Hello carreraboat! I see that you are relatively new. Do you have a 30' Carrera with twin engines? I knew of a few guys who have owned 30' Carrera's on Lake Michigan. I have riden on them several times. There are a very HEAVY boat, they sure ride extremely well in the rough! I even remember a guy who had a 24' Carrera that was very fast and nice.

As far as intakes go, I would also choose a dual plane intake. A good Edlebrock Performer intake or what they call an "Air Gap" dual plane intake would work very well. Dual plane intakes give you much better usable mid range torque and still gives you enough to kick it up to about 5000-5500rpm as blown1500 has said. Adding larger valves would give you about another 10-15hp. Are your heads bowl/pocket ported? Bore notching the cylinder block bores would add about 30hp as well but must be done properly and carefully. You could add the larger valves if you have the heads off the engine already, but I wouldn't go to the trouble and expense of removing the heads just to install larger valves unless you plan on doing a bowl/pocket port and a good valve job.

Bowl/pocket port $175-225
3-angle valve job $120-140
install larger intake valves/seats (stainless one piece) roughly $350 per engine
aluminum dual plane intake manifolds $195 each or so

Here's one thing you could try without much expense: Buy an aluminum dual plane intake manifold. On a decent day run your boat with what you already have (Dart intake) then on the same day if you can, install the new dual plane intake on your engine and give it a go. The dual plane intakes are cheap enough to do a test like this and then sell it if you don't need it. You may not get what you paid for it but at least you will KNOW what works best for the weight and application of your boat.

blown1500 can help you out if you need help. Best wishes

Your cam is not too far off, especially with the head work and intake swap. You could go up a little and still have a good idle and bottom end power. I'd probably try the Crane 139741 hydraulic roller. It has never let me down! You will loose on the bottom end, but you will pick up a lot at 5,000+. You must choose where you need the power the most. If you cruise at 2,500-3,200 a lot, you may want to keep what you have for a cam-just do the heads and intake. For more specific help, call me at 704-574-4020. That is a cell and I have it most of the time.

sorry guys i really apperciate your responce i have been following these boards for about three years everytime they change i have to re register i am a carrera dealer here in new mexico i am a 1 man operation . i really appreciate all your info you guys have tried just about every combo out there i guess i try and learn from other peoples mistakes . my boat is a 24' with a light lay up i have a shorty drive we boat on lakes hardley ever see big water . try to go to havasu as much as possiable . hey kaama what do you and blown 1500 do for a living my main gig besides the boat thing is i am a tool dealer for matco. i really appreciate the info any other things i should try i look foward to your input
bo

I'm just an exterminator turned offshore boat freak. I kill bugs for a living, but I grew up around boats on Lake Michigan since I was a kid.

And well, blown1500 is the real Offshore Hi-Performance Engine Builder Guru Extrordinare with an engineering degree. It's what he does for a living and when it comes to marine performance grade engines, (as Foghorn Leghorn would put it) I have quickly learned-----I say I have quickly learned that boy-----I say that boy will talk circles 'round you, me and about 1000 other people on this board even with his tongue blowed owff and half his mouth taped shut son!

carreraboat,
if you take an open plenum, dual, and a tunnel ram in a side by side comparison with only the intakes being changed on a motor on a dyno, at 3500 rpm's, the torque will be with in 5ft. lbs of each other. at 4500 rpm's you will have 10 ft lbs. more torque with the open plenum than the dual and 15 ftlbs more torque with the tunnel ram than the dual plane. at 5500 rpm's the single plane will make 15 ft lbs more torque than the dual and the tunnel ram will make over 20 ft.lbs. more torque than the dual plane.
keep in mind that low rpm use such as docking will be better with a dual plane due to a higher vacuum signal to the carb. if your not having a problem now than that doesn't matter. single planes intakes are also more sensitive to carb CFM size changes.
if you want 30 more hp per engine, knock off the casting ledges, machining seams,and casting seams below the valve seats with a die grinder, smooth out and widen the short side radius and clean up the bowls. that is the main area of flow restriction in the heads. all it will cost you is some sanding rolls. you don't need to pay a pro to do it. it's very easy. it is the best bang for your buck. i wouldn't waste money on bigger valves. if the chamber walls aren't relieved to accomodate the flow increase of bigger valves, they can actually cause a flow restriction from what you have now. if docking isn't a problem i'd stick with the dart manifold as well.
these are real world #'s and aren't guesses by the way.
good luck

Exterminator ehh kaama? Does that make you a PCO? I find that interesting because of what I do... make products for the pest control industry. It's not just a job, its an adventure!! We even have a huge cock roach colony. Exciting don't you think?

BT

that get's the RAG'S

thanks excal i think i will do just that !i really appreciate all of your guys advise
bo

excaleagle42,

Hmmm... not sure I totally agree with that although if that is what you have seen on a dyno I guess I can't argue with your experience.

Not trying to spilt hairs here, but here's what I have experienced a year or so ago just for a gentleman's argument sake:

A friend of mine "DanB" has a 509" naturally aspirated engine that he used a Crane 236*/244* on 112* lobes, 9.0 comp ratio, Holley 950cfm carb, with non ported Merlin cast iron 308cc heads and on Tyler Crocket's dyno it made 563hp @5500 and 620 foot pounds of torque @3400rpm while using an Edlebrock "Air-Gap" dual plane intake manifold.

My 540" naturally aspirated engines use the basically the same cams Crower 236*/244* on 114* lobes, 9.2 comp ratio, Holley 830cfm carbs, Dart pocket/bowl ported Pro-1 aluminum 310cc heads on Tom Earhart's dyno made 630hp @5400rpm and made 625 foot pounds of torque at 4500rpm while using a Dart single plane intake manifold. Torque was 583 foot pounds @3500rpm.

Again this is a 509 vs a 540! That's 37 ft.lbs. difference over the 540 of and at more of a usable cruising rpm range.

thanks i really appreciate your input gotta decide what to do gotta get the most out of of single motor package