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View Full Version : Prop, carb, rpm questions....


SickSation
08-21-2010, 09:09 PM
Long story short, I pulled my 454 mpi and swapped to a merc n/a 575hp 540.

What I had

prop- labbed 24p solas 3 blade
454 mpi 310hp
GPS- 66.2
RPM- 4300


What I now Have

prop- 28p 4 blade
540ci 575hp
GPS-68.4
RPM-4500
range- 4800-5200rpm

The boat still has a ton of bottom end. It comes out of the hole hard. I think i need a 30p. I think a big part of my problem is that the motor came with a quadrajet on it for some reason. will a bigger carb make that big of a difference? I expected to see very close to 80 if not faster. Boat is a 01 sunsation aggressor 25ft.

By the way I tried a 26p and the 28p with the same water conditions today and the boat was no faster top end and the RPMs were the same. I did have one more person with me... Anyone have any ideas?
Trim'd Up
08-22-2010, 08:17 AM
What kind of props are you trying? Do you have a dyno sheet on the engine? 575hp isn't much for a 540, you should be able to get that by accident.
OBNOXUS
08-22-2010, 09:29 AM
First put the 24 back on and see if 4300 is still 66 mph.

Turning a 4in bigger prop 200 rpm more and only going 2 mph faster doesnt add up
Ratickle
08-22-2010, 09:44 AM
Also, are you using a good GPS speedo?
Ratickle
08-22-2010, 09:46 AM
What kind of props are you trying? Do you have a dyno sheet on the engine? 575hp isn't much for a 540, you should be able to get that by accident.

The link to what he is using.


http://www.seriousoffshore.com/forums/showthread.php?t=18274&highlight=540
SickSation
08-22-2010, 07:24 PM
Also, are you using a good GPS speedo?

nuvi 255 gps. Yea its good.
SickSation
08-22-2010, 07:28 PM
First put the 24 back on and see if 4300 is still 66 mph.

Turning a 4in bigger prop 200 rpm more and only going 2 mph faster doesnt add up

I agree. Im very confuzed..:huh:
SickSation
08-23-2010, 08:02 AM
http://i29.photobucket.com/albums/c276/Sickinnovations/sparkarrestor2.jpg

http://i29.photobucket.com/albums/c276/Sickinnovations/motor.jpg

http://i29.photobucket.com/albums/c276/Sickinnovations/sparkarrestor.jpg
bajabob 718
09-07-2010, 07:39 PM
go with a 24bravo 1 prop .your motor is doging or a 25mirage that will get your rpms up .i had a 622hp 540 dart 150 gears bravo 1 drive runnig a 25mirage prop 5600rpm doing 80.4mph:cheers2:
SickSation
09-07-2010, 08:56 PM
go with a 24bravo 1 prop .your motor is doging or a 25mirage that will get your rpms up .i had a 622hp 540 dart 150 gears bravo 1 drive runnig a 25mirage prop 5600rpm doing 80.4mph:cheers2:

I guess I just expected more from this motor. I'm now turning 5000rpm on a 24 cupped solas at 73.3 gps. Guess I need to pull it this winter and freshin it up. maybe new heads as well. I'd like to see 80 or better. It's just crazy that it turns a 28 so easy. This motor has tons of bottom end. Just can't get the rpms out of it
bajabob 718
09-12-2010, 06:05 PM
HOW ABOUT A 24BRAVO 1 PROP THEY MAY GET YOU 75
SickSation
09-13-2010, 10:25 AM
HOW ABOUT A 24BRAVO 1 PROP THEY MAY GET YOU 75

I think im to the point of accepting what its got for the rest of the season which is about 3-4 weeks.. Im pullin it back out this winter and going to freshen it up, give him some nice heads, new cam, ect.. maybe a blower.. Id like to see at least 80-85, which should be very easy with a blower. Ive got some work to do and some $$ to spend.
bajabob 718
09-13-2010, 08:09 PM
I think im to the point of accepting what its got for the rest of the season which is about 3-4 weeks.. Im pullin it back out this winter and going to freshen it up, give him some nice heads, new cam, ect.. maybe a blower.. Id like to see at least 80-85, which should be very easy with a blower. Ive got some work to do and some $$ to spend.if you have a 540 ? i just got mine off the dyno 34deg. 680tq 718hp n/a:D