HOTTZU98

What do you guys think a ZT-280 will run Top end with a 454mag? I can get the boat for a good price,and may upgrade in a yr to a new 496mag.

zt260

I would say 62mph. The 496HO will run 67mph. GPS

RJBBC

A gain of 40 propshaft horsepower will get you 5mph in that hull? I was told by an engine builder it would take closer to 100hp to gain 5 mph at WOT. (454MAG 385HP, 496MAGHO 425HP)

zt260

If it were only 40HP more then the expected speed difference would be about 3mph, but from what I've seen the actual propshaft HP difference is more like 70, hence 5mph more.

boatn70

so whats the difference in the propshaft hp then, how do you get to the 70hp?????? isnt 385hp and 425hp prop shaft numbers? if not what are prop shaft numbers.....ive heard of the hp500 being 470.

i guess i just dont know!!! fill me in here zt260

Ck1flyer

As I understand it, the 496 Mag HO/425hp was suppose to be the replacement for the 502 Mag/415hp. I think propshaft hp for the 496 Mag HO is closer to maybe 450hp. I have a 496 Mag HO in my 270 Convincor (25’-9”) and it will run right up there with boats the same size that have HP500/470hp. Just seams like it has more power than what they indicate.

Now, that the 496 Mag HO has landed a solid reputation, Merc discontinued the HP500 and introduced the HP525. Kind of seems like the 496 Mag HO is replacing the HP500, not the old 502 Mag. Just my opinion here. I know the 496Mag HO is not a blue motor, and not as heavy duty internally, but it runs strong.

-Craig

boatn70

so when its said that a 502mag has 415hp is that propshaft??

Ck1flyer

Yes. I think some of the earlier 502's were 390 or 395hp.
-Craig

zt260

Merc calls the 496HO 425HP propshaft. The 454mag was rated several ways, but I believe the 385HP model was at the crank so subtract ~30HP for propshaft. Either way I'd still say the 454mag will only hit low 60's in a ZT280.

RJBBC

I have a 2000 454MAG in a 259 Convincor and it is rated 385 propshaft horsepower by Mercruiser Gas Sterndrives Specifications.