1987 Supra Pirata repower for surfing

Hi Everyone,

First off I have an 87 Pirata which is 23 feet long, closed bow with a stock mark IV, carbed 454 PCM engine, and a 72C velvet drive 1:1. It has a 4 blade prop on it right now, but i"m not sure what its specs are. I also already installed a fresh air exhaust. Unfortunately, the block was cracked after some serious overheating. My theory is weeds blocked the intake, Impeller ran dry, at some point steam formed in the system and the resulting pressure cracked two of the water jackets, allowing more steam and water into the engine.

So at a minimum, I need to replace the block. I'm looking at this as a possible opportunity to upgrade the motor when I otherwise wouldn't have, and I'm really only interested in this idea because I know the boat wasn't built with wake surfing in mind, and I will be running it with a lot of extra weight at low speeds. I've been doing a bunch of homework but have some specific questions.

My priority with this boat is to use it for surfing. Aside from that, it will probably spend plenty of time just putting around the lake or the occasional tubing/water skiing.

Budget: $6000-8000

So here are a few of the things I'm kicking around. A lot of these have been discussed pretty thoroughly in the forums, but a lot of people seem to be concerned about top speed, I am not. As long as I can get the boat to plane fairly easily and cruise at a reasonable speed I'm good. My concern is being able to fill it up with a bunch of weight, then pop 200+ pound men up onto a surfboard. I know a lot of the new surf boats have really high-power motors, but they are also heavier than what I have.

carb vs EFI:
From what I've been able to gather, you get a small boost to power and fuel economy by switching over to EFI, but not enough to ever pay itself off. I'm okay with that because I'm really after the easy starting and reliability of EFI, a little better fuel economy would just be a bonus.

So I definitely want to EFI the thing now but can't decide if MPI is worth the extra cost if TBI is good enough. Prior to the block cracking, I was planning on going TBI, but I think there's a good chance that my current intake could have warped and needs machining after the overheating event. instead of putting money into that I would rather pay a little more and pick up a used MPI intake for the new motor. Or, if I end up changing the motor to a 502 or something, I will need a new intake anyway.

Any input on the MPI/TBI debate would be appreciated! I have seen TBI kits for about 1500. I haven't seen any marine MPI complete kits, but I'm estimating I could do MPI around 2000.

Power:
The stock 454 is rated t 330 hp. I've read that that depends on some things like your intake and carb/EFI. It looks like my current setup may really be around 305 hp. I have the oval intake ports and I doubt it had been tuned any time recently.

I could switch over to either a 454 mag for a boost up to 385 hp or go for a 502 to make 415 horsepower without having to worry too much about compatibility issues since they are all based on the same 454 platform.

Modernizing:

my 454 is a mark IV. based on everything I have read, there is no point in switching to a gen 5, but the gen 6 may be a worthwhile upgrade? It has a better oil circulation setup and roller tappets vs the flat tappets in my current motor. Since I'm planning on switching over to EFI I will need a new fuel pump anyway but otherwise, it sounds like my old components would be compatible. I'm not sure if I would need to find new brackets for the impeller and alternator though.

Another option would be going for a 496 or 496 HO, but I don't see this working out for my budget. I'm also not clear on the advantages of these motors over the 454. Plus this option would require a lot more fussing around with making sure it fits in the doghouse and compatibility issues.

Oil:

I read an article that a lot of surf boats were having issues with the front two cylinders running light on oil due to the boat plowing so often with the nose up in the air and gravity working against it. I'm not sure if this is a real problem or not but I'm wondering if anyone has an opinion on high pressure, high volume oil pumps. I am interested in setting up the new motor with a remote oil filter for easy maintenance and it sounds like you want a high volume pump if you do that. Would that be good enough, or should I look at the high-pressure options?

Also, as I have been looking at long blocks, a lot of them say you need to replace an oil cooler if you have one. I see a cooler in my boat but it looks to only go to the transmission. If I don't have an oil cooler should I look into getting one?

I'll stop here for now. I appreciate any advice you have!

Honestly, the engine (aside from needing a rebuild) is fine, the prop is where you get the boat truly setup and dialed in for your application with your power available. Plus a prop is usually in the $500 range. Now I know that my application is not what you are looking for however, without changing anything on my boat (engine is "bone stock" original trans) except for a new prop, I picked up a bunch of acceleration, better hole shot, the engine does not need to run as fast to get the same top end speed and for me I smoothed out my wake in the process which is great for skiing which is all I do with my boat. There are going to be others on here that took an older boat and use it for wakeboarding and surfing and with a prop change they got the boat to do what they wanted and they might be able to chime in to help.

Jetlink makes a good point. It sounds like you're set on EFI, so do it. Other than that, rebuild the motor as needed maybe with a few desired upgrades, but there's probably no reason to get too carried away. Then, call Acme and give them your boat info so they can give you a recommendation on a prop to accomplish your needs.
Keep in mind that these boats were built for towing so maybe things don't need to be re-engineered so much.


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How hot did you get it? Its more likely you cracked the block by freezing last winter and that caused the overheat. You would have to melt every hose and exhaust to get it hot enough to warp an intake or crack a block. The boat you have is not lacking in horsepower. A upgrade in the power plant will not do anything for wakesurfing. My advice is to keep it stock and reliable. It was never built for wakesurfing . Your best option is to fix it with stock parts sell it and buy a wakesurf boat