CenturyUltra

I have a 1989 Century Ultra I with the 365 hp 454 MAG carb and Bravo outdrive. The motor is stock except for stainless marine headers and risers and has 345 hours on it. The boat runs 61 mph on GPS right now with a 23P Mirage Plus prop at 5200 rpms.

I just picked up stock heads, cam, intake and carb. off an HP 500. Is this a good upgrade? How much of an increase in hp and speed should I see? Any guesses on a prop? I know there are a lot of variables I'm just looking for some estimates.

Thanks

jeff1000man

In order to utelize that set up, you will need to turn up the RPM's. Probably have to propr it so it turns to 6000+. The cam in a 500HP is pretty big for a 454 with very light compresion. It will work, but you will have to rev it very hard.

Griff

The heads on both engines are the same, except for the HP500 heads have slightly larger valves. The HP500 cams made the engines prone to reversion. Make sure the valve springs on the heads are good.

You might see a 2-3mph gain.

CenturyUltra

well i certainly dont want to worry about reversion is this even worth doing?

mwdill

i have a friend that did that exact thing other than the cam he used was the same as a hp525 (741), he picked up a solid 8mph

offthefront

iTrader: (1)

I would go with the 741 cam ...or even better have Bob Madara spec one ...give Bob a call he's a straight shooter ...some head work would be nice too ....

Kinda makes me nervous thinking about a stock mag bottom end W/345hrs at 6K ...


Bob Madara
1-585-654-8583.

GO4BROKE

iTrader: (1)

Stock mag lower end is forged steel crank and rods, forged pistons. If gen 6 it has roller rockers. Its pretty stout. I wouldn't hesitate to do it if the motor has been maintained.

CenturyUltra

Thanks to all. Sounds like its worth doing. Should I be worried about reversion with the stainless marine exhaust and the HP 500 cam?

Griff

IMO, there are better choices for a cam than the carb HP500cam. You will be able to make the same power with a better idle and no chance of reversion.
The HP500 cam is on a 110 lobe sep and has a ot of overlap. You would be much better off with a cam on 112-114 lob sep.
I think the 741 is too big for a 454ci engine unless you spin it up to about 5800rpms. Something closer to the 731 cam would be better for a 454 and have better midrange torque.