be cheap. Good exhaust that might get a really optimistic 30-40 HP more will run you starting somewhere near $2k. That would (if you could get that) yield "maybe" 2 MPH.

You've got a 454, it's a 365hp so at least you've got the steel crank and rectangular port heads.
Merc knows what they're doing generally, so that leaves 2 options.
1) Build a copy of their 400/420 cyclone engine. That would require a cam, rockers, intake, exhaust, carb, and some head work. Cost would be $3-4K, depending how much work you can do. Speed increase would probably be 3-4mph.
2) Supercharge and build a 525SC copy. Add about $3K on top of the stuff listed in #1 and another 3-4mph.

What 3 blade prop????? Mirage Plus's are generally the fastest on Baja's. You may have a 2-3 mph gain with the right labbed prop.

Also, make sure the engine is tuned to perfection. Bump the timing up to 34*.

Thanks for the replies guys. Pretty interestind stuff. I ll look into the prop on my boat as far as model goes.

My thoughts are $1000 = 1mph. I ve got other things i want more than 2-3 mph on my boat.

I am new to this stuff and this forum so i wanted to ask.

Zs far as tuned to perfection. Obviously thats money well spent.

64 mph is pretty good for that boat. Leave it the hell alone and thank me later! This is a very slippery slope you're going to slide off of if your not careful.

Sounds good to me. I am new to fast boats and 64 can be a little scary when your not experienced. BUT I like being on the verge of out of control! Plus with my kids in the open bow....I dont want anyone to get hurt

That's exactly what I was thinking.

Change the oil, and enjoy.

you could buy a used prop 23mirage plus and send it too bblades and have it labbed it would be close to your non labbed 21 and you could pick up 3mph for cheap money. I know the merc rev 4 props work well to. art

I was kicking around the idea of trying a 23. Sorry for my stupidity but tell me what labbed is. and wehenyou say close to my 21 are you talking about hole shot?

Please keep in mind that I can only learn if I ask. Maybe an OSO vet could adopt me and that would speed up this learning curve!