New heads
 

Hello,
I was wondering if I changed the heads and intake on my 94' Mercruiser 350 vortec 260 hp will it give me any increase in speed? I am only looking for a 5- 10 more mph. I know I could go the route of changing to 383's, but I am trying to use these engines for now due to low hours. Any advice would be greatly appreciated. The boat is a 94' scarab 29 and its only reaching 58mph everything I read says it should be running in the mid 60's it has 23p props.

Are you sure they are vortec (8 bolt intake)? I don't think those were around in 94. If it is 260 horse it sounds like the traditional pre vortec 350. In that case changing to vortec heads would increase your power and if built correctly (heads/cam/intake etc. combintation) could give you another 100 horse per side.

Im saying its vortec because the valve cover bolts are in the middle. I will have to count the intake bolts.

Ayuh,.... Switchin' to Vortec heads, 'n matchin' intake will give ya 'bout 20 hp per motor,...

That might get ya 5 mph, or not,... probably more like 1 or 2,...

It's gonna take a Huge jump in horsepower to get 10 mph,....

Yea thats what I figured I would really be happy to get the boat to run in the mid 60's like every other one with this setup.

If I were you and knowing what I know now I would just enjoy it as is until it is about used up . You will be disappointed with the money you spend verses the performance gained . Save up some bucks during this period and when the time comes built a nice set of 383's . It will take a lot more horsepower and torque to get your 10mph . In the marine world , only or just don't belong in the same sentence as 10mph . I only wish someone would have given me this advice before I went and wasted tooo much money . I once stood where you stand . deep

I appreciate that advice I think that's what I am going to do. I will just build the two 383's while I enjoy what I have now.

THANKS!!!

If your serious about spending the $$ on Heads & Intake, you may as well bite the bullet and do the cams & a good performance exhaust while you're at it. Heads & Intake won't operate to their potential without enough cam to feed it and exhaust to let 'em breathe.

Everything you read say it should be in the 60's. I would research that more. Talk to someone running those speeds. What props, trim setting? Most important what rpm are they running. You could be down on power. Whats the timing set at? If it all checks out, what is the weight of your boat? Is it left in the water? Transom/stringers wet?

I have thought it could be the timing. The guy I bought the boat from said the timing was advanced 8 degrees I was told by my mechanic that we should power time it? The boat has never stayed in the water for man than 3 days and when I bought the boat everything was dry. I also feel that I should be able to get another 200 rpms out of it due to that it is maxing at 4600 right now.

I should also mention that this my first power boat I had all center consoles before buying this boat so sorry if I sound dumb.

34* total timing @ 3000rpm's . We all started from somewhere and were inexperienced , no worries about sounding that way .

58 m.p.h. sounds about right for twin 260 h.p. 350 cu.in. in a 26-29 foot performance boat. My ChrisCraft Stinger 260 did 58 m.p.h. stock.
With high rise intakes, rejetted carbs (Q-jets), taller flame arrestors, Crane Cams, roller rockers, World Product heads, and larger props (23" clevers with 1:50 ratio drives)
I increased the top end 5 m.p.h. to 63 with a light load of fuel. I'm not sure where you got the info that your boat "should" run 65+. I think it would take
350 MPI motors and a stepped hull to run those speeds stock. You will need to increase somewhere in the 150-200 h.p. range to reach your goal IMO.

Just wondering will mufflers affect the performance any?

my 27 Nova 3 did 63 max at 5300 rpm. motors were built to 350 hp though. 23 mirage props. anything u do for upgrades now will probably be usable on later 383's, so won't be money wasted. vortecs aren't the only head to consider for marine use. castings are a lil thin and crack a lot. I would consider Darts or Edelbrocks. mufflers don't cost much power. my nova was TOO loud with nothing but 18 inches of hose and tips hanging out above the platform. (not the way wellcraft set it up.) when the manifolds get old, that is the first upgrade u wanna do. PLUS that's the main thing that makes them look like high performance engines.