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View Full Version : MK IV 454s: HP420 vs 454MAG


handfulz28
06-30-2009, 06:39 PM
The 420 was rated at the crank correct? Can somebody confirm/deny that the MAG's 365hp (say '90-91 vintage) would be propshaft rated? I know the internals and other parts are different but I've got this nagging idea that a HP420TRS and a 454MAG Bravo will net very similar PSHP numbers.
gcarter
06-30-2009, 08:01 PM
Yep, there're a LOT of engine parts differences....
Do you really think there's that much loss in the Merc Trans?
I don't get it, when either the MT or Velvet Drive are in gear, there's no slip. The only loss I'm aware of is driving the hydraulic pump, couldn't be that much.
handfulz28
06-30-2009, 08:16 PM
The numbers I've seen are about 10% for the Bravo and 15% for TRS.

I'd be inclined to believe that the 454MAG @ 365pshp is a tad optimistic. But OTOH, the same model boat offered with both power packages were propped identical and put up similar numbers.
MOP
06-30-2009, 08:25 PM
Scott I would think the size of the gear case has a lot to do with speed, Ted said the Alpha is 2mph faster then a Bravo. The TRS has an even bigger case then the Bravo would the same not apply?
BERTRAM BOY
06-30-2009, 08:29 PM
I've been told that certain reputable shop in Miami that rebulds Merctrans uses a 5 h.p. drill press to test the transmission. Not sure about the TRS drive though.
handfulz28
07-01-2009, 10:01 AM
Still looking for confirmation that 420hp is crank, 365 is prop.
BUIZILLA
07-01-2009, 10:07 AM
don't hold your breath....

the 365 used a different intake, carb, and cam in most years...
handfulz28
07-01-2009, 10:45 AM
different heads, valvetrain, crank too...still doesn't answer the question. :confused:
BigGrizzly
07-03-2009, 08:11 AM
As for trans drag of the Merc trans I did a similar test as MP and found the same thing. I took it a step father with doing internal drag of a TRS vs an early Bravo1 to fing the drag is actually higer in the bravo, not much but it is there. As for the lower unit drag the early bravo is pretty bad and the Trs is the same diameter ( CLOSE) and has the advantage of NO water disturbing water pick up. With the information I have I would NOT change to even a new Bravo1-a weaker lower unit in reality.