Black Baja

iTrader: (2)

Bingo. And you need a cam in the motor that will carry the torque through the Rpm range after the motor makes peak torque. The right cam is not going to make the most peak torque. You have to sacrifice the peak numbers to get something that will carry the torque. The way I look as it is you have to balance torque in a marine engine...

powermizer

Ok, good info. I always figured a boat is faster with running closer to peak torque. Every boat I have had ran faster going with a 2 inch bigger prop than the prop that went to max RPM that Merc suggested.

MILD THUNDER

iTrader: (3)

If low RPM raw torque was king, you'd see 200mph Catamarans, running big diesels. There's alot more to making a boat run fast, than a torque reading.

An engine making 750hp at 6000, is making 656ft lbs at 6000. And engine making 800hp at 6000, is making 700 ft lbs at 6000. Its that simple.

Guys are always talking about torque torque torque, and ignore HP HP HP. HP is torque, and torque is HP. Horsepower is just a mathematical equation, derived from torque readings.

In a boat, I'd personally rather have an engine make 800hp at 6000, rather than 750hp at 6000, just to get a higher TQ reading from say, 3000-4500rpm. I don't drag race my boat. If you do, than that's a whole different conversation.

IF you look at this N/A 540 Full Force has, he wanted a 6k rpm engine that made 700hp. As you can see, there is a reason, his boat is not pulling past 5400rpm in the boat. The powerband is over there. If he wants to go faster, with same props, going to a setup that makes more low end power, isn't going to help his top speed. IF he wants to pull those props to say, 5700-5800rpm, he needs more power from 5400rpm+.

MILD THUNDER

iTrader: (3)

For the most part, I think the only reason to turn more RPM, is because you want MORE power. If your engine combo, doesn't make more power past a certain RPM point, than there is no point in spinning it faster. In the above combo, Full Force Tims, he doesn't want a 630hp engine. He wants a 700hp engine. He'd be very hard pressed to get 700HP, from an N/A 540 at 5400RPM on pump gas. So, whats the alternative? A better cam, and whatever components are needed, to spin the engine faster, to attain 700hp. The tradeoff? Usually is a loss of low speed torque.

However, in his scenerio, I think a cam change, along with an exhaust change, will get him more upper rpm power, and the exhaust should make up for the loss of low speed torque. A good exhaust setup, like a set of full length headers, will always boost torque, over a short runner manifold. Thats why tow rigs back in the day, always got a good set of headers as the first towing modification.

powermizer

I do see what your saying. Much easier to figure out how to make a car run a fas quarter mile. People always ask why run a blower if you can make the same power naturally aspirated. The thing is if you over cam a blower motor you can still get the boat on plane without dropping prop size. I like how blowers make everything a little more forgiving.

Black Baja

iTrader: (2)

I agree with this for the most part. Disagreement... If you put a nice set of headers on a 330hp merc in a boat it will net you a big fat 0. In Tim's case with the present cam I think he would get a little bump in performance. Now throw a big stick in the motor with a nice set of headers and you have something.

MILD THUNDER

iTrader: (3)

I agree as well. The old 454 330, prob does benefit from some headers, but, its not gonna be noticeable in a boat. Stick that 330 in a truck thats towing a 12k trailer, and the long tube headers will prob help a bit. But thats irrelevant here

In tims case, i agree with ya. If he puts in the right cam, intake, and some headers, it will prob feel like a new set of engines

mike tkach

iTrader: (3)

the manual oil temp control valve will also wake it up.sorry tim i could not resist.

articfriends

iTrader: (1)

Back to tims engines though, im still puzzled how bigger motors with less cam were faster with same props, should have peaked even earlier then layed over?

articfriends

iTrader: (1)

Back to OP 's question, have somone who knows what they are doing port the hell out of those merlin head exhaust ports to get ie up to 80/85%, your blower can shove 450 cfm thru there mediocre intake ports, its still got to burn and get out though and i dont care what anyone ssys, you dont have a pump helping the exhaust out like you do the intake in. I also think alot of of importance is stressed on good scavenging headers, keep in mind once you water cool a exhaust header its not working like a race car header, with that thought i just used stainless marine 3's, huge exhaust ports , i made 1050 hp on pump premium reliably with a procharged 540, over 1100 hp with 20% 110 oct, that cam was a 248 or 249/256 .050 (peaked around 5800/5900, pulled to 6300 before nose diving off face of earth) , 114, .660 lift if i remember right. I couldnt break 700 though with my merlin heads previously, however, i did go on to later have them full ported but never put them back on motor. At one point i made 950hp w my afr heads , when i went up to 1050 using same blower/intake i had more work done to exhaust ports than intakes, agsin, the sir is forced in but its still got to get out.