I currently have a 223 1989 cobalt condurre with a 330hp 454 motor 4 barrel q jet. The air intakes on the hull sides are roughly 2"tall and 12"long, the vent covers on the exterior of the hull are much longer so I could enlarge them if I needed to. There is one opening on port and one on starbord. These vents share intake with bildge blower, and have what appears to be a molded box on the inside to act as a plenum for the blower and intake air. I have not raised the hatch at speed to see if the engine responds to more air just putting the general question out there as to how large the vents need to be. They are not scoops type vents just horizontal bars with about 50% free area.

I know my motor and boat combo just doesnt perform any better after about 4000 rpm. but will spin up to rec rpm 4500. I know this motor has almost no hp gain above 4500 rpm with the standard pan cake intake manifold and peanut port heats.

Currently at 3000rpm speed is 33mph : 4000rpm I am at 54 mph, 4500 rpm at 58.5 mph. mid range acceleration is great, but to get 58.5 its a struggle.


LC

Opening your air intakes will do nothing to improve your performance... From what you post your speed seems pretty good... The faster you go the more power its going to take. In order to see any worth while speed increase you're going to have to replace at least the heads and intake and really you'll need a cam as well.. All that will cost around $3000 plus the labor to do it.. What prop are you spinning? Assuming you have a 23 pitch your at 11% slip which is very good!

Lowering the air temps inside your engine compartment by 10 degrees adds about 2% to your hp. It's a lot of cheap hp but the only good way to do that is to add a large scoop and an air box around your carb. You have to decide if it's worth cutting up your sunpad area for a couple of mph. Enlarging your side airvents by a small amount won't make a measurable difference.

Thanks for the info.

Air vents just seemed on the small side.

Prop is a 23p mirage +

Would be nice to have more power, but can justify the cost of modifications vs what I paid for the boat. Now if heads, cam, and intake got me to 70mph it would be a no brainer but I highly doubt it would... probly need 500hp or so to do that, maybe more.

LC

AFR 265 oval heads, new intake and a cam would get you to 500 hp... Give Bob Mandera a call, he helped me with my project and if you put my engine in your boat you would be well over 70 mph! If you're interested let me know and I'll PM you his number!

I don't think that hull will run 70 without changing the x dimension and a lot of hp. My buddy has the same boat and with a built 454, Sonny Leanord heads, intake and cam the best the boat will run is 59. He has tried different props and is currently running a hydromotive as this has performed the best. The boat handles and rides good it just wont go over 59 mph.

I would like to talk to your buddy. Not to many 223 owners

His came with a BBC and a Alpha from the factory. After rebuilding 4 Alphas he finally stepped up to a Bravo. The bravo set the drive lower in the water so there is more drag. I don't think it will do much better on mph unless the x dimension gets changed. They are good built boat and handle pretty good. Its kind of a running joke no matter what he does he will still run 59. He has a 502 in the shop that he is looking at building up but he is going to wait until he has problems with 454.