Hey guys. I'm new to this forum but I have been getting great info here for over a year!! To start with I'm terrible with computers and this forum stuff is tough to use!! Any way my question is this. I recently bought (from a member on here) a 98 active thunder tantrum with a 454 punched out to 468. The boat was supercharged but is not anymore. It is supposed to have about 610HP It has a BMAX out back with an imco lower. The bmax is a 1.3 drive ratio because it used to have 900HP. I'm only spinning a bravo 4 blade 22p. At 4000 rpm I'm running 54-55 mph. I'm not sure of the speeds at lower rpm. At wide open I'm at about 4900-5000 rpm and running about 67mph. This winter the motor is coming out and gonna be redone. I'm gonna try and squeeze 50 more HP out of it. My question is this...... Should I put 1.5 gears in the bmax? Is that my problem. I feel with that power in this boat I should be doing 75mph. Am I wrong? What should be done that won't wipe out the bank? Should I just supercharge it again?? Hahahaha Any help is greatly appreciated!!

If you do have a 610HP 454 you need to be spinning it to 6500+RPM's. (been there, done that, bought the Tshirt) Now you want to get 50 more ponies out of it, not a good idea. From experience the split from peak torque and HP was so far in the upper RPM range that it was pretty much useless except for WFO runs. Last year I re-cammed my engines. I now am making less HP probably more TQ, but usable power is now under 5700RPM's and my top speed pretty much stayed the same. My fuel efficiency is also better.

What are the specs on the current engine? And you probably should be using a 17p prop to get into the 6000+RPM range.

There isn't much chance you are making 610 horse in a 454 punched over .060 turning 5000. What heads are on it? If they are factory rectangle ports you are lucky if you are making 500. If the motor was originally purpose built for the procharger, it is probably low compression without it, and not cammed optimally. What did it run for speed with the blower? Might be the cheapest alternative to put a procharger back on it and go boating.

Thanks for the replys guys. I hope I'm replying properly(this forum stuff is new to me) I was told I should be spinning 6500 rpm I wasn't sure tho. Ok. It was supercharged and hit a top speed of 102mph. It then was spinning a 28p I think. It was then taken apart and a burnt valve was replaced. Thinner head gaskets were installed and a new cam. I do t know what can because it was built by pat musi. Pat musi then moved from NJ to NC and his shop apparently did not keep any build records during the move(and his customer service has really sucked in my opinion). The heads are dart aluminum with jesel valve train and Manley valves ground to a custom size. I recently had the head off to replace a valve and my motor guy stated "wow these are ported to the MAX). That's about all I can tell you. This winter I'm pulling the motor and replacing a piston that has a small ding in it. I just want to bring my speeds up a bit in the most economical way. What do u guys think? Wish I had a build sheet on the motor. It apparently dynoed at 613HP. If I were to spin a 17p what would that do to my cruise speed? I love cruising at 50mph!!

When I hear ported to the max that is not usually a good sign on a marine engine. Good for drag racing yes, boats not so much.

Frankly this motor seems awful high strung for a pleasure boat. You aren't going to cruise at 50 with a 17 pitch unless you like cruising at 5000 RPM. A torquier larger displacement motor would probably work better for you.

Pat Musi is the schit ! With boat motors I'm not sure, but with drag cars he is one of the children of the corn. You know, one that can eat most others. LOL.

Well what do u guys think I should do in winter? Have the gears changed in the bmax? I'd there a set of heads I should be looking for? Should I just say screw it and buy the blower for it!!!?? I forgot to mention that the motor still has flat top pistons in it. Should I get some top pistons and up the compression. I know these types of motors are not built to last and require work which I'm ok with. I obviously wanna go faster for the least amount of money(don't we all) bit I don't want to repair EVERY week!!

Hey SB, that's what I hear about pat musi. Apparently he is one of the best. I know he has done boat engines before so he should know what he is doing. I would really like to see a build sheet so I know what I'm working with but apparently they didn't keep any records. Whoever answer the phone here is t very polite either. I had to pull teeth just to get a valve spec

I would try less pitch before changing the gears. I would think you should be winding 5500+. Try less and less pitch until top speed falls off, that means HP falls off. What kind of ignition does it have?