Sunseeker Cobra 39 sluggish
 

Hi,

New to this forum but it looks great with lots of competent people.
I'm from Sweden and bought a Sunseeker Cobra 39 with 2 newly built 454. The boat weighs around 10k lbs.
The outdrives says TRS 330 and are newly built also.
By newly I mean 0 hours on them. The engines are also improved with better performing intakes, carburators and cam, should be around 400hp. (From 330 i guess)

Engines run great and shifting is very smooth. The problem is that it is very slow.
At 2000 rpm it's around 8 knots (~10 mph) and at 4000-4500 it seems to max out at ~20 mph.
Doesn't feel like slippage because it's equally slow from low rpm to high rpm.
The propellers are stainless "Ballistic" 14,5x19. The propellerblades are the cut kind, don't know the name for it, last piece in the end are cut.
We have asked the previous owner that ran the boat with original engines and he said he used those and accived at least 45-50mph.
The engines rev up very fast, seems like it doesn't have any resistance at all. Feels under geared (or over geared? )

Do you guys have any idea what this could be? The only thing that is not rebuilt is the trans thingy between the engine and the drive, could that one cause this kind of behavior?

Thank you in advance!

Around those number, yes.

If the props are Michigan Wheel's Ballistic XHS A series prop stamped 933519 (RH) / 937519 (LH) you may have 2 issues with them:
http://www.miwheel.com/propellers/brands/ballistic/

1) they are an economy prop designed for O/B that has been used by volvo penta on smaller boats
2) if equipped with plastic hubs or pressed in rubber hubs - you may very well have blown the hubs out under the engine torque/ weight of the boat so the prop shaft is spinning at a different rate than the props (and only getting worse)

What ignitions are you running

Those are the props, they are no good?

What does ignitions mean? Sparkplugs?

distributors, timing spark box, timing modules ?

Sorry, dont really know. I know some mechanic talked about some Merc lightning or some flashy name like that.

Engines runs well though, I can rev up to 5k easy and probably above that but with newly built engines I would like to stay below that. The boat should work anyway I belive.

What does O/B stand for?
We thought about the hubs and tried different props, unfortunately it was the same dimensions so speed was exactly the same but at least we could rule out that the hubs was slipping. The prop we used had a fixed one.

Have to ask so don't takequestinos personal:
Are you trimming the outdrives to best speed after you get on plane ?